CHEMISTRY PAPER 3 - 2017 MURANG'A MOCK EXAMINATION

INSTRUCTIONS: Answer all the questions in the spaces provided

1. You are provided with: 
   
   Potassium manganate ( VII) 
   solution A
   solution B, containing  6.3 g’ litre of dibasic acid H₂X.nH₂O
   Solution C₁ containing 4.0g/litre of  Sodium hydroxide solution.
   
   You are required to determine :
   1. The value of n in H₂X . nH₂ O
   2. How the rate of reaction of solution A with solution B varies with change in temperature.
      
      Procedure 1
      Fill the burette with solution B . Pipette  25cm³ of solution C  into a conical flask and titrate solution B  with Solution C using phenolphthalein indicator.
      Record your results in table below and repeat the titration to obtain consistent results:
      

      Burette readings	1	2	3
      Final readings (cm3)
      Initial readings (cm3)
      Volume of solution B used (cm3 )

      1. Determine the average volume of solution B used . ( 1mk)
      2. Calculate the concentration of solution C  in moles per litre (Na = 23.0, 16.0, H= 1.0 )   ( 1mk)
      3. Given that the equation of the reaction  taking place  and R.F.M  of X = 88
         H₂X _(aq) + 2NaOH _(aq) → Na₂X _(aq) + H₂O_(l)
         Calculate
         1. The number of moles of the dibasic acid solution B that reacted ( 2mks)
         2. The number of moles of the dibasic acid solution B in 1000cm³ of solution. ( 1mk)
         3. The  R.F.M of the dibasic acid, hydrated.   ( 1mk)
         4. The value of n in the formula  of the hydrated acid . ( 0 =16.0  H = 1.0)  ( 2mks)
            
            Procedure II
            
            1. Using a measuring cylinder, place  10cm³   portion of solution A  into 5’ test tubes placed in a test tube rack
            2. Clean the measuring cylinder and use it to place 10.0 cm3  of solution B into a boiling tube.
            3. Insert a thermometer in the solution B in the boiling tube and place the boiling  tube  in the attains a temperature of 40^o C.
            4. Remove the boiling tube from the water bath and place it in a test- tube rack and add the first portion of solution A. and at the same time start the stopwatch.
            5. Record the time taken for the purple  colour and the mixture to decolourise in table II
            6. Repeat the experiment using 10cm³ of solution B at 50^o , 60^o c, 70^o c  and 80^Oc.  Record the time in the table. Complete the table by computing 1h/t  sec^-1.
               

               Temperature of solution B	40	50	60	70	80
               Time of colour to decolourise (seconds ) 1/t sec-1

               1. Plot a graph of  1/t  ( sec -1) against temperature.  ( 3mks)
               2. From the graph , determine the time taken for decolourisation of the mixture, if the temperature of solution B was 65⁰C  (1mk)
               3. How does the rate of reaction of potassium manganite (VII) with oxalic acid vary with temperature. ( 1mk)
2. You are provided with solid Q . Carry out the tests below and record your observations and inferences
   In the spaces provided.
   1. Strongly heat a spatula – end full of solid Q in a dry test – tube.
   2.  
      1. Place the remaining solid Q  in a boiling tube. Add 10cm³of distilled water. Divide the solution into five portions.
         

         Observations	Inferences
         ½ mk	½ mk

      2. To the first portion, add aqueous lead (II) nitrate solution .
         

         Observations	Inferences
         1mk	1mk

      3. To the second portion add dilute nitric (V) acid followed by barium nitrate solution.
         

         Observations	Inferences
         1mk	1mk

      4. To the third portion add a few drops of sodium hydroxide until in excess.
         

         Observations	Inferences
         1mk	1mk

      5. To the fourth portion add few drops of aqueous ammonia until in excess
         

         Observations	Inferences
         ½ mk	½ mk

      6. To the fifth portion add few drops HCL acid. Warm the content
         

         Observations	Inferences
         ½ mk	½ mk

3. You are provided with solid L.  Carry out the tests and your observations and inferences
   1. Place about one third of solid L on a metallic spatula and burn it using Bunsen burner.
      

      Observations	Inferences
      ½ mk	½ mk

   2. Place the remaining solid L in a test tube Add about 6cm³ of distilled water and shake well. Retain the mixture for use in tests (C)
      

      Observations	Inferences
      ½ mk	½ mk

   3.  
      1. To about 2cm³ of te mixture add a small amount of sodium hydrogen carbonate.
         

         Observations	Inferences
         1mk	1mk

      2. To about  1cm³ of the mixture add 1cm³ of acidified potassium dichromate (VI) and warm
         

         Observations	Inferences
         1mk	1mk

      3. To about 2cm³ of the mixture  add two drops acidified potassium manganite (VII)
         

         Observations	Inferences
         1mk	1mk