Chemistry Unit 3 and 6

8/19/2019 Chemistry Unit 3 and 6

1/17

Flame test

1 Clean end of platinum/nichrome wire with(conc)HCl, burning off impurities in a roaring bunsen flame until there’s no persistent flame colouration

2 Moisten the end of the clean wire with (conc)HCl and then dip into the sample to be tested

3 Hold the sample at the edge of a roaring bunsen flame

ithium Carmine red Calcium !ric" red

#odium $ellow #trontium Crimson

%otassium ilac !arium &pple green

Gas Test

&mmonia 'H3 %ungent smell, Moist litmus paper red blue, (conc)HCl at mouth of bottle, white smo"e forms

Carbon dioide C2 %ass through lime water, turning lime water mil"*

CaCO3(s) + H2O(l) + CO2(g) Ca(HCO3)2(aq)

imewater C2 test Ca(OH)2(aq) + CO2(g) CaCO3(s) +hite ppt + H2O(l)

Chlorine Cl2 #wimming pool smell, moist litmus paper blue red bleached

H*drogen H2 ighted splint, burns with suea"* popH*drogen chloride HCl Moist litmus paper blue red

'itrogen(-.)oide '2 !rown gas, acrid smell, moist litmus paper blue red

*gen 2 lowing splint, relights

+ater 0apour H2 +hite anh*drous copper(--) sulphate white blue Cu#(s) H2(l) Cu#4H2(s)

r dr* blue cobalt chloride paper blue pin"

#ulphur dioide #2 &crid smell, moist litmus paper blue red

r potassium dichromate(.-) solution/paper from orange green

Cation Test Add NaOH(aq) Add NH4OH(aq)

&mmonium 'H 5 Heat, ammonia e0ol0ed, moist litmus paper red blue

H 5 Moist litmus paper blue red

5 &dd a carbonate, pass gas through lime water, C2 e0ol0ed turning lime water mil"*

Copper(--) Cu2 5 & little, blue ppt forms

5 -n ecess, insoluble

5 & little, blue ppt forms

5 -n ecess, dissol0es and a dar" blue solution forms

-ron(--) 6e2 5 & little, green ppt forms


5 & little, green ppt forms

5 -n ecess, insoluble-ron(---) 6e3 5 & little, brown ppt forms


5 & little, brown ppt forms


Calcium Ca2

Magnesium Mg2

5 & little, mil"* suspension forms


5 & little, mil"* suspension forms


7istinguish Mg from Ca through flame test

5 & little, mil"* suspension forms5 -n ecess, insoluble

5 & little, mil"* suspension forms5 -n ecess, insoluble

&luminium &l3

ead %b2

5 & little, white ppt forms

5 -n ecess, dissol0es gi0ing colourless solution



'o ppt with (dil)H2#/cold(dil)HCl/(dil)8-/(dil)'a2# #odium sulphide

5 & little, white ppt forms5 -n ecess, dissol0es gi0ing colourless solution

5 & little, white ppt forms5 -n ecess, insoluble

+hite ppt with (dil)H2# +hite ppt with cold(dil)HCl

$ellow ppt with (dil)8- !lac" ppt with (dil)'a2# #odium sulphide

9inc 9n2 5 & little, white ppt forms

5 -n ecess, dissol0es gi0ing colourless solution


5 -n ecess, dissol0es gi0ing colourless solutionAnion Test

Carbonate pH:1; C32


2/17

Synthetic ath!ays(#eries of reactions built up to con0ert one functional group into another)

5 Aeactions of functional groups assumed to be the same whether molecules are simple or complicated5 #*nthesis of the product molecule possible because in an* reaction of a functional group a product is formed capable of con0ersion

into other molecules

∆ H B(g)usedof mass

CD41=431 attach plunger with string

('H)2C3 reacts with both 1moldm acid haNard

5 #hould not affect identification since e0en if Mr is slightl* wrong it will still correspond to nearest roup 1 metal atomic mass

%lan an eperiment to identif* an acidic compound, molar mass for an acid estimated to be == O 2 g mol


3/17

(1)& sample of 'aCl was thought to contain an impurit* of !a('3)2 & student suggested a flame test

(a)(i)#uggest wh* a flame test on the miture would not be a satisfactor* wa* of detecting the presence of barium ions in the sample

(i) 5 *ellow/stronger/persistent 'a flame 5 bscures/!a flame NOT Pma"es it difficult to distinguish between the two coloursQ

(ii)#uggest a reagent that could be used to produce a ppt of a barium compound from a solution of the sample(ii) 5 (conc)H2#(solution) of an* soluble sulphate (Mg#, ('H)2#, 'a2#)

(2)(a)R(has H group)decolourised cold potassium manganate(.--) acidified with (dil)H2# acid, structure of R suggested b* thisF

(a)carbon double bond

(b)Complete oidation of R with potassium dichromate(.-) solution and (dil)H2# acid produces $ CHK structure for $F

(b)

H HH

C C HC C HC C )HC C H

H H)

2 3 ( # )

(c)#tructural formula for RF(c)

H HH H

C C C HC

H H) H

( 2 )

R must be a secondar* alcohol because "etone formed on oidation carbo*lic acid is not formed

(3)(a)+rite an ionic euation for the h*drol*sis of 1>bromobutane b* water (a)CHH?!r H2 → CH?H H !r


4/17

EDEXCEL AS CHEMISTRY UNIT 3 NOTES

Specification

a) Recognise the results of reactions of compounds specically mentioned in Units 1 and

2 of the specication and the results of tests for simple ions: carbonate,

hydrogencarbonate, sulphate(VI), sulphite, chloride, bromide, iodide, nitrate, ammonium,

lithium, sodium, potassium, magnesium, calcium, strontium and barium

Tests

nFormul

aTest Observatons

rbonate CO32-

Test !

Heat the solid in a test tube with a Bunsenburner.

It should decompose producing the oide

and carbon dioide. !.g.

Test for the gas using limewater solution.

"imewater should turn from

colourless to cloud# in thepresence of carbon dioide due to

precipitation of calciumcarbonate.

Test "$dd dilute HCl to the solid.

Test for the gas e%ol%ed using limewatersolution.

&igorous effer%escence."imewater should turn fromcolourless to cloud# in the

presence of carbon dioide due toprecipitation of calcium

carbonate.

$ro%en&arbonate HCO3-

Test

$dd calcium chloride to a

h#drogencarbonate solution.

'o precipitate forms since

calcium h#drogencarbonate is

soluble.

phate (&I) SO*2-

Test$dd barium chloride solution acidified withdilute HCl to the test solution.

+hite precipitate of bariumsulphate forms.

l'(te SO32-

Test

+arm the sulphite with dilute HCl.Test for gases using acidified potassiumdichromate(&I) solution (or paper)

The solution turns green.

lor$e Cl-

Test !

$dd concentrated sulphuric acid to the solidchloride.

+hite steam# acidic fumes are

seen - HCl fumes.

Test "

$dd dilute nitric acid to a solution of a chlorideto acidif# the solution. This eliminates an#

carbonates or sulphites.$dd sil%er nitrate to the solution.

$dd dilute ammonia solution.

+hite precipitate of $gCl forms.

Solid dissol%es.

om$e Br-

Test ! Steam# brownish acidic fumes

http://void%280%29/


5/17

$dd concentrated sulphuric acid to the solidbromide.

are seen.

Test "*$dd dilute nitric acid to a solution of a

bromide to acidif# the solution. Thiseliminates an# carbonates or sulphites.

$dd sil%er nitrate to the solution.$dd concentrated ammonia solution.

Cream precipitate of $gBr forms.

Solid dissol%es.

$$e I-

Test !$dd concentrated sulphuric acid to the solid

iodide.

,urple acidic fumes are seen. Themiture turns to a brown slurr#.

Test "

$dd dilute nitric acid to a solution of a iodideto acidif# the solution. This eliminates an#

carbonates or sulphites.

$dd sil%er nitrate to the solution.

$dd concentrated ammonia solution.

ellow precipitate of $gI forms.

Solid is insoluble.

trate 'O3-

Test !

Heat solid nitrate.

If group solid (not "i) then will decomposeto gi%e the nitrite and o#gen.

$ll other solid nitrates decompose to gi%e

the metal oide/ nitrogen dioide ando#gen.

O#gen gas is e%ol%ed that will

relight a glowing splint.

Brown gas is seen ('O2). O#gengas is also e%ol%ed and will

relight a glowing splint.

Test "

Boil nitrate solution with aluminium01e%ardasallo#/ in sodium h#droide solution.

Test %apour with red litmus paper.

"itmus paper turns blue in thepresence of ammonia.

mmonum 'H*

Test+arm ammonum &om'oun$ ,t(

NaOH-Test va'ours mme$atel# usn% $am'

re$ ltmus 'a'er-

'H3

turns the litmus paper blue.

(um "i

Test

1ip nichrome wire in HCl.

1ip wire in solid.

Heat wire in centre of flame.

Obser%e colour of flame.$ carmine red flame is seen.

$um 'a

Test


1ip wire in solid.


Obser%e colour of flame.

$ #ellow flame is seen.


6/17

tassum 4

Test1ip nichrome wire in HCl.

1ip wire in solid.



$ lilac flame is seen.

%nesum 5g2Test

$dd 'aOH solution to the magnesium solid.

$ white solid forms which isinsoluble in ecess 'aOH(a6).

This is 5g(OH)2(s)

l&um Ca2

Test


1ip wire in solid.



$ bric7 red flame is seen.

rontum Sr2

Test


1ip wire in solid.



$ crimson red flame is seen.

rum Ba2

Test


1ip wire in solid.



$ apple green flame is seen.

b) Recognise the chemical tests for simple gases, to include hydrogen, oygen, carbon

dioide, ammonia, chlorine, nitrogen dioide and sulphur dioide


7/17

Tests

meFormul

aTest Observatons

$ro%en H2 Ignite gas. S6uea7# pop is heard.

#%en O2,lace a glowing splint in asample of the gas.

The glowing splint relights.

bon

/$eCO2

Bubble gas through limewater(saturated solution of calcium

h#droide)

$ solution turns from colourless to cloud#. $ white(mil7#) precipitate of calcium carbonate forms which is

sparingl# soluble.

mona 'H3Test for gas using damp redlitmus paper.

"itmus paper turns blue.

orne Cl2

Test !

Test for gas using damp litmuspaper (red or blue)

Chlorine bleaches the litmus paper %er# 6uic7l#.

Test "Test for gas using moist starch-iodide paper.

The paper turns blue-blac7.

Test 3,ass gas through a solution of abromide.

The solution turns from colourless to orange.

Test 0

,ass gas through a solution of

an iodide.

The solution turns from colourless to brown (possibl#with a blac7 precipitate/ iodine).

ro%en

/$e'O2 'ot man# tests for this gas. The gas is brown.

'(ur/$e

SO2

Test !Bubble gas through a solutionof potassium dichromate (&I)

dissol%ed in sulphuric acid.

The solution turns from orange to green.

Test "

Bubble gas through a solutionof potassium manganate (&II)

dissol%ed in sulphuric acid.

The solution turns from purple to colourless.

c) !escribe the techni"ues used in #olumetric analysis and enthalpy change

measurements


8/17

Volumetric analysis

&olumetric anal#sis (titration) in%ol%es the reaction between two solutions. 8or one solution/ both the %olume and the

concentration are 7nown9 for the other/ the %olume onl# is 7nown. $pparatus used includes a burette/ a pipette and a

%olumetric flas7.

+(at s a stan$ar$ soluton1

$ solution for which concentration is accuratel# 7nown. The concentration ma# ha%e been found b# a pre%ious titration

or b# weighing the solute and ma7ing a solution of 7nown %olume. Such a solution is a primar# standard solution.

Ho, s a "2&m3 stan$ar$ soluton 're'are$1

• 5a7e sure that the balance is clean and dr#. +ipe it with a damp cloth.

• ,lace the weighing bottle on the pan and ta7e the balance (i.e. re-:ero it)

• Ta7e the bottle off the balance and add solid to it. This ensures that no spillages fall on the pan.

• Ta7e the balance of the weighing bottle solid and find the balance of solid b# subtraction.

• ;eplace on balance/ and if the re6uired amount is added/ withdraw the mass.

• +hen #ou ha%e the re6uired amount/ write its %alue down immediatel#.

• +ash out a 2


9/17

• Close the tap and fill the burette. $ small funnel should be used to add the solution but be careful not to

o%erfill the funnel.

• ;emo%e the funnel/ because titrating with a funnel in the burette can lead to serious error if a drop of li6uid in

the funnel stem falls into the burette during the titration.

• Bring the meniscus on to the scale b# opening the tap to allow solution to pass through the burette. There is

no particular reason to bring the meniscus eactl# to the :ero mar7.

• 5a7e sure that the burette is full to the tip of the >et.

• $fter a suitable indicator has been added to the solution in the conical flas7/ swirl the flas7 under the burette

with one hand whilst ad>usting the burette tap with #our other hand.

• $dd the solution in the burette to the conical flas7 slowl#/ swirling the flas7 all the time.

• $s the endpoint is approached/ the indicator will change colour more slowl#. The titrant should be added drop

b# drop near to the endpoint.

• ;epeat the titration until #ou ha%e three concordant titres/ i.e. %olumes that are similar. This means within

=.2cm3 or better if #ou ha%e been careful. Ta7ing the mean of three tires that differ b# cm3 or more is no

guarantee of an accurate answer.

Common n$&ators

• 5eth#l orange - #ellow in al7ali/ red in acid orange in neutral solutions(usuall# the end point of a titration)

• ,henolphthalein - pin7 in al7ali/ colourless in acid.

Enthalpy change measurements

• +eigh a spirit lamp (containing a li6uid alcohol) using a balance accurate to 3 decimal places. ;ecord the mass

measured.

• Ase a measuring c#linder to put == cm3 of distilled water into a small bea7er and clamps this at a fied

height abo%e the spirit lamp (about 2 cm).

• ;ecord the initial temperature of the water using a thermometer.

• "ight the lamp using a burning splint.

• Heat the water using the spirit lamp until the temperature has gone up b# about =C. Stir the water with the

thermometer the whole time.

• ,ut a cap on the spirit to stop the alcohol burning. The lid stops also stops further e%aporation of the li6uid

alcohol.

• ;eweigh the spirit lamp and record the mass.

• Calculate the enthalp# change

.ossble sour&es o4 error

• There ma# be heat loss due to the apparatus used and heat ma# ha%e dissipated through the insulating

material -- should use a pol#st#rene cup and insulation li7e a lid.

• The specific heat capacit# and densit# of water are used (and not of HCl).


10/17

• The masses of solid added to the acid are ignored.

• It is assumed that the specific heat capacit# of the pol#st#rene cup is negligible.

• Some heat is lost when the h#drogen or carbon dioide are e%ol%ed in the reactions.

d) !escribe the techni"ues used in simple organic preparations such as distillation and

heating under re$u

Heating under reflu - This allows reactions to occur slowl#/ o%er a long period of time/ without an# loss of %olatile

li6uid. The sol%ent e%aporates and is condensed and returns to the flas7.

Many organic reactions are slow and require prolonged heating

• To achie%e this without loss of li6uid/ reaction mitures are heated in a flas7 carr#ing a %ertical condenser.

• This is heating under reflu9 the sol%ent is condensed and returned to the flas7/ so the miture can be heated

as long as desired.

• To heat the round bottomed flas7/ either use a water bath/ an oil bath or a heated plate mantle. $ Bunsen

burner isnt reall# suitable.

Simple distillation

To separate a %olatile sol%ent from a miture

• Simple distillation is used where a %olatile component has to be separated from a miture/ the other

components of the miture being %er# much %olatile or non-%olatile.

• The miture is heated.

• The fraction that boils is collected within the temperature range of the fraction. (normall# or 2 degrees

before the boiling temperature)

• The condenser cools the fraction so it distils and is collected in the recei%ing flas7.


11/17

Fractional distillation

To separate mitures of %olatile li6uids.

• ;e-cr#stallisation - Ased to purif# a solid material b# remo%ing both soluble and insoluble impurities. The

choice of sol%ent is important. The substance must be easil# soluble in the boiling sol%ent and much less soluble at

room temperature. This ensures the smallest possible loss of material/ although some loss is ine%itable with this

techni6ue.

Re5Cr#stallsaton Met(o$

• 1issol%e the solid in the minimum amount of boiling sol%ent. This ensures that the solution is saturated with

respect to the main solute but not with respect to the impurities/ which are present in much smaller amounts.

• 8ilter the hot miture through a preheated filter funnel. This remo%es insoluble impurities. The hot funnel is

necessar# to pre%ent the solute cr#stallising and bloc7ing the funnel. 8iltration under %acuum using a Buchner

funnel is often preferred/ because it is fast.

• Cool the hot filtrate/ either to room temperature or/ if necessar#/ in a bath of iced water. ;apid cooling gi%es

small cr#stals/ slow cooling large ones. The large cr#stals are often less pure.

• 8ilter the cold miture using a Buchner funnel.

• +ash the cr#stals with a small amount of cold sol%ent. This remo%es an# impurit# remaining on the surface of

the cr#stals. $ small amount of cold sol%ent is used so that the cr#stals arent washed awa# 0 dont dissol%e.

• Suc7 the cr#stals as dr# as possible on the filter.

• Transfer the cr#stals to a desiccator to dr#. 1r#ing between filter paper is sometimes recommended/ but it is a

%er# poor method.

Melting point determination

This is used to determine the purit# of the re-cr#stallisation solid. ,lace small amount of the solid in the sealed end of

a capillar# tube. ,lace in the melting point apparatus. $ sharp melting point o%er a small range shows purit#/ when

compared with the set-boo7 %alue of a higher melting point/ that indicates an impure solid.

Organic tests

• Collect = cmD of the samples.

• Test the samples in the following order

• $l7enes E bromine water -- decolourises -- al7ene

• $lcohols E Spatula of solid ,Cl


12/17

e) recall and interpret details of the chemistry of the elements and compounds listed in

Units 1 and 2 of this specication

this includes the chemistr# of Groups / 2 and and the chemistr# associated with the organic compounds

listed in topic 2.2

Sulphate solubilit#

If a solution of an# sulphate is added to a solution of a group 2 metal compound then a precipitate is li7el#.

6rou' " on n soluton E44e&t o4 a$$n% a sul'(ate soluton

5g2 'o precipitate/ 5gSO* is soluble

Ca2 +hite precipitate of CaSO*

Sr2 +hite precipitate of SrSO*

Ba2 +hite precipitate of BaSO*

H#droide solubilit#

If sodium h#droide is added to a solution of a group 2 compound then a precipitate is li7el#.

6rou' " on n soluton E44e&t o4 a$$n% a (#$ro/$e soluton

5g2 8aint white precipitate of 5g(OH)2

Ca2 8aint white precipitate of Ca(OH)2

Sr2 8aint white precipitate of Sr(OH)2 on standing

Ba2 'o precipitate/ Ba(OH)2 is soluble

Heating carbonates and nitrates

Substan&e E44e&t o4 (eat

"ithium and all group 2 carbonates Carbon dioide detected

Sodium and potassium carbonates 'o effect (ecept water of cr#stallisation ma# be gi%en off)

Sodium and potassium nitrates O#gen onl# gas e%ol%ed

"ithium and all group 2 nitrates 'itrogen dioide and o#gen e%ol%ed

$ction of heat on compounds

• Carbonates - Carbon dioide is gi%en off.

• H#drogencarbonates - Carbon dioide and water formed.

• Group nitrates - 'itrite and o#gen formed.


13/17

• Group 2 nitrates - Oide/ brown fumes of nitrogen dioide and o#gen formed.

1istinguishing between h#drocarbons

• $l7ane Burn 0oidise0combust them. The# will burn with a #ellow flame and form CO2 and H2O (limited

suppl# of CO).

• $l7ene $ #ellow/ sootier flame is produced (due to the etra carbon and higher ratio of carbonh#drogen).

Identif#ing some functional groups

• $l7ene - $dd to orange bromine water. The al7ene will decolourise it.

• Halogenal7ane - Heat with sodium h#droide solution. $cidif# with dilute nitric acid and then test with sil%er

nitrate solution as with inorganic halides.

• $lcohols or carbo#lic acids containing C-OH - In a dr# test tube (i.e. dr# alcohol)/ add ,Cl


14/17

chemistry of the compounds listed in Units l and 2& 5afety considerations should relate to

specic eperiments not be of a general nature it 'ill be assumed that students 'ear

eye protection during all practical 'or&

Halogens are toic and harmful b# inhalation/ although iodine is much less so than chlorine or bromine/ because it is a

solid. Chlorine and bromine must alwa#s be used in a fume cupboard. "i6uid bromine causes serious burns an must be

handled with glo%es.

$mmonia is toic. Concentrated ammonia solutions should be handled in the fume cupboard.

Concentrated mineral acids are corrosi%e. If spilt on the hands/ washing with plent# of water is usuall# enough/ but

ad%ice must be sought. $cid in the e#e re6uires immediate attention and prompt professional medical attention.

Barium chloride solution and chromates and dichromates are etremel# poisonous and so should be used in the fume

cupboard0should not be inhaled.

Sodium or potassium h#droide or concentrated ammonia in the e#e is etremel# serious and must alwa#s recei%e

professional and immediate attention. Sodium h#droide and other al7ali metal h#droides are amongst the most

damaging of all common substances to s7in and other tissue. +ear glo%es/ goggles and an apron when handling these

solutions in high concentrations.

General safet#

• Toic0carcinogenic E use glo%es/ fume cupboard

• 8lammable E +ater baths/ no na7ed fumes.

• Harmful gases E Ase fume cupboard

• Corrosi%e E wear goggles0glo%es

• Spillage of concentrated acid E wash with plent# of water.


15/17

.nalysis of 6ransition 7etal +ompounds

$%C&&TAT%S+hen 2 aueous solutions are mied together and an insoluble compound is formed, this is "nown as precipitate, not a suspension4

Dhe obser0ation that a precipitate is formed should alwa*s be accompanied b* the colour of the ppt e0en if it iswhite4

#ome reagents should be added until the* are in ecess4 Dhis ma* result in a ppt forming and then dissol0ing in

ecess reagent4

(&) SO'& H*'$O&'% SO,T&ON (NaOH)

+hen dilute 'aH solution is added to a solution containing a metal ppt, the ppt of the insoluble h*droide

(e4g4 Mn(H)2 ) is formed4 %pt which are amphoteric (that acts both as base and acid) h*droides willdissol0e in ecess 'ah to gi0e a solution containg a comple ion (e4g4 TCr(H)KU3> )4

#tudents should assume that aueous 'aH should be added until it is in ecess e0en if it is not stated in

instruction4

OBS. ON ADDING

DIL.NaOH

OBS. ON ADDING

EXCESS NaOHLIKELY ION

8reen ppt/pt dissol#es to gi#e

green solution&+hromium (III)

9'hite ppt 'hichdarens to eposure to

air

/pt is insoluble 7anganese (II)

8reen ppt 'hich turns

bro'n on eposure to air/pt is insoluble Iron (II)

;ro'n ppt /pt is insoluble Iron (III)

8reen ppt /pt is insoluble %icel (II)

;lue ppt /pt is insoluble +opper (II)


16/17

;a2>5t2>+a2>

(&&) AON&A (NH3) SO,T&ON

7ilute aueous 'H3 when added to a solution containing a cation that will form the same h*droide as

'aH solution4

Lcess 'H3(a) ma* dissol0e the ppt to form a comple ion TCu('H3)(H2)2U24 #tudents must assumethat 'H3(a) must be added until in ecess4

OBS. ON ADDING DIL.

NH3 (AQ)

OBS. ON ADDING

EXCESS DIL. NH3 (AQ)LIKELY ION

8reen ppt/pt dissol#es to gi#e

green solution&+hromium (III)

9'hite ppt 'hich

darens to eposure to

air

/pt is insoluble 7anganese (II)

8reen ppt 'hich turns

bro'n on eposure to air/pt is insoluble Iron (II)

;ro'n ppt /pt is insoluble Iron (III)

8reen ppt ;lue 5olution %icel (II)

;lue ppt

!issol#es to gi#e a

darer blue solution

(royal bluedeep blue)

+opper (II)


17/17

H2O2 SO,T&ON (H*'$OG%N %$O&'%)

&ueous H22 can act both as an oidiNing agent and reducing agent often with an e0olution of *gen4

OBS ON ADDING H2O2 INFERENCE

;ro'n ppt 7anganate (VII), bro'n ppt ? 7n2

/urple solution is decolouri@ed 7anganate (VII) in acid solution

/ale green solution yello' Iron (II) to Iron (III) in acid solution

8reen ppt ? bro'n Iron (II) Aydroide

8reen alaline solution Bello' +hromium (III) to +hromate (VI)

;ro'n solution or blac ppt Iodine from Iodide in acid soluion

Documents

Chemistry Unit 3 and 6