Chemistry Paper 3 Questions - Maranda Mocks 2021/2022 Exams

CHEMISTRY
Paper 3 

Instructions to candidates

• Answer ALL the questions in the spaces provided.
• All working MUST be clearly shown.
• KNEC mathematical tables and silent non-programmable electronic calculators may be used.

Questions

1. You are provided with:
   • Solution A containing copper (II) ions
   • Solution B, 0.1M sodium thiosulphate
   • Solution C, Aqueous potassium iodide
   • Solution D, sodium hydroxide
   • Solution E, Starch indicator
     
     You are required to determine:
   • The concentration of copper (II) ions in Solution A
   • Enthalpy change of reaction between copper (II) ions and hydroxide ions
     
     
   • PROCEDURE I
     1. Using a pipette, place 25.0cm³ of Solution A in a 250ml volumetric flask. Add distilled water to make up to the mark. Label this as Solution A1. Retain THE REMAINING Solution A for use in Procedure II.
     2. Place Solution B in a burette. Using a clean pipette, place 25.0cm³ of Solution A1, in a 250ml conical flask. Add 10.0cm³ of potassium iodide, Solution C. Shake well, then add 2.0cm³ of starch indicator, Solution E. Titrate until a blue-black colour appears, and continue titrating until the blue-black colour just disappears. Record your readings in Table 1 below.
     3. Repeat step b) two more times and complete Table 1 below
        Table 1
        

        	I	II	III
        Final burette reading (cm3)
        Initial burette reading (cm3)
        Volume of Solution B used (cm3)

        (4 Marks)
        Calculate the:
        1. Average volume of Solution B used (1 Mark)
        2. Moles of sodium thiosulphate used (1 Mark)
        3. Concentration in moles per litre of copper (II) ions in Solution A given that the number of moles of copper (II) ions in 25.0cm³ of Solution A, are the same as the moles of sodium thiosulphate used. (2 Marks)
           
           
   • PROCEDURE II
     1. Using a clean burette, place 5.0cm3 of Solution D into each of six (6) test-tubes.
     2. Using a 100ml measuring cylinder, place 20.0cm3 of Solution A in a 100ml plastic beaker. Measure the temperature of Solution A and record it in Table 2 below.
     3. To Solution A in a beaker, add sodium hydroxide, Solution D from one of the test tubes. Stir the mixture with the thermometer and record it in Table 2, the maximum temperature reached. Continue with step d) IMMEDIATELY.
     4. Add the sodium hydroxide, Solution D, from another test-tube to the mixture obtained in c) above, stir and record the maximum temperature reached in Table 2. Continue adding the sodium hydroxide, Solution D, from each of the other four test-tubes, stirring the mixture and recording the maximum temperature each time and complete Table 2.
        Table 2
        

        Volume of sodium hydroxide Solution D added (cm3)	0	5	10	15	20	25
        Maximum temperature (°C)

        (4 Marks)
        1. On the grid provided, plot a graph of temperature against volume of sodium hydroxide, Solution D added (3 Marks)
        2. From the graph, determine:
           1. Volume of sodium hydroxide, Solution D, that reacted completely with 20.0cm³ of Solution A (2 Marks)
           2. The temperature change, ∆T, for the reaction (1 Mark)
        3. Enthalpy change of the reaction, per mole of copper (II) ions (2 Marks) (Heat capacity = 4.2Jg-1K^-1, density of the mixture = 1.0g/cm³)
2. You are provided with Solid F. Carry out the following tests and record your observations and inferences in the spaces provided.
   1. Place about one third of Solid F in a dry test tube. Heat the solid strongly and test any gas with both blue and red litmus paper
      

      Observations	Inferences

   2. Place the remaining amount of Solid F in a clean, dry test tube. Add about 15.0cm³ of distilled water and shake the mixture thoroughly. Divide the mixture into four test tubes, each containing about 2cm³
      

      Observations	Inferences

      
      
      1. To the first portion, add three drops of dilute hydrochloric acid
         

         Observations	Inferences

      2. To the second portion, add sodium hydroxide solution dropwise until excess.
         

         Observations	Inferences

      3. To the third portion, add ammonia solution dropwise until excess
         

         Observations	Inferences

      4. To the fourth portion, add 3 drops of Barium nitrate solution
         

         Observations	Inferences

3. You are provided with Solid G. Carry out the following tests and record your observations and inferences in the spaces provided.
   1. Place about one third of Solid G on a metallic spatula and burn it in a Bunsen burner flame
      

      Observations	Inferences

   2. Place the remaining amount of Solid G in a boiling tube. Add about 10cm3 of distilled water apers.com and shake. Use the mixture for tests i) to iii) below.
      1. To a 2cm³ portion of the mixture in a test tube, add 2 drops of acidified potassium dichromate (VI)
         

         Observations	Inferences

      2. To another 2cm³ portion of the mixture in a test tube, add two or three drops of acidified potassium manganate (VII)
         

         Observations	Inferences

      3. To another 2cm³ portion of the mixture in a test tube, determine the pH using universal indicator solution and chart.
         

         Observations	Inferences