Required Practical 4 - Temperature Changes

Question 1

How could you investigate the temperature change when different volumes of NaOH are added to HCl?

Answer 1

• Measure 25cm3 of HCl into a polystyrene cup
• Measure the starting temperature of HCl
• Add 5cm3 of NaOH to the cup
• Then stir the mixture and measure the maximum temperature reached. Record it in a table
• Repeat the experiment with increasing volumes of NaOH:
  10cm^3, 15cm^3, 20cm^3…

Question 2

Why might calculated energy values be different to a databook?

Answer 2

Energy gets lost to the surroundings

Question 3

If a reaction is exothermic, will the thermometer record an increase or decrease in temperature?

Answer 3

The thermometer will record an increase in temperature as energy will have been transferred to the surroundings

Question 4

How could you reduce the amount of heat energy lost to the surroundings?

Answer 4

• Mix the reactants in a polystyrene cup
• Place the polystyrene cup in a beaker of cotton wool
• Lid on the cup to reduce energy lost by evaporation

Question 5

When investigating the temperature change between two chemicals, why should the chemicals both start at the same temperature?

Answer 5

They need to be the same temperature so that their individual temperatures do not have an effect on the temperature recorded once combined

Question 6

How could you ensure that two reactants in separate test tubes were the same starting temperature?

Answer 6

• Place the test tubes in a water bath at 25°C.
• Use a thermometer to ensure the reactants are the same temperature.

Question 7

Why is it important to stir the mixture when taking a temperature reading?

Answer 7

• To ensure the temperature measured is consistent throughout the mixture.
• To ensure the reactants have fully reacted.

Question 8

Initially, a solution is 25oC. Another reactant is added and the temperature decreases. Is this reaction endothermic or exothermic?

Answer 8

Endothermic

Question 9

How could the temperature be measured more precisely and more reliably?

Answer 9

• More precise: Use a digital thermometer
• More reliable: Repeat the experiment and calculate a mean temperature measurement

Question 10

How could you test the effect of acid concentration on the energy released in a neutralisation reaction?

Answer 10

• Place both reactants in a water bath so they are the same temperature.
  Record the initial temperature.
• Add the alkali to the acid and record the final temperature
• Calculate the temperature change
• Repeat the process using different concentrations of acid
• Record the results for each concentration in a table

Question 11

What must be controlled when testing the effect of acid concentration in a neutralisation reaction?

Answer 11

• Alkali concentration
• Alkali volume
• Acid volume
• Initial temperatures of each reactant
• External temperatures

Question 12

How do you know when a reaction is complete?

Answer 12

Mass of reaction mixture/ volume of gas/ colour remains the same