KCSE Chemistry Q & A - MODEL 1998.PP2.QN.5

24/10/2020

KCSE Chemistry 1998 Topical Questions and Answers

All Questions Featuring Chemistry Form 1, Form 2, Form 3, Form 4, Paper 1, Paper 2 and Paper 3

In order to determine the molar of neutralization of sodium hydroxide, 100cm³ of 1M sodium hydroxide and 100cm³ of 1 M hydrochloric acid both at the same initial temperature were mixed and stirred continuously with a thermometer. The thermometer of the resulting solution was recorded after every 30 seconds until the highest temperature of the solution was attained.

Thereafter the temperature of the solution was recorded for a further two minutes

(a)

(i) Why was it necessary to stir the mixture of the two minutes
(ii) Write an ionic equation for the reaction which took place
(iii) The sketch below was obtained when the temperature of the mixture were plotted against time. Study and answer the questions that follow.

In order to determine the molar of neutralization of sodium hydroxide

I. What is the significance of point Y2?

II. Explain why there is a temperature change between points;

Y1 and Y2

Y3 and Y4

(iv) In the initial temperature for both solutions was 24.5⁰C and the highest temperature attained by the mixture was 30.9⁰C

Calculate the:

I. heat change for the reaction (specific heat capacity of the solution = 4.2Jg -1K-1 and the density of the solution = 1.0g/cm³

II. Molar heat of neutralization of sodium hydroxide

(v) Explain how the value of the molar heat of neutralization obtained in this experiment would compare with the one that would be obtained if the experiment was repeated using 100cm³ of 1 Methanoic acid instead of hydrochloric acid.

(b) On the grid provided below, draw an energy level diagram for the reaction between hydrochloric acid and sodium hydroxide

Expected Response