Lesson 3: Temperature changes (RP)

Question 1

What is the method for this RP?

Answer 1

1.) Use measuring cylinder to measure 30cm3 of HCl. Put in polystyrene cup.
2.) Stand polystyrene cup in beaker to make it more stable.
3.) Add thermometer
4.) Use measuring cylinder to measure 5cm3 of sodium hydroxide solution. Put in cup.
5.) Put plastic lid on the cup and place thermometer through the hole in the lid.
6.) Use thermometer to gently stir solution
7.) Record maximum temperature reached on thermometer.
8.) Rinse out and dry polystyrene cup.
9.) Repeat experiment at 10cm3 NaOH.
Keep increasing NaOH by 5cm3 until you reach 40cm3.
Repeat whole experiment and calculate a mean.

Question 2

What two substances am I reacting in this experiment?

Answer 2

• Dilute Hydrochloric acid
• Sodium hydroxide solution

Question 3

Why does the maximum temperature reached decrease at a certain volume of sodium hydroxide solution?

Answer 3

• Added too much NaOH, not enough HCl.
• Some NaOH is unable to react
• So the amount of energy released by reaction has already reached its maximum.
• Because we have added more solution, the energy is spread out over a greater volume - so temp decreases.

Question 4

Why do we use a polystyrene cup and plastic lid?

Answer 4

• Want to avoid heat loss.
• Polystyrene = good insulator = reduces heat loss from sides/ bottom.
• Plastic lid: reduces heat loss to the air.

Question 5

What is the control variable in this practical?

Answer 5

• Control variable = volume of hydrochloric acid used.