CHEMISTRY Paper 3 Questions and Answers - KCSE 2022 Past Papers

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PHYSICS Paper 1 Questions and Answers - KCSE 2022 Past Papers

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QUESTIONS;

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:
        
        heat change of the solution (assume specific heat capacity of solution = 4.2 Jg per degree, density of solution = 1.00 g cm3) (1mark)
        
        heat change, AH, in kJmol of sodium hydrogen carbonate (1 mark)
        
        heat change, AH,- AH, - AH, for the reaction of hydrochloric acid and one mole of aqueous sodium hydrogen carbonate (1 mark)
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)
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)

MARKING SCHEME:

QUESTION 1 :

Procedure (a) Table 1

Colours

Yellow/Orange
Red/Pink

Statement form
Colour change from yellow/orange to Red/Pink
i.e

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

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.
    Penalties
    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)
      NB:
      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).
  Conditions:
  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).
  Conditions
  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)
    NOTE
    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.
4. PRINCIPLES OF AVERAGING
  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)
    Penalties
    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)
      NOTE:
      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.
  Condtions
  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)
    NOTE:
    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 cm³Examiner's Working: ^{23.8+240 +24·0}/₃ = 23-93 cm³CALCULATIONS
      1. Moles of Compound B used:
        ^0.05X25/₁₀₀₀ OR ^0.05/₄₀ OR 0·05 XO-025
        =0.00125125 (¹/₂marks)
        Conditions:
        0-05 Must be transfered Intact Otherwise penalise FULLY for any strange figure wed other than 0.05
      2. Moles of HCl in C₂
        =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 cm₃of 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
        
        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
        
        For answer (ii) and (iii) penalise (¹/₂mark) On the answer the error is Outside ± 2 units in the 4th d.p.
        
        Transfered answers answers in (li) to must be intact. Otherwise penalise (¹/₂mark) for wrong transfer but penalise FULLY for Strange figure used•
        
        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 .
        
        Penalise (¹/₂mark) for arithmetic error in answer (iv) and (v) if error is outside ±2 units in the 3rd dip.
        
        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
        
        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.

COMPLETE TABLE (1mark)
Penalties
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
  NOTE:
  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
USE OF DECIMALS ........(½mark)
Tied to 1st and 2nd Rows Only
Conditions
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 d.ps, then should be .00, 25, 50, 75 Otherwise penalise FULLY
4. To award for deamal the initial and Final temperature readings MUST be shown
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.
NOTE:
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.
  CALCULATIONS
  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.
      Reject
      Moles = ^{Mass given} /_REMAH = MCT
      Accept
      Moles = ^Mass/ _{Molar 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.

PROCEDURE

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

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

CALCULATIONS

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

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

QUESTION 2

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

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

Observation	Inferences
Bromine water is not decolaunsid Yellows /orange colour of branine weather is eternal /persists does not change
Colour of bromine water remains the Same	NOTE Accept for 1/2 mk Unsaturated Organic compound absent Carbon-carbon double bond tripple bond
Reject: Colour of bromine waiter as brown red colour of the solution remales the Same The colour remains the Same

Add Na2CO3, and test the gas using a burning splint.

Observation	Inferences
Effervescance/ bubbles /fizzing	present
Colourless gas evolved that Extinguishes a burning Splint	Tied to effervescence bubbles fizzing
Reject Hissing (fizzling) Sizzling Colourless gase on its own	NOTE Accept for 1/2 mk Carboxylic alkancic and present in words Solution is acidic H⁺ /H3O present Reject COOH Solid M is acidic an acid

QUESTION 3

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.
	Penalties Penalise 1/2 mk for any Contradictory. Ion to a maximum. NOTE Ignore the mention of Pb²⁺,Al³⁺Zn²⁺ ions absent.

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⁺
	Note For any ion to eam credit it must have been correctly inferred in

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	5O4^2-
	Accep for ½mark SO₃^2-and CO₃²absent but both must be mentioned . Accept mention of the ions words
	Penalties Penalise FULLY for any Contradictory lon/s

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
NOTE: But Credit FULLY on the correct inference

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 NO₃,50₄^2-Conditions

Accept lons given in words for full credit.
For the cations and the anions to be awarded, they must have been correctly infered in 36, 3C and 3d
For 3d and 3d (1) penalise FULLY for any Contradictory ion-

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