Final Upper 6 Labs With Results and Marking Scheme 2011 2012 7

PRINCES TOWN WEST SECONDARY

CAPE UNIT 2

CHEMISTRY LABS

2011 - 2012

Princes Town West Secondary Unit 2 Chemistry Labs 1 | P a g e

# Title SkillsLab # 1 Organic Compounds : To determine which organic compound is contained in the bottles

labelled A, B, C and DLab # 2 Organic Compounds: To determine which organic compound is contained in the bottles

labelled P, Q, R and S.Lab # 3 Plan and Design : Organic ChemistryLab # 4 Organic Chemistry: To investigate the relative acidities of alcohols, phenols and

carboxylic acidsab # 5 Analytical Chemistry : The degree of uncertaintyLab # 6 CrystallizationLab # 7 Analytical Chemistry : Gravimetric Analysis - percentage oxalate in an unknown sampleLab # 8 Analytical Chemistry : Gravimetric Analysis - Vitamin C TabletLab# 9 Analytical Chemistry : Spectroscopy : UV/Vis Lab# 10 Analytical Chemistry : Quantitative Titration Lab# 11 Chromatography : Paper Chromatography Pigment in leavesLab# 12 Chromatography : Paper Chromatography InksLab# 13 Solvent ExtractionLab # 14 Plan Design: Environmental ChemistryLab # 15 Simple and Fractional DistillationLab # 16 Environmental Chemistry : Organic CompoundsLab # 17 Plan Design: To determine the acidity / pH of a soil sampleLab # 18 Analytical Chemistry Back TitrationLab # 19 Environmental test for pollutants in water.Lab # 20 Plan and Design : Analytical Chemistry (Gravimetric)


Lab # 1 Skills Assessed: O/R/R

Date: M/MA/IP/D

Title : Organic Compounds

Aim:

To determine which organic compound is contained in the bottles labelled A, B, C and D.

Apparatus and Material

:

1. Test Tubes2. Boiling Tubes3. 250 ml Beaker(Labelled Organic

Waste)4. Magnesium Powder or Turnings5. Sodium Carbonate

6. 2,4-dinitrophenyihydrazine7. Aqueous Silver Nitrate8. Aqueous Sodium Hydroxide9. Aqueous Ammonia10. Acidified Potassium

DichromateAqueous solutions, A, B, C and D. Each solution contains one of the following.

I. an alcoholII. an aldehyde

III. a carboxylic acid IV. a ketone

Procedure

:

1. You are to perform the tests below and from the results establish which type of organic compound is contained in each of A, B, C and D.

2. After each test discard the contents of the tubes into the 250 cm3 beaker, labelled organic waste. Rinse and re-use the tubes for the remaining tests.

3. Tests for gases are at the end of this lab sheet.:

Test (a)Place 1 cm depth of each of the solutions A, B, C and D into separate test-tubes.To each tube add a small quantity of magnesium powder or turnings.Identify any gas given off and record the test you used to make the identification.

Test (b)Place 1 cm depth of each of the solutions A, B, C and D into separate test-tubes.To each tube add a small quantity of powdered sodium carbonate.Identify any gas given off and record the test you used to make the identification.

Test (c)Place 1 cm depth of each of the solutions A, B, C and D into separate test-tubes.To each tube add 1 cm depth of 2,4-dinitrophenylhydrazine reagent.


Test (d)

Place 1 cm depth of each of the solutions A, B, C and D into separate test-tubes.Place 2 cm depth of aqueous silver nitrate in a boiling-tube and add to it 1 cm depth of aqueous sodium hydroxide. This will produce a precipitate of silver oxide.

Use a dropping pipette to add dilute aqueous ammonia to this mixture until the precipitate of silver oxide just dissolves.Do not add an excess of aqueous ammonia.To each of the tubes containing A, B, C and D add 1 cm depth of the silver-containing solution you have just prepared.

Test (e)Place 1 cm depth of each of the solutions A, B, C and D into separate boiling-tubes.To each tube add a few drops of acidified potassium dichromate(V1) to give a yellow-orange solution. Warm the tube gently.

Observations and Results

:

Aqueous Solutions

A(Alcohol)

B(Ketone)

C(Aldehyde)

D(Carboxylic Acid)

Test (a) No Rxn No Rxn No Rxn

Pop with glowing splint ∴ H2 gas given off. Hence Compound D is the acid.

Test (b) No Rxn No Rxn No Rxn

effervescence and gas bubbled through Ca(OH)White ppt formed.Gas given off COD is the carboxylic Acid.

Test (c)No Visible RxnNo ppt formed

Yellow brown/(orange) ppt formed ∴ Aldehyde or

Ketone

Yellow brown/(orange) ppt formed ∴ Aldehyde or

Ketone

No Visible RxnNo ppt formed

Test (d)No Visible RxnNo ppt formed


Silver ppt formed on ring of test tube ∴ silver mirror effect hence

compound C is the Aldehyde


Test (e)

Green solution formed

indicating Cr3+

ions hence an alcohol or aldehyde

No Visible Rxn

Green solution formed

indicating Cr3+

ions hence an alcohol or aldehyde

No Visible Rxn

Discussion : Test (a)o Compound D is the acid as H2 gas was given off and identified


by the pop with the glowing splint.

o 2 R−COOH (aq)+2 Mg(s) yields→

2 R−COO−¿ Mg( aq)

+¿ +H 2 (g)¿¿

Test (b)o Effervescence CO2 given off as confirmation with white ppt

forming in CaA(OH)2

o 2 R−COOH (aq)+Na2CO3(s) yields→

2 R−COO−¿ Na(aq)

+¿ +CO2 (g )+H 2 O( l)¿¿

o CO2 (g )+Ca(OH )2 yields→

CaCO3 (s )+ H 2O(l )

o ∴ Substance D is the acid as no other reactions were observed by the other substances. Test (c)

o Yellow brown (or orange) ppt seen for B and C indication it’s a carbonyl compound.

o ∴ Substance B and C are either a ketone or aldehydeoRCHO+C6 H 3 ( NO2 )2 . NH NH 2 yields

→RCH=NN C6 H 3 ( NO2 )2 ( s)+H 2O( l)

oR R' CO+C6 H 3 ( NO2)2 . NH NH 2 yields

→R ' RC=NN C6 H 3 ( NO2 )2 (s )+H 2O (l )

Test (d)

o 2 Ag (NH3)2(aq)+¿+RCHO(l)+3OH(aq)

−¿ yields→

2 Ag(s )+RCOO (aq )

−¿+ 4NH3 ( g ) +2H

2O (l ) ¿¿

¿

o Tollen’s reagent only reacts with aldehydes to give the silver mirror effect ∴ substance C is the aldehyde.

Test (e)o Substance A is an Alcohol because it reduces aqueous K2Cr2O7

to a green Cr3+ but did not react with either Tollen’s reagent or 2,4,-dinitrophenylhydrazine reagents.

o Substance B ∴ has to be the ketone by reason of elimination and its reaction with 2,4,-dinitrophenylhydrazine.

Conclusion :

gas test and test result

ammonia, NH3 turns damp red litmus paper blue

carbon dioxide, CO2gives a white ppt. with limewater(ppt. dissolves with excess CO2)

chlorine, 012 bleaches damp litmus paper

hydrogen, H2 'pops' with a lighted splint


oxygen, 02 relights a glowing splint

sulphur dioxide, 802turns potassium dichromate(VI) (aq) from orange to green



Date: M/MA/I P/D


Aim:

To determine which organic compound is contained in the bottles labelled P, Q, R and S.


:

1. Test Tubes2. Boiling Tubes3. 250 ml Beaker(Labelled Organic

Waste)4. Magnesium Powder or Turnings5. Sodium Carbonate

6. 2,4-dinitrophenyihydrazine7. Aqueous Silver Nitrate8. Aqueous Sodium Hydroxide9. Aqueous Ammonia10. Acidified Potassium

DichromateYou are provided with four organic substances P, Q, R and S.Each belongs to one of the following classes of compounds:

I. An aromatic alcoholII. An alkene

III. An alkaneIV. An alkyl halide

Procedure

:

1. You are to perform the tests below and from the results establish which type of organic compound is contained in each of P, Q, R and S.

2. After each test discard the contents of the tubes into the 250 cm3 beaker, labelled organic waste. Rinse and re-use the tubes for the remaining tests.

3. Gloves, eye protection and lab coats must be worn. The Fume hood must be used where specified.


:

Test (a)Place 5 drops of each of the substances P, Q, R and S into separate dry

test-tubes. Cover each test-tube completely with foil. In the fume

cupboard add 5 drops of bromine to each. Stopper for 5-10 minutes.

Test (b)Place 5 drops of each of the substances P, Q, R and S into separate dry

test-tubes. In the fume cupboard add 5 drops of bromine to each.

Expose to bright sunlight.Test (c)

Place 5 drops of each of the substances P, Q, R and S into separate dry

test-tubes. Add 2% aqueous potassium manganate(VII) drop wise.

Observe any changes within five minutes.

Test (d)

Place 2 drops of each of the substances P, Q, R and S into separate dry

test-tubes. To each tube add 1 cm depth of aqueous Iron(III) chloride

solution. Warm if necessary.

Test (e)Place 2 drops of each of the substances P, Q, R and S into separate dry

test-tubes. To each tube add 1 cm depth of aqueous silver nitrate

solution. Warm if necessary.


:

Aqueous Solutions

P Q R S

Test (a)

Test (b)

Test (c)

Test (d)

Test (e)

Discussion :

Conclusion :




Date: M/MA/IP/D

Title : Plan and Design : Organic Chemistry

Aim :

Case

:

You are provided with solutions VF 3, VF 4 and VF 5.The solutions are:1.0 mol dm–3 Propanone1.0 mol dm–3 Propanal0.5 mol dm–3 Propanoic AcidYou are to plan experiments that will enable you to identify the solution that matches each ofVF 3, VF 4 and VF 5.You have available the following apparatus:–10 °C to 110 °C thermometer,100 cm3 beaker, measuring cylinder, and the following reagentsLiAlH4, EDTA, Fehlings Reagent, 2,4 DNPH, and one of your choice.

(a) You are to identify, by the minimum number of practical steps, which of the solutions contains Propanone


:1. 2.

Procedure : 1.2.3.4.5.6.


:

Data Analysis and Interpretation

:

Discussion :


Conclusion :


Date: M/MA/I P/D

Title : Organic Chemistry

Aim : To investigate the relative acidities of alcohols, phenols and carboxylic acids

Theory

:

The relative acidities of alcohols, phenols and carboxylic acids depends on the ease at which the molecule gives up a proton to water in an aqueous solution. Strong acids are those which easily donate a proton and hence is fully ionised in an aqueous solution.

Example: HCl →

H+ + Cl-

Alcohols do not give up H+ ions readily due to the presence of the OH group, because the alkyl group donates electrons to the O atom, thereby decreasing the tendency for the H atom to ionise.

ROH + H2O RO- + H3O+

Phenols tend to give up H+ more readily than alcohols because electrons from the OH bond tends to be localized around the benzene ring, and thus increases the tendency for the H atom to ionise.

Carboxylic acids are the strongest acid of all the three, and tends to give up H+

more readily than alcohol and phenols. The carboxyl group tends to pull electrons away from the OH bond, hence weakening the OH bond and making it easier for the H atom to ionise. RCOOH + H2O RCOO- + H3O+


:

1. Samples of Ethanol, Phenol and Ethanoic acid.

2. Magnesium Ribbon3. Solid Na2CO3 4. Test tubes

5. Apparatus to test gas, splint, litmus, Ca(OH)2(aq)

6. pH meter / pH paper7. spatula8. Glass rod


http://upload.wikimedia.org/wikipedia/commons/b/b5/Carboxylic-acid.svg

Procedure:

1. A piece of Magnesium Ribbon was added to 4 cm3 of ethanol in a test tube and observations were recorded

2. Solid Na2CO3 was added to 4 cm3 of ethanol in a test tube and observations were recorded

3. The pH meter was then used to find the pH of ethanol, and this value was also recorded.

4. The above procedure was then repeated using phenol and ethanoic acid.


:

Table 1: Observation tableEthanol Phenol Ethanoic Acid

Magnesium RibbonSolid Na2CO3

pH


:

1. Which samples reacted with Mg? Write a balanced equation for any reaction which occurred.

2. Which samples reaction with Solid Na2CO3? Write a balanced equation for any reaction that occurred.

3. Use the results of the experiment to deduce the order of increasing acidities of the samples.

Discussion :

Conclusion :







Date: M/MA/IP/D

Title : Analytical Chemistry : The degree of uncertainty

Aim : To determine the degree of uncertainty between a measuring cylinder and a burette.


:1. 50 cm3 burette (Class A)2. 10 cm3 measuring cylinder (Class A)3. Distilled water

Procedure : 1. The burette was filled to a known volume and record the volume2. 25 drops of water was delivered drop wise into a measuring cylinder

and record both the measuring cylinder and new burette reading3. This process was repeated in steps of 25 drops until 200 drops were

delivered.4. The results were tabulated.5. A graph was drawn vol of burette against vol in cylinder6. A best fit line was drawn7. Calculate the Standard Deviation between volumes in the burette and

the measuring cylinder.


:

Table: 1 Readings obtained from the burette and measuring cylinder respectively.No. of Drops 25 50 75 100 125 150 200

Final Burette Reading / cm3

Initial Burette Reading / cm3

Total Vol of drops Burette / cm3

Vol in measuring cylinder / cm3

S.D. between Readings

Graph Draw a graph of volume of burette versus volume of measuring cylinder

Data Analysis :

1. From the graph determine when 4 cm3 of the burette is delivered the volume of measuring cylinder?

2. From the graph when 8.2 cm3 of water is delivered from the burette the reading in the measuring cylinder ?

3. Which instrument is considered to be accurate4. Which instrument is considered to be precise5. Explain your answer for questions 3 and 4.

Discussion :

Conclusion :


Lab # NA Skills Assessed: O/R/RDate: M/M

A/IP/D

Title : Analytical Chemistry : Measurements

Aim : Uncertainty of measurements of volumes and masses


:

1. Burette, 50 mL, Class B2. Graduated pipette, 10 mL, Class B3. Volumetric flasks, 25 mL, Class A

and B4. Measuring cylinder, 10 mL5. 15 Vials and stoppers6. Tissue

7. Top loading balance8. Analytical balance9. Unknown liquid, 200 mL.

(0.789 g ml-1)10. Distilled water11. Pipette filler

Procedure :Part A 1. All glassware was rinsed with distilled water, and then 2 mL of

unknown liquid provided.2. The empty vials and the volumetric flasks were labelled 3. The mass of the empty dried sample vials with their stoppers in place

were weighed. Precaution was taken no to interchange stoppers among vials.

4. The burette, graduated pipette, and measuring cylinder were used to transfer 10 mL of the unknown liquid into different vials.

5. The vials were stoppered and their loaded weights were recorded.6. This was repeated until a total of three (3) loaded sample vials for each

piece of measuring equipment.7. Results were recorded in Table 1.

Part B 1. Each volumetric flask was filled to the 25 mL mark with the unknown liquid ensuring that no liquid is spilled on the outside.

2. The volumetric flasks were stoppered and there loaded weights were recorded.

3. The unknown liquid in the flasks were completely transferred into a sample vial, again ensuring that no liquid is spilled on the outside.

4. The empty volumetric flasks with their stoppers were reweighed.5. Results were recorder in Table 1.

Part C 1. Using a top loading balance combined masses of 2, 4, 6, 8, and 10, 100 g weights were obtained.

2. A graph was plotted of mass versus number of weights to obtain a best


fit line through the points.

Part D 1. The weight of two 100 g weights were measured using a top loading balance first by:

a. The individual masses and b. The combined masses of two

2. This procedure was then repeated on an analytical balance.


:

Part A and B: Table 1: Uncertainty of Measurements of Volumetric ApparatusApparatus 1 2 3 Average

BuretteClass B ± 0.06

Loaded 19.1175 19.0251 18.9238Empty 11.0893 11.0073 10.8985Mass 8.0282 8.0178 8.0253 8.0238

Graduated PipetteClass B ± 0.06


Measuring CylinderClass B ± 0.1 @ 20°C


Volumetric Flask AClass B ± 0.02 @ 20°C


Volumetric Flask BClass B ± 0.04 @ 20°C


Part Ci. 100 g Weights Mass (g)

2 200.044 400.076 600.18 800.1410 1000.17

Slope 100.01625

ii. Mass (g) 10-100 g Weights

Mass( g) Average

Group 1 200.040 400.07 600.10

800.14 1000.17 100.016

Group 2 200.065 400.17 600.24

800.14 1000.36 100.037

Group 3 200.03 400.17 600.12

800.11 1000.2 100.021

Group 4 200.06 400.12 600.17

800.22 1000.07 100.001

Average Masses 100.019Part Diii. Mass 1-100 g

WeightTop Loading Balance Analytical Balance

A 100.02 100.003


B 100.02 100.001Average Mass 100.02 100.002Mass Both 100 g Weights 200.04 200.004

Graph

Part C

2 4 6 8 100

200

400

600

800

1000

1200

Graph showing Mass versus number of 100 g weights

Number of 100 g Weights

Mas

s(g)

Data Analysis

: Standard Deviation and Gossett T-Function of Part A and B

Standard Deviation =

Apparatus 1 2 3 Average ∑ (x−x )2

S.D.

∑ (x−x )2

2

Gossett’s T-Functiont= 4.302

λ=sd ×t ( p , n−1)

√n

Burette

Loaded 19.1175 19.0251 18.9238

Empty 11.0893 11.0073 10.8985

Mass 8.0282 8.0178 8.0253 8.0238

(x−x )2 0.0000197

0.0000356 0.000002351 5.761E-05 0.0054

Graduated Pipette

Loaded 18.8871 18.9043 19.0629

Empty 10.8947 10.8963 11.0264


Mass 7.9924 8.008 8.0365 8.0123

(x−x )2 0.000396 0.000018 0.000586 1.000E-03 0.0224

Measuring Cylinder

Loaded 18.7994 18.7795 18.9284

Empty 11.0705 11.0494 11.2151

Mass 7.7289 7.7301 7.7133 7.7241

(x−x )2 0.000023 0.000036 0.000117 1.757E-04 0.0094

Volumetric Flask A

Loaded 21.9282 21.917 21.915

Empty 14.0295 14.0325 14.0296

Mass 7.8987 7.8845 7.8854 7.8895

(x−x )2 0.000084 0.000025 0.000017 1.264E-04 0.0080

Volumetric Flask B

Loaded 23.6678 23.6576 23.6485

Empty 15.7382 15.7443 15.7562

Mass 7.9296 7.9133 7.8923 7.9117

(x−x )2 0.000319 0.000002 0.000378 6.993E-04 0.0187

Part C

99.995 100 100.005 100.01 100.015 100.02 100.025 100.03 100.035 100.040

2

4

6

8

10

12

Pool Average Masses From Class

Mass /g

Freq

uenc

y

Discussion :Part A The analysis showed that the burette showed reliable results when

compared to the other volumetric instruments having the lowest deviation from the means and an acceptable confidence level of <0.05.

The pipette in this experiment was the least accurate, having highest deviation when comparing means and an unacceptable confidence level. This result defies convention of the accuracy of the pipette and therefore the results suggest human error may have resulted in this disparity.

The measuring cylinder provided a reasonable accurate measure of volume in the Laboratory.


True Value Accurate Measure

Part B Comparing the accuracy of various Classes of volumetric apparatus it was clearly seen that Class A apparatus showed a high degree of accuracy when compared to Class B apparatus, which is expected by convention. The confidence level for the Class A was less than that of the Class B indicating the reliability in the results.

Part C The accuracy of Group experiment showed that Group 1 was the closest to the accurate value whilst the rest of the group even though were precise were not accurate.

Part D When comparing the analytical balance to the top loading balance it was found the analytical balance was more accurate in its measure of weights as expected by convention.

Conclusion

:

The experiment was conducted successfully. An understanding of measurements accuracy and precision was clearly exemplified.



Date: M/MA/I P/D

Title : Crystallization

Aim:

To determine the number of moles of water of crystallization in hydrated MgSO4.xH2O

Theory

:

Hydrated salts contain water of crystallization which can be removed by heating. The hydrated salt is heated and weighed repeatedly until a constant mass is obtained. This loss in mass of the salt can then be used to calculate the number of moles of water of crystallization.


:1. Hydrated Magnesium sulphate

MgSO4.xH2O2. Hard glass test tube and holder

3. Balance4. Bunsen burner

Procedure:

1. The empty hard glass test tube was weighed and this value was recorded.

2. 6 g of hydrated magnesium sulphate was then placed in the test tube and reweighed. Readings were recorded.

3. The test tube was then heated gently initially and then more strongly to remove any water that was present. Heating was stopped if the salt started to decompose or emit white fumes.

4. The test tube was allowed to cool and then the tube and its contents were reweighed and this value was recorded

5. The heating, cooling and weighing process was repeated until a constant mass was obtained. All the readings were recorded.


:

Table 1 Mass of hydrated magnesium sulphateMass of test tube and hydrated magnesium sulphate / gMass of empty test tube /gMass of hydrated magnesium sulphate /g

Table 2 Mass of hydrated magnesium sulphate after heatingMass of test tube and hydrated magnesium sulphate after heating / g

Mass of empty test tube /gMass of hydrated magnesium sulphate after heating /g

Data Analysis and

: 1. Number of moles of anhydrous MgSO4 in the sample2. Determine the mass of water driven out of the sample


Interpretation

3. Number of moles of water driven out from the sample4. Number of moles of water of crystallization in one mole of hydrated

MgSO4

= number of molesof water driven out ¿ the sample ¿

number of moles of anhydrous magnesium sulphate∈the sample

5. Write an equation for the formation of anhydrous MgSO4 from hydrated magnesium sulphate.

Discussion :

Conclusion :



Date: M/MA/I P/D

Title : Analytical Chemistry : Gravimetric Analysis

Aim:

Standardisation of a permanganate solution and determination of the percentage oxalate in an unknown sample


:

1. 4 – 250 mL conical flask2. Burette and funnel3. Retort stand and clamp4. 1 white tile5. 2 sample vials with stoppers6. Bunsen burner/ tripod / wire gauze7. Thermometer8. 25 mL measuring cylinder9. 10 mL measuring cylinder10. 25 mL Pipette and pipette filler

11. 2 spatulas12. Analytical balance13. K2C2O4.H2O salt14. 3.0 M H2SO4

15. ≈0.02 M KMnO4 solution16. Distilled water17. Unknown oxalate sample18. 250 mL volumetric flask19. Laboratory cloth

Procedure:

1. ~1.5 grams of K2C2O4.H2O salt (Potassium oxalate) was accurately weighed and dissolved properly into a 250 ml volumetric flask and then made up to the mark.

2. 25 ml of K2C2O4 standard was pipette into a conical flask and 15 mL of 3.0 M H2SO4 was added.

3. The mixture was heated to about 85°C with a Bunsen burner and ensuring it did not came to a boil temperature. The temperature was monitored with a clean thermometer.

4. Using a laboratory cloth to hold the flask the solution was titrated against permanganate with constant swirling until the pink colour of the permanganate begins to take a few seconds to fade.

5. The temperature was ensured to be about 70 °C before continuing to titrate drop-wise to reach the end point which was a pale pink colouration that persists.

6. The titration was repeated twice more to ensure reliability of the titre value.

7. The mass of the unknown was accurately weighed and dissolved in 50 mL of distilled water in a 250 mL Volumetric flask and then made up to the mark

8. 15 mL of 3M H2SO4 was added to the unknown oxalate solution and titrated with the standardised KMnO4 as outlined in procedure # 2 to 6.

9. The mass of the unknown was repeatedly weighed until the mass produced a titre value close to standardisation value of the permanganate.

Observation : Mass of K2C2O4.H2O salt used: ________ g


s and Results

Table: 1 Standardisation of KMnO4.Roug

h1 2 3 Averag

eFinal Burette Reading / cm3


Total Vol of Burette / cm3

Table: 2 Determination of the unknown concentration of oxalate. Roug

h1 2 3

Mass of unknown used /gFinal Burette Reading / cm3


Total Vol of Burette / cm3

Data Analysis

: 1. Calculation of the Molarity of the permanganate solution

2. Calculation of the percentage oxalate in the unknown mixture :3. Why the unknown was repeatedly weighed to produce a titre value

close to that of the permanganate.

Discussion :

Conclusion :



Date: M/MA/I P/D

Title : Analytical Chemistry : Gravimetric Analysis

Aim:

To determine the Ascorbic Acid concentration in a commercially available Vitamin C Tablet.

Theory

:

VITAMIN C ANALYSIS

Step 1: Potassium iodate reacts with iodide to form the complex trihalide

Anion I 3−¿: IO 3

−¿+8I −¿+6 H

+ ¿ yields→

3 I3

−¿+ 3H2

O ¿¿¿ ¿¿

Step 2: The trihalide ion reacts with vitamin C :

C6 H 8 O6+ I 3

−¿ yields→

C6 H 6 O6+2H +¿+3 I−¿¿¿ ¿

Step 3: Remaining trihalide is determined with thiosulfate

I 3−¿+2 S2 O3

2−¿ yields→

3 I−¿+ S

4O

62−¿¿¿

¿¿


: 1. 2 White tiles 2. 1 Wash bottle with distilled water3. 2 100 mL and 2 250 mL Beakers 4. 2 Spatulas5. 2 sample vials with stoppers 6. 3 25 mL Pipettes and 3 pipette fillers7. 1 250 mL, Volumetric flask 8. 2 25 mL, & 2 — 10 mL Measuring

cylinders9. 6 - 250 mL conical flasks 10. Analytical & top loading balances11. 2 — 50 mL Burettes and 2 funnels 12. 1000 mg vitamin C tablet in vial13. Cotton wool, tissue & lab cloth 14. KIO3 solution (2.1526 g L-1)15. 3 Filter funnels 16. M H2SO4

17. 1 Mortar and pestle 18. Sodium thiosulfate solution19. 2 Pasteur pipettes 20. 10% KI solution21. 2 Retort stands and clamps 22. Starch23. 1 Glass rod 24. 1 Wash bottle with distilled water

Procedure

:

PROCEDURE A: Standardization of Sodium Thiosulfate Solution Using Iodate Pipette 25 mL of the standard potassium iodate solution provided into a 250 mL conical flask. Add 15 mL of 1 M sulfuric acid to the flask followed by 10 mL of 10% potassium iodide solution. Titrate the liberated iodine against the sodium thiosulfate solution until the solution changes to a pale yellow. Then add 10 drops of starch solution and continue the titration until the blue colouration just disappears.

PROCEDURE B: Determination of Ascorbic Acid content of Vitamin C Tablet


Accurately weigh and record the mass of one Vitamin C tablet. Using a mortar and pestle pulverize the entire tablet. Transfer 500 mg of the powder (accurately weighed) to a 100 mL beaker and add 75 mL of 1M H2SO4. Agitate the mixture with a glass rod and gravity filter into a 250 mL volumetric flask. To filter the solution plug the stem of a funnel with a piece of cotton wool. Rinse the cotton with a small volume of 1M H2SO4 ensuring that the flow rate is moderate before beginning to filter the Vitamin C — H2SO4 mixture. Ensure that no solid material goes into the volumetric flask. If this happens you will need to re-filter. Make the solution up to 250 mL with 1M H2SO4. Pipette 25 mL of the vitamin C solution into a conical flask and add 25 mL of standard KIO3 solution by pipette. Add 10 mL of 10% KI solution to the mixture and titrate against the standardized thiosulfate solution until the solution becomes a very pale yellow. Add 10 drops of starch solution and continue the titration until the blue colouration just disappears. Repeat the experiment until a satisfactory average is obtained for the end point.


: Using a Suitable Tables Record Your Results.

Data Analysis

:

Use your average titre volume to calculate

1. The number of moles of 10; initially added to the solution

2. The number of moles of I; produced initially

3. The number of moles of I; which reacted with thiosulfate

4. The number of moles of I; which reacted with L-ascorbic acid

Discussion :

Conclusion :


Lab# 9 Skills Assessed: O/R/R

Date: M/M A/I P/D

Title : Analytical Chemistry : Spectroscopy : UV/Vis

Aim:

To determine the nitrate concentration in an unknown water sample using UV/vis spectroscopy and the use of Beer Lamberts Law.


:

1. Evolution 600 UV-Vis Spectrophotometer)

2. 10 ppm KNO3solution (100 mg dm3 anhydrous KNO3)

3. 5 – 50 cm3 volumetric flask4. Unknown water sample

5. 50 cm3 burette6. Cadmium reduction

mixture7. Test tubes8. Stopwatch

Procedure:

1. Using a burette serial dilutions were made of the KNO3 Standard by transferring 10, 20, 30, 40, and 50 cm3 of KNO3 into their respective volumetric flask.

2. Each flask was then made up to the mark using distilled water and labelled 2, 4, 6, 8, and 10 ppm respectively.

3. 5 cm3 of each standard was placed into a test tube and labelled, together with the blank which was distilled water and labelled (0 ppm) and the unknown sample.

4. A spatula of cadmium reduction mixture was added to each test tube and timed for 12 minutes for each reduction.

5. After the reduction the samples were then measured for Absorbance on the UV/Vis spectrophotometer at λ= 530 nm.

6. The results were tabulated and a standard curve was drawn.


:

Table: 1 Absorbance values of nitrate ions standards and unknownNO3

−¿¿ /

ppm

0 2 4 6 8 10 Unknown

Absorbance 0 0.053 0.1157 0.2167

0.2309

0.2622 0.1696

Graph 1. Plot a graph of Absorbance versus concentration of NO3−¿¿

Data Analysis :

2. From the graph infer the unknown concentration of the unknown sample

3. Using Beer-Lamberts Law A=εcl determine the concentration of the unknown sample

4. When the c = 12 ppm A= ? l = 0.5 cm determine the Absorbance

Discussion :


Conclusion :



Date: M/MA/I P/D

Title : Analytical Chemistry : Quantitative Titration

Aim

:

To determine the concentration of iron(II) ions in an unknown solution and, by a

graphical method, the volume of an aqueous solution of substance X that will oxidize the

iron(II) ions in 25 cm3 of the unknown.


:

1. A is 0.02 mol dm-3 potassium manganate(VII), KMnO4

2. B is the unknown containing iron(II) ions, Fe2+,

3. C is an aqueous solution of a substance X.

4. Under acid conditions X oxidizes iron(II) to iron(III).

Procedure

:

Experiment 1

1. Fill a burette with A, 0.02 mol dm-3 potassium manganate(VII), KMnO4.

2. Pipette 25.0 cm3 of B into a conical flask and add, using the measuring

cylinder provided 10 cm3 of 1 mol dm-3 sulphuric acid.

3. Run A from the burette into the conical flask until the first permanent

pale pink colour remains. This is the end point of the titration.

4. Record your burette readings in Table 1.

5. Repeat the titrations as many times as you think necessary to obtain

accurate results.

6. Make certain that the recorded results show the precision of your

practical work.

Experiment 2

1. Fill the second burette with C, the aqueous solution of X.

2. Pipette 25.0 cm3 of B into a conical flask and add, using the measuring

cylinder provided, 10 cm3 of 1 mol dm-3 sulphuric acid.

3. Add, from the second burette, 4.00 cm3 of X. This oxidizes some of

the Fe2+ that has been pipetted into the flask.

4. Titrate the remaining Fe2+ in the conical flask with A, potassium


manganate(VII) until the first permanent pale pink colour remains.

5. Record the volume of X added and your burette readings in table 2.

6. One accurate titration will be sufficient. Remember that the volume

added will be less than in Experiment 1 as some of the Fe2+ has been

oxidized by X.

7. Empty and rinse the conical flask.

8. Repeat Experiment 2, using the volumes of X shown in Table 2.

9. Record your results in Table 2.


:

Table 1: Titration of A, 0.02 mol dm-3 potassium manganate(VII), KMnO4

with B, the unknown.

Final burette reading/ cm3 25.50 26.20 25.40 28.80

Initial burette reading/

cm3 0.50 1.00 1.00 3.60

Volume of A used/ cm3

Table 2 Titration of B/X mixture with A, KMnO4

Volume of X added/ cm3 0.00 4.00 8.00 12.00

Final burette reading/ cm3 20.00 22.50 20.00

Initial burette reading/

cm3 0.05 6.50 8.05

Volume of A added/ cm3

↑ Copy and fill out the titration values

Data Analysis

:Experiment 1

(a) 25.0 cm3 of B reacted with …………….. cm3 of A.

Show which results you used to obtain this volume of A by placing a tick under the

readings in Table 1.

(b) Calculate how many moles of potassium manganate(VII) were run from

the burette into the conical flask during the titration of B with A.

(c) Use the half equations for the reaction

MnO4 (aq )−¿+8 H (aq )

+¿+5 e−¿ yields

→Mn( aq )

2+¿+4 H2

O( l) ¿ ¿

¿ ¿


Fe(aq)

2+¿ yields→

Fe( aq)3 +¿+e−¿¿¿ ¿

and your answer to (b) to calculate the concentration of Fe2+, in mol dm-3, in B.

Experiment 2(a) Plot the volume of A against the volume of X.

a. Your scale on the X axis should extend to 30.00 cm3.

(b) Draw the best-fit straight line through the plotted points.

(c) From your graph find the volume of X that reacts with the Fe2+ present in 25.0 cm3 of B.

Graph

Discussion :

Conclusion :



Date: M/M A/IP/D

Title : Chromatography

Theory

:

In this activity you will be experimenting with a technique called chromatography which will allow you to visually demonstrate that the pigment in leaves is a combination of several different coloured pigments.

This technique is useful in that it can separate and identify the various components of mixtures, such as those contained in plant pigments. A pigment is a substance that absorbs light at specific wavelengths, chlorophyll is one of these pigments. Its green-yellow in colour is due to the absorption of red, orange, blue, and violet wavelengths and the reflection of the green and yellow wavelengths. This occurs when white light (containing all of the light wavelengths, or the entire spectrum of colours) shines on the leaf surface, all of the wavelengths are absorbed except for the ones you see, which are green-yellow, those are the portions of the spectrum being reflected.

If the conditions are identical, the relative distance moved by a particular compound is the same from one mixture to another. This is why chromatography can be used to identify a compound. The actual identification requires a simple calculation as shown below:

R f=Distance travelled by componet

Distance travelled by mobile phase

It is important to remember that several factors can influence the reliability of the Rf value, these include humidity, temperature, solvent, pigment extract preparation, and the amounts of the material present. Values are comparable only when the extracts are prepared in the same way and the chromatograms are prepared identically and developed together in the same container.

Acetone is flammable (even the amount found in nail polish remover), keep it away from sparks or open flames. Wear eye protection, especially if using pure acetone.

Aim : To separate the different pigments in plant leaves


: 1. Cone-type (size 4) coffee filter paper (or Whatman #1 chromatography paper)

2. large glass jars 3. acetone

5. capillary tubes 6. fresh spinach 7. mortar and pestle 8. clean sand


4. distilled water

Procedure

:

1. Each lab group (or individual if not working in groups) will need 4 strips of filter paper, approximately 6 inches long and 1 inch wide, 2 chromatography development containers (500 ml beakers or large fruit jars work well), 2 large rubber bands (able to stretch around the vessels from the mouth to the bottom of the vessel), 2 solvents, water and either pure acetone, or nail polish remover.

2. Do the following with both fresh spinach leaves; tear leaf material and place in a glass container, cover with acetone (this should be done the day before the actual lab activity). An alternative pigment extraction technique is to use a mortar and pestle. Place plant material the vessel, add a little clean sand, some acetone and then grind until a dark green liquid appears. Both techniques yield very dark pigments with which to work. Be certain to keep the pigments apart throughout the entire activity.

3. Place one of each solvents (water and acetone, or nail polish remover) in the chromatography vessels and stretch a rubber band length-wise around each vessel. The rubber band will be the mechanism for hanging the chromatography strips.

4. Make a pencil mark on each of the 2 chromatography strips, in the center, directly above the point of the strip, about 1 inch from the tip of the paper. Using a capillary tube, or tooth pick, apply the plant pigment to each filter paper strip. This is done by touching the tooth pick or capillary tube which has been dipped in the pigment, to the pencil mark. Make an application, then wave the paper gently to dry it a little before the next application. Be patient, you will need 12 to 15 applications.

5. By now you should have 2 strips with spinach pigment. Suspend one of each in each of the chromatography development vessels. You can attach them with paper clips, or simply fold over a portion of the end and it should hang in place. The tip of each strip should just touch the solvent.

6. Wait 20 to 30 minutes for the chromatograms to develop. Remove the chromatograms. Mark with a pencil (NOT a pen) where the solvent stopped as it moved up the chromatogram. This is called the solvent front. Mark also where each pigment stopped moving up the chromatogram. Using the equation below, determine a reference number for each pigment on the chromatograms. Depending on which chromatogram you are viewing, you should see greens, yellow/yellow orange, and red. All measurements should be in mm. (Any material which did not move from the pencil dot is insoluble).


:

Note: each pigment has a special name, green = chlorophyll a or b yellow/yellow orange = carotene red = anthocyanin brown = xanthophyll


Data Analysis

:

1. Determine the Rf (ratio of fronts) value for each spot using the formula (remember there may be more than one calculation per spot):



Discussion :

Conclusion :



Date: M/M A/I P/D

Title : Chromatography

Aim:

To determine the various colours present in food colouring dye and ink pens using chromatography.


:

1. 8" Aluminum pie plate2. Toothpicks3. Food coloring4. Large Coffee filters5. Pencil

6. Rubbing alcohol (70% Isopropyl Alcohol)7. "Expresso" ink pens8. Measuring cup 9. Ruler

Procedure:

1. Measure approximately 1cm from the edge of the coffee filter and mark eight evenly spaced lines around the filter lightly with a pencil (do not use ink).

2. Use a toothpick to spot the four food colouring dyes on one-half of the coffee filter along the pencil mark. On the other half, spot the filter using the pens. Allow each spot to dry and then re-spot two or three more times

3. After the coffee filter has been spotted, mark the top of each spot with your pencil. Below each spot, in pencil, label the colour and if it is pen or food colouring. (Due to the small space below the spot, it may be easier to label "p" for pen, "g" for green, etc.)

4. Place the spotted coffee filter "upside down" in the aluminium pie plate.5. Fill the pie plate (the chromatographic chamber) with rubbing alcohol to

a level just below the spots on the filter.6. Once the chromatogram has developed and the alcohol travels to the

"top" of the coffee filter, remove the filter from the plate. Using a pencil, mark the final position of the solvent. Click here to view a video of this procedure.

7. Next place a pencil mark at the end of each colour. Note that some of the initial spots separated into multiple colours- be sure to mark each colour

8. Allow the filter to air dry.9. Determine and record the distance travelled by the mobile phase by

measuring the distance (in mm) from the top of each of the initial spots (original pencil marks) to the final position of the solvent

10. Determine and record the distance travelled by each colour by measuring the distance (in mm) from the pencil mark at the top of each of the initial spots to the mark indicating the end of each colour it produced.



:

Data Analysis

:

2. Determine the Rf (ratio of fronts) value for each spot using the formula (remember there may be more than one calculation per spot):



Discussion :

Conclusion :



Date: M/M A/I P/D

Title : Solvent Extraction

Theory

:

Introduction:

The aim of this experiment is to determine the equilibrium constant, K, for the distribution of ethanoic acid (CH3COOH, also known as acetic acid) between two immiscible solvents, diethyl ether and water, using an acid-base titration. The dynamic equilibrium at the solvent boundary may be represented by eq. 2

[CH¿¿3COOH ](aq)

k1⇋k2

[CH ¿¿3 COOH ]ether eq .2¿¿

where k1 and k2 are the rate constants of the forward and reverse processes.At equilibrium the rates of the forward and reverse processes are equal (eq. 3),

k 1[CH ¿¿3COOH ](aq)=k2[CH¿¿3COOH ](ether)eq .3¿¿

and the equilibrium constant may then be defined in terms of solute concentrations or rate constants according to eq. 4.

K=[CH ¿¿3 COOH ](ether )

[CH ¿¿3 COOH ](aq )=k1

k2

eq .4 ¿¿

Aim:

To determine the equilibrium constant, K, for the distribution of ethanoic acid (CH3COOH, also known as acetic acid) between two immiscible solvents, diethyl ether and water, using an acid-base titration.


:

1. Graduated 100 cm3 measuring cylinder;

2. 250 cm3 separating funnel;3. Three 100 cm3 conical flasks;4. 10 cm3 pipette; 50 cm3 burette;5. 0.1 M sodium hydroxide solution;

6. Distilled water;7. Diethyl ether;8. 0.5 M aqueous ethanoic acid;9. 0.125 M aqueous ethanoic acid;10. Phenolphthalein indicator

solution.

Procedure:

1. Using a measuring cylinder, add as accurately as possible 50 cm3 of 0.5 mol dm-

3 aqueous ethanoic acid and 50 cm3 of diethyl ether into a 250 cm3 separating funnel.

2. Allow the mixture to stand for at least twenty minutes, shaking occasionally (remember to release the pressure after shaking by inverting the funnel, holding on to the stopper and opening the tap).


3. Run off the lower (aqueous) phase into a clean 100 cm3 conical flask, making sure no ether is drained off. Now run off the interface portion and discard it and leave the ether layer phase in the separating funnel.

4. Pipette 10 cm3 of each phase into separate 100 cm3 conical flasks and add a few drops of phenolphthalein indicator. Titrate both solutions with 0.1 mol dm-3 sodium hydroxide solution until the solution retains a permanent pink colour.

5. Repeat the titrations with two further 10 cm3 aliquots.6. Repeat steps 1-3 using 0.125 mol dm-3 aqueous ethanoic acid in place of the 0.5

mol dm-3 solution.


:

Data Analysis

:

Treatment of Results1. Write a balanced equation for the reaction between ethanoic acid and sodium

hydroxide.2. From the volumes of sodium hydroxide solution required to neutralise the

ethanoic acid, calculate the number of moles of ethanoic acid in each 10 cm3 aliquot you titrated and, hence, evaluate the ethanoic acid concentration for each solution.

3. Using the ethanoic acid concentrations you have determined, evaluate the equilibrium constant, K, using eq. 4 for both initial ethanoic acid concentrations.

4. Do the values of K obtained using 0.5 mol dm-3 and 0.125 mol dm-3 ethanoic acid differ? Is this to be expected?

Discussion :

Conclusion :



Date: M/MA/IP/D

Title : Plan Design: Analytical Chemistry

Case

:

Contamination of drinking water supplies from industrial waste is a result of various types of industrial processes and disposal practices. Industries that use large amounts of water for processing have the potential to pollute waterways through the discharge of their waste into streams and rivers, or by run-off and seepage of stored wastes into nearby water sources. From this information, is it possible to determine if effluents from ISPAT is sufficient to cause adverse effects on the quality of drinking water.

Hypothesis :

Aim :

Theory :


:1. 2.

Procedure : 1.2.3.4.

Variables :

Expected Observations and Results

:

Data Analysis

: 1.

2.

Precautions :


Lab # NA Skills Assessed: O/R/R

Date: M/MA/IP/D

Title : Organic Chemistry

Aim : To distinguish between alkanes and alkenes

Theory

:

Alkanes are saturated compounds which are relatively inert. They undergo very few reactions which include combustion, cracking and free radical substitution with halogens such as chlorine and bromine. Substitution reaction requires the presence of UV light which is needed to split the inert halogens to from the reactive free radicals.Alkenes on the other hand, are unsaturated compounds which takes part in a wide range of addition reactions due to the presence of the double bond in alkene molecules. The double bonds in alkenes are an electron rich centre which allows it to undergo electrophilic reactions and react with oxidizing agents.

Alkenes decolorize a solution of bromine in 1, 1, 1 trichloroethane

CH3CCl3

C6H12 + Br2 →

C6H12Br2 Hexene reddish – brown colourless 1,2 dibromohexane

Alkenes decolorize an acidified solution of potassium manganate (VII)

KMnO4/H+

C6H12 + →

C6H12(OH)2 Hexene colourless hexane – 1,2 - diol


:1. 1 % bromine in 1,1,1 trichloroethane2. 0.02 mol dm-3 KMnO4

3. Dilute H2SO4

4. Samples of Hexane and Hexene labelled A and B

5. Test tubes

Procedure:

1. To 2 cm3 of sample A in a test tube, bromine was added drop by drop. Solution was stirred and observations were made and recorded.

2. A few drops of dilute H2SO4 was added to 1 cm3 of KMnO4. The acidified KMnO4 was then added drop by drop to another test tube containing 2 cm3 of sample A. The mixture was stirred and observations were made and recorded.

3. Steps 1 and 2 were then repeated with sample B



:

Table 1 Observation tableStep Sample A Sample BOn addition of Bromine Solution turns colourless No visible reactionOn addition of acidified KMnO4.

Solution turns colourless No visible reaction


:

1. Deduce which sample is an alkane and which is an alkene

Sample A is an Alkene and Sample B is an Alkane.

2. Outline the mechanisms for any reactions which occurred.Alkenes contain a double bond, which is an electron rich centre, and in the presence of bromine in 1, 1, 1-trichloroethane, Br2 is added across the double bond, causing decolourization of the bromine solution from brown to colourless, via an addition reaction.

CH3CCl3

C6H12 + Br2 →

C6H12Br2 Hexene reddish – brown colourless 1,2 dibromohexane

Alkenes react with potassium manganate(VII) solution. If the potassium manganate(VII) solution is acidified with dilute sulphuric acid, the purple solution becomes colourless. Manganate(VII) ions are a strong oxidising agent, and they will oxidise the hexene to a diol, while the manganate(VII) ions are reduced to manganese(II) ions.Manganate (VII) ions are purple in solution whereas manganese(II) ions are colourless, and hence there will be a colour change from purple to colourless in the presence of the alkene.

KMnO4/H+

C6H12 + →

C6H12(OH)2 Hexene colourless hexane – 1,2 – diol

Neither of these reactions will occur with the alkane, and so there will be no colour change in the presence of the alkane.

Conclusion : Sample A is Hexene and Sample B is Hexane



Date: M/MA/I P/D

Title : Carbonyl Compounds

Aim : Investigating Carbonyl Compounds

Theory

:

Aldehydes and ketones are carbonyl compounds which contains the carbonyl group

. Aldehydes have a single alkyl or acyl group attached to the carbon atom whilst ketones have two. They both react with 2, 4 dinitrophenylhydrazine (2,4 – DNPH) to give orange precipitates.

Mild oxidising agents such as Tollen’s and Fehling’s reagents can oxidise aldehydes but not ketones. Hence this reaction can be used to distinguish the both of them.

Tollen’s reagent forms a silver mirror on the wall of the test tube and Fehlings solution gives a red-brown precipitate of Copper (I) Oxide.

Three samples are given, two of which are carbonyl compounds, one is an aldehye and the other is a ketone.


:

1. Samples B, C and D2. 2, 4 – DNPH (dissolve 2 g of 2, 4-

DNPH in 4 cm3 of conc. H2SO4, 30 cm3 of methanol and 10 cm3 of water.

3. Fehling’s reagent4. Aqueous NH3 and

AgNO3

5. Measuring cylinders6. Test tubes

Procedure:

1. 3 cm3 of 2,4 – DNPH was added to a few drops of sample B in a test tube and observations were made and recorded.

2. To 3 cm3 of AgNO3 in a test tube, ammonia solution was then added dropwise, while shaking the solution until the precipitate formed re-dissolved. A few drops of sample B was then added to this tube (Tollens Test) and observations were made and recorded.

3. A few drops of sample B was added to Fehlings reagent in a test tube and the tube was gently heated. Observations were recorded.

4. Steps 1-3 was then repeated for Sample C and D.


:

Table 1 ObservationsSolution added Sample B Sample C Sample D

2,4- DNPH Orange precipitate formed

Orange precipitate formed

No visible reaction

AgNO3 and NH3 No visible reaction Silver mirror formed on test tube

No visible reaction

Fehlings reagent No visible reaction Red-brown precipitate

No visible reaction


http://en.wikipedia.org/wiki/Image:Carbonyl-general.png


:

1. Deduce which of the samples are carbonyl compounds.

Sample B and Sample C are both Carbonyl compounds since they both reacted with 2, 4 dinitrophenylhydrazine to give an orange precipitate.

2. Deduce which of the samples is an aldehyde

Sample C is an aldehyde since it was oxidised by both Tollen’s reagent and Fehlings reagent where it formed a silver mirror and a red- brown precipitate respectively. Mild oxidising agents can oxidise aldehydes, but not ketones.

Tollens Test:

CH3CHO(l) + 2Ag+(aq) + H2O(l) →

CH3COOH (aq) + 2Ag(s) + 2H+(aq)

Fehlings reagent gives a red brown precipitate of copper (I) Oxide:

CH3CHO(l) + 2Cu2+(aq) + 2H2O(l) →

CH3COOH (aq) + Cu2O(s) + 4H+(aq)

3. Deduce which sample is a ketone:

Sample B is the ketone, since it gave an orange precipitate with 2, 4 dinitrophenylhydrazine, which means that it is a carbonyl compound, but it showed no reaction with the weak oxidising agents Tollens reagent and Fehlings reagent.

These two tests are used to distinguish between an aldehyde and a ketone.

Discussion

:

Tollens reagent and Fehlings reagent are weak oxidising agents Can be used to distinguish between aldehydes and ketones Shows not reaction with ketones Gives a silver mirror test and red-brown precipitate with aldehydes

Conclusion : Sample B is the ketone and Sample C is an aldehyde.



Date: M/MA/I P/D


Aim : To investigate the oxidation of alcohols

Theory

:

Primary alcohols are readily oxidised to carboxylic acids by a variety of oxidising agents such as acidified potassium dichromate (VI).

Cr2O72- (aq) + 14H+

(aq) + 6e- →

2Cr3+ (aq) + 7H2O(l)

Orange green

Primary alcohols are firstly oxidised to aldehydes and then to carboxylic acids. Secondary alcohols are oxidised to ketones and tertiary alcohols are resistant to oxidation.


:

1. Ethanol2. 5 g dm-3 Potassium dichromate

(VI) solution3. Test tubes4. Water bath

5. Concentrated sulphuric acid

6. Measuring cylinders7. Bunsen burner and

tripod stand

Procedure : 1. 5 cm3 of ethanol was placed in a test tube.2. To this tube, 2 cm3 of potassium dichromate (VI) solution was added,

followed by 3-4 drops of concentrated H2SO4

3. The tube containing this mixture was then placed in a water bath at 60 ºC and any colour change was recorded.

4. The mixture was then allowed to cool and the scent of vinegar was identified coming from the reaction mixture.


:

Table 1: Observations On addition of potassium dichromate (VI) solution

Solution in test tube turned orange colour

On addition of concentrated H2SO4 and heat Colour change from orange →

yellow

→ Light green

→ blue

After cooling The scent of vinegar was noted and two layers were present in the tube, one clear and the other cloudy


: 1. Write equations for any reactions that occurred

An acidified dichromate ion readily accepts electrons and this makes it a powerful oxidising agent.


Cr2O72- (aq) + 14H+

(aq) + 6e- →

2Cr3+ (aq) + 7H2O(l)

Orange green

Initially, the colour of the solution is orange due to the dichromate ions. On oxidation of ethanol, which is a primary alcohol, an aldehyde is formed firstly. Cr2O7

2-/H+

CH3CH2OH(aq) →

CH3HC=O + 2H+ + 2e-

The aldehyde is further oxidised to a carboxylic acid, ethanoic acid.

CH3HC=O + H2O →

CH3COOH + 2H+ + 2e-

2. Describe how this experiment can be scaled up to obtain a pure sample of ethanoic acid.

Discussion : Discuss the principles on which the breathalyser test is based?.

Potassium dichromate, K2Cr2O7, is a yellow-orange compound. When alcohol vapour makes contact with the yellow-coated crystals, the colour changes from yellow to green. The degree of the colour change is directly related to the level of alcohol in the suspect's breath. The oldest breathalyzer models pass breath through a solution of potassium dichromate, which oxidizes ethanol to acetic acid, changing color in the process

Cr6+ →

Cr3+

Orange Green

Conclusion :


http://en.wikipedia.org/wiki/Acetic_acid

http://en.wikipedia.org/wiki/Oxidizes

http://en.wikipedia.org/wiki/Potassium_dichromate


Date: M/MA/I P/D


Aim : To investigate the formation of esters

Theory

:

When an alcohol reacts with a carboxylic acid in the presence of concentrated sulphuric acid, an ester is formed.

RCOOH(l) + R ٰ OH(l) →

RCOOR ٰ (l) + H2O (l)

The ester is recognised by its distinctive fruity smell.


:

1. Ethanol2. Glacial ethanoic acid3. Cold water4. Bunsen burner and tripod5. Boiling tube

6. Concentrated sulphuric acid

7. Measuring cylinders8. Beaker9. Water bath

Procedure:

1. 5 cm3 of ethanol and 5 cm3 of ethanoic acid were placed in a boiling tube.

2. To this tube, 1 cm3 of concentrated H2SO4 was then added.3. The tube containing this mixture was then placed in a water bath at

60 ºC and observations were made.4. After heating the mixture in the water bath for 10 minutes, it was

then poured into a beaker containing ice cold water. Observations were made and recorded.


:

Table 1: Observations On mixing ethanoic acid and ethanol No visible reactionOn addition of concentrated H2SO4 and heat No visible reactionOn pouring mixture in beaker containing ice cold water

Two distinct layers were visible. The top layer was insoluble and cloudy and a sweet fruity smell was emitted.


: 1. Write equations for any reactions that occurred

Ethanol and Ethanoic acid react together to from an ester, ethyl ethanoate

CH3COOH(l) + CH3CH2OH(l) →

CH3COOHCH2CH3(l) + H2O(l)


2. What is responsible for the smell obtained.

The formation of the ester, ethyl ethanoate, which has a fruity smell, is the compound that is responsible for the fruity smell emitted during the reaction.

3. Why is the reaction mixture poured into cold water?

Discussion

:

Ethanoic acid + ethanol →

ethyl ethanoate + water

ethyl ethanoate is a volatile ester with a characteristic fruity smell. Ester formation is an example of a condensation reaction, where

there is elimination of water, and formation of the ester bond.

Conclusion :



Date: M/M A/I P/D

Title : Simple and Fractional Distillation

Aim:

To compare the efficiency of separation of an ethanol- water mixture by simple and fractional distillation.

Theory

:

Simple distillation is used to separate volatile liquids from non- volatile ones with different boiling points. If the boiling points difference between two liquids is less than 60 degrees, then fractional distillation is used instead.Ethanol and water are miscible solvents whose boiling points are 78ºC and 100ºC respectively, and hence fractional distillation is more appropriate for their separation.


:

1. Simple and Fractional distillation apparatus

2. 50-50 mixture of ethanol and water3. Thermometer

4. 50 cm3 measuring cylinder5. Anti-bumping granules6. Hot plate

Procedure

:

1. The class was divided into two groups. One group carried out simple distillation and the other group carried out fractional distillation. The information and data obtained by both groups were then shared within the two groups.

2. The distillation apparatus was set up, using a measuring cylinder as the collecting vessel.

3. 50 cm3 of ethanol- water mixture together with some anti-bumping granules were added to the distilling flask. The flask was then attached to the rest of the apparatus.

4. The distilling flask was placed on a hot plate5. The temperature was recorded when the first drop of distillate came

out.6. The temperature was recorded for every 3 cm3 of distillate that came

out7. Distillation was stopped when there was about 5 cm3 of mixture in the

distilling flask.


:

Table 1 : Temperature readings for distillate collected during fractional distillationVolume of Distillate / cm3 Temperature / ºC

1st drop0306091215


1821242730

Table 2 : Temperature readings for distillate collected during simple distillationVolume of Distillate / cm3 Temperature / ºC

03060912151821242730

Graph1. Plot graph of temperature of distillate against volume of distillate for

simple and fractional distillation on the same axes.

Data Analysis :

1. Use your graph to deduce which type of distillation separates the mixture better

2. Explain graph


:

1. Write a balanced equation for the reaction between hydrochloric acid and sodium hydroxide

Discussion : How would heating more rapidly affect distillation? What effect would using a longer column have on fractional

distillation?

Conclusion :



Date: M/MA/I P/D

Title : Organic Compound

Aim : To analyse substance X4

Theory : Sample X4 is an organic compound which contains four Carbon atoms.


:

1. Sample X4

2. Bromine solution3. Solid Na2CO3

4. Test tubes and test tube racks

5. 2, 4 – DNPH6. Bench reagents :

AgNO3(aq), NH3(aq), NaOH(aq), I2(aq)

7. Measuring cylinder

Procedure:

1. Bromine solution was added dropwise to 3 cm3 of sample X4 and observations were made and recorded

2. Solid Na2CO3 was added to 3 cm3 of sample X4 and observations were made and recorded

3. 2, 4 – DNPH was added dropwise to 3 cm3 of sample X4 and observations were made and recorded

4. Ammonia solution was added dropwise to 4 cm3 of AgNO3 until the precipitate that formed just re dissolved. (Tollens Reagent). A few drops of Sample X4 was then added to this reagent. Any observations made were recorded.

5. 2 cm3 of Iodine solution was added to 3 cm3 of sample X4 . NaOH was then added dropwise while gently shaking. Any observations made were recorded.


:

Table 1: Observations and Inferences made during the experimentTests Observations Inferences

On addition of Bromine solution

On addition of Solid Na2CO3

On addition of 2,4 DNPHOn addition of Tollens

ReagentOn addition of Iodine

Solution

Discussion :


Conclusion :


Lab # 17 Skills Assessed: O/R/RDate: M/M

A/IP/D

Title : Plan Design: To determine the acidity / pH of a soil sample

Case

:

Soil pH is a measure of hydronium ion (H3O+, or more commonly the H+) activity in the soil solution. Soil pH influences many facets of crop production and soil chemistry, including availabilities of nutrients and toxic substances, activities and nature of microbial populations, and activities of certain pesticides. Soils with pH values below 7 are referred to as "acid" and those with pH values above 7 as "alkaline"; soils at pH 7 are referred to as "neutral." Most crops grow best if the soil pH is between 6.0 and 7.5.

Mr. Smith, a farmer, wants to increase his yield of vegetables, but of lately, he finds that his plants are not thriving well. His neighbour tells him that his soil may be too acidic for the plants to grow well, and suggests that he test the pH of his soil to confirm.Plan and Design an experiment to test for the pH of the soil, using a pH meter.


:

1. pH meter2. Electronic balance3. Paper cups4. Standard buffer solutions of pH 2, 4, 7

and 9 for calibrating pH meter

5. Pipettes6. Soil sample7. Deionized water8. Stirrer

Procedure:

1. Calibrate the pH meter over the appropriate range using the standard buffer solutions.

2. Weigh 5 g of sieved, air dried soil sample and place into a paper cup.3. Add 5 ml deionized water to the sample of soil in the paper cup4. Stir the sample for a minute, and then leave to settle for 30 minutes to

form a slurry5. After formation of slurry, place electrodes of the pH meter into the slurry

and read the pH, ensuring that the electrodes tips are in the slurry.6. Repeat the above procedure at least twice for accuracy.


:

Table 1 : Recorded pH of soil sampleSamples pH

Sample 1Sample 2Sample 3

Discussion:

Which type of water (distilled, deionized, tap water) is preferred, and give reasons why?

Theoretically, if the pH of a soil sample is 2, and you want to obtain the optimum pH for best growth of crop, that is, a pH between 6.0 and 7.5, what procedures can be done to this soil sample in order to achieve this optimum pH?

Give two precautions that should be undertaken when carrying out your


experiment?

Conclusion :

Lab # NA Skills Assessed: O/R/RDate: M/M

A/IP/D

Title : Plan Design: To purify a sample of rock salt

Case

:

Rock salt, also known as halite, or impure NaCl, is typically formed by the evaporation of salty sea water which contains dissolved Na+ and Cl- ions, as well as other impurities such as potassium and sulphates. Rock salt is also applied to road beds in cold climates to help reduce the freezing point of water on the road, and since saline has a lower freezing point that water, putting rock salt on ice will cause it to melt. Table salt is essential for human life. A large amount of the commercially mined rock salt is prepared for human consumption. Plan and design an experiment to obtain pure NaCl, or table salt, from a sample of impure rock salt. Include how you would be able to find the percentage of mass of salt crystals recovered from the sample of rock salt.


:

1. Sample of rock salt2. Balance / Scale3. Filter paper and funnel4. Bunsen burner

5. Conical flasks6. Distilled water7. Ice bath8. Beakers

Procedure : 1. Weigh 10 g of the rock salt using the electronic balance2. Place this sample in a beaker, and then dissolve it in a small amount of hot

water, while stirring the mixture3. Weigh a sheet of filter paper and record this value4. After dissolving the sample of rock salt, then filter the mixture, collecting

the filtrate in a conical flask5. Allow the filtrate in the conical flask to cool by placing in into an ice bath,

to recrystallize the NaCl6. Filter the crystals with distilled water to allow for any soluble impurities

to be removed7. Wash, dry and weigh the crystals within the filter paper.


:

Table 1 : Mass of rock saltMass of rock salt / g

Table 2 : Mass of purified saltMass of filter paper and crystals / gMass of filter paper / gMass of crystals / g

Data Analysis

: 1. Mass of purified crystals (g) = mass of filter paper and crystals (g) – mass of filter


paper (g)

2. Percentage by mass of salt crystals recovered from the sample of rock salt

= mass of purified crystals(g)

mass of rock salt (g) x 100

Discussion : Conclusion :

Lab # 18 Skills Assessed: O/R/RDate: M/M

A/I P/D

Title : Analytical Chemistry Back Titration

Aim:

To determine the mass of 2-ethanoylhydroxy-benzoic acid in a commercial brand of an aspirin tablet by back titration

Theory

:

Aspirin is an analgesic compound which has to ability to reduce inflammation and hence acts as both a pain killer and a fever reducer. The active ingredient in aspirin tablet is 2-ethanoylhydroxy-benzoic acid (acetylsalicylic acid), the ester linkage in aspirin is hydrolyzed/broken by alkalis to form ethanoate ions and 2-hydroxybenzoate (salicylate) ions.

CH3COOC6H4COOH + 2OH- →

CH3COO- + HOC6H4COO- + H2O

An aspirin tablet can be hydrolyzed with excess sodium hydroxide and then back titrated with hydrochloric acid. The amount of alkali used for the hydrolysis can then be calculated and from this information, the mass of 2-ethanoylhydroxy-benzoic acid in an aspirin tablet can be determined.


:

1. Aspirin tablets2. Standard 0.2 mol dm-3 NaOH3. Standard 0.1 mol dm-3 HCl4. 50 cm3 burette

5. 25 cm3 pipette6. 3 conical flasks7. Bunsen burner 8. Phenolphthalein indicator

Procedure:

1. 25 cm3 of NaOH was pipetted into a conical flask and one aspirin tablet was added to this flask. The solution was then warmed gently to allow the tablet to dissolve.

2. The solution was then cooled, and three drops of Phenolphthalein indicator was then added to it.

3. This solution was then titrated with hydrochloric acid.4. Steps 1 to 3 were then repeated until accurate results were obtained.


:Table 1: Volume of HCl used in the titration

Rough AccurateFinal burette reading / cm3 8.6 17.2 25.8 34.3


Initial burette reading / cm3 0.0 8.6 17.2 25.8Volume of HCl used / cm3 8.6 8.6 8.6 8.5

25 cm3 of aspirin and NaOH required 8.6 cm3 of HCl in the titration.

Discussion:

1. Write a balanced equation for the reaction between hydrochloric acid and sodium hydroxide

2. Calculate the number of moles of NaOH in the 25 cm3 of alkali used.3. F ind the number of moles of HCl used in the titration

4. How many moles of NaOH reacted with HCl in the titration5. How many moles of NaOH reacted with the 2-ethanoylhydroxy-benzoic

acid in one aspirin tablet.6. Calculate the number of moles of 2-ethanoylhydroxy-benzoic acid in one

aspirin tablet.7. Determine the mass of 2-ethanoylhydroxy-benzoic acid in one aspirin

tablet.Conclusion :



Date: M/M A/I P/D

Title : Environmental

Aim : To test for pollutants in water

Theory

:

Pollutants found in water include cyanide, lead (II) ions, nitrates and phosphates. Cyanide is converted to thiocyanate when it reacts with sulphur. This ion is found in effluents from mining and industrial factories. Certain pesticides also contain thiocyanate ion as the main ingredient. Phosphates are nitrates are present in fertilizers and detergents, and these can also pollute the waterways.

Carry out the following procedure to test for SCN-, NO3-, PO4

3- and Pb2+.

SCN- gives a blood red colour on addition of aqueous iron (III) nitrate.PO4

3- gives a bright yellow precipitate when warmed with ammonium molybdateNO3

- is identified via the brown ring testA white precipitate is formed with Pb2+ on addition of hydrochloric acid.


:

1. Samples of Polluted water P, Q and R

2. 0.1 mol dm-3 iron (III) nitrate solution

3. 0.1 mol dm-3 ammonium molybdate4. Solid iron (II) sulphate5. Bunsen burner 6. spatula

7. Conc. H2SO4 8. Conc. HNO3

9. Bench HCl and H2SO4

10. Test tubes11. Water bath

Procedure:

1. Iron (III) Nitrate was added drop by drop to 2 cm3 of sample P in a test tube. Observations were made and recorded.

2. 2 cm3 of sample P in a test tube was acidified with dilute H2SO4. Half a spatula of solid iron (II) sulphate was then added to the acidified sample.

3. To this acidified sample of P, 0.5 cm3 of Conc. H2SO4 was then carefully added, by letting it flow down the side of the test tube. The mixture was then left undisturbed until two separate layers were formed within the test tube. Observations were made ad recorded.

4. 2 cm3 of sample P in a test tube was acidified with Conc. HNO3. A little amount of ammonium molybdate was then added and the tube was then gently warmed in a water bath. Observations were made and recorded.

5. Dilute HCl was added to 2 cm3 of sample P in a test tube. The


mixture was then heated for one minute and then allowed to cool. Any observations were recorded.

6. Steps 1-5 were then repeated for both sample Q and R


:

Table 1 : Observations made during the experiment for all three samples P, Q and R

SamplesObservations with:

Fe(NO3)3(aq) Fe2+(aq)/conc. H2SO4 (NH4)2MoO4(aq) HCl (aq)

PQR

Data Analysis and Interpretation :

1. Deduce which of the samples of water are polluted with: Thiocyanate ions Nitrate ions Phosphate ions Lead (II) ionsJustify your answers.

Conclusion :



Date: M/M A/I P/D

Title : Plan and Design : Organic Chemistry

Aim : Organic

Case

:

Mr. Smith wants to buy a new car. He has a choice of vehicles which run on leaded gasoline, unleaded gasoline, compressed natural gas, and diesel. His environmentally conscious friend suggests he buys a car which contributes to the least amount of pollution. Suggest which fuel is most environmentally friendly and plan and design an experiment to test your suggestion.


:1. 2.

Procedure : 1.2.3.4.5.6.


:


:

Discussion :

Conclusion :




Date: M/M A/I P/D

Title : Plan and Design : Analytical Chemistry (Gravimetric)

Aim :

Case

:

Caesium nitrate, CsNO3, decomposes on heating.The decomposition is represented by one of the following equations.

4CsNO3(s) 2Cs2O(s) + 4NO2(g) + O2(g)2CsNO3(s) 2CsNO2(s) + O2(g)

You are to devise a method of heating the solid nitrate, collecting the gas given off and measuring its volume.From the experimental results you are to determine which is the correct equation for the decomposition.

Information that may be used to prove your plan and design.The molar volume of gas, Vm, is 24.0 dm3 mol–1 under room conditions.Nitrogen dioxide, NO2, a toxic gas, is soluble in water.Oxygen, O2, is not soluble in water.[Ar; Cs, 133.0; N, 14.0; O, 16.0.]


:1. 2.

Procedure : 1.2.3.4.5.6.

Diagram :


:


:

Discussion :


Conclusion :


Documents

Final Upper 6 Labs With Results and Marking Scheme 2011 2012 7