Chemistry Paper 3 Questions and Answers with Confidentials - Form 4 Opener Term 1 Exams 2022

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CHEMISTRY
PAPER 3

Instructions

  • Attempt all the questions in the spaces provided.


Questions

Question One

You have been provided with:

  • 0.5g Divalent MCO3 labeled P
  • 0.5M hydrochloric acid labeled A
  • 1.0M Sodium hydroxide labeled B
  • Phenolphthalein indicator

PROCEDURE:

  • Weigh exactly 0.5g of a divalent metal carbonate, MCO3
  • Put the weighed carbonate in a conical flask
  • Add to it 30.0cm3 of 0.5M hydrochloric acid solution A
  • Add 2 – 3 drops of phenolphthalein indicator in the resulting solution.
  • Titrate the solution against a 1.0M Sodium hydroxide solution until the colour of the solution just turns pink permanently.
  • Record your results in the table below.
  • Repeat the experiment three times to complete the table. (4 mks)
    Titration 1 2 3
    Final burette reading (cm3)      
    Initial burette reading (cm3)      
    Volume of the base used (cm3)      

    1. Calculate the average volume of base used to neutralize the excess acid. (1 mk)
    2. Determine:
      1. The number of moles of base used. (2 mks)
      2.        
        1. The volume of the acid that was neutralized by the base. (2 mks)
        2. The number of moles of acid that reacted with the carbonate. (2 mks)
    3.        
      1. Write the equation for the reaction between the acid and carbonate. (1 mk)
      2. Determine the number of moles of the carbonate in the sample. (2 mks)
      3. Determine the relative formula mass of the carbonate. (2 mks)
      4. Determine the relative atomic mass of M. (3 mks)

Question Two
You are provided with solid P. Carry out the tests below and record your observations and inferences.

  • Put all solid P in a boiling tube and add about 5cm3 of distilled water. Shake until all solid dissolves.
    1. Place about 2cm3 portion of the solution in a test tube and add aqueous ammonia drop wise until in excess. 
      Observation Inferences
                                                                                                                 
    2. Dip a clean end of a glass rod into the remaining solution and then place it in the Bunsen burner flame. Note the colour of the flame above the glass rod.
      Observation Inferences
                                                                                                                 
    3. Place about 2cm portion of the solution in a test tube of barium nitrate solution. Retain this content for the test in (d) below.
      Observation Inferences
                                                                                                                 
    4. To the content in (c) above add 4 drops of 2m HNO3 following by 2 drops of acidified potassium manganet (vii).
      Observation Inferences
                                                                                                                 

Question Three
You are provided with solid K. carry out the tests below and record your observation and inferences in the spaces provided

  1. scoop a half portion of the solid using a clean metallic spatula and introduce it to a non-luminous flame of Bunsen burner to burn.
    Observation Inferences
                                                                                                               
  2.        
    1. Put the remaining portion of solid K. in a boiling tube and add about 10cm3 of distilled water. shake and divide the solution into three portion.
      Observation Inferences
                                                                                                                 
    2. To the 1st portion, add about 4 drops of acidified potassium manganite (Vii) solution.
      Observation Inferences
                                                                                                                 
    3. To the 2nd portion, add 3 drops of acidified potassium dichromate (vi) solution.
      Observation Inferences
                                                                                                                 
    4. To the 3rd portion, determine the pH using universal indicator paper.
      Observation Inferences
                                                                                                                 


Confidential

  1.      
    • 0.5G DIVALENT METAL CARBONATE. MCO3
    • 0.50M hydrochloric acid.
    • Phenolphthalein indicator
    • 1.0M sodium hydroxide
  2.      
    • 2m NH3 SUPPLIED WITH A DROPPER
    • 0.5 Ba(No3)2 supplied with a dropper.
    • 2M HNO3 supplied with a dropper
    • KMnO4/ H+ supplied with a dropper
    • K2Cr2O7 supplied with a dropper
    • 10 ml measuring cylinder.
    • Each candidate to have: - solid P NaSO3
    • Solid K maleic acid
    • Universal indicator.


Marking Scheme

Question One

  1. Calculate the average volume of base used to neutralize the excess acid. (1 mk)
    • ( 5.1 + 5.0 + 5.0) = 5.0cm2
             3
  2. Determine:
    1. The number of moles of base used. (2 mks)
      1000cm3 → 0.1m 
      5cm3→ x 
      (1.0 x5cm³) = 0.005 mole
      (1000cm3)
    2.          
      1. The volume of the acid that was neutralized by the base. (2 mks)
        • 0.50M → 1000cm3           HCL+NaOH
          NaCl + H₂O
                   2
          0.005 → x
        • (0.005 x1000cm³) = 10.0cm3
                   0.50

      2. The number of moles of acid that reacted with the carbonate. (2 mks)
        • (30cm3 – 10cm3) = 20cm3
          0.50Mole x 20cm3   =0.1 mole
                1000 cm
  3.                 
    1. Write the equation for the reaction between the acid and carbonate. (1 mk)
      • MCO3(S) + 2 HCl m → MCl2 + CO2 + H2O

    2. Determine the number of moles of the carbonate in the sample. (2 mks)
      • mole ratio 1:2
        MCO3: 2HCl 
        (0.10mole) = 0.005 mole
               2

    3. Determine the relative formula mass of the carbonate. (2 mks)
      • mass of 0.005 mole = 0.50g
        mass of 1.0 mole =      (0.50g)      =100g
                                       (0.005 mole)

    4. Determine the relative atomic mass of M. (3 mks)
      • R.F.M (MCO3) = 100g
        m+12+48 =100g
        R.A.M of M = (100-60)g = 40g)

Question Two
You are provided with solid P. Carry out the tests below and record your observations and inferences.

  • Put all solid P in a boiling tube and add about 5cm3 of distilled water. Shake until all solid dissolves.
    1. Place about 2cm3 portion of the solution in a test tube and add aqueous ammonia drop wise until in excess. 
      Observation Inferences
            No white precipitate                                                          K+ Na+ suspected                                            
    2. Dip a clean end of a glass rod into the remaining solution and then place it in the Bunsen burner flame. Note the colour of the flame above the glass rod.
      Observation Inferences
             It burns with a yellow flame                                                            Na+ Present                                       
    3. Place about 2cm portion of the solution in a test tube of barium nitrate solution. Retain this content for the test in (d) below.
      Observation Inferences
        White precipitate is formed                                                   SO42-, CO32-, SO32-                                 
    4. To the content in (c) above add 4 drops of 2M HNO3 following by 2 drops of acidified potassium manganate (vii).
      Observation Inferences
             White ppt dissolves and purple solution is decolorized                                                     SO32- confirmed                                               

Question Three
You are provided with solid K. carry out the tests below and record your observation and inferences in the spaces provided.

  1. Scoop a half portion of the solid using a clean metallic spatula and introduce it to a non- luminous flame of Bunsen burner to burn.
    Observation Inferences
         It burns with yellow sooty smocky flame                     C= C -c=c- suspected or R-OH, R-C –OH high            
  2.            
    1. Put the remaining portion of solid K. in a boiling tube and add about 10cm3 of distilled water. Shake and divide the solution into three portions.
      Observation Inferences
                Dissolve forming colourless solution                    Polar compound             
    2. To the 1St portion, add about 4 drops of acidified potassium manganite (Vii) solution.
      Observation Inferences
        The solution changes from purple to colourless       C=C, -C= C- R-OH suspected lCOOH        
    3. To the 2nd portion, add 3 drops of acidified potassium dichromate (vi) solution.
      Observation Inferences
             The solution changes from orange to green                      R – OH Confirm  
    4. To the 3rd portion, determine the PH using universal indicator paper.
      Observation Inferences
              PH 4-6            Weak acid or weakly acidic    

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