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

• 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 cm³ of 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 cm³ of 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