Chemistry Paper 3 Questions and Answers with Confidentials - Form 4 Opener Term 1 Exams 2022

CHEMISTRY
PAPER 3

Instructions

• Attempt all the questions in the spaces provided.

Questions

Question One

You have been provided with:

• 0.5g Divalent MCO3 labeled P
• 0.5M hydrochloric acid labeled A
• 1.0M Sodium hydroxide labeled B
• Phenolphthalein indicator

PROCEDURE:

• Weigh exactly 0.5g of a divalent metal carbonate, MCO3
• Put the weighed carbonate in a conical flask
• Add to it 30.0cm3 of 0.5M hydrochloric acid solution A
• Add 2 – 3 drops of phenolphthalein indicator in the resulting solution.
• Titrate the solution against a 1.0M Sodium hydroxide solution until the colour of the solution just turns pink permanently.
• Record your results in the table below.
• Repeat the experiment three times to complete the table. (4 mks)
  

  Titration	1	2	3
  Final burette reading (cm3)
  Initial burette reading (cm3)
  Volume of the base used (cm3)

  
  
  1. Calculate the average volume of base used to neutralize the excess acid. (1 mk)
  2. Determine:
     1. The number of moles of base used. (2 mks)
     2.        
        1. The volume of the acid that was neutralized by the base. (2 mks)
        2. The number of moles of acid that reacted with the carbonate. (2 mks)
  3.        
     1. Write the equation for the reaction between the acid and carbonate. (1 mk)
     2. Determine the number of moles of the carbonate in the sample. (2 mks)
     3. Determine the relative formula mass of the carbonate. (2 mks)
     4. Determine the relative atomic mass of M. (3 mks)

Question Two
You are provided with solid P. Carry out the tests below and record your observations and inferences.

• Put all solid P in a boiling tube and add about 5cm3 of distilled water. Shake until all solid dissolves.
  1. Place about 2cm³ portion of the solution in a test tube and add aqueous ammonia drop wise until in excess. 
     

     Observation	Inferences

  2. Dip a clean end of a glass rod into the remaining solution and then place it in the Bunsen burner flame. Note the colour of the flame above the glass rod.
     

     Observation	Inferences

  3. Place about 2cm portion of the solution in a test tube of barium nitrate solution. Retain this content for the test in (d) below.
     

     Observation	Inferences

  4. To the content in (c) above add 4 drops of 2m HNO3 following by 2 drops of acidified potassium manganet (vii).
     

     Observation	Inferences

Question Three
You are provided with solid K. carry out the tests below and record your observation and inferences in the spaces provided

1. scoop a half portion of the solid using a clean metallic spatula and introduce it to a non-luminous flame of Bunsen burner to burn.
   

   Observation	Inferences

2.        
   1. Put the remaining portion of solid K. in a boiling tube and add about 10cm3 of distilled water. shake and divide the solution into three portion.
      

      Observation	Inferences

   2. To the 1^st portion, add about 4 drops of acidified potassium manganite (Vii) solution.
      

      Observation	Inferences

   3. To the 2^nd portion, add 3 drops of acidified potassium dichromate (vi) solution.
      

      Observation	Inferences

   4. To the 3^rd portion, determine the pH using universal indicator paper.
      

      Observation	Inferences

Confidential

1.      
   • 0.5G DIVALENT METAL CARBONATE. MCO3
   • 0.50M hydrochloric acid.
   • Phenolphthalein indicator
   • 1.0M sodium hydroxide
2.      
   • 2m NH₃ SUPPLIED WITH A DROPPER
   • 0.5 Ba(No₃)₂ supplied with a dropper.
   • 2M HNO₃ supplied with a dropper
   • KMnO₄/ H⁺ supplied with a dropper
   • K₂Cr₂O₇ supplied with a dropper
   • 10 ml measuring cylinder.
   • Each candidate to have: - solid P NaSO₃
   • Solid K maleic acid
   • Universal indicator.

Marking Scheme

Question One

1. Calculate the average volume of base used to neutralize the excess acid. (1 mk)
   • ( 5.1 + 5.0 + 5.0) = 5.0cm2
            3
2. Determine:
   1. The number of moles of base used. (2 mks)
      1000cm3 → 0.1m 
      5cm3→ x 
      (1.0 x5cm³) = 0.005 mole
      (1000cm3)
   2.          
      1. The volume of the acid that was neutralized by the base. (2 mks)
         • 0.50M → 1000cm³           HCL+NaOH
           NaCl + H₂O
                    2
           0.005 → x
         • (0.005 x1000cm³) = 10.0cm³
                    0.50
           
           
      2. The number of moles of acid that reacted with the carbonate. (2 mks)
         • (30cm³ – 10cm³) = 20cm³
           0.50Mole x 20cm³   =0.1 mole
                 1000 cm³ 
3.                 
   1. Write the equation for the reaction between the acid and carbonate. (1 mk)
      • MCO_3(S) + 2 HCl m → MCl₂ + CO₂ + H₂O
        
        
   2. Determine the number of moles of the carbonate in the sample. (2 mks)
      • mole ratio 1:2
        MCO₃: 2HCl 
        (0.10mole) = 0.005 mole
               2
        
        
   3. Determine the relative formula mass of the carbonate. (2 mks)
      • mass of 0.005 mole = 0.50g
        mass of 1.0 mole =      (0.50g)      =100g
                                       (0.005 mole)
        
        
   4. Determine the relative atomic mass of M. (3 mks)
      • R.F.M (MCO₃) = 100g
        m+12+48 =100g
        R.A.M of M = (100-60)g = 40g)

Question Two
You are provided with solid P. Carry out the tests below and record your observations and inferences.

• Put all solid P in a boiling tube and add about 5cm3 of distilled water. Shake until all solid dissolves.
  1. Place about 2cm3 portion of the solution in a test tube and add aqueous ammonia drop wise until in excess. 
     

     Observation	Inferences
     No white precipitate	K+ Na+ suspected

  2. Dip a clean end of a glass rod into the remaining solution and then place it in the Bunsen burner flame. Note the colour of the flame above the glass rod.
     

     Observation	Inferences
     It burns with a yellow flame	Na+ Present

  3. Place about 2cm portion of the solution in a test tube of barium nitrate solution. Retain this content for the test in (d) below.
     

     Observation	Inferences
     White precipitate is formed	SO42-, CO32-, SO32-

  4. To the content in (c) above add 4 drops of 2M HNO3 following by 2 drops of acidified potassium manganate (vii).
     

     Observation	Inferences
     White ppt dissolves and purple solution is decolorized	SO32- confirmed

Question Three
You are provided with solid K. carry out the tests below and record your observation and inferences in the spaces provided.

1. Scoop a half portion of the solid using a clean metallic spatula and introduce it to a non- luminous flame of Bunsen burner to burn.
   

   Observation	Inferences
   It burns with yellow sooty smocky flame	C= C -c=c- suspected or R-OH, R-C –OH high

2.            
   1. Put the remaining portion of solid K. in a boiling tube and add about 10cm3 of distilled water. Shake and divide the solution into three portions.
      

      Observation	Inferences
      Dissolve forming colourless solution	Polar compound

   2. To the 1^St portion, add about 4 drops of acidified potassium manganite (Vii) solution.
      

      Observation	Inferences
      The solution changes from purple to colourless	C=C, -C= C- R-OH suspected lCOOH

   3. To the 2nd portion, add 3 drops of acidified potassium dichromate (vi) solution.
      

      Observation	Inferences
      The solution changes from orange to green	R – OH Confirm

   4. To the 3rd portion, determine the PH using universal indicator paper.
      

      Observation	Inferences
      PH 4-6	Weak acid or weakly acidic