Chemistry Paper 3 Questions and Answers - Form 3 End Term 1 Exams 2022

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  • You are provided with each of the following.
    • Sodium hydroxide solution marked R.
    • 0.1 m hydrochloric acid solution marked B.
    • A pipette
    • A burette
    • 2 conical flasks
    • A dropping/ thistle funnel
  • You are required to determine the molarity of sodium hydroxide (NaoH) solution used.
  • N.B. Rinse the burette with the solution to be used in it.

Procedure

  1. Using a pipette, transfer 25 cmof solution R into conical flasks.
  2. Add 2 drops of phenolphthalein indicator.
  3. Fill a clean burette with 0.1M hydrochloric acid labeled B to the mark and read the initial level of the acid accurately.
  4. Run the acid solution B in about 1 cm portions, swirl the liquid in the flasks after each addition of the acid. Add more of the solution B till end point.
  5. Record the final reading of the burette accurately and record or fill the observation table below (3mks)
    Titration 1 2 3
    Final burette reading (cm3)      
    Initial burette reading (cm3)      
    Volume of acid solution B used      
    1. Calculate the average volume of the acid solution (B) used (1mk)
    2. Calculate the number of moles of the acid solution B used (3mks)
    3. Write the chemical equation for the reaction between solution R and B in the experiment above (3mks)
    4. Calculate the number of moles of Sodium hydroxide solution B used (5mks)
    5. Calculate the molarity of Sodium Hydroxide (5mks)


MARKING SCHEME

  • You are provided with each of the following.
    • Sodium hydroxide solution marked R.
    • 0.1 m hydrochloric acid solution marked B.
    • A pipette
    • A burette
    • 2 conical flasks
    • A dropping/ thistle funnel
  • You are required to determine the molarity of sodium hydroxide (NaoH) solution used.
  • N.B. Rinse the burette with the solution to be used in it.

Procedure

  1. Using a pipette, transfer 25 cmof solution R into conical flasks.
  2. Add 2 drops of phenolphthalein indicator.
  3. Fill a clean burette with 0.1M hydrochloric acid labeled B to the mark and read the initial level of the acid accurately.
  4. Run the acid solution B in about 1 cm portions, swirl the liquid in the flasks after each addition of the acid. Add more of the solution B till end point.
  5. Record the final reading of the burette accurately and record or fill the observation table below (3mks)
    Titration 1 2 3
    Final burette reading (cm3) 22.40 21.00 42.00
    Initial burette reading (cm3) 0.00 0.00  
    Volume of acid solution B used 22.40 21.00 21.00
    1. Calculate the average volume of the acid solution (B) used (1mk)
      (21.00 + 21.00) ½ = 21.00cm2
                 2
    2. Calculate the number of moles of the acid solution B used (3mks)
      Number of moles = Moles x volume 
                                        1000cm3
      0.1 x 21.00cm2
        1000cm2
      = 0.021moles
    3. Write the chemical equation for the reaction between solution R and B in the experiment above (3mks)
      HCL(aq) + NaOH(aq) NaCl(aq) + H2O(l)
      • Correct equation 1
      • State symbol 1
      • Balanced 1
    4. Calculate the number of moles of Sodium hydroxide solution B used (5mks)
      • From the reaction in (iii) above:
      • Reaction Mole ration 1:1
      • Therefore 25 cm3 of NaoH contains 0.021
        No of Mole of NaoH = 0.021 Moles
    5. Calculate the molarity of Sodium Hydroxide (5mks)
      • 25cm3 of NaoH contains 0.0021 Moles
      • 1000 cm3 of NaoH contains
        0.0021m x 1000cm3
                    25 cm3
        ANS= 0.084 M

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