THE UNITED REPUBLIC OF TANZANIA

PRESIDENT’S OFFICE REGIONAL ADMINISTRATION AND LOCAL GOVERMENT

IRINGA DISTRICT COUNCIL

FORM IV PRE-MOCK EXAMINATION MAY 2021

032 CHEMISTRY 2A

TIME; 2:30HOURS (ACTUAL PRACTICAL A)

 

 

INSTRUCTIONS:

  1. This paper consists of two questions.

  1. Answer all questions.
  2. Qualitative Analysis Guidance Pamphlets may be used after a thorough check by the supervisor.
  3. Each question carries 25 marks
  4. Cellular phones and any authorised materials are not allowed in the examination room.
  5. Write your Examination number on every page of your answer booklet(s)
  6. You may use the following constant:

Atomic masses:

H=1, C=12, O=16, K=39, S=32

1litre=1dm3=1000cm3

 

 

  1. You are provided with the following solutions:

    U: 0.05M sulphuric acid solution.

    T: Containing 1.4g of metal hydroxide (YOH) dissolved in 250cm3 of the solution.

    M.O: Methyl orange.

    Procedures:

  2. Put solution U into the burette, pipette 25cm3 or 20cm3 of solution T into titration flask. Put two to three drops of methyl orange into the titration flask. Titrate solution U from the burette against solution T in the titration flask until colour change is observed. Note the burette readings. Repeat the procedures to obtain three more readings in a tabular form.

     

     

 

QUESTIONS:

  1. (i)…………cm3 of T required ………….cm3 of U for complete reaction.

    (ii)The colour change at end point was from…………………to …………………….

  2. (i)Write a balanced chemical and ionic equation for the reaction between solution U and T.

    (ii)State a reason to why methyl orange indicator is used.

    (iii)State which solution is titrant and analyate?

  3. Calculate the concentration of solution T in,

    (i) mol/dm3 (ii) g/dm3

  4. Calculate

    (i) The molar mass of metal hydroxide YOH

    (ii) The atomic mass of Y

    (iii) Name element Y

  5. Mention two application of volumetric analysis in medicine.

     

     

     

     

     

     

  6. You are provided with the following:

    A: Containing 1M sodium thiosulphate (Na2S2O4)

    B: Containing 0.1M Nitric acid (HNO3)

    C: Distilled water,

    Piece of paper

    Stop-watch

     

     

    Procedures

    1. Using measuring cylinder measure 5cm3 of solution A and put 100cm3 beaker.
    2. Measure 5cm3 of solution B and put into 100cm3beaker containing solution A and immediately start the stop- watch.
    3. Swirl the contents in the 100cm3 beaker and put the beaker on the top of mark X on piece of the ‘paper. Watch the mixture from the above and observe changes.
    4. Switch off the stop –watch when the mark X disappears.
    5. Record the time taken for the later X to disappear.
    6. Repeat procedures (i) to (v) using the data shown in Table 1.

       

     

     

     

    Table1

Experiment

Volume of B cm3

Volume of A cm3

Volume of Distilled water cm3

Time (s)

1

5

5

0

 

2

5

4

1

 

3

5

3

2

 

4

5

2

3

 

 

 

 

QUESTIONS.

 

  1. What is the aim of the whole experiment?
  2. Complete Table1
  3. With state symbols, write the balanced chemical for the reaction between A and B.
  4. Which the substance was produced during the reaction which obscured letter X?
  5. Why did the cross X disappear?
  6. Write two main allotropes and two uses of the product which obscured the cross X
  7. Plot the graph of volume of A ( Na2S2O3) solution against time (s)

 

 

 

 

 


 

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