CHEMISTRY PAPER 3 Questions and Answers - Form 3 End Term 1 Exams 2023

INSTRUCTIONS.

Answer all the questions in the spaces provided.

1.  PROCEDURE.
   Pipette 25cm 3 of solution C into a 250ml flask.
   Add 2-3 drops of phenolphthalein indicator.
   Fill the burette with solution B 0.5MHcl then titrate.
   Repeat this procedure two more times.
   Record your result in the table.
   
   

   Titratio	I	II	III
   Final burette reading
   Initial burette reading
   Volume of solution B used

   Calculate
   1. The average volume of solution B used. (2mks)
   2. Calculate the number of moles of sodium hydroxide solution C pipetted. (3mks)
   3. Calculate the number of moles of hydrochloric acid solution B that reacted with sodium hydroxide in (II) above. (3mks)
   4. Calculate the molarity of hydrochloric acid solution B. (3mks)
2. You are provided with solid T. Carry out the experiment in the table and record the results in the spaces provided.
   1. Put all of T in boiling tube. Add 20cm³ of distilled water and stir gently, filter the product and divide the filtrate into three portion.
      Retain the residue.
      
      

      Observation (1mk)	Inference (1mk)

   2. To the first portion add a few drops of 2M NaOH solution and then in excess.
      
      

      Observation (2mks)	Inferences (2mks)

   3. To the second portion add few drops of 2M ammonia solution and then in excess.
      
      

      Observations (2mks)	Inferences (2mks)

   4. To the third portion add a few drops of barium chloride solution followed by dilute hydrochloric acid.
      
      

      Observations (2mks)	Inferences (1mk)

3.  Add 2cm³ of dilute hydrochloric acid to the residue. Ensure some residue remains undissolved. Decant to get a solution. Divide the solution into two portion. Carry out the following experiments.
   
   1. To the first portion add a few drops of sodium hydroxide solution and then in excess.
      
      

      Observation (2mks)	Inferences (1mk)

   2. To the second portion add a few drops of ammonia solution and then in excess.
      
      

      Observation (2mk)	Inferences (1mk)

      Divide the residue into two portions. Carry out the following experiment.
   3. To the first portion add a few drops of dilute nitric (IV) acid.
      
      

      Observation (1mk)	Inferences (2mks)

   4. To the second portion, add acidified potassium dichromate (IV).
      
      

      Observation (1mk)	Inference (1mk)

 MARKING SCHEME

INSTRUCTIONS.

Answer all the questions in the spaces provided

1. PROCEDURE
   .Pipette 25cm3 of solution C into a 250ml flask.
   Add 2-3 drops of phenolphthalein indicator.
   Fill the burette with solution B 0.5MHcl then titrate.
   Repeat this procedure two more times.
   Record your result in the table.
   
   

   Titration	I	II	III
   Final burette reading
   Initial burette reading
   Volume of solution B used

   Calculate:
   1. The average volume of solution B used. (2mks)
   2. Calculate the number of moles of sodium hydroxide solution C pipetted. (3mks)
   3. Calculate the number of moles of hydrochloric acid solution B that reacted with sodium hydroxide in (II) above. (3mks)
   4. Calculate the molarity of hydrochloric acid solution B. (3mks)
2. You are provided with solid T. Carry out the experiment in the table and record the results in the spaces provided.
   1. Put all of T in boiling tube. Add 20cm3 of distilled water and stir gently, filter the product and divide the filtrate into three portion. Retain the residue.
      
      

      Observation (1mk)	Inference (1mk)
      Salts dissolves sparingly

   2. To the first portion add a few drops of 2M NaOH solution and then in excess.
      
      

      Observation  (2mks)	Inferences (2mks)
      White precipitate dissolves in excess	Zn2+, Pb2+, or Al3+ present

   3. To the second portion add few drops of 2M ammonia solution and then in excess.
      
      

      Observations (2mks)	Inferences (2mks)
      White precipitate dissolves in excess	Zn2+ present Pb2+, Al3+ absent

   4. To the third portion add a few drops of barium chloride solution followed by dilute hydrochloric  acid.
      
      

      Observations (2mks)	Inferences (1mk)
      White precipitate insoluble in acid	So42-

3. Add 2cm3 of dilute hydrochloric acid to the residue. Ensure some residue remains undissolved. Decant to get a solution. Divide the solution into two portion. Carry out the following experiments.
   1. To the first portion add a few drops of sodium hydroxide solution and then in excess.
      
      

      Observation (2mks)	Inferences (1mk)
      Blue precipitate insoluble in excess	Cu2+

   2.  To the second portion add a few drops of ammonia solution and then in excess.
      
      

      Observation (2mk)	Inferences (1mk)
      Blue precipitate soluble in excess forming a deep blue solution	Cu2+

      Divide the residue into two portions. Carry out the following experiment.
      1. To the first portion add a few drops of dilute nitric (IV) acid.
         
         

         Observation (1mk)	Inferences (2mks)
         Effervescence	Cu32 or So32-

      2. To the second portion, add acidified potassium dichromate (IV).
         
         

         Observation (1mk)	Inference (1mk)
         Orange colour present	Co32- present , So2-3