Chemistry Paper 3 Questions and Answers with Confidentials- Bunamfan Cluster Pre Mock Exam 2022

 Instructions

• Answer all the questions
• You are not allowed to start working with the apparatus for the first 15 minutes of the 2 hours and 15 minutes. This time is to enable you to read the question paper and make sure you have all chemicals and apparatus that you may need.
• All workings must be clearly shown where necessary.
• Electronic calculators may be used.

Questions

1. You are provided with:
   • Acidified aqueous potassium manganate(VII), KMnO4, solution A,.
   • Solution B containing 11.75g of ammoniumiron(II)sulphate, (NH4)2Fe(SO4)2.6H2O dissolved in 500 cm3of solution.
   • Solution C containing 1.25g of a dibasic acid, H2X. 2H2O dissolved in 250cm3 of solution.
     
     You are required to:
   • Standardize solution A using solution B.
   • Use the standardized solution A to determine the concentration of solution C.
   • Determine the molecular mass of X.
     
     
   • Procedure I:
     Fill the burette with solution A.Using a pipette and pipette filler, place 25 cm3of solution B into a 250 ml conical flask. Titrate solution A with B until a permanent pink colour just appears.Record your results in table 1 below. Repeat this procedure two more times and complete table 1.
     
     TABLE 1
     

     Titration	I	II	III
     Final buretter reading cm3
     Initial burette reading cm3
     Volume of solution A used cm3

     
     (4 marks)
     1. Calculate the average volume of solution A used. (1 mark)
     2. Calculate the concentration of B in moles per litre. (RFM of B is 392) (1 mark)
     3. Calculate the number of moles of iron (II)ions in the 25 cm3 of solution B. (1 mk)
     4. Calculate the concentration of manganate(VII)ions in solution A in moles per litre given: (1 mk)
        MnO4- (aq) + 5Fe2+ (aq) + 8H+ (aq) Mn2+ (aq) + 5Fe3+ (aq) + 4H2O (l)
        
        
   • Procedure II:
     Pipette 25 cm³ of solution C into a conical flask. Heat this solution to about 70°C and titrate the hot solution C with solution A in the burette until a permanent pink colour just appears. Shake thoroughly during titration. Record your results in table II. Repeat this procedure to complete table II.
     
     TABLE II
     

     Titration	I	II	III
     Final buretter reading cm3
     Initial burette reading cm3
     Volume of solution A used cm3

     
     (4 mks)
     5. Calculate the average volume of solution A used in table II.. (1 mark)
     6. Calculate the number of moles of manganate (VII) ions in table II above. (1 mk)
     7. Given that 2 moles of of manganate (VII) ions react with 5 moles of the dibasic acid C, calculate the number of moles of the dibasic acid used in moles per litre. (1 mk)
     8. Calculate the:
        1. Formula mass of the dibasic acid, solution C.(H = 1.0, O = 16.0) (1 mk)
        2. Formula mass of X in the dibasic acid C.(1 mk)
2. You are provided with solid M. Carry out the tests and write your observations and inferences in the spaces provided.
   1. Describe the appearance of solid P. (1 mark)
      

      Appearance

   2. Place the solid M in a boiling tube. Add about 12cm3of distilled water and Shake well.Divide the solution into five portions and carry out the tests below.
      1. To the first portion, dip both red and blue litmus paper.
         

         Observation	Inferences

      2. To the second portion, add sodium hydroxide solution dropwise until in excess.
         

         Observation	Inferences

      3. To the third portion, add aqueous ammonia dropwise until in excess.
         

         Observation	Inferences

      4. To the fourth portion, add three drops of sodium chloride solution.
         

         Observation	Inferences

      5. To the fifth portion, add two drops of barium nitrate followed by five drops of nitric(V) acid.
         

         Observation	Inferences

3. You are provided with solid P. Carry out the following tests and record your observations and inferences in the spaces provided.
   1. Place about one third of the solid P on a clean metallic spatula and ignite using a Bunsen burner.
      

      Observation	Inferences

   2. Place the remaining solid P in a boiling tube. Add about 10cm3of distilled water and Shake well.
      

      Observation	Inferences

   3. Divide the mixture into three portions.
      1. To the first portion add two drops of acidified potassiummanganate(VII).
         

         Observation	Inferences

      2. To the second portion, add two drops of bromine water.
         

         Observation	Inferences

      3. To the third portion, describe the procedure you can use to determine the PH using the reagents given.
         

         Procedure

      4. Carry out your procedure in (iii) to determine the PH.
         

         Observation	Inferences

Confidential

APPARATUS

1. 100cm3of solution A, 0.02M KMnO4.
2. 100cm3of solution B, 0.06 M ammonium iron(II)sulphate, (NH4)2Fe(SO4)2.6H2O
3. 100cm3 of Solution C, 0.04M oxalic acid
4. 1 g Solid M, aluminium sulphate.
5. 0.5g solid P, oxalic acid in a stoppered container
6. Burette
7. Pipette and pipette filler.
8. 2 conical flasks
9. Clamp, boss and stand.
10. 1 boiling tube.
11. 5 clean test tubes
12. Distilled water in wash bottle.
13. Clean Metallic spatula
14. Bunsen burner.
15. PH chart
16. Universal indicator solution.
17. Red and blue litmus paper.

COMMON REAGENTS

1. 0.2M Sodium hydroxide, NaOH solution with a dropper.
2. Ammonia solution with a dropper.
3. Barium nitrate solution, Ba(NO3)2 with a dropper.
4. Dilute Nitric (V)acid solution with a dropper
5. Acidified potassium manganate (VII)solution with a dropper.
6. Bromine water with dropper.
7. Sodium chloride solution with a dropper.

Marking Scheme

QUESTION 1

Complete table……………… 1mk or ½ mk or 0
Decimal…………………….. 1mk or 0
Accuracy…………………….1 mk or ½ mk or 0
Principles of averaging………1 mk or ½ mk or 0
Final accuracy……………… 1 mk or ½ mk or 0

1. Calculate the average volume of solution M used. (1 mark)
   • V = a +b+c/3 or a+b/2 or b+c/2
     Working…………………….1/2 mk
     Correct ans………………….1/2 mk
     Correct to atleast 2dp unless exactly to 1dp or whole no.
2. Concentration (1 mark)
   
   • 23.5/392 = 0.06M
     Ans should be exact otherwise penalize ½ mk/
3. Calculate number of moles of solution Fe2+ in 25 cm3. (1 mark)
   25 x 0.06/1000 = 0.0026 moles
   Ans in 4dp otherwise penalize ½ mk for rounding off.
4. The concentration 1 marks)
   
   • Mole ratio 5:1
     Moles in c x 5 = ans
     Ans x1000/ av volume
     = final ans
     
     PROCEDURE II
5. Calculate the average volume of solution A used in table II.. (1 mark) AS IN TABLE 1
6. Calculate the number of moles of manganate (VII) ions in table II above. (1 mk)
   • Ans in (d) av volume table 2 / 1000
     = correct ans.
7. Given that 2 moles of of manganate (VII) ions react with 5 moles of the dibasic acid C, calculate the number of moles of the dibasic acid used in moles per litre. (1 mk)
   • Mole ratio = 2:5,
   • Moles of dibasic acid= Ans in (f) x 5/2 = ans
     Molarity = ans x 1000/25
     =correct ans
8. Calculate the:
   1. Formula mass of the dibasic acid, solution C.(H = 1.0, O = 16.0) (1 mk)
      5/ ans in (g)
      Correct ans .
      Ans can be whole number or DP
   2. Formula mass of X in the dibasic acid C.(1 mk)
      Ans in h(I) = 2+x+2(18)
      X = Ans in h(I) - 38
      = Correct ans.
      ANS BETWEEN 80-90 otherwise penalize ½ mk
      Ans can be whole number or dp.

QUESTION 2
You are provided with solid M. carry out the tests and write your observations and inferences in the spaces provided.

1. Describe the appearance of solid M. (1 mark)
   

   Appearance

   White solid/white powder/white crystal (1 mark)

2. Place the solid M in a boiling tube. Add about 12cm3of distilled water and Shake well. Divide the solution into five portions and carry out the tests below.
   1. To the first portion, dip both red and blue litmus paper.
      

      Observation	Inferences
      Blue litmus changes red…. ½ mk Red litmus paper remain red…1/2 mk (1 mark)	Acidic solution. (1 mark)

   2. To the second portion, add sodium hydroxide solution dropwise until in excess.
      

      Observations	Inferences
      White ppt that dissolves in excess to form a colourless solution (1 mark)	Zn2+/Al3+/Pb2+ (1 mark)

   3. To the third portion, add aqueous ammonia dropwise until in excess.
      

      Observations	Inferences
      White ppt that is insoluble (1 mark)	Al3+/Pb2+ (1 mark)

   4. To the fourth portion, add three drops of sodium chloride solution.
      

      Observations	Inferences
      No white ppt (1 mark)	Al3+ present… 1 mk Award 1/2mk for Pb2+ absent if Al3+ is not inferred. (1 mark)

   5. To the fifth portion, add two drops of barium nitrate followed by five drops of nitric(V) acid.
      

      Observations	Inferences
      White ppt…..1/2 mk No effervescence….1/2 mk (1 mark)	SO42- present. Award ½ mk for SO32- and CO32- ABSENT if SO42- is not binferred. (1 mark)

QUESTION 3

You are provided with solid P. Carry out the following tests and record your observations and inferences in the spaces provided.

1. Place about one third of the solid P on a clean metallic spatula and ignite using a Bunsen burner.
   

   Observations	Inferences
   Melts to a colourless liquid that burns with yellow sooty flamE (1 mark)	=C=C= ……1 mk Or triple bond structure..  (1 mark)

2. Place the remaining solid P in a boiling tube. Add about 10cm3of distilled water and Shake well.
   

   Observations	Inferences
   Dissolves to form a colourless solution ( 1/2 mark)	Polar/ soluble substance (1/2 mark)

3. Divide the mixture into three portions.
   1. To the first portion add two drops of acidified potassium manganate(VII).
      

      Observations	Inferences
      Purple potassium manganate(VII) solution changes colourless/ decolourised. (1 mark)	=C=C= ……1/2 mk or triple bond structure. ROH …..1/2 mk

   2. To the second portion, add two drops of bromine water.
      

      Observations	Inferences
      Orange bromine water changes colourless/ decolourised. (1 mark)	=C=C= OR TRIPLE BOND STRUCTURE. (1 mark)

   3. To the third portion, describe the procedure you can use to determine the PH using the reagents given.
      

      Procedure:

      To the solution add few drops of universal indicator solution. Match colour with PH chart to get corresponding PH. (1 mark)

   4. Carry out your procedure in (iii) to determine the PH.
      

      Observations	Inferences
      PH= 4 or 5 or 6 ………1 mk Reject range of PH eg PH 4-6 (1 mark)	Weakly acidic. (1 mark)