CHEMISTRY PAPER 3 - KCSE 2019 MARANDA MOCK EXAMINATION

1. You are provided with
   2.0m NaoH solution labelled B
   H₂ SO₄ acid solution labelled A `
   
   You are to:
   1. Prepare a dilute solution of NaoH solution.                                                                                   
   2. Determine the concentration of H₂SO₄in moles per litre.
      PROCEDURE1
      Using a pipette 25.0cm³ of solution B and place it into 250cm³ volumetric flask.
      Add about 200cm³ of distilled water and share well.
      Add more water to make up to 250cm³mark. Label this solution C.
      1. Calculate the concentration of the dilute solution C in moles per litres.                             [2mks]
         
         PROCEDURE 2
         Fill the burette with solution A and record the readings in the table below.
         Pipette 25cm³ of dilute solution C and place it into 250ml conical flask.
         Add 2-3 drops of phenolphthalein indicator.
         Titrate with solution A.
         Record your results in the table below.
         Repeat the titration two or more times and complete the table.   [4mks]
         
         

         Titration no	I	II	III
         Final burette reading (cm3)
         Initial burette reading(cm3)
         Volume of solution A(cm3)

         
         
         1. Determine average volume of the acid (solution A) used.  [1mk]
         2. Determine moles of dilute solution C in the volume used.     [2mks]
         3. Write an equation for the reaction between NaoH and H₂SO₄ acid.    [2mks]
         4. Determine the number of moles of A (H₂SO₄) used.      [2mks]
         5. Determine the concentration of A (H₂SO₄) in moles per litre.      [2mks]

2. You are provided with the following
   2m sodium hydroxide solution
   2m hydrochloric acid
   You are required to determine the molar enthalpy of neutralization of the acid using sodium hydroxide.
   
   PROCEDURE
   1. Measure out 20cm³ of acid into a clean plastic beaker.
   2. Record the temperature of this solution in the table below
   3. Measure 5cm³ of sodium hydroxide and add it to the hydrochloric acid.
   4. Stir with the thermometer and record the maximum temperature reached.
   5. Repeat the above procedure adding 5cm³ portions of sodium hydroxide until the total volume of the solution is 50cm³. [3mks]
      

      Volume of acid(cm3)	20	20	20	20	20	20	20
      Volume of NaoH added cm3	0	5	10	15	20	25	30
      Temperature( c)of solution

      
      You are required to:
      1. Plot a graph of temperature rise against sodium hydroxide added.                                 [4mks]
      2. From your graph
         1. Determine the expected temperature rise.       [2mks]
         2. Calculate the molar enthalpy of neutralization for this reaction. (C=4.2J/g/ ) assume density of solution is 1gcm^-3)
         3. The theoretical molar heat of neutralization is -57.2kj/mol-1.Compare your value in [ii] above with the theoretical value. Give the reasons for any differences noted between these two values.[2mks]

3. You are provided with solid N carry out the tests below and record your observations and inferences.
   1. Place a spatular of N in a test tube and add 5cm³ of water and shake well divide the solution in to three portions.       [1mk]
      

      OBSERVATION	INFERENCE

   2. Addsodium hydroxide to the first portion drop wise while observing till in excess.      [2mks]
      

      OBSERVATION	INFERENCE

   3. Add ammonia solution to the second portion drop wise until in excess.   [2mks]
      

      OBSERVATION	INFERENCE

   4. Add four drops of potassium iodide solution to the third portion.        [2mks]
      

      OBSERVATION	INFERENCE

   5. Put spatular of solid P in a test tube and add 5cm³ of water and shake well. Add three drops of acid bariumnitrate followed by 5 drops of nitric acid.   [4mks]
      

      OBSERVATION	INFERENCE

MARKING SCHEME

PROCEDURE 1

1.  
   1. 2 moles →1000cm³ =0.05 moles
      ?              25cm³
      0.05 moles-250cm^{3 =}0.2m
      
      PROCEDURE II
      Complete table - 1
      Decimal           - 1
      Arithmetic       -  1
      Accuracy         -  1 ± 0.2
   2. =12.5cm³
   3. 0.2 moles→1000cm³ =0005 moles
           ?             25cm³
   4. 2NaoH _[aq]+H₂SO_4[aq]→NaSO_4[aq]+2H2O_[l]
   5. Mole ratio
      A:C                         C=0.0025moles
      1:2                          A= =0.0025 moles
   6. 0.0025→answer a
                    1000

2. Table
   Complete table 1
   Decimal point    1
   Trend                    1
   1. Graph
      
      Axis        - Mk each
      Scale- Mk each
      Plotting
      Curve
   2.  
      1. answer from the graph
      2. Use MCDθ
         Mass=50 1=50g.
         From MCDθ→50g J/g/ C answer in b [i] above.
      3. Theoretical value is higher than the obtained value
         Heat lost to the surrounding
         Heat absorbed by the apparatus
3.  
   1.  
      

      Observation	Inference
      It dissolves into ]a colourless solution mk]	Soluble salt[ NoCu2+,Fe2+ or Fe3+[ ]

   2.  
      

      Observation	Inference
      White precipitate soluble in excess [1mk]	Pb2+,Zn2+,Al3+ ions present[ 1mk]

   3.  
      

      Observation	Inference
      White precipitate insoluble in excess	Pb2+,Al3+ ions present

   4.  
      

      Observation	Inference
      Yellow precipitate formed	Pb 2+ ions present

   5.  
      

      Observation	Inference
      White precipitate [1mk]	SO42- ions
      Don’t dissolve on adding nitric acid	Presence of NO,SO32- ions