BIOLOGY(PRACTICAL)PAPER 3 -Questions and Answers

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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

                                                                                                     (4 marks)

• Calculate the average volume of solution A used.                 (1 mark)

• Calculate the concentration of B in moles per litre. (RFM of B is 392)                                                                                            (1 mark)

• Calculate the number of moles of iron (II)ions in the 25 cm³ of solution B.                                                                                                 (1 mk)

• 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 1I

                                                                                                         (4 mks)

• Calculate the average volume of solution A used in table II..  (1 mark)

• Calculate the number of moles of manganate (VII) ions in table II above.                                                                                       (1 mk)

• 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)

• Calculate the:
• Formula mass of the dibasic acid, solution C.(H = 1.0, O = 16.0)                                                                  (1 mk)

• Formula mass of X in the dibasic acid C.(1 mk)

• You are provided with solid M. Carry out the tests and write your observations and inferences in the spaces provided.
• Describe the appearance of solid P.                                                     (1 mark)

• 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.

• To the first portion, dip both red and blue litmus paper.

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

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

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

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

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

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

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

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

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

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