Required Practical: Investigating Temperature Changes

Section 1 of 7Aim and variables

Aim

• Aim To find how the temperature change in a neutralisation depends on the volume of alkali added to a fixed volume of acid.

Variables

• Variables Independent: volume of sodium hydroxide solution.
• Dependentmaximum temperature reached.
• Controlvolume and concentration of acid, concentration of alkali, starting temperature, same cup and lid.

Prediction

• Prediction The temperature should rise as more alkali is added, reach a peak at the volume that neutralises the acid,
  • then fall as extra cold alkali only dilutes the mixture.

Section 2 of 7Method

1

Stand a polystyrene cup inside a beaker for support and insulation.

2

Measure 25 cm³ of 2 mol/dm³ hydrochloric acid with a measuring cylinder and pour it into the cup.

3

Record the temperature of the acid.

4

Add 5 cm³ of 2 mol/dm³ sodium hydroxide, fit the lid, and stir gently with the thermometer.

5

Record the highest temperature reached.

6

Repeat with fresh acid, adding 10, 15, 20 up to 40 cm³ of alkali each time.

7

Repeat the whole experiment and calculate mean maximum temperatures.

Section 3 of 7Processing the data

Step	Action
Temperature change	Final maximum temperature − starting temperature
Mean	Add the repeat values and divide by the number of repeats; ignore anomalies
Graph	Plot volume of alkali (x-axis) against temperature change or maximum temperature (y-axis)
Lines of best fit	Draw two straight lines, one through the rising points and one through the falling points
Neutralisation point	Read off the volume at which the lines meet

Section 4 of 7Improving reliability and accuracy

Sources of error

Heat loss

• Heat loss Heat escapes to the air; use an insulated cup, a lid and stir gently.

Measuring volumes

• Measuring volumes Use a burette or pipette in place of a measuring cylinder for better precision.

Starting temperature

• Starting temperature Make sure both solutions are at the same starting temperature.

Repeats

• Repeats Take repeats and calculate a mean to spot anomalies.

Section 5 of 7Safety

1Eye protection

• Eye protection Wear goggles throughout.

2Corrosive alkali

• Corrosive alkali 2 mol/dm³ sodium hydroxide can burn skin; wash splashes immediately.

3Acid

• Acid Hydrochloric acid is an irritant.

4Stable cup

• Stable cup Keep the cup in a beaker so it does not tip.

Section 6 of 7Key terms

Term	Meaning
Calorimeter	An insulated container used to measure energy changes in a reaction.
Exothermic	Releasing energy to the surroundings.
Neutralisation point	The volume of alkali that exactly reacts with the acid.
Anomaly	A result that does not fit the pattern of the other data.
Mean	The average of repeated measurements.

Section 7 of 7Exam technique

1

Using the first temperature reading instead of the maximum.

2

Joining the points with a single curve instead of two straight lines to find the peak.

3

Using a metal beaker as the only container, which loses heat quickly.

4

Not stirring, which gives uneven temperature readings.