CHEMISTRY Paper 3 Questions and Answers - KCSE 2022 Past Papers

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    1. You are provided with the following:
      Solution A   - Indicator solution
      Solution B  -0.05 M compound B
      Solution C1 -Hydrochloric acid to be used in Questions 1(a) and (b)
      You are required to determine the concentration in moles per litre of hydrochloric acid in solution C1.

      PROCEDURE I (a)
      1. Place two test tubes in a test tube rack. To the first test tube, place about 2 cm3 of solution B. To the second test tube, place about 2 cm3 of solution CI.
      2. Add 2 drops of indicator solution A to each of the test tubes, shake and note the colour of each solution. Record the colours in Table 1.
         Solution  Colour
         Solution B+ indicator solution A  
         Solution CI+ indicator solution A  
                                                                                                                                                                                                             (1 mark)
        Complete the following statement:
        In the titration of solution B (in a conical flask) with hydrochloric acid using indicator solution A, the colour change at the end point is from................. to .................. (1 mark)

        PROCEDURE II (a)
        1. Using a pipette and pipette filler, pipette 25.0 cm3 of solution C1 into a 250ml volumetric flask. Add distilled water to the mark. Label this as solution C2.
        2. Fill a burette with solution C2.
        3. Using a clean pipette and pipette filler, place 25.0 cm3 of solution B in a 250ml conical flask.
        4. Titrate solution B with solution C2 using 3 drops of indicator solution A. Record the results in Table 2.
          Calculate the:
          1. average volume of solution C2 used. (1 mark)
          2. number of moles of compound B used (1 mark)
          3. number of moles of hydrochloric acid used (1 mole of compound B reacts with 2 moles of hydrochloric acid). (1 mark)
          4. concentration in moles per litre, of hydrochloric acid in solution C2. (1 mark)
          5. concentration in moles per litre, of hydrochloric acid in solution C1. (1 mark)
    2. You are provided with two portions of solid D and sodium hydrogen carbonate each weighing 2.5g.
      You are required to determine the heat of reaction of hydrochloric acid with aqueous sodium hydrogen carbonate.
      PROCEDURE 1 (b)
      1. Using a 100 ml measuring cylinder, measure 30 cm3 of distilled water and place it in a 100 ml plastic benker.
      2. Measure the temperature of the distilled water and record in Table 3.
      3. Add one of the portions of solid D to the water. Stir with the thermometer and measure the minimum temperature reached. Record the reading in Table 3.
         Final temperature of the solution, "C  
         Initial temperature of water, "C  
         Temperature change, °C  
                                                                                                                                                                                                                 (11⁄2 marks)
        Calculate the:
        1. heat change of the solution (assume specific heat capacity of solution = 4.2 Jg-l per degree, density of solution 1.00g cm3 (1 mark)
        2. number of moles of sodium hydrogen carbonate, solid D used (relative formula mass - 84) (1 mark)
        3. heat change, AH, in kJmol of sodium hydrogen carbonate (1 mark)

          PROCEDURE II (b)
          1. Clean the 100ml plastic beaker.
          2. Repeat procedure I (b) using the second portion of solid D and 30 cm3 of solution C1 instead of 30 cm3 of distilled water.
          3. Record the results in Table 4.
             Final temperature of solution °C  
             Initial temperature of solution C1, °C  
             Temperature change, °C  
                                                                                                                                                                                                       (11⁄2 marks)
            Calculate the:
            1. heat change of the solution (assume specific heat capacity of solution = 4.2 Jg per degree, density of solution = 1.00 g cm3) (1mark)
            2. heat change, AH, in kJmol of sodium hydrogen carbonate (1 mark)
            3. heat change, AH,- AH, - AH, for the reaction of hydrochloric acid and one mole of aqueous sodium hydrogen carbonate (1 mark)
  2. You are provided with an organic compound, solid M.
    Carry out the following tests and record the observations and inferences in the spaces provided.
    1. Place about one-fifth of solid M on a metallic spatula and burn it using a Bunsen burner flame.
       Observations  Inferences
                                                                                                                                                                                         (1 mark)                                                                              (1 mark)
    2. Place the remaining amount of solid M in a boiling tube. Add about 15 cm3 of distilled water and shake to dissolve. Use about 2 cm3 portions of the solution, in a test tube, for each of the following tests.
      1. To the first portion, add 3 drops of acidified potassium dichromate(VI).
        Warm the mixture.
         Observations  Inferences
                                                                                                                                                                                            (1mark)                                                                        (1 mark)
      2. To the second portion, add 3 drops of bromine water
         Observations  Inferences
                                                                                                                                                                                             (1 mark)                                                                            (1 mark)
      3. To the third portion, add all the solid sodium carbonate provided. Test any gases produced with a burning splint.
         Observations  Inferences
                                                                                                                                                                                              (1 mark)                                                                               (1 mark)
  3. You are provided with solution N. Carry out the following tests and record the observations and inferences in the spaces provided. Use about 2 cm3 portions, in a test tube, for each of the tests.
    1. To the first portion, add aqueous sodium hydroxide dropwise until in excess.
       Observations  Inferences
                                                                                                                                                                                                  (1 mark)                                                                                   (1 mark)
    2. Warm the second portion and then add aqueous ammonia dropwise until in excess.
       Observations  Inferences
                                                                                                                                                                                                     (1 mark)                                                                              (1 mark)
    3. To the third portion, add 3 drops of aqueous barium nitrate. Shake and then add about 1 cm3 dilute nitric(V) acid.
       Observations  Inferences
    4. Place about 1 cm3 of aqueous sodium hydroxide in a test tube, then add the fourth portion of solution N.)
      1. Heat the mixture and test any gases produced with red litmus paper 
         Observations  Inferences
      2. Rewarm the mixture obtained in (d)(i) above, then add the piece of folded aluminium foil provided. Test any gases produced with red litmus paper
         Observations  Inferences
        Identify a cation and two anions in solution N.
        Cation:  (1⁄2 mark)
        Anions:  (1⁄2 mark) 



Procedure (a) Table 1



Statement form
Colour change from yellow/orange to Red/Pink 

From Colour Correctly mentioned in Solution B. to the Colour Correctly mentioned in CI of the Table 1 for 1 Mk. Otherwise penalise fully.

Procedure II (a

  1. Table 2        (5 Marks)
    Award a total of 5 marks distributed as follows:
    1. COMPLETE TABLE  (1Mark)
      1. Complete table with 3 titrations done  (1mark)
      2. Incomplete Table With 2 titrations clone(1/2 mark).
      3. Incomplete table with I titration done.... O Mk.
        1. wrong arithmetics/subtraction
        2. Inverted lable
        3. Burette readings beyond 50.0 cm3 unless explained
        4. Unrealistic Values (titre) le too low (below 10cm3)or too high (greater than 100 cm3)
          Penalise (1/2 mark) each of the above mistakes to a maximum of  1⁄2 mark.
          le, Penalise 1⁄2 mark once
    2. USE OF DECIMALS    (1 mark)
      (Tied to the first and and Second Rows Only).
      1. Accept 1 or 2 clecitnal places used consistently for 1 mk. Otherwise Penalise FULLY, le award  0mark)
      2. If 2 dip are used, then the 2nd d. p must be a O' or '5'. Otherwise penalise FULLY le, award (1mark).
      3. Accept Inconsistency in the use of Zero as the initial buretle reading i.e 0, 0·0, 0·00, 00·0,00·00
    3. ACCURACY     (1 mark).
      Compare the Candidates correct titre values with the School Value (SV).
      1. If at least one titre value is within ±0.1 cm3 of S.V award (1mark).
      2. If no value (titie) is within ±0.1 cm³ but at least one is within ±0.2 cm³ of S&V award( 1⁄2 mark).
      3. if none of the litre Values is within ±0.2 cm3 of SV award (0mark)
        1. if there is Wrong arittimatic subtraction in the lable, Compare the SV with the worked out correct titre/s and award accordingly.
        2. If no S.V is given by the teacher or the School value Can not be worked out from the teacher's value (litres) Using Principles of Averaging then the
          1. Write down all the Candidates' correct average per session and sample those that are close them to get the S.V.
          2. if the Candidate's correct average titres care too Varied then use KNEC Values  of 13-60/13-72/ 13-73
        3. Where there are two possible S•Vs from the Teachers' titre Values, both should be Written on the Candidate's Script and the one closer to the Candidate's value be used for awarding accuracy and Final Accuracy.
          eg: 24.9 ,25.0 ,25.2
           S.V 24.9+250/2 = 24-950m³ OR   25-0+252/2 =251cm³
        4. Tick the Candidates' chosen  litre on the lable If it earns a mark, before posting the mark.
      Conditions  (1mark).
      1. Values averaged must be shown and be within ± 0.2 cm3 of each other
      2. If three Consistent litrations are done and averaged award (1mark).
      3. If three litrations are done but only two are consistent and averaged .... (1mark).
      4. if only two tilations ne done, are consistent but and averaged  (1mark)
      5. if three litrations are done, are consistent but only two are avaraged .(1mark)
      6. if three inconsistent titrations are done and averaged  award  (0 mark)
      7. if only two inconsistent litrations are done and averaged award (0mark).
      8. If Only One Hition is done award   (0mark)
        1. Penalise (1/2 mark) for Wrong arithmetics in the answer of the error is outside ± 2 in the 2nd dip
        2. Penalise (1/2 marks) if no working is shown but correct answer is given
        3. penalise fully le coward (1mark) if no working is shown and the answer given is wrong.
        4. For wrong working With Corred ansive award (0Mark.) £g:
          25 +25+25=75/3 = 25
          26 +25+25=25    (The dots should not be assumed (to be division)
          1. Accept answer if it work out exactly to a whole No., or 1 dp and award FULLY
          2. The working of average value must be marked before the mark for principle of averaging is posted to the table 2.
          3. Accept rounding off Fruncation of answer to ad⋅p eg: 24.666 as 24.66 or 24-67 otherwise penalise  (1/2 mark)
            if answer is rounded off troncated to I dp or Whole number (iv) Units may or may not be given, but when given MUST be correct, Otherwise Penalise( 1⁄2 mark) for Wrong units attfachal.
    5. FINAL ACCURACY   (1mark) 
       (Tied to the connect average Titre)
      Compare the Candidates average as follows.
      1. if Within ±0.10 cm3 of S.V  (1 mark)
      2. if not Within ±0.10 cm3 of Sov but within ±0.2 cm³ of S.V.... /1⁄2 (1mark).
      3. If beyond ±0.20 cm3 of S.V aword (0marks)
        1. Where there are two possible average tires Use the one Which is closer to the SV and award accordingly..
        2. If Wrong titre Values are averaged by the Candidate pick the Correct fitre values if any following the principles of Averaging, average and award accordingly. Eg: 238 240 24.0
          Candidates' Working 24.0+240/2  = 24.0 cm3
          Examiner's Working: 23.8+240 +24·0/3 = 23-93 cm3
          1. Moles of Compound B used:
            0.05X25/1000  OR  0.05/40 OR  0·05 XO-025
               =0.00125125 (1/2marks)
            0-05 Must be transfered Intact Otherwise penalise FULLY  for any strange figure wed other than 0.05
          2. Moles of HCl in C 
            =2x Ans (1) above 2
            = Correct Ans
          3. Concentration of HCl in C2 in poles. per litre
            =Ans (ii) above X1000/Average litre / ans(1)
            = Correct answer   OR Concentration of HCl in C2
             = 0·05 X 25 x2/Average litre 
             = Correct answer √2.
          4. Concentration of Hcl in Cl
            Moles of HCl in 250 cmof Cl
            Ans (iv) x 250/1000 Or 250×ans(iii)/average littre 
            Same as mole 25 cm3 of Cl
            Concentration in Cl = Y×1000/25
               =correct abswer (1/2mark)   OR
            General Notes
            1. Answer (ii) and answer (iii) MUST be at least 4 d.p unless it work out exactly to less than 4 dop, Otherwise Penalise( 1/2 mark) for rounding off or truncating to less than 4d.p
            2. For answer (ii) and (iii) penalise (1/2mark) On the answer the error is Outside ± 2 units in the 4th d.p.
            3. Transfered answers answers in  (li) to must be intact. Otherwise penalise (1/2mark) for wrong transfer but penalise FULLY for Strange figure used•
            4. Answers (IN) and (V) MUST be at least 3 dp unless they work out exactly to less than 3d.p. Otherwise Penalise (1/2mark) for rounding off truncating to less than 3d.p .
            5. Penalise (1/2mark) for arithmetic error in answer (iv) and (v) if error is outside ±2 units in the 3rd dip.
            6. For answer (i) to (V), units may or may not be given but if given MUST be correct Otherwise penalise (1/2mark) for Wrong units attached.
              M, moles (litre, moles/dm3, moles/1000 cm3 mol/litre mol-1 
            7. Ans (V) MUST be within the range of 1.3 to 2.3 Otherwise Penalise (½mark) on the answer.

Procedure 1(b)

Table 3 ............(2marks)s
Award a total of 2 Marks distributed as follows.

  1. COMPLETE TABLE   (1mark)
    1. Where initial temperature reading is lower than the final temperature reading
    2. Unreadistic temperature reading (below 9.0°C and above 40°C
    3. Wrong arithmetics / Subtraction/ Missing ΔT
    4. Giving more than I set of temperature readings or entries
      1. Penalise (½mark) for each of the above mistakes to a maximum of( 1⁄2mark) le penalise (½mark) ONCE
      2. Award ink for Complete table if final temperature reading is equal to the initial temperature reading or where final or initial temperature is missing
      3. Ignore the sign of AT
  2. USE OF DECIMALS ........(½mark)
    Tied to 1st and 2nd Rows Only
    1. All temperature readings MUST be recorded Consistently as whole numbers or 1d.p or 2d.p. Otherwise. Penalise FULLY.
    2. If readings are recorded to I dp, then the decimal Should be Oor•5 Otherwise penalise FULLY
    3. If readings are recorded to 2, then should be .00, 25, 50, 75 Otherwise penalise FULLY
    4. To award for deamal the initial and Final temperature readings MUST be shown
  3. ACCURACY. ........(½mark)
    Compare the Candidate's initial temperature reading to the S.V (Teacher's initial temperature reading) and award /1⁄2 Mk if Within ± 2 units of school value. Otherwise award (0mk) for accuracy.
    1. If Candidate's Value Karns a mark tick (V) the reading in the table. If no School value is given by the teacher or where the value is Unrealistic, record all values. Sample close ones and average the Candidate's initial temperature readings per session.
    2. If Candidates Values are too varied then we the KNEC Value of 23.5 as the SV
    3. S.V Must be written on top of each Candidates' lable 3
    4. Where there are more than one set of temperature readings for accuracy Marking Point, Use the set whore ΔT is used" Calculation 1b However where ΔT is not used in Ib(i) then ALL Sets MUST Meet the Criteria for accuracy.
      1. Heat change = 30×4·2×ΔT
        = Correct answer  ½
      2. Moles =225/84  
        = 0.02976
      3. AH = Ans 1b(1)J/Ans 1b(ii)x1000
        = Correct ans
        General Note; 
        1. in 1b (i) to 1b(ii) if the expressions are not shown but the answer given is Correct award ½mk for the answer.
        2. In 1b(i) Correct units MUST be shown Otherwise penalise ½ mk for Missing or Wrong units attached. I
          Correct units are: J, J KJ, joules
        3. In 1b(i) accept an error of Zunits on the 4th. in joules (J) or on 3rd d. p if in kJ. Otherwise penalise. ½mrk  on the answer.
        4. In 1b(i) Ignore the sign in the answer
        5. In 1b(ii)  2.5 MUST be transfered intact, Otherwise. Penalise FULLY for my strange value used.
        6. In IbGD penalise 12 mk for Wrong answer if arithmetica enor is outside ± 2 units in the 4th d-p
        7. In 1b(iii) accept an error of ±2 units 3rd dip on the answer. Otherwise penalise /1⁄2 ink
        8. In 1601) Penalise 1/2 mk on the answer if a tve sign is missing
        9. 1b(ii) and 1b(ii) units may or may not be shown but if written. MUST be correct. Otherwise penalise ½Mk on the answer
        10. From 1b(i) to 1b(ii) formulae. are not a must-but penalise 1⁄2 mk.  if Wrong formulae shown.
          Moles = Mass given /REM 
          AH = MCT
          Moles = MassMolar Mass/Formula Mass 
          ΔΗ - ΜΟΔΙ
          AH = MCO
          ΔΗ =ΜΟΔΟ
          Q = MCΔT
        11. In 16(1) and 1b(iii) accept correct transfer of Values even if rejected earlier Otherwise penalise ½Mk for but penalise FULLY for Strange Value used.


Table 4 ..................(2marks)

Mark as table 3 but KNEC Value use 24.0°C.


1b(i) mark as 1b(i) use ΔT of table 4

General note ;
Apply the general note of procedure 1b
IIb(iii) heat change ΔH= ΔH2- ΔH
  heat change = Ansiib(ii) -1b(iii)
=corret ans

Conditons / penalties

  1. Penalise ½mk on the answer if tre sign orf and correct Units is or are missing- Correct
  2. Accept Transfer of answer I b (11) and 11 b(11) even if rejected earlier but penalise fuLLY for any Strange value used.
  3. If the expression is missing but the answer is Correct award ½mk for the correct answer
  4. The ans should be as expected. Otherwise pendise / mk on the answer.


  1.  Observations  inferences
     Solidburn with a yellow (sooty (smoky |
    Luminous flame
       Accept any of the following statements for full Credit
        Unsaturated organic Compound
        Organic compound with hig C H ratio 
        Long Chain Organic compound 
       Carbo Carbon double triple bond present in words
    1. Add 3 drops of acidified potassium dichromate (vi)and warm 
       Observations  inferences 
       Orange potassium dichromate (vi) does not change to green."  ROH absent
       Orange Colour of potassium dichromate (VI) Persists is retained / remains / does not change.  Alkohol/Alkanol absent in words. but reject-OH
       Orange colour does not change/persists/ retained remains  
    2.  Observation  Inferences
       Bromine water is not decolaunsid Yellows /orange colour of branine weather is eternal /persists does not change  Chemp3qn2b
       Colour of bromine water remains the Same

      Accept for 1/2 mk
      Unsaturated Organic compound absent

      Carbon-carbon double bond tripple bond

      Colour of bromine waiter as brown red
      colour of the solution remales the Same 
      The colour remains the Same
    3. Add Na2CO3, and test the gas using a burning splint.
       Observation  Inferences
       Effervescance/ bubbles /fizzing  Chemp3qn2biiipresent 
       Colourless gas evolved that Extinguishes a burning Splint Tied to effervescence bubbles fizzing
      Hissing (fizzling) Sizzling
      Colourless gase on its own

      Accept for 1/2 mk
       Carboxylic alkancic and present in words
      Solution is acidic
       H+ /H3O present  
      Solid M is acidic an acid


    1. Add NaOH dropwise until in excess
       Observations  Inferences
       While Ppt Solid Suspension /1⁄2 Insoluble in excess.  Ca22+, Mg2+,Ba2+ present 
         Award ½mk each to a maximum. of 1 mk 
      Accept lons Written in words for full credit.
      Penalise 1/2 mk for any Contradictory. Ion to a maximum. 
      Ignore the mention of Pb2+ ,Al3+  Zn2+ ions absent.
    2. Warm and add NH3 raw dropwise until in excess.
       Observations  Inferences
       White Ppt/solid /Suspension Insoluble in excess    Mg2+  present
          Accept Ca2+ / Ba2+ absent. for ½mk in the absence of Mg2+
      For any ion to eam credit it must have been correctly inferred in 
    3. Add 3 drops of Ba(NO3), then 1 cm3 dil HNO3(aq)
       Observations  Inferences
       While PPE solid suspension insoluble in addition of dilute nitric acid/ No effervesces/No bubbles  5O42-
         Accep for ½mark
      SO32- and  CO3absent  but both must be mentioned .
      Accept mention of the ions words
      Penalise FULLY for any Contradictory lon/s
    4. place I cm3 of NaOH, Add Seln then heat Mixture and test the gas
       Observations  infererences
       Red litmus paper remains red  or 
      Red litmus paper does not turn blue or
      Red Colour of litmus paper does not change remains the Same

       NH4+ absent 
       Accept for 1mk
      Red litmus paper remains.
      No effect on red litmus Paper 
      No change on red litmus Paper
      Red litmus paper does not Change to blue
      But Credit FULLY on the correct inference
    5. Warm the Mixture and add the folded Als, test gas with litmus
       Observations  Inferences 
       Effervescence bubbles of a colourless gas  NO3 Present
       Red litmus paper turns to blue  Tied to red litmus paper turning blue!
      Pungent Smelling gas Nitrate ion Written In words for 1⁄2 marks
      Identification of the cation and two anions
      Cation: Mg2+ 
      Anion NO3,5042-
      1. Accept lons given in words for full credit.
      2. For the cations and the anions to be awarded, they must have been correctly infered in 36, 3C and 3d
      3. For 3d and 3d (1) penalise FULLY for any Contradictory ion-
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