2021 Mock Chemistry Paper 3 with AnswersKenya High School


1. Solution A is prepared by dissolving 6.3g of the organic acid H2C2O4.nH2O in water to make a litre of the solution.

Solution B: 0.1M NaOH solution

Phenolphthalein indicator

Clamp and stand

Burette and pipette.

You are required to determine the value of n in the organic acid H2C2O4. nH2O Procedure.

Fill the burette with solution A and adjust the volume to zero mark.

Add 2 to 3 drops of phenolphthalein indicator and titrate solution A against solution B until the colour just permanently changes.

Record your results in the table below.

Repeat the procedure two more times to obtain concordant results.

Final burette reading (cm3)
Initial burette reading (cm3)
Volume of solution A used (cm3)


b) Calculate the average volume of solution A used. 1mark

c) Calculate the moles of sodium hydroxide in the volume of solution B used. 2marks

d) Given that solution B – Sodium hydroxide and solution A organic acid react in the ration of 2:1, calculate the number of moles of the organic acid –solution A used? 2marks

e) Calculate the moles of organic acid solution A used per litre of solution 2marks

f) Calculate the relative formula masses of the organic acid solution A 3marks

g) Calculate the value of n in H2C2O4.nH2O(H=1, C=12, O=16) 3marks

2.You are provided with CBI. Carry out the test below. Write your observation and inferences in the spaces provided.

a) Using a clean spatula, heat about one third of the solid CBI in a non- luminous Bunsen burner flame.

Observation                          Inferences                              

b) Put a half spatula endful of CBI in a test tube. Heat gently and then strongly.

Test for any gas produced using litmus papers.

Observation                          Inferences                              

c) Put 2cm3 of dilute hydrochloric acid into a test tube. Add ¼ endful of CBI into the test tube. Test for any gas procedure.

Observation                          Inferences                              

3.You are provided with solid Q, carry out the test below.

Record your observations and inferences in the table. Identify any gas (es) evolved.

Place all the solid Q provided into boiling tube and add distilled water until the tube is ¼ full.

Divide it into five portions.

a) To the 1st portion add ammonia solution drop wise until excess.

Observation                          Inferences                              

b) (i) To the 2nd portion add sodium hydroxide solution dropwise until in excess. Keep the resulting mixture for the next test.

Observation                          Inferences                              

ii) Warm the preserved mixture from b (i) above

Observation                          Inferences                              

c) i) To the 3rd portion add silver nitrate solution. Preserve the mixture for the next test.

Observation                          Inferences                              

ii) To the preserved mixture in c (i) above add diluted nitric acid.

Observation                          Inferences                              

d) To the 4th portion add dilute Barium nitrate solution followed by dilute nitric acid. To the 5th portion add 2-3 drops of conc. Nitric acid. War

Observation                          Inferences                              

e) To the 5th portion add 2-3 drops of conc. Nitric acid.

Warm the mixture and allow to cool. Add sodium hydroxide solution dropwise until in excess.

Observation                          Inferences                              

Kenya High Mock Chemistry Paper 3 2021 Answers

Question one

(a) Complete table √1mkComplete table with 3 titres √1mkIncomplete table with 2 titres √½ mkIncomplete table with 1 titre −0 mk

ConditionsPenalize ½ mk for unrealistic values unless where explainedPenalize ½ mk for any inversion of tablePenalize ½ mk for any arithmetic error

NB: penalize a maximum of ½ mk for any of the conditions above.

Decimal √1mk

Award 1mk for 1d.p. or 2 d.p used consistently

If 2d.p used, 2ndd.p. can only be “0” or “5”

Accuracy √1mk

Award 1mk for any value + 0.1 of s.v.

Award ½ mk for any value + 0.2 of s.v.

Award 0mk (penalize fully) for any value beyond + 0.2 of s.v.

Principles of averaging √1mkValues averaged must be consistentIf 3 titres but only 2 are consistent and averaged award 1mkIf 3 titres done and averaged award 1mkIf 3 titres done and inconsistent and averaged award 0mkIf 3 titres done and all are consistent but only 2 are averaged award 0mk

Final answer √1mkAward 1mk for ans. + 0.1 of s.v.Award ½mk for ans. + 0.2 of s.v.Award 0mk ifansnot within + 0.2 of s.v.Marks awarder as follows: CT 1mk

(b) Average titre = t1 + t2 + t3 = (√½ mk)Correct Ans ½ mk

(c) Moles of NAOH = M x V 1000 = 0.1 x 25√1mk = 0.0025moles √1mk

Question 2

Yellow flame √1mkNa+ ions √1mk
Colourless, odourless gas produced
Gas turns moist blue litmus paper red
Red litmus paper remains red
Droplets of colourless liquid on cooler parts of test tube Any 2 x ½ = √1mk
Gas acidic
CO 32- , HCO3- ions
Hydrated salt / water of crystallization
Any 2 correct x ½ = √1mk
Effervescence / bubbles
Colourless , odourless gas produced
Gas turns moist blue litmus paper red
Red litmus paper remains red
Any 4 x ½ = √2mks
CO 32- , HCO3- ions
Gas acidic
Any 2 x 1 = √2mks

Question 3

Pale green ppt√½ mk
insoluble in excess √½ mk
Pale green ppt√½ mk
Insoluble in excess √½ mk
Gas with pungent . chocking smell 1mk
Moist red litmus paper turns to blue 1mk
Blue litmus paper remains blue any 2 x 1 = √2mks
Gas basic √½ mk
NH4+ ions present√½ mk
White pptCO 32-, Cl-ions , SO32-
White ppt√½ mk
Insoluble / persists √½ mk
Cl- ions √1mk
White ppt√½ mk
Insoluble √½ mk
SO42- ions √1mk
Pale green solution turns to yellow solution √1mk
Brown ppt insoluble in excess √1mk
Fe2+ oxidized to Fe3+ ions
√½ mk
Fe3+ ions confirmed √½ mk