Answer to Selected Topics 2012

Q17

Procedure

1.Measure [20 -200] cm3 of sodium hydroxide [0.1-2.0] mol dm-3 solution.

2.Pour the solution into a polystyrene cup.

3.Record the initial temperature of the solution.

4.Measure [20 – 200] cm3 of hydrochloric acid [0.1 – 2.0] mol dm-3.

5.Pour the solution into another polystyrene cup.

6.Record the initial temperature of the solution

7.Pour hydrochloric acid into sodium hydroxide solution.

8.Stir the mixture.

Record the highest temperature reached.                (7 marks)

Working

•Initial temperature of hydrochloric acid = T1

•Initial temperature of sodium hydroxide = T2

•Average initial temperature =  = Ta

•Highest temperature = Tb

•Heat given out = 200 x 4.2 x (Tb  - Ta) = x J                  1 mark

•Heat of neutralization =  -x/0.1 /1000    kJ mol-1                                 

                                      or         -x/0.1     J mol-1                  1mark