Chemistry Paper 3 Questions, Answers and Confidential - Sunrise 2 Evaluation Mock Exams 2022

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Instructions to candidates

  • Sign and write the date of examination in the spaces provided above.
  • Answer all the questions in the spaces provided.
  • You are not allowed to start working with the apparatus for the first 15 minutes of the 2¼ hours allowed for this paper. This time is to enable you to read the question paper and make sure you have all the chemicals and apparatus that you may require.
  • All working MUST be clearly shown where necessary.
  • Mathematical tables and electronic calculators may be used.

For Examiner’s Use Only

Questions

Maximum Score

Candidate’s score

1

22

 

2

10

 

3

08

 

QUESTIONS

  1. You are provided with;
    • 4.0g of solid P. Hydrated dibasic acid H2C2O4.nH2O
    • 0.2M sodium hydroxide Solution X

You are required to determine the;

  1. Solubility of solid P
  2. Value of n in the formula H2C2O4.nH2O

Procedure

  1. Fill the burette with distilled water
  2. Place all solid P in a boiling tube
  3. Transfer 4cm3 of distilled water from the burette into the boiling tube containing solid P
  4. Heat the mixture while stirring with the thermometer to a temperature of about 80ºC.
  5. Allow the mixture to cool while stirring with a thermometer. You may use cold water in a beaker to enhance cooling.
  6. Record the temperature at which the crystals start to form in table 1 below.
  7. Add a further 2cm3 of distilled water from the burette to the mixture in the boiling tube.
  8. Repeat procedure (iv) and (v) above and record the crystallization temperature. Complete the table below by adding the volumes of distilled water as indicated. (Preserve the contents of the boiling tube to be used in procedure II)
  9. Calculate the solubility of solid P in g/100g of water and complete table 1.

Table 1

Volume of  distilled water

Crystallization temperature

Solubility of solid P in g/100g of water

4

   

6

   

8

   

10

   

12

   

(7 marks)

  1. On the grid provided, plot a graph of solubility of solid P(y-axis) against crystallization temperature. (3 marks)

  2. From the graph determine;
    1. The solubility of solid P at 60ºC. (1 mark)
    2. The temperature at which 40g of P dissolves in 50g of water. (1 mark)
    3. The mass of P that crystallizes out when the mixture is cooled from 55ºC to 45ºC. (1 mark)

Procedure II

  1. Transfer all the contents of the boiling tube in procedure 1 to a clean 250ml volumetric flask.
  2. Add distilled water to the mark, shake thoroughly.
  3. Label the resulting solution as Q.
  4. Fill the burette with solution Q.
  5. Pipette 25cm3 of solution X into a clean conical flask. Add three drops of phenolphthalein indicator.
  6. Titrate Q against X to an accurate end point.
  7. Record your results in table II below.

Table II

(4 marks)

Calculate;

  1. Average volume of Q used. (1 mark)
  2.                      
    1. Moles of solution X used. (1 mark)
    2. Moles of solution Q used. (1 mark)
    3. Concentration of solution Q in moles per litre. (1 mark)
  3. Determine the value of n in the formula H2C2O4. nH2O (2 marks)
    (H=1.0, C=12.0, O=16.0)

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

  1. Place about one-third of solid R in dry test-tube. Heat the solid strongly and test any gas with both blue and red litmus papers.

                Observations

    Inferences

     (1½ marks)   (1 mark)
  2. Place the remaining amount of solid R in a boiling tube. Add about 15cm3 of distilled water and shake. Divide the mixture into four test tubes each containing about 2cm3.
    1. To the first portion, add four drops of dilute hydrochloric acid.

                  Observations

      Inferences

       (1 mark)   (2 marks)
    2. To the second portion, add two or three drops of aqueous barium nitrate.

                  Observations

      Inferences

       (½ mark)  (½ mark)
    3. To the third portion, add aqueous sodium hydroxide dropwise until in excess.

                  Observations

      Inferences

       (1 mark)  (1 mark)
    4. To the fourth portion, add aqueous ammonia dropwise until in excess.

                  Observations

      Inferences

       (1 mark)   (½ mark)

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

  1. Place about one-third of solid S on a clean metallic spatula and burn it in a Bunsen burner flame.

                Observations

    Inferences

     (1 mark)  (1 mark)
  2. Place the remaining amount of solid S in a boiling tube. Add about 10cm3 of distilled water and shake. Use the mixture for tests (i) and (iii) below.

                Observations

    Inferences

     (½ mark)   (½ mark)
    1. Using about 2cm3 of the mixture in a test-tube, determine the PH using universal indicator paper and chart.

                  Observations

      Inferences

       (½ mark)   (½ mark)
    2. To about 2cm3 of the mixture in a test-tube, add two or three drops of acidified potassium manganate (VII).

                  Observations

      Inferences

       (1 mark)  (1 mark)
    3. To about 2cm3 of the mixture in a test-tube add two drops of acidified potassium dichromate (VI).

                  Observations

      Inferences

       (1 mark)   (1 mark)

MARKING SCHEME

  1. You are provided with;
    • 4.0g of solid P. Hydrated dibasic acid H2C2O4.nH2O
    • 0.2M sodium hydroxide Solution X

You are required to determine the;

  1. Solubility of solid P
  2. Value of n in the formula H2C2O4.nH2O

Procedure

  1. Fill the burette with distilled water
  2. Place all solid P in a boiling tube
  3. Transfer 4cm3 of distilled water from the burette into the boiling tube containing solid P
  4. Heat the mixture while stirring with the thermometer to a temperature of about 80ºC.
  5. Allow the mixture to cool while stirring with a thermometer. You may use cold water in a beaker to enhance cooling.
  6. Record the temperature at which the crystals start to form in table 1 below.
  7. Add a further 2cm3 of distilled water from the burette to the mixture in the boiling tube.
  8. Repeat procedure (iv) and (v) above and record the crystallization temperature. Complete the table below by adding the volumes of distilled water as indicated. (Preserve the contents of the boiling tube to be used in procedure II)
  9. Calculate the solubility of solid P in g/100g of water and complete table 1.

Table 1

Volume of  distilled water

Crystallization temperature  0C

Solubility of solid P in g/100g of water

4

65

100

6

55

66.7

8

48

50.0

10

43

40

12

38

33.3

(7 marks)

  1. Complete  table ……. 5 marks
  2. award 1/2 mk for each entry of temperature and correct calculation of solubility. Total (5mks)
  3. Decimal….. 1mk
    • Award 1/2 mk for temperature expressed as whole numbers or to 1 decimal place consistently.
    • Award      1/2 mk for solubility expressed to 1dp unless it works out to a whole no. 
  4. Accuracy ….. 1/2mk
    • Compare candidates first temperature reading with that of the teacher. Award ½ mk
      if its within +-2ºC
  5. Trend ……1/2 mk
    • Award ½ mk if temperature readings show gradual decrease 
  1. On the grid provided, plot a graph of solubility of solid P(y-axis) against crystallization temperature. (3 marks)
    fillled graph adada
    • scale – ½ should cover at least half of the no. of squares
    • Labelling ½mk both axes should be correctly labelled
    • Plotting 1mk all points plotted correctly
    • Line 1mk smooth curve
  2. From the graph determine;
    1. The solubility of solid P at 60ºC. (1 mark)

      780g/100g of H2O   1mk
      1mk for correct reading 
      ½ mk for showing   if reading is not correct

    2. The temperature at which 40g of P dissolves in 50g of water. (1 mark)
      (100×40)/50=80g/100g of H2O ½ mk
      = 56ºC ½ mk
      ½ mk for correct reading
    3. The mass of P that crystallizes out when the mixture is cooled from 55ºC to 45ºC. (1 mark)
      65-41 =24g
      ½ mk for reading
      ½ mk correct answer

final burette reading

(4 marks)

NOTE:
Complete table decimal, accuracy and final accuracy are marked as in table 1

Procedure II

  1. Transfer all the contents of the boiling tube in procedure 1 to a clean 250ml volumetric flask.
  2. Add distilled water to the mark, shake thoroughly.
  3. Label the resulting solution as Q.
  4. Fill the burette with solution Q.
  5. Pipette 25cm3 of solution X into a clean conical flask. Add three drops of phenolphthalein indicator.
  6. Titrate Q against X to an accurate end point.
  7. Record your results in table II below.

Table II

(4 marks)

Calculate;

  1. Average volume of Q used. (1 mark)
    (16.8+16.9+17.0)/3= 16.9
    values averaged must be within +-0.2 of each other
  2.                      
    1. Moles of solution X used. (1 mark)
      (25×0.2)/1000 = 0.005
    2. Moles of solution Q used. (1 mark)
      (0.005×1)/2=0.0025
    3. Concentration of solution Q in moles per litre. (1 mark)

       (250×0.0025)/16.9=0.03698

      (1000×0.03698)/250=0.14792  

  3. Determine the value of n in the formula H2C2O4. nH2O (2 marks)
    (H=1.0, C=12.0, O=16.0)
    Concentration in g/l
    (1000×4)/250=16g/l
    Molar mass = (16×1)/0.14792 108.17 (ans in c)/(ans in b (iii))
    H_2 C_2 O_4.nH_2 O
    2×2×12×4×16×18n=108.17
    18n=10^8.17-90
    18n=18.7
    n=1

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

  1. Place about one-third of solid R in dry test-tube. Heat the solid strongly and test any gas with both blue and red litmus papers.

                Observations

    Inferences

     (1½ marks) 

    colourless liquid on the cooler parts of the test tube

    red litmus blue

    blue litmus paper remains blue

     (1 mark)

    it is a hydrated salt/contains water of crystallisation (tied to colourless liquid on cooler parts of the test tube)
    NH4+ present (tied to red litmus turns blue)

  2. Place the remaining amount of solid R in a boiling tube. Add about 15cm3 of distilled water and shake. Divide the mixture into four test tubes each containing about 2cm3.
    1. To the first portion, add four drops of dilute hydrochloric acid.

                  Observations

      Inferences

      No effervescence / no bubbles

      No white PPt

      CO32- ,  SO32- absent

      Pb 2+ Ag+ absent (each ion ½ mk)

    2. To the second portion, add two or three drops of aqueous barium nitrate.

                  Observations

      Inferences

      White PPt

      SO42-   present

    3. To the third portion, add aqueous sodium hydroxide dropwise until in excess.

                  Observations

      Inferences

      White PPt

      Soluble in excess

      Zn2+, Al 3+ present

    4. To the fourth portion, add aqueous ammonia dropwise until in excess.

                  Observations

      Inferences

      White PPt ½ mk

      Insoluble in excess ½ mk

      Al 3+ present

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

  1. Place about one-third of solid S on a clean metallic spatula and burn it in a Bunsen burner flame.

                Observations

    Inferences

     (1 mark)

    It burns with a yellow/sooty/smocky flame 1mk

     (1 mark)

    Present or unsaturated organic compound 1mk

  2. Place the remaining amount of solid S in a boiling tube. Add about 10cm3 of distilled water and shake. Use the mixture for tests (i) and (iii) below.

                Observations

    Inferences

    Dissolves to form a colourless solution ½ mk

    Polar organic compound

    Accept polar compound 1/2 mk

    1. Using about 2cm3 of the mixture in a test-tube, determine the PH using universal indicator paper and chart.

                  Observations

      Inferences

      PH= 1

      Accept PH=2, or 3

      Reject   PH given as a range

      Strongly acid ½ mk

      Ignore acidic  H+/H3O+

      Reject strong acid

    2. To about 2cm3 of the mixture in a test-tube, add two or three drops of acidified potassium manganate (VII).

                  Observations

      Inferences

       (1 mark)

      Acidified potassinon manganate (VII) is decolourized/ turns from purple to colourless

       (1 mark)

      R-OH present

    3. To about 2cm3 of the mixture in a test-tube add two drops of acidified potassium dichromate (VI).

                  Observations

      Inferences

      Acidified potassium dichromate (VI) turns from orange to green 1mk

      R- OH present  1mk


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