Required Practical 4: Temperature Changes

Question 1

How do we investigate the variables that affect temperature changes in chemical reactions?

Answer 1

1) We start by using a measuring cylinder to measure 30cm³ of dilute hydrochloric acid.
2) We then transfer the acid into a polystyrene cup.
3) Now we stand the polystyrene cup inside a beaker so it doesn’t fall over.
4) Next we use a thermometer to measure the temperature of the acid and we record this in a table.
5) Now we use a measuring cylinder to measure 5cm³ of sodium hydroxide solution and we transfer this to the polystyrene cup.
6) At tis point we fit a plastic lid to the cup and place the thermometer through the hole in the lid and the bulb of the thermometer must be in the solution.
7) Stir the solution with the thermometer gently. Since the reaction is exothermic, it releases energy meaning the temperature of the solution will increase.
8) Record the highest temperature reached.
9) We now rinse out and dry the polystyrene cup.
10) We repeat the whole experiment using 10cm³ of sodium hydroxide solution.
11) Carry out the experiment several more times and each time we increase the volume of sodium hydroxide solution by 5cm³ until we reach a maximum of 40cm³.
12) At this point, we repeat the whole experiment one more time so that we have two sets of results and now calculate a mean and plot a graph.

Question 2

Why do we use a polystyrene cup with a lid?

Answer 2

Because its a good thermal insulator and reduces heat loss through the sides and the bottom and the lid reduces heat to the air.