CHEMISTRY PAPER 3 - KCSE 2019 ALLIANCE GIRLS MOCK EXAMINATION (WITH MARKING SCHEME)

QUESTION 1
You are provided with:

• Solid A 5.0g (COOH)_2· H₂O
• Solution B 0.13M KMnO₄

Task

1. You are supposed to determine the solubility of A at different temperatures.
2. Determine the number of moles of water of crystallization in solid A.

PROCEDURE 1

1. Using a burette, add 4cm3 of distilled water to solid A in a boiling tube.
   1. Head the mixture while stirring with the thermometer to about 80⁰
   2. When the whole solid dissolves, allow the solution to cool while stirring with the thermometer
   3. Note the temperature at which crystals first appear and record this temperature in the table 1 below.
2. Using a burrete add 2cm³ more into the content of the boiling tube and warm until the solid dissolve.
   1. Remove from the flame and allow the solution to cool in air while stirring.
   2. Record the temperature at which crystal first appear in table 1.
   3. Repeat procedure (b) 3 more times and complete table 1 below.
   4. Retain the content of the boiling tube for procedure II

Table 1

1. Draw a graph of solubility of solid A (vertical axis) against temperature (3mks)
2. From your graph determine the solubility of solid A at 60⁰C (1mk)

PROCEDURE II

1. Transfer the contents of the boiling tube into a 250ml volumetric flask.
   1. Add distilled water up to the mark
   2. Label this solution A
2. Using a clean pipette and a pipette filler, transfer 25ml of solution A into a conical flask.
   1. Warm the mixture up to 60⁰C
   2. Fill a burette with solution B
   3. Titrate B against the hot solution A until a permanent pink colour persist
   4. Read your results in Table 2 below
3. Repeat (b) 2 more times are record your results in the table 2 below.

TABLE 2

1. Calculate the average volume of solution B used (1mk)
2. Calculate the number of moles of B used (1mk)
3. Given 2 moles of KMnO₄ react with 5 moles of A, calculate the number of moles of A in 25cm³ (1mk)
4. Calculate the molarity of A (1mk)
5. Determine the molar mass of A (1mk)
6. Determine the value of X (1mk)
   (C=12, O=16 H=1)

QUESTION 2

You are provided with solid C. Use it to carry the test below. Dissolve the whole of C into 10cm3 of water and divide it into five portions.

1. To the 1^st portion add sodium sulphate solution.
   

   Observations	Inferences
   (1mk)	(1½mks)

2. To the 2^nd portion add Ammonia solution dropwise until in Excess.
   

   Observations	Inferences
   (1mk)	(1½mks)

3. To the 3^rd portion add sodium Hydroxide dropwise until in Excess.
   

   Observations	Inferences
   (1mk)	(1½mks)

4. To the forth portion add Lead (II) Nitrate solution
   

   Observations	Inferences
   (1mk)	(1½mks)

5. To the last portion add Barium Nitrate solution
   

   Observations	Inferences
   (1mk)	(1½mks)

QUESTION 3

You are provided with liquid D use it to carry the test below. Divide liquid D into four equal portions

1. To the 1^st portion add sodium hydrogen carbonate
   

   Observations	Inferences
   (1mk)	(1½mks)

2. To the 2^nd portion add acidified potassium manganite (VII) (KmnO₄)
   

   Observations	Inferences
   (1mk)	(1½mks)

3. To the 3^rd portion add Bromine water
   

   Observations	Inferences
   (1mk)	(1½mks)

4. To the last portion add potassium dichromate(VI0) and wrm.
   

   Observations	Inferences
   (1mk)	(1½mks)

MARKING SCHEME

QUESTION1
TABLE 1

AWARD a total of 7 MKS Distributed as follows.

1. Complete table – 4mks
   Condition and penalties
   • A table with 8-10 values                    award 4
   • A table with 6-7 values                      a ward 3
   • A table with 4- 5 values                     award 2
   • A table with 2-3 values                      award 1
   • A table with 1 value                           award ½
   • A table with no value                                    
     award 0
     
     Penalties
   • Penalize ½ mk for each wrong value of solubility
   • Penalize ½ one for unrealistic temperature readings ½ above 90⁰C and below 10⁰C

2. DECIMALS TIED TO TEMPARATURE -1Mk
   Accept;
   1. Whole numbers
   2. Idecimal place where the decimal should be 0 or 5 i.e 70.0 or 70.5
   3. Accept 2 decimal places where it should be .00, .25,.50 or .75
      NB: If no consistence penalize fully.

3. TREND – Tied to temperature i.e it should be decreasing (1mk)
4. Accuracy – tied to temperature when 4cm³ of water was added 
   Accept 2⁰C of the school value.
5. GRAPH – award a total of 3mks distributed as follows.
   1. Labling (½mks)
      Both axis should be labeled if one is not or wronglylabeled award O
      Ignore units but if indicated they should be right otherwise penalize fully
   2. Scale – (½mks)
      The actual plotting should be halfof the page
      Peralize fully if scale changes on the way both axis must be correct.
      Plots (1mk)
      
      4-5 correct plots award (1mk)
      3 correct plots award (½mks)
      Less than 3 correct plots award 0
   3. Line – a smooth curve passing through 3 or more correct plots award 1mk
      Otherwise award 0
   4. award ½ mk for sloping or the graph
      award ½ mk for calculating
      
      NB:
   5. Award fully for calculation from correct graph even if not shown on the graph
   6. Reject any value from a wrong graph.

TABLE 2

Award a total of 5mks distributed as follows

1. Complete table (1mk)
   • Complete table with 3 titration 1mk
   • Incomplete table with 2 titrations ½ mk
   • Incomplete table with 1 titration 0 mks
     
     Penalties
   • Wrong arithmetic
   • Invented table
   • Unrealistic values i.e burette reading with more than 50cm³ and less than 1cm³
   • Unrealistic titre values
     NB: PENETICE ½ once
2. Use of decimals (1mk) (Tied to the 1^st and 2^nd row only)
   Accept 1 or 2 decimal places used consistently otherwise penalize fully
   If 2 dp are used the 2^nd should be a “O” OR “5” e.g 20.10 or 20.15 otherwise penalize fully
   Accept the use of Zero as the initial burette reading i.e 0,0.0 or 0.0
3. Accuracy (1mk)
   Complete the candidate value with the school value (S.V)
   • If within 1 of the school value award 1mk
   • If within 2 of S.V ward ½mk otherwise award 0
     NB: Tick the candidate value that deserves a credit
4. PRINCIPLE OF AVERAGING   1MK
   Conditions
   • If 3 titration done but only two are consistence and averaged award 1mk
   • If 3 titration are done and consistency and averaged award 1mk
   • If two titration are done and are consistency and averaged award 1mk
   • If three consistency titration one done but 2 are averaged award 0
   • If three 3 titration are done and are inconsistence and are done averaged award zero
   • If two titration are done and are inconsistence and are averaged award 0
     
     PERALTIES
   • Penalize ½ for wrong arithmetic
   • penalize ½mk if no working is shown and answer is correct
   • penalize fully if no working is shown and answer given is wrong
   • Accept rounding off or truncation to the 2^ndp
     e.g 12.666      12.67
     or
     12.66            12.66
     
     NB:
   • The working of average must be marked before the mark for averaging is award in table 2.
   • Accept the average volume if it work out exactly to a whole number.
     FINAL ACCURACY  (1MK)
     Tiled to correct average time.
     Compare the candidate average time to the school value.
   • If within 1 award 1mks
   • If with n 2 award ½ mk
     Otherwise award 0
     
     NB:
   • If there are 2 possible correct average titre, use the one the one close to the school value and award accordingly.
   • If wrong value are averaged, pick the correct values average for the candidate and award accordingly.
   • Record the marks as follows besides the table to the right.
     CT       – 1mk
     D         - 1mk
     A          -1mk
     PA       -1mk
     FA       - 1mk
     Total 05 mks
     1. Calculate the number of moles of B used
        

QUESTION 2

QUESTION 3