Chemistry Paper 3 Questions and Answers with Confidential - Sukellemo Joint Pre Mock Exams 2023

INSTRUCTIONS TO CANDIDATES

• Answer all the questions in the spaces provided in the question paper.
• You are not allowed to start working with the apparatus for the first 15 minutes of the 2 ¼hours allowed for this paper. This time is to enable you to read through the question paper and make sure you have all the chemicals and apparatus that you may need.
• Candidates should answer the questions in English.

Question 1

You are provided with;

• Acid A labelled as Solution A.
• 2.0 M sodium hydroxide solution labelled as Solution B.
• Solution C containing 25.0g per litre of an alkanoic acid.

You are required to determine;

• The Molar mass of the alkanoic acid
• Reaction ratio between sodium hydroxide and acid A.

PROCEDURE I
Using a pipette and a pipette filler, place 25cm³ of solution B in to a 250ml volumetric flask. Add about 200cm³ of distilled water. Shake well. Add more distilled water up to the mark and label this as solution B 1 .

Retain the remaining solution B for use in procedure II.

Fill the burette with solution C.
Using a clean pipette and pipette filler, place 25cm³ of solution B 1 into a 250ml conical flask.
Add two drops of phenolphthalein indicator to solution B 1 in the conical flask and titrate with solution C.
Record your results in table 1.
Repeat the titration two more times and complete the table 1 below. (4marks)

Table 1

Determine;

1. The average volume of solution C used (1mark)
2. The concentration of solution B 1 in moles per litre (2marks)
3. The concentration of alkanoic acid in solution C in moles per litre. (1 mole of C reacts three moles of the B 1 during titration) (2marks)
4. The Molar mass of the alkanoic acid. (1mark)

PROCEDURE II

Fill a clean burrete with solution A. Place 5cm³ of solution A into a 100ml plastic beaker. Measure the initial temperature of solution A in the beaker and record in table 2. Using a 50ml measuring cylinder, measure 25cm³ of solution B and add it to solution A in the beaker and immediately stir the mixture with a thermometer. Record the maximum temperature reached in table 2. Discard the mixture in the plastic beaker.

Repeat the experiment with other sets of volumes of solution A and B as shown in table 2 and complete table 2 below. (4marks)

Table 2

1. On the grid provided, plot a graph of change in temperature (vertical axis) against volume of solution A (3marks).
2. From the graph determine the volume of solution A which gave the maximum change in temperature (1mark)
3. Determine the volume of solution B that reacted with the volume of solution A.(1mark)
4. Calculate;
   1. The ratio between volume of solution A and B that neutralized one another. (1mark)
   2. The concentration in moles per litre of the acid in solution A. (Assume that the volume ratio is the same as the mole ratio) (2marks)

Question 2.

You are provided with solid D. Carry out the following tests and write your observations and inferences in the spaces provided.

1. Place about a half of solid D in a test tube and heat strongly. Test any gases produced with both red and blue litmus papers.
   

   Observations (2marks)	Inferences (1mark)

2. Place the rest of solid in a boiling tube and add about 10cm³ of distilled water. Shake well.
   To a 2cm³ portion of the solution, add about 1cm 3 of hydrogen peroxide and shake well. To the resulting mixture, add aqueous sodium hydroxide dropwise until in excess.

   Observations (1½marks)	Inferences (½mark)

3. You are provided with solution E. Carry out the following tests and write your observations in the spaces provided. Divide solution E into two portions.
   1. To the first portion, of solution E, add three drops of barium nitrate solution. Retain the mixture for use in test (ii) below.

      Observations (1marks)	Inferences (1mark)

   2. To the mixture obtained in (c(i) above, add about 2cm³ of 2M nitric V acid.

      Observations (1marks)	Inferences (1mark)

   3. To the second portion of solution E, add two drops of acidified potassium dichromate VI and warm the mixture.
      

      Observations (1marks)	Inferences (1mark)

Question 3.

You are provided with substance F. Use it to carry out the tests that follows. Record your observations and inferences in the spaces provided.

1. Describe the appearance of substance F (½ mark)
2. Scoop a little of substance F using a clean metallic spatula and ignite it in a Bunsen burner flame.

   Observations (½marks)	Inferences (½mark)

3. Place about 2cm³ of substance F in a clean test tube and add solid G, sodium hydrogen carbonate provided.

   Observations (1marks)	Inferences (½mark)

4. Place about 2cm³ of substance F in a test tube and add 2cm³ of acidified potassium dichromate VI and warm the mixture.

   Observations (1marks)	Inferences (1mark)

5. Place about 2cm³ of substance F and add 2cm³ of distilled water.

   Observations (1marks)	Inferences (1mark)

CONFIDENTIAL

1. About 100cm³ of solution A Labeled Solution A.
2. About 120cm³ of solution B labeled Solution B.
3. About 70cm³ of solution C labeled Solution C.
4. About 0.5g of solid D (Ammonium iron II sulphate) (NH₄)₂ Fe(SO₄)₂ .6H₂O labeled as Solid D.
5. About 4cm³ of solution E (1M sodium sulphite) in a test tube labeled Solution E.
6. About 10cm³ of substance F (absolute ethanol) in a stoppered boiling tube labelled Substance F.
7. About 0.2g of solid G (Sodium hydrogen carbonate) in a stoppered container labelled as Solid G
8. One pipette 25.0ml.
9. One pipette filler.
10. One volumetric flask 250.0ml.
11. One label.
12. Three conical flasks 250.0ml.
13. One 10.0ml measuring cylinder.
14. One 50.0/100.0ml measuring cylinder.
15. One 100.0ml plastic beaker.
16. One thermometer -10°C to 110°C.
17. One clean metallic spatula
18. 1 blue litmus paper
19. 1 red litmus paper
20. Six clean dry test tubes in a test tube rack.

ACCESS TO.

1. Source of heat.
2. Phenolphthalein indicator supplied with a dropper.
3. 2M Nitric V acid supplied with a dropper.
4. Barium nitrate solution supplied with a dropper
5. Acidified potassium dichromate VI supplied with a dropper.
6. 20 volume hydrogen peroxide
7. 2M sodium hydroxide supplied with a dropper.
8. Distilled water in a wash bottle.

PREPARATIONS.

• Solution A is prepared by taking 190.0cm³ of concentrated hydrochloric acid (35% and density 1.18g/cm³) and adding it to 600cm³ of distilled water in a 1 litre volumetric flask and diluting it to the mark.
• Solution B is prepared by dissolving 80.0g of sodium hydroxide pellets in 800cm³ of distilled water in a 1 litre volumetric flask and then diluting it to the mark.
• Solution C is prepared by dissolving 25g of solid C(citric acid, C₃H₅O(COOH)₃) in 600cm³ of
  distilled water in a 1 litre volumetric flask and then diluting it to the mark.
• Barium nitrate is prepared by dissolving 26g of solid barium nitrate in about 600cm³ of distilled water in a 1 litre volumetric flask and then diluting it to the mark.
• Acidified potassium dichromate VI is prepared by dissolving 25g of solid potassium dichromate VI in 200cm³ of 2M sulphuric VI acid, quantitatively transfer the mixture into a 1 litre volumetric flask and then diluting it with distilled water to the mark.
• Solution E is prepared by dissolving 40.0g of sodium sulphite in a bout 500cm³ of distilled water then diluting it to one litre.

MARKING SCHEME

QUESTION 1

Procedure I

Table 1  5 marks
Distributed as follows

1. COMPLETE TABLE ....... 1mk
   1. Complete table with 3 titrations done...1mk
   2. Incomplete table with 2 titrations done.... ½mk
   3. Incomplete table with only one titration done...0mk
      Penalties
      1. Wrong arithmetic/ Subtraction
      2. Inverted table
      3. Burette readings beyond 50cm³ unless explained.
      4. Unrealistic titre values i.e. too low (below. 1.0cm³) or too high(greater than 100.0cm³)
         NB: Penalize 1⁄2mk ONCE for any of the above mistakes.
2. USE OF DECIMALS......1mk
   (Tied to 1^st and 2^nd rows only)
   Conditions
   1. Accept 1 or 2  decimal places consistently used for 1mk otherwise penalise FULLY (award 0mk)
   2. If  2 decimal places are used, then the 2^nd decimal place must be "0" or "5" Otherwise penalise fully (Award omk).
   3. Accept inconsistencies. in the use of zeros as initial burette readings e.g 0.0, 0, 0.00, 00.0, 00.00
3. ACCURACY.....1mk
   Compare the candidate's correct titre value with the school value (s.v)
   1. If atleast one titre value is within ± 0.10cm³ of s.v award 1mk
   2. If no titre value is within ±0.10cm³ of the s.v but atleast one is within ±0.20cm³ of s.v.....award ½mk
   3. If none of the titre values is within ±0.20cm³ award 0mk
      NOTE
      1. If there was wrong arithmetic/substraction in table, compare the S.V with the worked out correct titres and award accordingly.
      2. If no s.v is given by the teacher or the s.v cannot be worked out form the principles of averaging , then
         1. Sample the candidate's values and avergae those that are close to get the s.v
         2. If the candidates' values. are too varied then use 12.7 cm³
      3.  where there are two possible s.v from the teacher's titre values, both should be written on the candidate's script and the one closer to candidate's values be used for awarding accuracy and final accuracy
      4. Tick(✔) the candidates's chosen titre on the table if it earns a mark before posting the mark.
4. PRINCIPLES OF AVERAGING ...1mk.
   Condition
   1. Values averaged MUST be shown and must be within ±0.20cm³ of each other.
   2. If 3 consistent titrations are done and averaged ...1mk
   3. If 3 titrations are done but only two are consistent and averaged ...1mk
   4. If only two titrations are done are consistent and averaged ...1mk
   5. If 3 titrations are done, are consistent but only two are averaged ....0mk
   6. If 3 titrations are done. are inconsistent and averaged .... award 0mk
   7. If only two titrations are done, are consistent and averaged, award 0mk
   8. If only one titration. done...0mk
      Penalties
      1. Penalise ½mk for wrong arithmetic in the answer if error is outside ±units in the second decimal place.
      2. Penalise ½ mk  if NO WORKING is shown but correct answer is given.
      3. Penalise FULLY (award 0mk) if no working is shown and answer given is wrong.
      4. For wrong working with correct answer award 0mk e.g
         25.0 + 25.0 + 25.0 = ⁷⁵/₃ = 25.0
         OR
         where the division line is missing
         NOTE
         1. Accept answer is it works out exactly to a whole number or to 1 decimal place and award FULLY
         2. The working of average value must be marked before the mark for principles of averaging is awarded to the table 1.
         3. Accept rounding off/ trancation of answer is rounded off/trancated to 1 d.p or to a whole number.
         4. Units may or may not be given but when given must be correct otherwise penalise ½mk for wrong units attached.
5. FINAL ACCURACY.
   1. If within ±0.10cm³ of s.v ....1mk
   2. If not within ±0.10cm³ of s.v but within ±0.20cm³ of s.v ....½mk
   3. If beyond ±0.20cm³ of s.v ......0mk
      NOTE
      1. where there are two possible average titres, use the one which is closest to the s.v and award accordingly.
      2. lf wrong titrations are averaged pick .the correct titres (if any) following the principles of averaging, average and award accordingly.

CALCULATIONS

(b) 25 × 2  ✔½ = 0.05 ✔½
       1000
1000 × 0.05  ✔½ = 0.2M  ✔½
      250

(c) 0.2 × 25 = 0.005  ✔½
        1000
          OR
    0.05 × 25 = 0.005
         250
    0.005 × 1 = 0.00166  ✔½
           3
  1000 × 0.00166  ✔½= correct answer  ✔½
       titre value
(d)          25               ✔½ = correct answer  ✔½
     answer from (c)

NOTES

1. For part b  and C. the Values must be transferred intact otherwise penalise fully for strange figures used. 
2. For part b and c the units may or may not be given, but if given must be correct e.g
   M// moles per litre // moles / dm³ // moles / 1000cm³ // moles/L // moles L^-1 Otherwise penalise 1mk for wrong units e.g mols
3. For part b and C the answer must be written to atleast 4dp unless it works out into a value that is less than 4dp otherwise penalise ½ mk at the answer.
4. For part b the answer must be  within 01-03 otherwise penalise ½mk at the answer.
5. For part d, penalise ½mnk if units are given otherwise mark accordingly.
6. For part d the answer must be written to atleast 2 dp unless it works out into a value that is less than 2dp
7. For part d, the answer must be between 180-210 otherwise penalise ½mk.
   NB For an error in part (v)(vi) and (vii) penalise ½mk once

Procedure II
Table 2

Distributed as follows

1. COMPLETE TABLE ....1mk
   Award 1mk for complete table with 6 readings.
   penalties
   1. Penalise ½ mk. for each space not filled to a maximum of 1mk Subject to atleast 4 readings otherwise penalise fullly/
   2. penalise ½mk once for unrealistic initial temperature reading (when volume of A=5cm³) ( i.e below 10°C or above 50°C)
   3. Penalise ½mk once the temp. readings are constant for the row of 'maximum temperature'
   4. Penalise 1⁄2 mk if there is arithmetic error if any of the columns.
2. USE OF DECIMALS... 1mk
   Subject to atleast two readings in 1st and 2^nd row.
   Conditions
   Must be consistently recorded. as a whole number consistently or to 1d.p recorded as .5 or .0 otherwise penalise fully.
3.  ACCURACY...1mk
   Compare the candidate's initial temperature reading  when volume of A = 5cm³,and award 1mark if with ± 2.0°C of the s.v otherwise penalise fully. (award 0mk)
   candidate's initial tempertaure reading if credited
4. TRENDS...1mk
   Award 1^st ½mk for continuous rise in temperature upto a maximum and the ^2nd ½mk for temperature being either constant at maximum, followed by a continuous drop after the maximum e.g 
   

GRAPH...3 marks

Distributed as follows

1. LABELLING ...½mk
   Award ½mk if both axes are correctly labelled
   Penalties
   1. Penalise fully for inverted axes
   2. Penalise fully for wrong units used otherwise ignore if units are omitted.
   3. Penalise fully if only one axis is labelled.
2. SCALE:....½mk
   Conditions
   1. Area covered by the plots should be atleast half of the grid provided ie 31⁄2 big squares. vertical by 4 big squares (horizontal)
   2. Scale interval chosen must be consistent on both axes.
   3. Scale chosen must be able to accommodate all plots/points whether plotted or not
      NB
      1. Award for correct scale even if the axes are inverted.
      2. Penalise fully in any of the above conditions is not met.
3. PLOTTING:...1nk
   1. If 5 or 6 points are correctly plotted.... 1mk.
   2. If 3 or 4 points. are correctly plotted...mk.
   3. If <3 points are correctly plotted ...0mk
      NB
      1. If scale interval. are inconsistent, credit correct plots (if any) within the first scale interval and treat all others as wrong.
      2. Accept correct plots even if the axes are inverted and award accordingly.
      3. Mark all the plots on the graph ( ✔ or x) depending on whether they are correct or not respectively.
4. LINE/SHAPE:...1mk
   Conditions
   1. Accept two straight lines intersecting on extrapolation with the first line passing through the initid temperature, for 1mk 
   2. Accept two straight lines not extrapolated whether joined or not for ½mk on condition that the first line passes through the initial temperature
      expected graph versions
      
      NB: The two extrapolated lines. must meet above the highest plot otherwise pendise. ½ mk/mark accordingly.

(b) (i) Accept correct volume of  A from a correctly extrapolated graph for 1mk. ½mk for showing and ½ for correctly reading what has been shown.

(ii) Award 0mk for volume of A stated from a wrong graph.

(c) (30 − answer form (b))  ✔½ = correct answer  ✔½
(d) (i)     answer b       :        answer c       ✔½  = correct answer  ✔½
         smallest volume   smallest volum
NB: penalise ½mk if the answer is outside ratio of 1:1

(ii) 2 × volume of answer (c)  ✔½ = correct answer  ✔½ Step I
                10000
Mole ratio A:B = 1: 1
Answer from Step I × 1000  ✔½ = correct answer  ✔½
    answer from (b)

QUESTION 2

1. 
   

   Observations (2marks)	Inferences (1mark)
   Gas that changes a red litmus paper blue is produced ✔½  Blue litmus paper remains blue ✔½  Colourless liquid is formed on the cooler parts of the test tube ✔½ OR   Vapour condenses on the cooler parts of the test tube white sublimate ✔½	NH4+ present ✔½  Solid D is hydrated ✔½  Penalise fully for contradictory ion mentioned as either present  or absent

2.  
   

   Observations (2marks)	Inferences (1mark)
   (Green solution) changes to yellow/ yellow solution is formed ✔½ Brown precipitate ✔½ Insoluble in excess ✔½	Fe2+ oxidised to Fe3+ ✔½

3.  
   
   1.  
      

      Observations (2marks)	Inferences (1mark)
      White precipitate ✔1	SO42−, SO32−, CO32− present ✔1 all 3 - 1mk      2 - ½mk      1 - 0mk   Penalise ½mk to a maximum of 1mk for any contradictory ion

   2.  
      

      Observations (2marks)	Inferences (1mark)
      Effervescence  ✔1 White precipitate dissolves ✔1	SO32−, CO32− present ✔1  Conditions i) Only award if the two anions had correctly been inferred in c(i) ii) Accept for ½mk SO42− absent only if it had been correctly inferred in c(i) above iii) Penalise fully for any other ion mentioned here.

   3.  
      

      Observations (2marks)	Inferences (1mark)
      Orange acidified potassium dichromate (vi) changes to green  ✔1	SO32− present ✔1 i) Penalise fully for any contradictory ion. ii) Award only if it had been scored in past c(ii)

QUESTION 3

1. Colourless liquid ✔½
2.  
   

   Observations (2marks)	Inferences (1mark)
   Liquid burns with a blue flame ✔½	\       /   C = C   ✔½  OR  C ≡ C absent   /        \                  /       \  Penalise fully for any other functional group mentioned as either present or absent.

3.  
   

   Observations (2marks)	Inferences (1mark)
   No effervescence ✔1	R −COOH/ −COOH absent ✔1  i) Accept for ½mk H3O+/H+ absent ii) Penalise fully for any other functional group mentioned as absent/ present

4.  
   

   Observations (2marks)	Inferences (1mark)
   Orange acidified potassium dichromate VI changes to green	R − OH present penalise fully for any contradictory functional group

5.  
   

   Observations (2marks)	Inferences (1mark)
   Substance is miscible with water	Substance F is polar