CHEMISTRY PAPER 3 - KCSE 2019 ALLIANCE MOCK EXAMINATION

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QUESTION 1

  • You are provided with solution K and L
  • Solution K is 1M H2SO4
  • Solution L contains 8.7g of the hydroxide of metal M {with formulae MOH] in 600cm3 of the solution
  • You are required to carry out the experiment to determine;
  • Concentration of solution L
  • R.A.M of metal M

Procedure

  1. Measure 75cm3 of solution K and put into a clean 250cm3 volumetric flask and add distilled water up to the mark label this solution W
  2. Fill a clean burette with solution W
  3. Pipette 25cm3 of solution L into a clean conical flask and add 2 drops of phenolphthalein indicator
  4. Titrate the solution W in the burette against solution L in the conical flask and record the results in the table below
  5. Repeat {3} and {4} above as you fill the table below.

TABLE 1

 

I

II

III

Final burette reading {cm3}

     

Initial burette reading {cm3}

     

Volume of solution W used {cm3}

     
  1. Calculate the;
    1. Average volume of solution W used                                                                          [1mk]
    2. Concentration of solution W                                                                                         [1mk]
    3. Number of moles of solution W that reacted with each 25cm3 portion of solution L {2mks]
  2. Calculate the;
    1. Number of moles of the metal hydroxide {MOH} in solution L that reacted with each portion of solution W [2mks]
    2. Concentration of solution L                                                                                         [1mk]
    3. Number of moles of the metal hydroxide [MOH]in 600cm3 of solution L               [2mks]
    4. R.A.M of metal M                                                                                                     [2mks]
      [0=16, H=1]

QUESTION 2

You are provided with solution N and P

  • Solution N is 2M HCl
  • Solution P is 0.16M sodium thiosulphate
  • You are required to carry out the experiment below to determine how concentration affects the rate of reaction between HCl and sodium thiosulphate solutions

PROCEDURE

  1. Fill a clean burette with solution P. Measure 25cm3 of the solution P from the burette into a clean 100cm3 glass beaker and place on a white piece of paper with a cross[x] marked on it
  1. Add 10cm3 of solution N into it and immediately start a stop watch and note the time taken for the cross beneath the mixture to become invisible
  2. Clean the 100cm3 beaker and measure into it 20cm3 of solution P form the burette, and add 5cm3 of distilled water into the solution solution
  3. Repeat step [2] above and note the time taken for the cross to become invisible
  4. Repeat the experiment using volumes indicated on the table below and as you record the results

TABLE 2

Expt

1

2

3

4

5

Volume of solution p(cm3)

25

20

15

10

5

Volume of water added to solution p{cm3}

0

5

10

15

20

Volume of solution   N

10

10

10

10

10

Time taken for the cross to become invisible [in seconds]

         

1/t S-1

 

 

 

 

 

(4mks)

  1. plot a graph of  against volume of solution P on the grid provided                                 [3mk]
  2. From the graph
    1. Determine the time taken for the cross to become invisible when 12.5cm3 of solution P is used        [2mks]
    2. Explain the effect of concentration on the rate of reaction between HCl and sodium thiosulphate solution     [2mks]

QUESTION 3

  • You are provided with solids Q and R
  • You are required to carry out the tests below as you record your observations and inferences

    SOLID Q
  • Add about 5cm3 of distilled water to solid Q, shake the mixture thoroughly for a while and then filter it
    NOTE: Retain both the filtrate and the residue for the tests below

 

TEST

OBSERVATIONS

INFERENCES

(a){i}

Divide the filtrate into 4 portion

-To the first portion, add 4 drops of NaOH

    

 

    

 

{ii}

Scoop the 2nd portion on a metallic spatula

and ignite on a non-luminous flame

    

 

    

 

{iii}

To the 3rd portion, add 2 drops of Pb{NO3}[aq]

    

 

    

 

{iv}

To the 4th portion ,add acidified KmnO4

    

 

    

 

b{i}

Put the residue in a test tube and add about 2cm3 of HNO3

    

 

    

 

{ii}

To the mixture in b{i} above, add 2 drops of KI solution

    

 

    

 

SOLID R

 

TEST

OBSERVATIONS

INFERENCES

(a)

Scoop a portion of solid R on a

Metallic spatula and burn on a

Non-luminous flame

    

 

    

 

(b){i]

Put the remaining portion of solid R into a clean test tube and add about 3cm3of distilled water, shake and divide into 2 portions

    

 

    

 

{ii}

To the 1st portion, add 2 drops of acidified KMnO4 and warm

    

 

    

 

{iii}

To the 2nd portion add NaCO3

    

 

    

 



MARKING SCHEME 

QUESTION 1
TABLE 1

  • complete table CT  1 mk
  • decimal point D 1 mk
  • accuracy A (tied to school value)1 mk
  • principal of averaging 1 mk
    1.  
      1. Average volume / final accuracy 1(tied to school value)
        NB theoretically expected value = 15.0 cm3
      2.  
        chem3riode

QUESTION 2
TABLE 2

  • complete table CT1mk
  • decimal point D 1mk
  • trend (increasing time )1mk
  • 1/t row completed 1mk
    1. Graph
      1. Plotting 1mk
      2. Scale 1mk
        Straight line touching origin (0, 0) 1mk
    2. Correctly read value from the graph  1mk
    3. Correct reciprocal of value read from the graph  1mk
    4. Rate at reaction increase with increase in concentration of the sodium thiosulphate because increase in concentration increases number of successfulcollisions

      Question 3
  1. Solid Q
     

    Observation

    inferences

    i)                     

    No white ppt formed ½ mk

    Ca 2+ Mg2+, Pb2+, Al3+ Zn2+ Absent 1mk

    ii)                   

    Burns with a golden yellow flame ½ mk

    Na+ confirmed 1mk

    iii)                 

    White ppt formed ½ mk

    Cl-, SO42-, SO32-,CO32-1mk

    iv)                 

    KMNO4 decolorized½ mk

    SO32-, Confirmed1mk

    B(i)

    Effervescence occurs ½ mk

    CO32-, SO32-1mk

    ii)

    Yellow ppt formed½ mk

    Pb2+ confirmed1mk

  2. Solid R
     

    Observation

    inferences

    a

    Burns with a yellow sooty flame½ mk

    =C = C = ,  = C = C =@1/2 mks

    B(i)

    Dissolves½ mk forming a colorless solution½ mk

    Polar substance½ mk

    ii)

    KMNO4 decolorized½ mk

    ROH,  =C = C =,   = C = C =1mk

    ii)

    Effervescence½ mk

    H+ or RCOOH1mk

     
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