Titrations P

Acid Base TitrationsAcid Base Titrations

Keith WarneKeith Warne

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Titration Calculations.Titration Calculations.

(COOH)(COOH)22.2H.2H22O O Unknown Unknown BaseBase (NaOH) (NaOH)OXALIC ACIDOXALIC ACID STANDARDSTANDARD SOLUTION SOLUTION

ccb b = ………….. mol.dm= ………….. mol.dm-3-3

(COOH)(COOH)22.2H.2H22O + 2NaOH --> NaO + 2NaOH --> Na22(COO)(COO)2 2 + 4H + 4H22OO

250 cm3

………..g

?

Concentration and Concentration and volume known volume known

accuratelyaccurately!!

nnvv

C =C =

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Standard SolutionA standard solution is one for which

the concentration is precisely known.

Since

c = ................/..................

= .................

Needed:• The number of moles of solute (from

...............)• The volume of solution.

These values must be accurately determined.

Mass is determined accurately using an electronic balance.

1.60gsolute

Volume is measured using a

Volumetric flask.• 250 cm3

• 100 cm3 • 200 cm3

250 cm3






Weighing TechniqueProcedure - Weighing by difference.

1. .............. scales and clean the pan.

2. Weigh the weighing ....................

3. Add (................................) the required amount of salt. Take care not to drop any salt onto the pan.

4. Transfer the salt to a ................. beaker.

5. ................................ the weighing container.

6. ......................... the final mass of the container from the mass of salt and container to give the mass of salt transferred to the beaker.

Mass is determined accurately using an balance (electronic or triple beam).

• Possible accuracies of 0.1 - 0.0001g

2.45g

(COOH)2

Results: Mass salt + container: ………… Final Mass container: …………

Mass salt transferred:






Making a standard solution. 1. Rinse a clean & dry 100 cm3 beaker

with a little distilled water.

2. Transfer the correctly weighed amount of salt to the beaker. ........................... .............................................................

3. Add distilled water to the salt and stir gently with a glass rod until all salt is dissolved. DO NOT REMOVE THE ROD FROM THE SOLUTION NOR ALLOW ANY DROPS OF SOLUTION

TO .........................................

4. Add ALL the solution to a volumetric flask via funnel. Ensure glass rod and beaker are thoroughly rinsed. (Include

...................................)

4. Add enough solvent to bring the level

........................................

………..g

solute

250 cm3






Making a standard solution. 1. Use a dropper to bring the

level up to the mark.

2. The BOTTOM of the meniscus must .................. .......................... THE LINE of the flask.

3. The flask should then be ........................ at least ........ times to ensure thorough mixing.

The bottom of the meniscus must JUST touch the line!!! 250 cm3

Drag here






Titration Proceedure.Titration Proceedure.

ACIDACID STANDARD STANDARD SOLUTIONSOLUTION

unknown BASEBASE

1. Rinse# the burette with distilled ................and then with small quantities of the ............................................solution.

2. Fill the burette with the standard ......................solution.

3. Take the ......................................reading. Does not have to be ..............

4. Rinse # a clean conical flask with .........................................

5. Rinse # a clean pipette with the .................................solution.

6. Pippette 25cm3 of the ...............................solution into the conical flask.

7. Add 3-5 drops of a suitable .......................to the conical flask.

8. Titrate the acid against the base until the FIRST ..................................................COLOUR CHANGE.

9. Note down the volume of acid and repeat this procedure with a fresh conical flask until ...................................RESULTS are obtained. ~0.1 cm3.







ACIDACID STANDARD SOLUTIONSTANDARD SOLUTION

a ACIDa ACID + + b BASEb BASE salt + water

AT THE END POINTAT THE END POINT

molesmoles ............ ............moles moles ........................

== ........................

unknown BASEBASE

......................

......................== ........

........

25cm3

= 0.025dm3

C(mol.dm-3)V (dm-3)






CCaaVVaa

CCbbVVbb

==aabb

Conc of acid = ? x (trying to find)

Volume of acid –

burette = ......................

Molar ratio from ........................... reaction a = acid coefficient (2) b = base coef. (1)

(1)Na2 CO3 + 2 HCl 2NaCl + H2O + CO2

Conc of base= your

..................... soln. Worked out.

Vol. of base= ........................ (25cm3)

Solve for x

Titration Calculations






Titration Calculations.

(COOH)2.2H2O • Unknown Base (NaOH)OXALIC ACIDOXALIC ACID STANDARDSTANDARD SOLUTION SOLUTION

ccb b = ………….. mol.dm= ………….. mol.dm-3-3

(COOH)(COOH)22.2H.2H22O + 2NaOH --> NaO + 2NaOH --> Na22(COO)(COO)2 2 + 4H + 4H22OO

250 cm3

………..g

?

Concentration and Concentration and volume known volume known

accuratelyaccurately!!

nnvv

C =C = CCaaVVaa

CCbbVVbb

== aabb






(COO)(COO)22.2H.2H22O O

MMrr = (2(12+32+1)+2(18)= 126 = (2(12+32+1)+2(18)= 126

6.4g in 1l (1dm6.4g in 1l (1dm33))

Moles(ACID) = m/MMoles(ACID) = m/Mrr

= 6.4/(126) = 6.4/(126)

= 0.05mol/1dm= 0.05mol/1dm33

Concentration (ACID) = 0.05 MConcentration (ACID) = 0.05 M

Unknown Base (NaOH)Unknown Base (NaOH)OXALIC ACID OXALIC ACID STANDARD SOLUTIONSTANDARD SOLUTION

AT THE END POINTAT THE END POINT

(1)(1)(COO)(COO)22.2H.2H22O + O + 22NaOH --> NaNaOH --> Na22(COO)(COO)2 2 + 4H + 4H22OO

One mole of acid One mole of acid reacts withreacts with 2 moles of base. 2 moles of base..: n(acid) .: n(acid) : : n(base) n(base) 11 : : 2 2

CCaaVVaa

CCbbVVbb

==1122


Titration ExampleTitration Example If 22.3 cmIf 22.3 cm-3 -3 of a standard hydrochloric acid solution (0.15 of a standard hydrochloric acid solution (0.15

M) was required to reach end point with 25 cmM) was required to reach end point with 25 cm-3-3 of an of an unknown sodium carbonate solution, what is the unknown sodium carbonate solution, what is the concentration of the sodium carbonate solution?concentration of the sodium carbonate solution?

2HCl + Na2HCl + Na22COCO3 3 2NaCl + CO 2NaCl + CO2 2 + H+ H22OO

CCaaVVaa

CCbbVVbb

== 1122

(0.15) (0.0223)(0.15) (0.0223)CCbb (0.025) (0.025)

1122

==

CCbb = = = = 0.268 M0.268 M2*(0.15) (0.0223)2*(0.15) (0.0223)1* (0.025)1* (0.025)





NameName

of indicator of indicator

Colour Colour acidacid

Colour Colour basebase

pH pH rangerange

Methyl OrangeMethyl Orange RedRed YellowYellow 3 - 43 - 4

Bromothymol BlueBromothymol Blue YellowYellow BlueBlue 6 - 86 - 8

PhenolphthaleinPhenolphthalein ClearClear RedRed 8 - 108 - 10







pH

0

....

Amount of ............ added

...

The end The end point has a point has a pH lower pH lower than 7 than 7 because because the SALT the SALT of a of a STRONG STRONG acid and a acid and a weak base weak base is is ACIDIC!!ACIDIC!!

WEAK BASE

STRONG ACID

END POINT

STRONG ACID WEAK BASESTRONG ACID WEAK BASE

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STRONG BASE WEAK ACID

Strong acid/strong baseStrong acid/strong base ....................................................................

Strong acid/weak baseStrong acid/weak base ....................................................................

Weak acid/strong baseWeak acid/strong base ....................................................................

pH

0

14

Moles of base added

7

Strong acid

Weak acid

Weak base

Strong base

Blue

Bromothymol blue

Yellow

Methyl OrangeRed

Pink

PhenolphthalienColourless

STRONG BASE STRONG ACID

WEAK BASE STRONG ACID



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Titrations P