Qualitative Analysis

1. Qualitative analysis is a series of tests conducted on a chemical substance to identify the salt component or components in it.2. Through qualitative analysis, the cation and anion present in a salt are determined.3. To identify the cation and anion in a salt, the following tests are usually conducted. Complete the diagram.UNKNOWN SALT

2. Observed colour of salts3. Add distilled water1. Physical properties

NO2SO42-CO32-

Cl2CO2NO3 -

5. Test for gases4. Effect of heat

Gas releasedInference : Presence of Soluble?

Reagent

Yes

Damp blue litmus paperIon in aqueous solution

6. Confirmatory tests for ions

8. Test for cations

9. Test for specific cations7. Test for anions

8.a)Using NaOH8 b)Using NH3 (aq)

4. Colour of Salts

a. Most salts are colourless aqueous solution or white salts.

b. Salts of transition metals are coloured because they form coloured ions. Examples : IonColour

(a)copper (II) ions, Cu2+

(b) iron (II) ions, Fe2+

(c)iron (III) ions, Fe3+

c. Complete the following table : Solid

Aqueous

Salts/Metal oxide

Colourless

K+, Na+, Ca2+, Mg2+, Al3+, Zn2+, Pb2+, NH+

Green

Insoluble

Light green

Fe2+ example: FeSO4 ,FeCl2 ,Fe(NO3)2

Blue

Blue

Brown

Fe3+

Black

CuO

Yellow when hot white when cold

Insoluble

ZnO

Brown when hot yellow when cold

Insoluble

5. Comfirmatory test for several gases.

a) Complete the following table :

GasColourSmellEffect on damp litmus paperReagent usedConfirmatory test

Hydrogen

Colourless

Lighted splinterMethod : Bring a lighted splinter to the mouth of test tube.Observation : Gives '______' sound

Oxygen

Odourless

Glowing splinterMethod :

Observation :

Carbon dioxide

Odourless

Lime waterMethod : Bubble the gas produced into ________________ Observation :

Ammonia

Colourless

ChlorineGreenish yellow

Pungent

Blue to red, then _______

Nitrogen dioxide

Pungent

Sulphur dioxide

Colourless

Pungent

Blue to red

Method :

Observation :

Hydrogen chlorideColourless

Pungent

Blue to red

Method : Dip a glass rod in concentrated ammonia solution an insert into the test tubeObservation : White fumes formed

6. Effect of Heat on Salts

a) Most compounds which decompose leave behind oxides.

Salt metal oxide + gas (residue identification (gas identification refers to specific cation refers to anion) only)b) heatsaltType og gas releasedColour of residueCan predict the identity of ______ presence in saltCan predict the identity of ________ presence in salt

c) Draw the correct labeled diagram for the set-up to test carbon dioxide gas liberated when the carbonate salt is heated strongly.

14

d) Write down the chemical equations for the reactions that occur :

IonCarbonate saltNitrate saltSulphate saltChloride salt

Is not decomposed by heatDecompose into O2 gas and metal nitriteSulphate salts usually do not decomposeChloride salts do not decompose except NH4Cl

K+No reaction2KNO3 2 KNO2 + O2No reactionNo reaction

Na+No reactionNo reactionNo reaction

Decompose into metallic oxide and CO2Decompose into metal oxide, NO2 and O2

Ca2+CaCO3 CaO + CO2No reactionNo reaction

Mg2+No reactionNo reaction

A13+No reactionNo reaction

ZnSO4, CuSO4 and Fe2(SO4)3 decompose when heated to produce metal oxide and SO3

Zn2+No reaction

Fe3+No reaction

Pb2+No reactionNo reaction

Cu2+No reaction

Decompose into metal, NO2 and O2

Ag+No reactionNo reaction

Decompose into NH3, CO2 and waterDecompose into nitrous oxide N2O and waterSublimes when heated to produce NH3 (g) and H2SO4 (g)Sublimes when heated to produce NH3 (g) and HCl (g)

NH4+

Carbonate + acid gas CO2Chloride + H2SO4 gas HClNitrate + conc.H2SO4 gas NO2

7. Confirmatory test for anions

a) Complete the following diagram :

Unknown Salt solution

+ ______+ ______

+ H2SO4 dilute+ _______+ _____________+ dilute acidGas turns limewater ___________

+ HNO3+ ______

_________ precipitateformed________ ring formed

________ ion confirmed________ ion confirmed_________ ion confirmedSO42- ion confirmed

8. Confirmatory test for cations

a) The presence of cation can be detected by using two common alkalis i) Sodium hydroxide solution, NaOH and ii) Ammonia solution, NH3.

The function of the alkalis is to produce a precipitate, that is __________ ________________.

Metal ion + hydroxide ion metal hydroxide

c) Complete the diagram below :

d) Complete the diagram below :

c) Confirmatory tests for Fe2+, Fe3+, Pb2+ and NH4+

damp

d) Complete the following diagram to summarises the qualitative analysis of cations in salts.

e. If a salt X is given as zinc nitrate, how can we test the compound to confirm the presence of Zn2+ and NO3- ions in that salt?

Conduct the experiment as follows :

ExperimentObservationInference

1. Observed the colour of salt X White salt

2. _______ some solid X in a test tube and observe : (a) the colour of gases released (b) the effect on damp _____ litmus (c) the effect on _________ splintd) observed the colour of residue when hot and cool.

_________ gas.

_____ litmus turns _____.

_________ _________ splint.

Residue colour :Hot : _________Cool : _______________ gas released. Acidic gas.

O2 released.

Probably NO3- present.

Probably ______ present.

3. Add _________ _________ to X to make solution.

____________ in waterX is soluble salt

4. Add ________ _______ solution, followed by ________. Mix. Slowly, add 5-6 drops of _____________ ________ along test tube side. (Do not shake)_________ _______ formed.

Confirms presence of ________, ____

5. To salt solution, ________ a little NaOH(aq), then add it to_________.

Maybe ____, ____, or Al3+.

6. To salt solution, add a little ______ (aq), then add it to _________.

________ _________, soluble in excess NH3.

Confirms presence of ______ ion.

CONCLUSION : The ions present in salt X are confirmed as _____ and _____ ions.

Structural question

1.Figure 2 shows a flow chart summarizing the series of changes for a compound T.

Solid TSolution YGas V+Solid UGas V+Solution WWhite precipitate soluble in excessSolid UGas Y+Gas Z++ dilute nitric acidHeated upHeated up+ dilute hydrochloric acid+ ammonia solution

Solid U is yellow in colour when hot and white in colour when cooled.

(a)What is solid U? [ 1 mark ] _________________________________________________________________________________(b)Name the cation and anion in solid T. [ 2 marks ] _________________________________________________________________________________(c )(i)Name gas V. [ 1 mark ] _________________________________________________________________________________(ii)What is observed when gas V is passed through limewater? [ 1 mark ] _________________________________________________________________________________(iii) Write the chemical equation for reaction between gas T with limewater. [ 3 marks]_________________________________________________________________________________(e)(i)Name solution Y. [ 1 mark ] _________________________________________________________________________________(ii)Describe briefly a chemical test to identify the anion in solution Y. [ 3 marks ] _________________________________________________________________________________ _________________________________________________________________________________ _________________________________________________________________________________(f)Name the type of reaction which occurs when solid U reacts with dilute hydrochloric acid to form solution W. [ 1 mark ] _________________________________________________________________________________

(g)(i)What are gas Y and gas Z ? [ 2 marks ] _________________________________________________________________________________(ii)Write the balance chemical equation for the effect of heat on solution Y.[ 1 mark ] _________________________________________________________________________________

2.Figure 3 summarises the series of reactions that involves lead compounds.

Heated up

Mix of gases K and L+Solid JLead(II)nitrate

Add dilute nitricacidAdd dilute hydrochloricacid

Solution NWhite precipitate M

Figure 3

(a)What is solid J ?[ 1 mark ](b)What is the colour of solid J when hot and cooled ?[ 1 mark ](c )Write a balance chemical equation to represent the effect of heat on lead(II) nitrate to form solid J and a mixture of gas K and N.[ 3 marks ](d)(i)Name precipitate M.[ 1 mark ](ii)State a way to test compound M.[ 1 mark ](iii) Write the ionic equation to show then formation of precipitate M.[ 1 mark ](e)Sodium hydroxide solution is added little by little into solution N until there is no more change. What can be observed ?[ 1 mark ](f)How can you obtain dry crystal salt, N , from solution N ?[ 3 marks ](g)A piece of zinc is put into solution N.(i)Predict the observation.[ 1 mark ](ii)Write the chemical equation to represent the reaction which has occurred. [ 1 mark ]

Gas K[Brown colour and acidified]

+

Gas L[Colourless]

+

Solid M

Compound J

Heat

Dissolved inwater

White precipitate Q Dissolved in excess sodium hydroxide solution

Reaction II

Colourless J solutionWhite precipitate R

Reaction I+ NaOH (aq)+ Na2SO4 (aq)

Figure 3

3.Figure 3 shows a series of process done by a student to identify a compound J.

(a)With refer to reaction I, white precipitate Q is formed which is soluble in excess sodium hydroxide solution. Name all the ions which are probably presence in solution J. [ 1 mark ]

(b)Referring to reaction I and II, name the cation presence in solution J.[ 1 mark ]

(c )Write down the ionic equation for the reaction forming the white precipitate, R.[ 3 marks ](d) (i)Name two cations which produced white precipitate that will not dissolve in excess sodium hydroxide solution.[ 1 mark ]

(ii) State one confirmatory test for one cation presence in (d)(i). [ 3 marks ]