5. Energy changes (required practical 4 - temperature changes)

Question 1

What is the practical?

Answer 1

investigating the temperature change in an exothermic reaction

Question 2

What is the independent variable for the practical?

Answer 2

the volume of sodium hydroxide solution

Question 3

What is the dependent variable?

Answer 3

the maximum temperature reached

Question 4

What are the control variables?

Answer 4

• volume of hydrochloric acid
• the concentrations of the HCI and the sodium hydroxide solution

Question 5

What are the steps for the practical?

Answer 5

1. Use a measuring cylinder to measure 30m3 of dilute hydrochloric acid
2. Transfer the acid into a polystyrene cup
3. Stand the polystyrene cup inside a beaker
4. Use a thermometer to measure the temperature of the acid and record this in a table
5. Use a measuring cylinder to measure 5cm3 of sodium hydroxide solution and transfer this into the polystyrene cup
6. Fit a plastic lid into the cup and place a thermometer through the hole in the lid, with the bulb of the thermometer in the solution
7. Use the thermometer to gently stir the solution
8. Look for the temperature rise on the thermometer, as it is an exothermic reaction, then when the reading stops changing record the highest temperature reached
9. Rinse and dry the polystyrene cup
10. repeat experiment again increasing the volume of sodium hydroxide solution by 5cm3 each time until a maximum of 40cm3 is reached
11. Then repeat the whole experiment again so you have 2 sets of results, and then calculate a mean maximum temperature for the volumes of sodium hydroxide
12. Plot a graph of your results

Question 6

Why do we stand the polystyrene cup inside a beaker?

Answer 6

to stop the cup from falling over

Question 7

As the volume of sodium hydroxide solution increases, why does the maximum temperature reached increase?

Answer 7

• when you add more sodium hydroxide particles, they react with hydrochloric acid
• this is an exothermic reaction, so more energy is reached, meaning the temperature increases

Question 8

Why is a maximum temperature reached?

Answer 8

• as you are adding so much sodium hydroxide that there is not enough hydrochloric acid
• so some of the sodium hydroxide cannot react
• so the amount of energy released has reached a maximum

Question 9

At a certain volume of sodium hydroxide solution, why does the maximum temperature start to decrease?

Answer 9

• in each experiment, a greater volume of solution is added
• so the energy released is spread out into a greater volume

Question 10

Why do you use a polystyrene cup with a lid?

Answer 10

• polystyrene is a good thermal insulator so reduces heat loss from the sides and the bottom
• the lid reduces heat loss to the air