Chemistry Paper 3 Questions, Answers and Confidential - Arise and Shine Mock Exams 2022

Instructions to candidates.

1. Write your name and index number in the spaces provided above.
2. Answer all questions in the spaces provided in the question paper.
3. Mathematical tables (KNEC) and silent electronic calculators may be used.
4. All workings must be clearly shown where necessary.
5. Candidates should answer the questions in English.

For examiners use only.

Question	Maximum score	Candidate’s score
1	22
2	10
3	8
Total score	40

QUESTIONS 

1. You are provided with
   1. 0.3g of metal F.
   2. 100cm³ of 1.0M hydrochloric acid solution labelled as solution G.
   3. 120cm³ of 0.1M sodium hydroxide solution, labelled as solution H.
   4.  Screened methyl orange indicators solution.
      1. You are required to determine the Relative Atomic Mass of metal F.
         Procedure
         1. Using a burette, measure 50.0cm³ of solution G into a clean 250ml beaker.
         2. Add the WHOLE AMOUNT of F provided into the beaker containing 50.0cm3 of solution G and stir well with a glass rod until ALL the solid metal reacts completely.
         3. Transfer the mixture left in the beaker after the reaction into a 250ml Volumetric flask. Rinse the beaker as well as the glass rod with distilled water and transfer ALL the rinsings into the volumetric flask. Make up the volume of the solution in the volumetric flask up to the calibration mark with distilled water, cover the flask with a stopper, shake well and label as solution Q.
         4. Fill a clean burette with solution Q.
         5. Pipette 25.0cm³ of solution H into a 250ml conical flask, add 3 drops of screened methyl orange indicator solution and titrate against solution Q from the burette.
            A change in colour of the mixture from green to pink marks the end point of titration.
            Record your results in table 1.
         6. Repeat the titration TWO more times to complete table I.
            Table I
            

            Titration	1	2	3
            Final burette reading, cm3
            Initial burette reading,cm3
            Volume of solution Q used,cm3

            (4 marks)
            Average volume of Q used, cm³ ………………………………………………….. (1 mark)
         7. Calculate:
            1. Calculate the number of moles of HCl in 50.0cm³ of solution G. (1 mark)
            2. Determine the number of moles of NaOH in 25.0cm³ of solution H. (1 mark)
            3. Determine the number of moles of HCl in the average volume of solution Q useD in the titration. (1 mark)
            4. Calculate the moles of HCl left unreacted after the reaction between F and solution G. (1 mark)
            5. Determine the moles of HCl that reacted with metal F. (1 mark)
            6. Given that metal F forms a divalent cation, determine the moles of metal F that reacted with hydrochloric acid. (1 mark)
            7. Determine the Relative Atomic mass of metal F. (1 mark)
      2. You are provided with
         1. 2.00g of solid K.
         2. A thermometer
         3. Distilled water
         4. Boiling tube
         5. Hot water bath.
            You are required to determine the temperatures at which solutions of known concentrations of compound K becomes saturated and plot solubility curve.
            Procedure.
            1. Transfer the whole amount of solid K supplied to you into clean dry boiling tube.
            2. Using a burette, add 5.0cm³ of distilled water into the boiling tube with solid K
            3. Put the boiling tubeinto a beaker of hot water bath and warm the boiling tube, while continuously stirring the content with thermometer, until the crystals of K dissolve/disappear
               (DO NOT BREAK THE THERMOMETER)
            4. Remove the boiling tube from the hot water bath and allow the content to cool slowly while stirring with the thermometer. Not the temperature at which crystals
               FIRST form/reappear and record this temperature in Table 2.
            5. Add a further 2.00cm³ of distilled water from the burette into the boiling tube containing the mixture and repeat steps (c) and (d) above. Continue this way until the volume of water added to boiling tube is 5.00cm³.
            6. Complete Table 2 by calculating the solubility of compound K in water at different temperatures.
               

               Total volume of water added (cm3)	Temperature at which crystals first appear (oc)	Solubility of compound K in water (g/100g water)
               5.00
               7.00
               9.00
               11.00
               13.00
               15.00

               (6 marks)
            7. On the grid provided plot a graph of solubility of compound K (vertical axis) against temperature. (3 marks)
               
            8. From your graph determines the solubility of K in water at 25.0ºc. (1 mark)
2. You are provided with 10cm3 of solution R containing TWO cations and ONE anions carry out the tests below and record your observations and inferences in the spaces provided.
   1. Add 20cm³ of 2M sodium hydroxide to all of solution R provided. Shake well. Filter the mixture into a conical flask. Retain both the filtrate and residue.
      

      Observation	Inference
      (1/2 mark)	(1/2 mark)

   2. To about 2cm³ of the filtrate, add 1cm³ of 2cm³ of 2M nitric acid. Retain the mixture.
      

      Observation	Inference
      (1/2 mark)	(1/2 mark)

      Divide the mixture in (b) above into TWO portions
      1. To the FIRST portion, add aqueous sodium hydroxide solution drop wise until in excess.
         

         Observation	Inference
         (1 mark)	(1 mark)

      2. To the SECOND portion, add 2M aqueous ammonia solution DROPWISE until in excess.
         

         Observation	Inference
         (1 mark)	(1 mark)

   3. To about 2cm³ of the filtrate, add 3 drops of 2M hydrochloric acid
      

      Observation	Inference
      (1/2  mark)	(1/2 mark)

   4. To about 2cm³ of the filtrate, add about 1cm³ of acidified Barium chloride solution
      

      Observation	Inference
      (1/2  mark)	(1/2 mark)

   5. To the RESIDUE add about 5cm³ of dilute nitric acid and filter into a clean test tube. To about 2cm³ of this filtrate add 2M aqueous. Ammonia solution dropwise until in excess and filter into clean test tube.
      

      Observation	Inference
      (1  mark)	(1 mark)

3. You are provided with solid Z.
   Carry out tests below. Write your observations and inferences in the spaces provided.
   1. Scoop a little of solid Z (using a clean spatula and burn it in a |Bunsen burner flame.
      

      Observation	Inference
      (1 mark)	(1 mark)

   2. To the remaining portion, add about 6m3 of distilled water and shake. Divide the mixture into two portions
      

      Observation	Inference
      (1 mark)	(1 mark)

   3. To the second portion, add the whole of sodium carbonate provided.
      

      Observation	Inference
      (1 mark)	(1 mark)

   4. To a little amount of Z, add sodium carbonate.
      

      Observation	Inference
      (1 mark)	(1 mark)

CONFIDENTIAL

Instructions to schools
In addition to the lab fittings and Apparatus found in the laboratory, each candidate should require;

1. One burette 0-5ml
2. One 20ml pipette
3. Three conical flasks
4. One volumetric flask
5. One complete retort hand.
6. One white tile
7. One pipette filler
8. One test-tube rack
9. Six test tubes
10. Two boiling tubes
11. Filter paper -2
12. Filter funnel -1
13. Measuring cylinder 100ml-1
14. Measuring cylinder 10ml
15. Wash bottle – with water (distiled)
16. One metallic spatula
17. Solution G – 1M HCl
18. Solution H – 0.1M NaOH
19. Solid/metal F – 0.3g Magnesium powder
20. Solid Z – 1 spatula maleic acid in a stoppered container.
21. Solid K – Potassium chlorate 2g KClO₃
22. Solid R – mixture of Al₂(SO₄)₃ and CuSO₄ at Ratio of 1:1.(Provide 10cm³ of solution R)
23. Thermometer – 10 to 110^oc
24. 1g Na₂CO₃ – In a stoppered container

Access to:

1. Source of Heat
2. Water bath of hot water
3. 2MNaOH_(aq)
4. 2MNH_3(aq)
5. 2M HNO₃
6. 2M HCl
7. 5m Barium chloride(acidified)
8. Acidified Potassium Manganate (VII) solution

MARKING SCHEME

1. Table 1……………………………………………………5mks

(i). Complete table ………………………………………..1mk
Conditions

• Complete table with 3 titrations done …..….1mk
• Incomplete table with only 2 titrations ½ mk
• Incomplete table with only 1 titration one ……...0mk
• For no titration done ….…..0mk

NOTE: where NO Titration done penalize FULLY for ALL the marking points for table
Penalties
Before awarding a mark for complete table
The examiner MUST  ensure that none of the following mistakes is there in the table – otherwise penalize  ½ k for EACH mistake to a maximum penalty of ½ mk i.e penalize ½ mk ONCE even if there are 2 or more mistakes

• Wrong arithmetic/subtraction
• Inverted table
• Burette readings beyond 50.0cm³, except where explained.
• Unrealistic titre values i.e. titres <1.0cm³ or>100cm³.

(ii). Use of decimals (tied to 2^nd and 3^rd rows ONLY) ……………….1mk
Conditions
Either 1 or 2 decimal places used consistently
If 2 decimal places are used then 2^nd decimal place MUST be either 0 or 5

(iii). Accuracy (tied to correct titre values only……………………..1mk
Compare the candidate’s correct titre values with the school values i.e. Teacher’s Average tire
Conditions

• If at least one titre value is ± 0.1cm³ of school value award ……………1mk
• If NO titre value is within ±0.1cm³ 0.1cm³ of school value but at least one titre value is within ±0.2cm³ of school value then award ………….1/2 mk
• If NONE of the titre values is within ±0.2cm³ of the SV award …….0mk

(iv). Principles of averaging …….1mk

• If 3 consistent values average -------1mk
• If 3 titrations done,2 consistent values average d……..1mk
• If 2 titrations done , inconsistent and averaged ……0mk
• If 3 inconsistent titrations average …..0

 (v) Final accuracy (tied to correct average titred………..1mk)
Compare the candidate correct average tire with the SV and award accordingly

• If within 1cm³ of S.V award …..1mk
• If NOT within ±0.1cm³ of S.V but is within ±0.2cm³ of S,V award ….. ½ mk
• If > ±0.2cm³ of S, V award …… ½ mk
  • Complete table ….1mk
  • Use of decimals ……1mk
  • Accuracies ……1mk
  • Principles of Averaging …....1mk
  • Final Accuracy ….1mk
                                Total 5mks

(vi). Calculations
(i). Mols of Hcl is 50cm³ of solution G
=  50 x 1  ^1/2 = 0.05 moles ^1/2 
    1000
NB units may be given or NOT given but if given  MUST  be correct

(ii). Moles of NaOH in 25cm³ of solution H
= 50 x 0.1   ^1/2 = 0.025 moles ^1/2 
     1000

(iii). Mole of HCl in average volume of
Solution Q used.
                        = mole ratio
NaOH : Hcl     =1:1 ^1/2
                        = correct newer ^1/2 

(iv). Moles of Hcl unreacted
            = answer (iii) above x 250 = correct answer ^1/2
                      Average tire
OR
= Answer in (i) – Answer in (iii) ^1/2
= Correct answer ^1/2

(v). Moles of HCl reacted with F
= Answer in (i) = Answer in (iv)  
= Correct answer ^1/2

(vi). Moles of metal F reacted
= ½ x Answer (v) above ^1/2
= Correct answer ^1/2

(vii) R.A.M for F
= 0.3     ^1/2= correct answer
  Answer (vi)

Table 2………………………………………….6mks
            Distribution.
(a). Complete  table ………………3 mks
Conditions/penalties

• Award ½ mk for EACH experiment completely done
• Penalize ½ mk for EACH solubility value either wrongly worked out or NOT worked to maximum of 1mk.
• Penalize ½ mk if ALL temperature readings in the table are CONSTANT.

(b). Use of decimals tied to temperature readings)……………….1mk

• Accept ONLY if all readings recorded consistently either as whole Numbers or to one decimal places of -0 or -5 otherwise penalize FULLY.

(c). Accuracy …………………………1mk

• Compare candidate’s first temperature reading i.e. when 5cm³ of water is added with school value if within 0^oc of S.V award 1mk otherwise award 0mk

(d). Trend ……………………..1mk
Award mark for Temperature readings showing a continuous Drop otherwise penalize Fully

• Complete table            3mks
• Use of decimals          1mk
• Accuracy                     1mk
• Trend 1mk
                                  06mks

Graph……………………………..3mks
Award 3 mks – distribution

A. Labelling of Axes …………….^1/2 mk
Award ½ mk if both axes correctly Tabelled
Penalties

• Penalize FULLY for inversion on axes
• Penalize FULLY for wrong units given, ignore if units are NOT given
• Penalize FULLY if only one axis is labelled

B. Scale …………….¹/2 mk
Conditions

• Area covered by the graph plots must be at least 8 big squares on both axes
• Scale interval must be consistent on each axis
• Scale chosen must accommodate all the plots

C. Plotting
Conditions

• If 6 or 5 points correctly plotted award …………..…1mk
• If only 4 or 3 points are correctly plotted award ……^1/2 mk
• If less than 3 parts correctly plotted award …….0

D. Curve ………………………….1mk
Award 1mk for a smooth curve which is rising an joining at least three correctly plotted points

• Graph-                         ….3mks
• Labelling of Axes       …..½ mk
• Scale                            …..1/2  mk
• Plotting                       …..1mk
• Curve                          ……1mk
                                       03mks

H. Solubility of K at 25^oC using the graph
= correct showing on graph ½
= correct answer ½ mk

Question 2
(a)

observation	Inference
Colourless filtrate Blue precipitate ½	Zn2+,Al3+,Pb2+present Cu2+P Present

(b)

observation	Inference
No effervescence ½	½

(b.i).

observation	Inference
No white precipitate  ½ Dissolves in excess ½	Zn2+,Al3+,Pb2+present

(b)(ii).

observation	Inference
white precipitate  ½ dissolves in excess ½	Al3+,Pb2+ present

c)

observation	Inference
No white precipitate  ½ No effervescence	Al3+, present Pb2+ absent 1/2

(d).

observation	Inference
white precipitate  ½	SO42- present    1 ½

e).

Observation	Inference
blue precipitat dissolve to form deep blue solution	Cu2+ in present

3.(a).

Observation	Inference
burns with yellow sooty/smoky flame  1mk	Unsaturated  organelle compound

(b).

Observation	Inference
Dissolve to form colourless solution mk	Polar substance

c).

Observation	Inference
Purple potassium manganite (VII) decolorized mk

(d).

Observation	Inference
Effervescence occurs  mk	R – COOH present  1 mk

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