Chemistry Paper 3 Questions and Answers With Confidential - Maranda Post Mocks 2020/2021

1. You are provided with:

• Solid F
• 2.OM Hydrochloric acid, Solution G
• 0.1M Sodium hydroxide, Solution H

You are required to:

• Determine the enthalpy change AH, for the reaction between solid F and one mole of hydrochloric acid.

Procedure A

Using a burette, place 20.0cm³ of 2.0M Hydrochloric acid, solution G in a 100ml beaker provided. Measure the temperature of the solution after every half-minute and record the values in table below. At exactly 2 minute, add all of solid F to the acid. Stir the mixture gently with the thermometer. Measure the temperature of the mixture after every half-minute and record the values in table 1. (Retain the mixture for use in procedure B).

Table 1

1. Plot graph of temperature (Y-axis) against time. (3 marks)
2. Using the graph, determine the change in temperature AT (1 mark)
3. Calculate the heat change for the reaction(Assume that the specific heat capacity of the mixture is 4.2jg^-1K^-1 and the density of the mixture is 1gcm^-3) (1 mark)

Procedure B

Rinse the burette thoroughly and fill it with sodium hydroxide, Solution H. Transfer all the contents of the 100ml beaker used in procedure A into a 250ml volumetric flask. Add distilled water to make up to the mark. Label this solution C. Using a pipette place 25.0cm of solution Cinto a 250ml conical flask. Add two or three drops of phenolphthalein indicator and titrate against sodium hydroxide. Record your results in table 2. Repeat titration two more times and complete table 2.

Table 2

(4 marks)

Calculate the:

1. average volume of sodium hydroxide used. (1 mark)
2. the number of moles of:
   1. sodium hydroxide used. (1 marks)
   2. hydrochloric acid in 25 cm³ of solution C. (1 mark)
   3. hydrochloric acid in 250 cm³ of solution C. (1 mark)
   4. hydrochloric acid in 20.0 cm³ of solution G. (1 mark)
   5. hydrochloric acid that reacted with solid F (1 mark)
3. Calculate the enthalpy of reaction between solid F and one mole of hydrochloric acid (1¹/₂ marks)

2. You are provided with substance R. Carry out the tests below. Write your observations and inferences in the spaces provided.

1. Describe the appearance of substance R. (1 mark)
2. Place the remaining amount of substance R in a boiling tube. Add about 10 cm³ of distilled water and shake well. Use 2 cm³ portions for each of the tests below.
   1. To one portion, add aqueous ammonia dropwise until in excess.
      

      Observation	Inference
      (1mark)	(1mark)

   2. Describe a test that can be used to confirm the ions inferred in (b) (i) above from the materials provided.
      

      Test	Expected Observations
      (1mark)	(1mark)

   3. To a second portion, carry out the test describe in (b) (ii) above and record the observation and inferences in the spaces provided.
      

      Observation	Inference
      (½ mark)	(1mark)

3. To a third portion, add two drops of lead (II) nitrate and warm. 
   

   Observation	Inference
   (1mark)	(1mark)

3. You are provided with substance Z. Carry out the following tests and record your observations and inferences in the spaces provided.

1. Place about one third of substance Z on a metallic spatula and burn it with a non luminous Bunsen burner flame.
   

   Observation	Inference
   (1mark)	(1mark)

2. Dissolve all of the remaining substance Z in about 10 cm³ of distilled water in a boiling tube. Use about 2 cm³ portions of the solution of substance Z in a test tube for each of the tests (b) (i), (ii), (iii) and (iv).
   1. Add about 1 cm³ of acidified potassium dichromate(VI).
      

      Observation	Inference
      (1mark)	(1mark)

   2. Add about 1 cm³ of acidified potassium manganate(VII).
      

      Observation	Inference
      (1mark)	(1mark)

   3. Add the piece of magnesium ribbon provided.
      

      Observation	Inference
      (1mark)	(1mark)

   4. Determine the pH of the solution of substance Z.
      

      Method used	Inference
      (1mark)	(1mark)

Marking Scheme

1.  
   
2. ΔT = 26 - 19 = 7^oC 
   Showing on the graph
3. ΔH = mcθ
   = 20 x 4.2 x ans
   =correct ans
   
   ΔH = mcθ
   = 20 x 4.2 x ans
          1000

Calculate the

1. Titre 1 + titre 2 + titre 3
              3
   Average titre
2. 1. 0.1 x average titre
           1000
      =correct ans
   2. Mole ratio NaOH:HCL is 1:1
      Moles of HCl = ans b(1)
   3. 250 x ans b(ii)
          25
      Correct ans
      =ans b(ii) x 10
   4. (2 x 20)/1000 = 0.04moles
   5. Ans(b)(iv) - Ans(b)(iii)
      =correct ans
      =0.04 - Ans(b)(iii)
      =correct ans
3. Ans(b)(iii)
   Ans(b)(v)
   =correct ans in J/mol
   = Ans(b)(iii)
   Ans(b)(v) x 1000
   =Correct ans in KJmol^-1

2. You are provided with substance R

1. White/colourless crystalline solid or white/colourless crystals NB: Penalise fully for contradicting colour.
2.  
   1.  
      

      Observation	Inference
      No white PPT (1mark)	Zn2+,Al3+, Pb2+, Mg2+ absent. 1/2mk each for each ion mentioned. Penalize 1/2mk for each contradictory ion to a max of 2 mks. (1mark)

   2.  
   3.  
3.  
   

   Observation	Inference
   White ppt, soluble on warming. (1mark)	Cl-, Br-  (1mark)

3. You are provided with substance Z. Carry out the following tests and record your observations and inferences in the spaces provided.

1. Place about one third of substance Z on a metallic spatula and burn it with a non luminous Bunsen burner flame.
   

   Observation	Inference
   -Burns with a non sooty flame/blue non sooty flame. (1mark)	Ignore:Alkane/alkynes absent (1mark)

2. Dissolve all of the remaining substance Z in about 10 cm³ of distilled water in a boiling tube. Use about 2 cm³ portions of the solution of substance Z in a test tube for each of the tests (b) (i), (ii), (iii) and (iv).
   1. Add about 1 cm³ of acidified potassium dichromate(VI).
      

      Observation	Inference
      Orange colour of acidifid potassium dichromate(VI)does not turn green (1mark)	R-OH absent (1mark)

   2. Add about 1 cm³ of acidified potassium manganate(VII).
      

      Observation	Inference
      -Purple acidified potassium manganate(VII) does not decoulorise/does not turn colourless. (1mark)	or R-OH absent(1mark)

   3. Add the piece of magnesium ribbon provided.
      

      Observation	Inference
      Effervescence/bubbles of a colourless gas produced. Accept 1/2mk colourless gas produced. (1mark)	H+,H3O+, R-COOH (1mark) Reject: An acid/solution is an acid. Accpet for 1/2mk -Alkanoic acid/carboxylic acid

   4. Determine the pH of the solution of substance Z.
      

      Method used	Inference
      -To about 2 cm3 of solution Z, add 2 drops of universal indicator solution -Match the colour of the solution obtained with the pH chart and note the pH, -pH = 1 or pH = 2(1mark)	-Strongly acidic Reject -Strong acid -Acid solution (1mark)

Confidential

INSTRUCTIONS

In addition to the fittings and apparatus found in a chemistry laboratory, each candidate will require the following:

1. Each candidate
   1. One burette 0 50 ml
   2. One pipette 25.0 ml and a pipette filler
   3. One Filter funnel
   4. Two clean and dry 250ml conical flasks
   5. Six clean and dry test-tubes
   6. One boiling tube
   7. 2.1g of solid F weighed accurately and supplied in a dry stoppered container
   8. About 500cm³ of distilled water supplied in a wash bottle
   9. One 250ml volumetric flask supplied with a stopper
   10. One 10ml measuring cylinder
   11. One metallic spatula
   12. One piece of glass rod
   13. 1cm long magnesium ribbon
   14. About 60cm of solution G
   15. About 130cm of solution H
   16. 100ml beaker
   17. .-10°C to 110°C Thermometer
   18. Stop watch/stop clock
   19. One sticker/label
   20. pH chart
   21. About 0.5g of substance R
   22. About 0.5g of substance Z
   23. A White tile
2. Access to:
   1. Phenolphthalein indicator supplied with a dropper
   2. Bunsen burner
   3. Universal indicator solution supplied with a dropper
   4. 2.0M lead (II) nitrate solution supplied with a dropper
   5. 2.0M aqueous ammonia supplied with a dropper
   6. Acidified potassium manganate (VII) supplied with a dropper
   7. Acidified potassium dichromate (VI) supplied with a dropper

Note:

1. Solid F is hydrated Sodium hydrogen carbonate.
2. Solid R is Sodium Chloride
3. Substance Z is succinic acid
4. Solution G is 2.0M Flydrochloric Acid prepared by dissolving 172cm³ of Conc. Hydrochloric Acid (Density 1.18g/cm³) in 400cm³ of distilled water and diluting with distilled water to make one litre solution.
5. Solution H is 0.1M Sodium hydroxide, is prepared by dissolving 4.0g of sodium hydroxide in 700cm³ of distilled water and diluting it to 1 litre.
6. Acidified potassium dichromate(VI) is prepared by dissolving 30g of potassium dichromate(VI) in 200cm³ of 2M sulphuric(VI) acid and diluting with distilled water to 1 litre.
7. Acidified potassium manganate(VII) is prepared by dissolving 3.0g of solid potassium manganate (VII) in 200cm of 2M sulphuric(VI) acid and diluting with distilled water to 1 litre.