CHEMISTRY PAPER 3 - 2019 LAINAKU JOINT MOCK EVALUATION EXAMINATION

1. You are provided with:
   • Sodium hydroxide labelled solution A
   • 128M hydrochloric acid labelled solution B
   • Carboxylic acid labelled solution C
     
     You are required to:                                                                                          
   • Standardize solution D with solution B
     Determine the:
   • Reaction ratio between sodium hydroxide, solution A and the carboxylic acid, solution C
   • Concentration of solution C in moles per litre.
     Procedure1                                                         
     Pipette 25 cm³ of solution A into a 250 cm³ beaker. Add distilled water to make up to 150 cm³. Label this solution D.
     Fill the burette with solution B. Pipette 25cm³ of solution D into a 250cm³ conical flask. Add 2 dropsofphenolphthalein indicator and titrate with solution B. Record your results in table 1. Repeat the titration two more times and complete the table
     

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

      (4 marks)

1. Determine the average volume of solution B (1mark
2. Calculate the concentration in moles per litre of sodium hydroxide in:
   Solution D                         (2marks)
   Solution A                                     (1mark)
   
   Procedure 2
   Using a clean burette, place 16cm³ of solution C into a 100 ml plastic beaker. Take the initial temperature of the solution and record it in table 2. Using a clean measuring cylinder, measure 4cm³ of solution A and add it to solution C in the 100ml beaker. Stir the mixture immediately with the thermometer and record in table 2 the maximum (final) temperature reached. Repeat the experiment with the other sets of volumes of C and Ain table 2 and complete it.
   (Rinse the thermometer and the beaker with distilled water after each experiment. It is assumed that the initial temperatures for solution A and C are equal at room temperature.)
   

   Volume of solution C (cm3)	16	12	8	6	4	2
   Volume of solution A (cm3)	4	8	12	14	16	18
   Final temperature (0C)
   Initial temperature (0C)
   Change in temperature, ∆T (0C)

   (6marks)

1. On the grid provided, plot a graph of ∆T (vertical axis) against the volume of sodium hydroxide, solution A                       ( 3marks)
2. From the graph, determine the volume of sodium hydroxide, solution A required to neutralize the carboxylic acid     (1mark)
3. Calculate the volume of carboxylic acid, solution C used for neutralization (1mark)
   Calculate the
   1. Ratio between the volumes of solutions A and C (1mark)
   2. Concentration in moles per litre of the carboxylic acid, solution C.
      (Assume that the volume ratio is the same as the mole ratio)              (2marks)
4. You are provided with solid E. Carry out the tests below and record your observations and inferences in the spaces provided.
   Place all the solid E in a boiling tube, add 10cm³of distilled water and shake.
   

   OBSERVATION	INFERENCE

5. To about 1cm³ of the solution, add 2M sodium hydroxide drop wise until in excess
   

   OBSERVATION	INFERENCE

          
6. Place 1cm³ of the solution in a test-tube and add 2 to3 drops of 2M sulphuric (VI) acid.
   

   OBSERVATION	INFERENCE

7. To about 1cm³ of the solution, add 4-5 drops of 2M lead (II) nitrate solution and warm.
   

   OBSERVATION	INFERENCE

3. You are provided with solid F. Carry out the tests below and record your observations and inferences in the spaces provided.
   Place all of solid F into a boiling tube. Add 10cm³ of distilled water and shake well. Use 2cm³ portions of the mixture for the following reactions
   

   OBSERVATION	INFERENCE

1. Test the PH of first portion using the universal indicator paper.
   

   OBSERVATION	INFERENCE

   (1mark)                                                                        (1mark)
2. To the second portion, add three drops of bromine water.
   

   OBSERVATION	INFERENCE

   (1mark)                                                                          (1mark)
3. To the third portion, add 2 drops of acidified potassium manganate (VII) and shake well
   

   OBSERVATION	INFERENCE

                           (1mark)                                                           (1mark)
4. To the fourth portion, add all the sodium hydrogen carbonate provided.
   

   OBSERVATION	INFERENCE

                           (1mark)                                               (1mark)

MARKING SCHEME

PROCEDURE I

Table . . . . .. (5 marks) Expected average titre = 32.6cm³

1. Complete table . . . . . . (1 mark)
   Conditions
   1. 3 titrations done . . . . . .(1 mark)
   2. 2 titrations done . . . . . . (½ mark)
   3. 1 titration done . . . . . . . 0 mark
      
      Penalties
      Penalise ½ mark only ONCE for any of the following
      1. Wrong arithmetic / subtraction
      2. Inverted table
      3. Unrealistic burette readings and titre values i.e. burette readings beyond 50cm³, unless explained or titre values less than 1cm³ or in hundreds.
2. Use of decimal . . . . . (1 mark)
   (Tied to 1st and 2nd row only)
   Conditions
   1. Accept 1 or 2 decimal places used consistently, otherwise penalise fully.
   2. If 2d.p used, the second decimal place must be '0' or '5', otherwise penalise fully.
   3. Accept inconsistency in the use of zeros as the initial burette reading e.g. 0, 0.0 or 0.00.
3. Accuracy . . . . . . .(1 mark
   Compare the candidate's correct titre values with the school value and tick (ü) the chosen value if it earns a mark and award as follows:
   1. If at least one titre value is within ± 0.1 of SV . . . . . (1 mark)
   2. If at least one titre value is within ± 0.2 of S.V. . . . . .(½ mark)
   3. If none is within ± 0.2 of S.V. . . . . . . (0 mark)
      NOTE
      1. The school value must be written above the table.
      2. If there was wrong arithmetic or no subtraction, then work out the correct value and compare the correctly worked out value with the S.V and award accordingly.
      3. If no school value is given or cannot be worked out from the teachers' values as per the principles of averaging then; sample from all the candidates; correct average titre values.
4. Principles of averaging . . . . . .(1 mark)
   (/V₁ + V₂ + V3)/3 = correct answer
   If answer has decimals rounding off should be to 2 decimals otherwise penalise for rounding to 1 decimal.
   Values averaged must be consistent within ± 0.2 of each other.
   1. 3 consistent titrations done and averaged . . . . . 1 mark
   2. 3 titration done but only 2 are consistent and averaged . . . .1 mark
   3. Only 2 titrations done, are consistent and averaged . . . . 1 mark
   4. 3 consistent titrations done but only 2 are averaged . . . .. 0 mark
   5. 3 inconsistent titrations done and averaged . . . . . 0 mark
      NOTE.
      1. The mark for principles of averaging is awarded after marking the working and answer for calculating the average volume of solution C.
      2. Penalise ½ mark if no working is shown but correct answer is given.
      3. Penalise fully if no working shown but answer given in wrong or wrong working done and correct answer given
      4. Accept rounding off or trancation of answer to at least 2 decimal places, otherwise penalise ½ mark for rounding off to less than 2 decimal places, unless the answer works out exactaly to a whole number or to 1 decimal place.
5. Final accuracy . . . . . . .(1 mark)
   Compare the candidates' correct averaged titre with the school value used in III and award as follows.
   1. If within ± 0.1 of school value . . . . . .1 mark
   2. If within ± 0.2 of school value . . . . . .1 mark
   3. If not within ± 0.2 of S.V. . . . . . . . . . 0 mark
      
      NB
      If wrong principles of averaging is used by the candidate, then pick the correct values ( if any), average and award accordingly.
      
      CALCULATIONS
      1. Mol of B in av= (0.128 x 32.6)/1000 =0.0042 molP^1/2
         Mol of NaOH in D =0.0042 molP^1/2
         Molarity = (0.0042 x 1000)/ 25P^1/2 =0.1669 MP^1/2
         
         Conditions and penalties.
         Accept correct answer for ½ mark if working is not shown
         Penalise fully for any strange figure used in the working
         Answer to be to atleast 4 decimal places, otherwise penalise ½ mark for rounding off to less than 4dp, unless it works out exactly to lesser number of decimal places.
         Answer should be as expected, otherwise penalise ½ mark for wrong arithmetic.
         Units may not be shown, but if shown must be correct, otherwise penalise ½ mark for wrong units.
         
         
      2. Mol of NaOH of D in 150 = (150 X 0.0042)/25 = 0.0252 molP^1/2
         25 cm³of A contain 0.0252 mol
         Molarity = (1000 x 0.0252)/25 = 1.0008 MP^1/2
         
         Conditions and penalties.
         Penalise ½ mark for wrong transfer of answer b(I), otherwise penalise fully for any strange figure used.
         Apply all the conditions and penalties in b(I) above.

PROCEDURE 2

1. Complete table . . . . . . . (2 mark)
   1. Complete table with 6 readings . . . . . 2 marks
   2. Incomplete table with 4 - 5 readings . . . . . . .1 mark
   3. Incomplete table with less than 4 readings . . . . . . . 0 mark
      
      Penalties
      Penalise ½ mark for unrealistic initial temperature reading i.e. if reading is below 10°C or above 40° C
2. Decimal . . . . . . . (1 mark)
   (Subject to atleast 2 readings.
   Must be consistently recorded as whole numbers or to one decimal place of '0' or '5', otherwise penalise fully.
3. Accuracy . . . . . .(1 mark)
   Compare the candidate final temperature reading at vol of C = 16 with the school value. Award 1 mark if within ± 2°C of the S.V, otherwise penalise fully.
   NB Place a tick ( P) on the candidates initial temperature reading if credited.
4. Trend . . . . . . .(2 mark)
   Award the first 1/2 mark if temperature rise
   Award the second ½ mark for temperature either being constant at higher then steadily followed by drop.
5. Graph . . . . . . 3 marks
6. Labelling of axes . . . . . ½ marks
   Award ½ mark if both axes are labelled correctly.
   
   Conditions.
   1. Penalise fully for inverted axes
   2. Penalise fully if only ONE axis is labelled
   3. Penalise fully for wrong units used, otherwise ignore if units are not shown.
7. Scale . . . . . . . ½ mark
   The area covered by the actual plots should be atleast half of the grid provided on both axes
   The scale chosen must be able to accommodate all the points whether plotted or not.
   Scale interval must be uniformly caliberated on both axes.
   
   NOTE:
   1. Penalise fully if any of the above conditions is not met.
   2. Award for correct scale even if the axes are inverted.
8. Plotting . . . . . . 1 mark
   1. if 5-6 points correctly plotted . . . . . 1 mark
   2. If 3-4 points correctly plotted . . . . . .½ mark
   3. If less than 5 points correctly plotted . . . 0 mark
      
      NOTE:
      1. Mark all the plots on the graph by placing a tick (P) if correct or a cross (×) if wrong.
      2. Accept correct plots even if the axes are inverted and award accordingly.
      3. If scale interval are inconsistent, credit only correct plots (if any) within the first correct scale interval and treat all the others as wrong.
9. Line/shape . . . . . .(1 mark)
   Accept two straight lines and each extrapolated to meet on extrapolation for 1 mark.
   Showing DT correctly on the graph . . . . .½ mark
   Correct value of DT stated . . . . . . . . . . . .½ mark
   1. Vol of C + volA = 20 cm³ P^1/2
      Vol of C = 20 – 10 = 10 cm³P^1/2 
                                                                                                      
      Conditions
      Penalise ½ mark for wrong transfer of average titre of answer B(ii) otherwise penalise fully for any strange figure.
      1. ratio = 1:1P¹
         molarity of A = 1.008 MP¹
         Ratio 1:1
         Molarity of C = 1.008 MP¹

2. You are provided with solid E. Carry out the tests below and record your observations and inferences in the spaces provided. Place all the solid E in a boiling tube, add 10cm3 of distilled water and shake well until all the solid dissolves.
   

   OBSERVATION	INFERENCE
   Solid dissolves to form a colourless solution	Soluble salt Cu2+ Fe2+ Fe2+ absent

   
   To about 1cm³ of the solution, add 2M sodium hydroxide drop wise until in excess
   
   

   OBSERVATION	INFERENCE
   White precipitate, insoluble in excess,	Ca2+   ,Mg2+ present

   (1mark)                                                           (1mark)
3. Place 1cm³ of the solution in a test-tube and add 2 to3 drops of 2M sulphuric (VI) acid.
   
   

   OBSERVATION	INFERENCE
   White precipitate	Ca2+present

   Penalise inference fully if Ca²⁺ not mentioned in (I)above.                      
   1. To about 1cm³ of the solution, add 4-5 drops of 2M lead (II) nitrate solution and warm
      
      

      OBSERVATION	INFERENCE
      White precipitate, dissolves on warming Reject: dissolves in excess	Cl- present.

      You are provided with solid F. Carry out the tests below and record your observations and inferences in the spaces provided.
      Place all of solid F into a boiling tube. Add 10cm³ of distilled water and shake well. Use 2cm³ portions of the mixture for the following reactions.
      
      

      OBSERVATION	INFERENCE
      Solid dissolves to form a colourless solution	Polar substance

      
      Test the first portion with universal indicator papers. 
       
      

      OBSERVATION	INFERENCE
      PH = 4 or 5	Weakly Acidic substance.

      
      

      OBSERVATION	INFERENCE
      Yellow colour of bromine water persists	P1absent

                                      

1. To the second portion, add three drops of bromine water.
   

   OBSERVATION	INFERENCE
   Yellow colour of bromine water persists	P1absent

2. To the third portion, add 2 drops of acidified potassium manganate (VII) and shake well
   
   

   OBSERVATION	INFERENCE
   Purple colour of acidified potassium manganate (VII) persists	, P1/2R-OH P1/2absent

   
   To the fourth portion, add a little solid G, sodium hydrogen carbonate. 
   
   

   OBSERVATION	INFERENCE
   Bubbles/effervescence	R-COOH