Chemistry Paper 3 Questions and Answers with Confidential - Form 4 End Term 1 Exams 2023

• Answer all the questions in the spaces provided.

1. You are provided with:
   Solution M 0.5M Hydrochloric acid.
   Solution F containing 15.3g/litre of basic compound G₂X.
   You are required to determine the relative atomic mass of G.
   
   Procedure.
   Place solution M in a burette, pipette 25cm³ of solution F into a 250cm³ conical flask. Add two drops of melthy/orange indicator and titrate. Record your results in the table below. Repeat the procedure two more times and complete table 1. (4mks)
   

   	I	II	III
   Final burette reading
   Initial burette reading
   Volume of solution M used

   1. What is the average volume of solution M? (1mk)
   2. Given that one mole of F reacts with 2 moles of M; calculate the:
      1. Number of moles basic compound G₂X in the volume of solution F used. (1mk)
      2. Concentration of solution F in moles per litre. (1mk)
      3. Relative formula mass of the basic compound, G₂X. (1mk)
      4. Relative atomic mass of G. (relative formula mass of X=60, atomic mass of H=1.0, O=16.0)
2. You are provided with;
   1.89g solid P, solid P is a dibasic acid H₂X.
   0.5M solution of the dibasic acid, H₂X, solution V
   Sodium hydroxide, solution K.
   You are required to determine:
   1. The molar heat of solution of solid P.
      The heat of reaction of one mole of the dibasic acid with sodium hydroxide.
   2. Calculate the heat of reaction of solid H2X with aqueous sodium hydroxide.
      
      PROCEDURE 1
      Place 30cm³ of distilled water into a 100ml plastic beaker. Measure the initial temperature of the water and record it in the table II below. Add all the solid Pat once; stir the mixture carefully with the thermometer until all the solid dissolves. Measure the final temperature reached and record it in the table II. (2mks)
      

      Final temperature (°C)
      Initial temperature (°C)

      1. Determine the change in temperature T₁. ( ½ mk)
      2. Calculate the;
         1. Heat change when H₂X dissolves in water, (Assuming the heat capacity of the solution is 4.2Jg^-1K^-1 and density is 1g/cm³.(2mks)
         2. Number of moles of the acid that were used (Relative Formula mass of H₂X is 126) (1mk)
         3. Molar heat of solution H₁ of the acid H₂X. (1mk)
            
            PROCEDURE II.
            Place 30cm³ of solution V into a 100cm³ beaker. Measure the initial temperature and record it in table III below. Measure 30cm³ of sodium hydroxide, solution K. Add all the 30cm³ of solution K at once to V in the beaker, stir the mixture with the thermometer. Measure the final temperature reached and record it in table III.
            

            Final temperature (°C)
            Initial temperature (°C)

            1. Determine the change in temperature, T₂. (½ mk)
            2. Determine the;
               1. Heat change for the reaction (assume the heat capacity of the solution is 4.2Jg^-1K^-1 and density is 1g/cm³) (2mks)
               2. Number of moles of acid used. (H₂X) (1mk)
               3. Heat of reaction H₂ of one mole of the acid H₂X with sodium hydroxide. (1mk)
            3. Given that:
                                                                          H₂O
               H₁ is the heat fir reaction H₂X(s) 2H+(aq) + X^2-(aq)
               H₂ is the heat for the reaction H⁺(aq) OH⁻(aq)   H₂O(l)
               Calculate H₃ for the reaction, H₂X(s) +2OH⁻(aq)   2H₂O(l) + X²⁻(aq) (2mks)
3.  
   1. You are provided with solid Q. Carry out test indicated below and record your observations and deductions in the table below.
      1. Place a spatula full of Q in a boiling tube. Add about 10cm3 of distilled  water and shake. Divide the resultant mixture into 4 portions. (2mks)
         

         Observation	Inference

      2. To the  first portion, add Barium nitrate solution followed by dilute nitric acid. (1mk)

         Observation	Inference

      3. To the second portion add 2 – 3 drops of sodium hydroxide till in excess. (1mk)
         
         

         Observation	Inference

      4. To the third portion add 2 – 3 drops of ammonia solutions till in excess. (1mk)
         
         

         Observation	Inference

   2. You are provided with liquid X. you are required to carry the test below.
      1. Place 1cm³ of substance X in a test tube. Add a small piece of sodium carbonate solid. (1mk)
         
         

         Observation	Inference

      2. To about 3cm³ of X in a boiling tube, add acidified potassium chromate (VI) and warm. (1mk)
          
         

         Observation	Inference

      3. To about 3cm³ of x add acidified potassium manganate (VII) (1mk)
      4. Dip a glass rod in liquid X and ignite. (2mks)
         
         

         Observation	Inference

CONFIDENTIAL

1. About 50cm³ of solution V
2. About 50cm³ of solution K.
3. 1.89g of solid P accurately weighed into a stoppered container.
4. Thermometer.
5. 5 dry test tubes in a test tube rack.
6. Spatula
7. Bunsen burner.
8. About 120cm³ of solution M.
9. About 90cm³ of solution F.
10. About 10cm³ of liquid X.
11. Solid Q weighed about 1g.
12. Blue and red litmus papers.
13. A boiling tube.
14. Glass rod.

Access to:

1. Bunsen burner
2. 2 M sodium hydroxide with a dropper.
3. 2M Ammonium hydroxide with a dropper.
4. Barium nitrate solution (1M)
5. Lead nitrate solution (1M)
6. 1M Nitric (V) acid.
7. Methyl orange with a dropper.
8. Acidified potassium dichromate (VI) with a dropper.
9. Acidified potassium manganate (VII).

MARKING SCHEME

1. You are provided with:
   Solution M 0.5M Hydrochloric acid.
   Solution F containing 15.3g/litre of basic compound G₂X.
   You are required to determine the relative atomic mass of G.
   Procedure.
   Place solution M in a burette, pipette 25cm³ of solution F into a 250cm³ conical flask. Add two drops of melthy/orange indicator and titrate. Record your results in the table below. Repeat the procedure two more times and complete table 1. (4mks)
   
   

   	I	II	III
   Final burette reading
   Initial burette reading
   Volume of solution M used

   • CT
   • D1
   • A1
   • PA1
   • FA1
     1. What is the average volume of solution M? (1mk)
        • Award mark for averaging of values with a range of 0.2cm³.
          Volume (x) = 13.4cm³
     2. Given that one mole of F reacts with 2 moles of M; calculate the:
        1. Number of moles basic compound G2X in the volume of solution F used. (1mk)
           Moles of HCl = vol x 0.2 = 0.0002 x  moles
                                      1000
           Moles of G₂X.10H₂O = 0.0002x = 0.0001x moles
                                                     2
        2. Concentration of solution F in moles per litre. (1mk)
           Concentration = moles x 1000
                                               Vol
                                  = 0.0001 x X 1000
                                              25
                                  = 0.004xM
        3. Relative formular mass of the basic compound, G₂X. (1mk)
           R.F.M  =   Mass per litre  
                           Concentration
            15.3      = 3825g 
           0.004x         x
        4. Relative atomic mass of G. (relative formula mass of X= 60, atomic mass of H =1.0, O=16.0)
           2G + 60 + 10(18) = 3825
                                             x
           2G = 3825 − 240
                       x
           G = (3825 − 120) = G = 23
                      2x
2. You are provided with;
   1.89g solid P, solid P is a dibasic acid H₂X.
   0.5M solution of the dibasic acid, H₂X, solution V
   Sodium hydroxide, solution K.
   You are required to determine:
   1.  
      1. The molar heat of solution of solid P.
      2. The heat of reaction of one mole of the dibasic acid with sodium hydroxide.
   2. Calculate the heat of reaction of solid H₂X with aqueous sodium hydroxide.
      PROCEDURE 1  
      Place 30cm³ of distilled water into a 100ml plastic beaker. Measure the initial temperature of the water and record it in the table II below. Add all the solid Pat once; stir the mixture carefully with the thermometer until all the solid dissolves. Measure the final temperature reached and record it in the table II. (2mks)
      
      

      Final temperature (°C)
      Initial temperature (°C)

      CT ½
      D ½
      A 1
      1. Determine the change in temperature ∆T₁. ( ½ mk)
         ∆T = Final temp – Initial temp
      2. Calculate the;
         1. Heat change when H2X dissolves in water, (Assuming the heat capacity of the solution is 4.2Jg^-1K^-1 and density is 1g/cm³.(2mks)
            ∆H = mC∆T₁
            =   30   × 4.2 × ∆T
               1000
            = 0.126 X ∆T₁ KJ
         2. Number of moles of the acid that were used (Relative Formula mass of H₂X is 126) (1mk)
            No of moles = Mass = 1.89 = 0.015moles
                                     RFM     126
         3. Molar heat of solution H1 of the acid H2X. (1mk)
            0.015 moles → 0.126 × ∆T₁ KJ
            1 mole →                   ?
            1×0.126×∆T₁ = −8.4 × ∆T₁KJmol⁻¹
                 0.015
            PROCEDURE II.
            Place 30cm³ of solution V into a 100cm³ beaker. Measure the initial temperature and record it in table III below. Measure 30cm³ of sodium hydroxide, solution K. Add all the 30cm³ of solution K at once to V in the beaker, stir the mixture with the thermometer. Measure the final temperature reached and record it in table III.
            
            

            Final temperature (°C)
            Initial temperature (°C)

            CT ½
            D ½
            A 1
            1. Determine the change in temperature, T₂. (½ mk)
               ∆T₂ = Final temp – Initial temp
            2. Determine the;
               1. Heat change for the reaction (assume the heat capacity of the solution is 4.2Jg^-1K^-1 and density is 1g/cm³) (2mks)
                  ∆H =   60   ×4.2 × ∆T₂
                           1000
                  = 0.252 X ∆T KJ
               2. Number of moles of acid used. (H2X) (1mk)
                  Moles =   MV   = 0.5 × 30 = 0.015moles
                                1000       1000
               3. Heat of reaction H₂ of one mole of the acid H₂X with sodium hydroxide. (1mk)
                  0.015 Moles → 0.252 X ∆T₂ KJ
                  1 mole → ?
                  1×0.252×∆T = −16.8 ×∆T₂KJ/mol 
                      0.015
            3. Given that:                                                           H₂O
               H₁ is the heat fir reaction H₂X(s) 2H+(aq) + X^2-(aq)
               H₂ is the heat for the reaction H⁺(aq) OH⁻(aq)   H₂O(l)
               Calculate H₃ for the reaction, H₂X(s) +2OH⁻(aq)   2H₂O(l) + X²⁻(aq) (2mks)
               H₂X(s) → 2H⁺(aq) + X2⁻(aq)  −8.4 X ∆T₁ KJ/mol
               2H⁺(aq) + 2OH⁻(aq) →  2H₂O(l) – 16.8 X ∆T₂ KJ/mol X2
               H₂X(s) + 2OH⁻(aq) → 2H₂O(l) + X2⁻ (aq)   ∆H = −8.4T₁ + −16.8 X 2T₂
               = −8.4T₁ – 33.6T₂
3.  
   1. You are provided with solid Q. Carry out test indicated below and record your observations and deductions in the table below.
      1. Place a spatula full of Q in a boiling tube. Add about 10cm3 of distilled  water and shake. Divide the resultant mixture into 4 portions. (2mks)
         
         

         Observation	Inference
         Solid dissolves to produce colourless solution    (1mk)	Soluble salt.    (1mk)

      2. To the first portion, add Barium nitrate solution followed by dilute nitric acid. (1mk)
         
         

         Observation	Inference
         A white ppt insoluble on addition of HNO3	SO2−4 , present

      3. To the second portion add 2 – 3 drops of sodium hydroxide till in excess. (1mk)

         Observation	Inference
         A white precipitate soluble in excess NaOH(aq)	Zn2+, Pb2+ present.

      4. To the third portion add 2 – 3 drops of ammonia solutions till in excess. (1mk)

         Observation	Inference
         A white ppt soluble in excess NH3(aq)	Zn2+ present

          
   2. You are provided with liquid X. you are required to carry the test below.
      1. Place 1cm³ of substance X in a test tube. Add a small piece of sodium carbonate solid. (1mk)

         Observation	Inference
         No effervescence	H+/ COOH absent

      2. To about 3cm³ of X in a boiling tube, add acidified potassium chromate (VI) and warm. (1mk)
         
         

         Observation	Inference
         K2Cr2O7/H+ changes from orange to green.	R-OH present

      3. To about 3cm³ of x add acidified potassium manganate (VII) (1mk)

         Observation	Inference
         KMnO4/H+ changes from purple to colourless	R – OH present

      4. Dip a glass rod in liquid X and ignite. (2mks)
         

         Observation	Inference
         Burns with a blue flame	-  C – C – or R – OH present or saturated organic compound.