Chemistry Paper 3 WASSCE (PC), 2016

Question 1

 

D was prepared by diluting 35.0 cm3 of saturated solution of sodium trioxocarbonate ( IV ) at 250 C to 1 dm3.

Solution E is 0.0905 moldm-3 trioxonitrate ( V ) acid.

Titration of 20.0 cm3 portions of D with E using methyl orange as indicator gave the following results:

  1. (i) Copy and complete the table.
    (ii) Calculate the average volume of E used.
    Equation of reaction:
  2. From the information provided, calculate the;
    (i) concentration of D in moldm-3;
    (ii) solubility of Na2CO3 in D moldm-3 at 250C;
    (iii) volume of the saturated solution that should be evaporated to yield 25g of Na2CO3;
    (iv) mass of CO2 released when 1 dm3 of the saturated solution reacted.
    [ Na = 23.0; C = 12.0; O = 16.0; H = 1.0; N = 14.0 ] [21 marks]

Observation

 

It was a popular question among the candidates. Majority of them were familiar with the question. In part ( a ), few candidates could not subtract the initial reading from the final reading on the titration table. In part ( b ), majority of the candidates performed very well, but few of them could not determine the mole ratio.

The expected answers include:


  1. (i)

    (ii)
    (iii)
    (iv)