Chemistry Paper 3 Questions And Answers - Form 4 Term 2 Opener 2021

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INSTRUCTIONS TO CANDIDATES

  • Answer all the questions.
  • You are not allowed to start working with the apparatus for the first 15 minutes of the 2 ¼ 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 you need.
  • All working must be clearly shown where necessary.
  • Mathematical tables and electronic calculators may be used.

Question 1 (20marks)

You are provided with;

  • Solid A in a boiling tube
  • Solution B, sodium hydroxide
  • 0.125M.monobasic acid, solution C

You are required to;

  1. Determine molarity of solution B
  2. Determine solubility of solid A

Procedure I

  1. Using a measuring cylinder ,place 50cm3 of solution B into an empty 250ml beaker. Add 100cm3 of distilled water to the solution. Labe this solution as solution D.
  2. Fill the burette with solution C
  3. Using pipette filler, place 25cm3 of solution d into a 250ml conical flask. Add two drops of phenolphathatlein indicator.
  4. Titrate solution D with solution C
  5. Record your results in table 1 . repeat the titration two more times and complete table 1.
       I   II   III 
     Final burette reading (cm3      
     Initial burette reading (cm3      
     Volume of solution C used (cm3)      
    (4mks)
    1. Calculate average volume of solution C used. (1mk)
    2. Calculate moles of solution C used in the experiment. (1mk)
    3. Calculate moles of solution D used. (1mk)
    4. Calculate molarity of solution D (1mk)
    5. Calculate molarity of solution B. (2mks)

Procedure II

  1. Using measuring cylinder add 20cm3 of distilled water to solid A in the boiling tube. Using a glass rod, stir the mixture thoroughly for about three minutes.
  2. Filter the mixture obtained into a dry 250ml volumetric flask. Label the filtrate solution A.
  3. Clean the burette and fill it with solution A.
  4. Using a pipette and pipette filler, place 25cm3 of solution D into a 250ml conical flask . Add two drops of phenolphthalein indicator.
  5. Titrate solution D with solution A. record your results in table 2
  6. Repeat the titration two more times and complete table 2.

    Table 2
       I   II   III 
     Final burette reading (cm3      
     Initial burette reading (cm3      
     Volume of solution C used (cm3)      
    (4mks)
    Calculate;
    1. Average volume of solution A used (1mk)
    2. Moles of solution D used (1mk)
    3. Moles of solution A used given that 2 moles of solution A requires 1 mole o f solution D for complete neutralization (1mk)
    4. Solubility o solid A given that density of the solution formed is 1g/cm3 and RFM of A = 126. (2mks)

Question 2

You are provided with solid D. perform the following test and write the observations and inferences.

  1. Place solid D into a boiling tube and add 10cm3 of distilled water. Shake the boiling tube and filter. Keep the residue for test.Divide the filtrate into four portions.
      Observation  Inferences  
              (1mk)          (1mk)
    1. To the first portion, add sodium hydroxide dropwise until in excess.
        Observation  Inferences  
                (1mk)          (1mk)
    2. To the second portion, add ammonioa solution dropwise until in excess.
        Observation  Inferences  
                (1mk)          (1mk)
    3. To the third portion, add a few drops of Lead(II) nitrate solution
        Observation  Inferences  
                (½mk)          (½mk)
    4. To the fourth portion, add a few drops of barium nitration solution followed by dilute nitric (v) acid.
        Observation  Inferences  
                (1mk)          (1mk)
  2. Place the residue into attest tube and add 10cm3of dilute nitric (v) acid and shake until the solid dissolves.
      Observation  Inferences  
              (½mk)          (½mk)

    1. To the first portion, add sodium hydroxide dropwise until in excess.
        Observation  Inferences  
                (1mk)          (1mk)
    2. To the second portion, add ammonia solution dropwise until in excess.
        Observation  Inferences  
                (1mk)          (1mk)
    3. To the third portion, add a few drops of sodium sulphate solution.
        Observation  Inferences  
                (½mk)          (½mk)

Question 3

You are provided with solid L . Carry out the tests below and record your observation and inferences in the space provided.

  1. Heat half spatula of solid L in a non-luminous flame of aBunsen burner.
      Observation  Inferences  
              (1mk)          (1mk)


  2. Add 5cm3 of distilled to the remaining solid L and shale well. Divide the solution into two portion.
    1. To the first portion, add a few drops of acidified potassium manganate (VII) and warm.
        Observation  Inferences  
                (1mk)          (1mk)
    2. To the second portion, add a quarter spatula and fill of sodium hydrogen carbonate.
        Observation  Inferences  
                (1mk)          (1mk)

MARKING SCHEME

QUESTION 1
PROCEDURE 1
TABLE 1

   I   II   III 
 Final burette reading (cm3  20.0   20.0   20.0 
 Initial burette reading (cm3  0.0  0.0  0.0
 Volume of solution C used (cm3)  20.0  20.0  20.0

CT-1
AP-1
AC-1
AV-1
FA-1
5

  1.  
    1. Average volume = 20.0 + 20.0 +20.0 = 20.0cm3
                                             3
    2. Moles of solution C = 0.125 X litre √½ = Ans √½
                                         1000
    3. Moles of solution D = 1 X ans a(ii) = Ans √½
    4. Molarity of solution D = Ans a(iii) X 1000 √½ = Ans√½
                                                  25
    5. Molarity of solution B
      Mconc. x Vconc. = Mdi X Mdi√½
      Molarity = Ans a(iv) x 150√1 = Ans√½
                                 50

      TABLE 2

         I   II   III 
       Final burette reading (cm3  15.8   15.8   15.8 
       Initial burette reading (cm3  0.0  0.0  0.0
       Volume of solution C used (cm3)  15.8  15.8  15.8

      C.T -1
      A.P -1
      AC-1
      AV-1
      F.A-1
      5
  2.  
    1. Average volume of sol A = 15.8 + 15.8 + 15.8 = 15.8(cm3)
                                                             3
    2. Moles of solution D used = Ans a(iv) x 25 √½ = Ans (cm3) √½
                                                     1000
    3. Moles of sol A = Ans b(ii) √½ = Ans√½
                                   2
    4. Solubility of solid A
      Titre volume = Ans b (iii)
      100cm3 = 100 x Ans b (iii) = moles√½
                               Titre
      Solubility = 100 x Ans b (iii) √1 x 126
                               Titre
      = Ans√½

QUESTION 2

 No.   Observation   Inference 
 (a) Colour less filtrate√½  
white residue√½   
 Cu2+, Fe2+ , Fe3+ , √½
 absent in both filtrate and residue √½
 (i)  White ppt√½ soluble in excess√½  Zn2+ ,Pb2+ , Al3+ ,√1
 (ii)  White ppt√½ soluble in excess √½  Zn2+√1
 (iii)  White ppt√½  SO32- √½ CO32− Cl
 (b) Effervescence / bubbles of colours less ordour less gas √½  CO32-√½
 (i)  White ppti)√½ soluble in excess√½  Pb2+ , Zn2+ , Al3+ √1
 (ii)  White ppt√½ insoluble in excess√½  Pb2+ , Al3+ √1
 (iii)  White ppt formed  Pb2+√½

QUESTION 3

 No.   Observation   Inference 
 (a)  Solid melts and burns with yellow sooty flame √1   F4 Chem PP3 ans 3a opener 2021
 (b) (i)   Purple potassium manganate
Solution turns colourles √1
 F4 Chem PP3 ans 3b opener 2021
 (ii)  Effervescence / bubble of colourles gas √1  F4 Chem PP3 ans 3c opener 2021

 


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