Chemistry Paper 3 Questions and Answers - Sukellemo Joint Mock Examinations July 2020

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INSTRUCTIONS TO THE CANDIDATES:

  • Write your name and index number in the spaces provided
  • Sign and write the date of examination in the spaces provided
  • Answer all the questions in the spaces provided. 
  • Mathematical tables and electronic calculators may be used.
  • All working MUST be clearly shown where necessary. 
  • Use the first 15minutes of the 24 hours to ascertain you have all the chemicals and apparatus that you may need.

For Examiners use Only

QUESTION  MAXIMUM SCORE  CANDIDATES SCORE 
 1  14  
 2  08  
 3  18  
 TOTAL  40  


QUESTIONS

QUESTION 1 .

  • You are provided with solution K and solution M 
  • Solution K is 1.25M hydrochloric acid
  • Solution M is 0.16M hydroxide of metal M with formulae M(OH)x where x is a whole number
  • You are required to carry out the experiment to determine the value of x

PROCEDURE

  1. Using a measuring cylinder, measure 50cm3 of solution K into a clean 250cm3 volumetric flask and make up to the mark with distilled water and label this solution W 
  2. Fill a clean burette with solution W 
  3. Pipette 25cm3 of solution M into a clean conical flask and add 2 drops of phenolphthalein indicator 
  4. Titrate solution M in the conical flask against solution K from the burette and record the results in the table below
  5. Repeat [3) and (4) above as you record the results in the table below
  II  III 
FINAL BURETTE READING [cm3)       
INITIAL BURETTE READING[cm3]      
VOLUME OF SOLUTION W USED      
  1. Calculate the; [4mks]
    1. Average volume of solution W (1mk)
    2. Concentration of solution W [2mks)
    3. Number of moles of hydrochloric acid [in solution W] that reacted with each 25cm3 portion of the solution of the metal hydroxide (solution M] [12mks]
    4. Number of moles of the metal hydroxide solution M] that reacted with each portion of hydrochloric acid (solution W]
      [2mks)
  2. Determine the value of X [2mks)

QUESTION 2
You are provided with:

  1. 0.21M glucose solution V. 
  2. 0.02M potassium Manganese (VII) solution W.
  3. 1.0M aqueous sulphuric (VI) acid.

You are required to determine the rate of reaction between solution W and V at different temperature.
Procedure:

  • Place 2cm3 of solution W into a 250ml beakers using 100ml measuring cylinder add 50cm3 of 1.ON sulphuric (VI) acid to the beaker containing solution W.
  • Warm the mixture to about 65°C. Stop warming and allow the mixture to cool.
  • When the temperature is exactly 60°C add 15cm of solution V and start the stopwatch immediatel
  • Stir the mixture and measure the time taken for the color of the mixture to change from purple to colorless.
  • Record the time in the table below also record the temperature at which the mixture becomes colorless. Clean the beaker and repeat the procedure at temperature 55°C, 50°C and 45°C instead o 60°C.
    1. Calculate I/t and complete the table below. (2 marks)
      Temp. before mixing (°C)         
      Temp. when solution becomes colorless (°C)        
      Time in (seconds)        
      I/t(S-1)        
      1. Plot a graph of I/t(S-1) (y-axis) against temperature at the point when the Solution becomes colorless. (3mks)
        q7 ujgjsd
      2. From your graph:
        1. Determine the time that the reaction would take if the temperature at which the solution becomes colorless is 42.5°C. (2 marks)
        2. Describe the slope of your graphs. (1 mark)

2. You are provided with substance P. You are required to write the procedure and the expecte results and then carry out the tests, write your observation and inferences in the space provided.
SOLID PIS SUSPECTED TO BE SODIUM SULPHATE
REAGENTS;

  • FLAME AND GLASS ROD
  • BARIUM NITRATE
  • DILUTE NITRIC V ACID
  • DISTILLED WATER
  • SODIUM HYDROXIDE SOLUTION
  1. Write the procedures for the tests to be carried out to confirm the identity of solid P using the reagents given above and give the expected observations in each case.
    TEST 1
    EXPECTED ................................................ (1 mark)
    OBSERVATION................................................(1 mark)
    TEST 2
    EXPECTED ................................................ (1 mark)
    OBSERVATION ................................................(1 mark)
    TEST 3 
    EXPECTED ................................................(1/2 mark)
    OBSERVATION................................................(1/2 mark)
    TEST 4
    EXPECTED ................................................(1 mark)
    OBSERVATION................................................(1 mark)
  2. Carry out the tests written in A above and in each case give the observations and inference
    TEST 1.
    Observation................................................ (1 mark)
    Inference................................................(1 mark)
    TEST 2
    Observation................................................ (1 mark)
    Inference................................................(1 mark)
    TEST 3.
    Observation................................................ (1/2 mark)
    Inference................................................(1/2 mark)
    TEST 4.
    Observation................................................ (1 mark)
    Inference................................................(1 mark)

2. You are provided with solid F. carry out the following tests and record the observations and
inferences in the spaces provided. 

  1. Place about one-third of solid F on clean metallic spatula and burn it in a Bunsen burner flame
    Observation................................................ (1/2 mark)
    Inference................................................(1/2 mark)
  2. Place the remaining amount of solid F in a boiling tube. Add about 10cm3 of distilled water and shake. Use the mixture for the tests (i) and (iii) below. Observation................................................ (1/2 mark)
    Inference................................................(1/2 mark)
  3. To about 2cm3 of the mixture in the test tube, add two or three drops of acidified potassium manganate (VII)Observation................................................ (1 mark)
    Inference................................................(1 mark)


MARKING SCHEME

QUESTION 1
Table

  II  III 
FINAL BURETTE READING [cm3)       
INITIAL BURETTE READING[cm3]      
VOLUME OF SOLUTION W USED 15.9  16.0 16.1
  1. Calculate the
    1. Average volume of solution W
      Average = 16.0cm3
    2. Concentration of solution W
      M1V1 =  M2V2
      12.5 x 50 =  M2 x 250
      M2 = 1.25 x 50 = 0.25m
                   250
    3. Number of moles of hydrochloric acid (in solution W) that reacted with each 25vm3 portion of the solution of the metal hydroxide (solution M)
      1000cm3 = 0.25moles
      Ans in (a) (i) 16.0cm3 = 16.0 x 0.25 = 0.004 moles
                                              1000 
    4. Number of moles of the metal hydroxide (solution M) that reacted with each portion of hydrochloric acid (solution W)
      1000cm3 =  0.16moles
      25cm3 =?
      = 25 x 0.16 = 0.004 moles
           1000
      b) Determine value of x
      Mole ratio: 0.004: 0.004
                            1 : 1
      HCl(aq) + M(OH) → MCL(aq) + H2O(l)

QUESTION 2
A. Write the procedures for the tests to be carried out to confirm identify of solid P using the reagents given above and give the expected observations in each case

Test 1  Expected Observation 
To a little of solid P in a  boiling tube, add 10ml of  distilled water and shake. divide the mixture into 3 equal portions  Solid dissolves to form colourless solution
Test 2 Expected Observation
the 1st portion add sodium hydroxide dropwise until in excess No white precipitate is formed
Test 3 Expected Observation
the second portion dip a ass and burn in a non luminous flame Yellow flame
Test 4 Expected Observation
To the 3rd portion add 3 drops of Ba(NO3) followed by equal amount of ΗNO3 White precipitate which is insoluble in the acid

B. Carry out tests written in A above and in cach case give the observations and inferences

TEST 1   
Observation Inference 
Solid dissolves to form colourless solution Soluble salt Cu2+, Fe3+, Fe2+ absent
TEST 3  
Observation Inference
No white precipitate Na+, K+, NH4+ present
2 ions = 1/2mk 3
ions = 1 mk
1 ion= 0mk
TEST 4  
Observation Inference
Yellow flame Na+ confirmed
TEST 5  
Observation Inference
white precipitate soluble when acid is added SO32+ , CO32+ present

2. You are provided with solid F, carry out following tests

  1. Place about one-third of solid F on a clean metallic spatula and burn it in a Bunsen burner flame
    Observation Inference
    Melts and burns with a yellow soot flame q2 vutgsuyhdf
     Place the remaining amount of solid F in a boiling tube. Add about 10cm of distilled water and shake. Use the
  2. mixture for the tests (i) and (iii) below
     
    Observation  Inference
    Solid dissolves in water to  form a uniform colourless solution F is polar compound
  3. To about 2cm3 of the mixture in the test tube, add two or three drops of acidified potassium manganite (VII)
     
    Observation  Inference
    Acidified purple potassium manganite (VII) is decolourised. Accept present (change to colourless (original & final colour) ans kjaghd

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