Chemistry Paper 3 Questions and Answers with Confidential - Samia Joint Mock Examination 2023

INSTRUCTIONS TO CANDIDATES:

• Answer all the 
• You are NOT allowed to start working with the apparatus for the first 15 minutes of the 24 hours allowed for this paper. This time is to enable you read the question paper and make sure you have all the chemicals and apparatus that you may need.
• All working MUST be clearly shown where necessary.
• Mathematical tables and electronic calculators may be used.

QUESTION 1

1. You are provided with:
   • Solution A,containing 39.2g/l of FeSO₄(NH₄)₂SO4.nH₂O
   • Solution B Containing 3.0g/l of KMnO₄.
     You are required to determine;
   • The concentration of solution A in moles per litre
   • The number of moles of (n) of water of crystallization in FeSO4(NH4)2SO4.nH2O
     Procedure
   • Fill the burette with solution A.
   • Using a pipette filler, pipette 25.0cm3 of solution B into a conical flask and titrate with solution A until a purple colour just appears.
   • Record the volume of solution A used in the table below. Repeat the experiment twice and fill the table.
     Table 1
     

     Titrations	1	2	4
     Final burette reading (cm3)
     Initial burette reading (cm3)
     Volume of solution A (cm3)

                                                                                                                    (4mks)
     
     1. Calculate the average volume of solution A used   (Imk)
     2. Determine;
        1. Concentration of solution B in moles per litre, (K=39,Mn=55,0=16) (Imk)
        2. Number of moles of solution B used. (1mk)
     3. Given that the ionic equation for the reaction is:
        MnO₄⁻_(aq) + 8H⁺_(aq) + 5Fe²⁺_(aq) → Mn²⁺_(aq) + 5Fe³⁺_(aq) + 4H₂O (1)
        Determine the number of moles of solution A used.   (1mk)
     4. Determine the;
        1. Concentration of solution A in mole per litre (1mk) 
        2. Relative formula mass of FeSO₄(NH₄)₂SO4.nH₂O  (1mk)
        3. Number of moles of water of crystallization (n) in FeSO4(NH4)2SO4.nH2O (1mk)
2. You are provided with
   - Magnesium ribbon labeled M
   - 2.0M Sulphuric (VI) acid, solution N
   You are required to determine the rate of reaction between magnesium and sulphuric (VI) acid at different concentrations.
   Procedure
   Place six test tubes on a test-tube rack and label them 1, 2, 3, 4, 5 and 6. Using a 10cm3
   Measuring cylinder, measure out volumes of 2.0M of sulphuric (VI) acid (solution N) as shown in the table II below and pour them in the corresponding test tubes. Wash the measuring cylinder and use it to measure the volume of the distilled water as indicated in the table II and pour in the corresponding test tubes. Cut out six pieces each of 1 cm length of magnesium ribbon. Transfer all of the solution in the test tube 1 into a clean 100 ml plastic beaker. Place one piece of magnesium into the beaker and start a stop watch immediately. Swirl the beaker continuously ensuring that magnesium is always inside the solution Record in the table II the time taken for the magnesium ribbon to disappear. Wash the beaker each time and repeat the procedure for each of the solutions in the test tubes 2, 3, 4, 5, and 6
   Table II
   

   Test tube number	1	2	3	4	5	6
   Volume of solution N (cm3)	10	9	8	7	6	5
   Volume of distilled water (cm3)	0	1	2	3	4	5
   Time taken (seconds)
   Rate of reaction, 1/t (s1)

                                                                                                                                                    (5mks)
   1. Plot a graph of rate of reaction (¹/_t) (y-axis) against the volume of N used.  (3mks)                                             
   2. Using the graph, determine the time that would be taken for one centimeter of magnesium ribbon to disappear if the number of moles of N used was 0.015 moles  (2mks)
3. 1. 
      You are provided with solid P. Carry out the tests below and record your observations and inferences in the spaces provided.
      1. Place solid P in a boiling tube. Add about 10cm3 of distilled water and shake.
         

         Observation	Inference
         (1mk)	(1mk)

      2. To about 1cm³ of the solution add aqueous sodium hydroxide drop wise till in excess
         

         Observation	Inference
         (1mk)	(1mk)

      3. Scoop a little of the solution using a metallic spatula and burn over a non-luminous flame.
         

         Observation	Inference
         (1⁄2 mk)	(1⁄2 mk)

      4. To about 1cm³ of the solution add three drops of lead (II) nitrate solution.
         

         Observation	Inference
         (1⁄2 mk)	(1mk)

      5. To about 1cm³ of the solution add a few drops of barium chloride solution followed by about 3cm³ of dilute nitric acid.
         

         Observation	Inference
         (1 mk)	(½ mk)

      6. To about 1cm³ of the solution add a few drops of acidified potassium dichromate (VI).
         

         Observation	Inference
         (1⁄2 mk)	(1⁄2 mk)

   2. You are provided with solid M.Use it for the following tests.
      1. Using a metallic spatula, ignite about one half of solid M in a Bunsen flame
         

         Observation	Inference
         (1mk)	(1mk)

      2. Place the other half of solid M into a boiling tube. Add about 10 cm³ of distilled water and shake well. Use the solution for the following tests.
         Place 2 cm³ of the solution in a test tube and add 3 drops of acidified potassium manganate (VII) and warm.
         

         Observation	Inference
         (1⁄2 mk)	(1mk)

      3. To about 2cm³ of the solution obtained in (b) above, add 3 drops of acidified potassium dichromate (VI).
         

         Observation	Inference
         (1⁄2 mk)	(1⁄2 mk)

      4. To about 2cm³ of solution obtained in (b) above, add 3 drops of bromine water and warm.
         

         Observation	Inference
         (1⁄2 mk)	(1mk)

      5. To about 2cm³ of solution obtained in (b) above, add the sodium hydrogen carbonate provided.
         

         Observation	Inference
         (1⁄2 mk)	(1⁄2 mk)

      6. To about 2cm³ of solution obtained in (b) above, add 3 drops of universal indicator solution.
         

         Observation	Inference
         (1⁄2 mk)	(1⁄2 mk)

      7. To about 2cm³ of solution obtained in (b) above, add 5 drops of ethanol followed by three drops of 2M Sulphuric (VI) acid and warm.
         

         Observation	Inference
         (1⁄2 mk)	(1⁄2 mk)

CONFIDENTIAL

Each student to be supplied with:

1. Solid P – about 0.5g sodium sulphite
2. Solid M – about 0.5g oxalic acid
3. About 0.5g sodium hydrogen carbonate
4. 200cm³ solution A
5. 100cm³ solution B
6. 100cm³ 2M sulphuric (VI) acid, solution N
7. About 10cm long magnesium ribbon labeled M

APPARATUS

• One stop watch
• One conical flask
• One 100ml plastic beaker
• 2 boiling tubes
• Test tube holder
• 10ml measuring cylinder
• About 500ml of distilled water in a wash bottle
• One 50ml burette
• One 50ml pipette
• Retort stand
• White tile
• Pipette filler
• Filter funnel
• Test tube rack
• 6 test tubes
• 6 labels
• One metallic spatula

ACCESS TO

• Source of heat
• 2M Barium chloride solution with dropper
• 2M sodium hydroxide with dropper
• 2M nitric (V) acid with dropper
• Lead (II) nitrate solution with a dropper
• Acidified potassium manganate (VII) with dropper
• Acidified potassium dichromate (VI) with dropper
• Bromine water in a stoppered reagent bottle with a dropper
• Universal indicator solution with a dropper
• pH chart (make sure it corresponds to the indicator provided)
• Ethanol supplied with a dropper
• 2M sulphuric (VI) acid with a dropper

NOTES.

• Solution A is prepared by dissolving exactly 39.2g of FeSO₄(NH₄)₂SO₄.nH₂O in 600cm³ of distilled water and dilute with distilled water to one litre(Freshly prepared).
• Solution B is prepared by dissolving 3.0g of KMnO₄ in 400ml of 2M H₂SO₄ and distilled water to one litre.

MARKING SCHEME

Question 1

1. Complete table √1mk
   Complete table with 3 titres √1mk
   Incomplete table with 2 titres √½ mk
   Incomplete table with 1 titre  0 mk
   Conditions

   •  

     Penalize ½ mk for unrealistic values unless where explained
   • Penalize ½ mk for any inversion of table
   • Penalize ½ mk for any arithmetic error
     NB: penalize a maximum of ½ mk for any of the conditions above.
2. 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”

3. 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.

4. Principles of averaging √1mk
   Values averaged must be consistent
   If 3 titres but only 2 are consistent and averaged award 1mk
   If 3 titres done, consistent and averaged award 1mk
   If 3 titres done and inconsistent and averaged award 0mk
   If 3 titres done and all are consistent but only 2 are averaged award 0mk

5. Final answer √1mk
   Award 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 awarded as follows: CT 1mk
                                               D   1mk
                                               A    1mk
                                               PA  1mk
                                               FA  1mk
                                                     5mks

1. 1. Average titre = t₁ + t₂ + t₃ (√½ mk)
                                     3
      = Correct Ans ½ mk
   2.  
      1. = 3.0          ٧ ½
            158
         = 0.018987M ٧ ½Penalize ½ mk if rounded off to less than 4d.p.
                                   - Reject formulae Molarity = mass
                                                                                R.F.M
                                   - Accept formulae Molarity = mass g/l
                                                                                Molar mass
                                   - Accept any other alternative correct method
      2. = ans in b (i) X 25      ٧ ½ Accept any other correct method
                   1000
         = correct ans, b (ii) ٧ ½
   3. = Ans. in b (ii) X 5 ٧ ½
      = correct ans. (c) ٧ ½
   4.  
      1. = 1000 X ans. in (c)     ٧ ½
                   Ans. in (a)
         = correct ans d (i)٧ ½
      2. Molar Mass =     39.2         ٧ ½
                                Ans. in d (i)
         = correct answer d (ii) ٧ ½
      3. 284 + 18n = ans. in d (ii) ٧ ½
                       n = correct ans. ٧ ½   Must be a whole number at the final answer, otherwise penalize ½ mk.
                                                          Answer must range between 1 – 10 otherwise penalize ½ mk)

QUESTION TWO

Table II

• Complete table (all spaces filled with realistic values) = (3mks)
  - ½ mk for each column with time value and correct rate of reaction
  -Penalize 1½ mk if rate of reaction values are written as fractions.
• Consistent Decimals = (½ mk)
  - Use (atleast 3 decimal places for rate of reaction otherwise penalize fully) and whole numbers or one decimal place used consistently for time otherwise penalize fully)
• Accuracy = (1mk)
  - Compare time taken before adding water to the school value; those within ±3 seconds of school value credit 1mk. Otherwise penalize fully.
• Trend is tied to time reading (time increases as more water is added) = (½ mk)
  - penalize fully if some of the time values are equal or less than the previous one as you go across the table.)
  
  

1.   
                                  
   Marking Points
   • Labeling of both axes (with units indicated) = ( ½mk)
   • Scale (½ of grid used on both axes) = ( ½mk)
   • Plotting (5 points or more correctly plotted) = (1mk)
                   4 points or more correctly plotted = ½ mk
   • Straight line (line of best fit with + ve gradient. Use of a ruler) = (1mk)
                            Should pass through at least 3 correctly plotted points
2. Let x be volume of solution N used;
        If 2moles = 1000cm³
        0.015moles =  0.015 x 1000 = 7.5cm³  ٧ ½
                                          2
   From the graph 7.5cm³ = 0.0204s-1٧ ½
   Therefore ¹/_t = 0.0204
                      t =   1        ٧ ½
                          0.0204
                      t = 49 seconds ٧ ½

QUESTION THREE

1.  
   1.  
      

      Observation	Inference
      Dissolves٧ ½ to form a               colourless    solution٧ ½	Polar substance   ½ mk       Coloured ions absent e.g. Fe2+, Fe3+, Cu2+ ½ mk         - Polar substance is tied to      dissolves   - Coloured ions absent is        tied to colourless solution

   2.  
      

      Observation	Inference
      No white precipitate formed             1mk	Zn2+, Al3+, Pb2+, Ca2+,Mg2+     absent.

       5 ions correct award 2mks
       4 ions correct award 1mk
       3 ions correct award ½mk
       Penalize any contradictory ions ½ mk eachto a maximum of 2mrks
   3.  
      

      Observation	Inference
      Burns with a yellow flame             (1⁄2 mk)	Na+ present                              (1⁄2 mk)

   4.   
      

      Observation	Inference
      White precipitate formed     (1⁄2 mk)	SO42−, SO32−, CO32−, Cl−             present   At least 4 ions – 1mk    3 ions – ½ mk

   5.  
      

      Observation	Inference
      White precipitate formed   ½ mk   Effervescence  Bubbles  Dissolves in acid ½ mk ½mk  (1⁄2 mk)	CO32− or SO32−present   (1⁄2 mk)

   6.  
      

      Observation	Inference
      Orange colour of acidified potassium  dichromate (VI) changes to green   (1⁄2 mk)   Reject: turns in place of changes	SO32− present          (1⁄2 mk)

2.  
   1.  
      

      Observation	Inference
      Burns with yellow   sooty flame (1mk)	-C C- or =C=C= present 1mk  Observe rule on carbon bonds @1mk for   any one functional group. If one is     wrong, penalize fully.

   2.  
      

      Observation	Inference
      Purple acidified potassium manganate (VII)     decolourised /purple of acidified potassium   manganate (VII) colour changes to colourless   ( ½ mk) - Reject turns in place of changes - Reject purple colour decolourised on its     own/purple colour changes to colourless	= C=C= or -C C- or R-OH present Observe rule on carbon bonds   (1mk)

   3.  
      

      Observation	Inference
      Orange colour of acidified potassium   dichromate (VI) persists/ Orange colour of   acidified potassium dichromate (VI) remains   orange ( ½ mk)	R – OH absent    ½ mk Penalize fully for any other functional group

   4.  
      

      Observation	Inference
      Yellow bromine water   persists ½ mk	= C=C= or -C C- absent  (1mk)

   5.  
      

      Observation	Inference
      Effervescence occurs     ( ½ mk)    Bubbles    Fizzing    Reject   - Fizzling   - hissing   - sizzling	R-COOH present   (accept –COOH or H+) for ½ mk    Reject: COOH

   6.  
      

      Observation	Inference
      pH = 2      (1⁄2 mk)	Strongly acidic           (1⁄2 mk)

   7.  
      

      Observation	Inference
      Pleasant smell    ( ½ mk)  Accept: Fruity smell  Reject: Sweet smell	R-COOH present    ( ½ mk)