# 9.3 Core Practical 13: Investigating Specific Latent Heat

## Core Practical 13: Investigating Specific Latent Heat

#### Aims of the Experiment

• To determine the specific latent heat of ice

#### Variables:

• Independent variable = Energy of the heater (Joulemeter) (J)
• Dependent variable = The temperature, T of the ice/water (°C)
• Control variables:
• Repeat readings with same energy supplied by heater
• Mass of ice in each set up
• Time for experiment in each set up

#### Equipment List

• Resolution of measuring equipment:
• Joulemeter = 1 J
• Electronic balance = 0.1 g
• Thermometer = 0.1 °C

#### Method

1. Set up the experiment and the control
• Attach the funnels to retort stands, place the filter paper inside and add a heater (also on a retort stand) inside one of the funnels - ensure the heater is not touching the funnel

• Use a spoon and an electronic balance to measure out 50 g of crushed ice into a beaker and pour into each funnel
• Add a beaker below each funnel and place on top of an electronic balance
1. Wait until the ice reaches 0 °C.
• This is when it starts to melt and water starts to drip out of both funnels into the beakers below.
• Check the temperature with a thermometer in each funnel
2. Turn on the heater
• Set the heater to supply 10, 000 Joules of energy to the experiment funnel
3. Wait until the reading on the Joulemeter says 10, 000 J
• Turn the heater off
4. Read and record the mass of each beaker of water on each electronic balance
5. Repeat the experiment at least 3 times and calculate the average mass, m for the water in each beaker
• m= average mass of water in beaker A
• mB = average mass of water in beaker B
6. Calculate the mass of the melted ice and convert into kg
• Δm = m- mB
• Mass in g ÷ 1000 = Mass in kg
7. Calculate the specific latent heat of fusion of ice to water using the equation ΔE = LΔm
• ΔE = Energy supplied by the heater = 10 000 J
• L = Specific latent heat of fusion
• Δ= mass of ice

#### Analysis of Results

• The results obtained a latent heat of fusion of 330 000 J
• The actual value of the latent heat of fusion for ice is 334 000 J
• The percentage error in this value is  = 1.2%

#### Evaluating the Experiment

Systematic Errors:

• Make sure you zero the electronic balances when the beakers are empty
• Always check that the ice has reached 0 °C by reading the thermometer at eye level
• This experiment requires accurate determination of energy transfers
• To improve the accuracy, consider applying lagging or insulation to the funnels and beakers - this will reduce the amount of energy lost to the surroundings

Random Errors:

• The heater should be switched off and allowed to cool between readings
• So the rate of heating and the starting temperature of the heater is the same
• Calculate the average mass of the water
• This will reduce random errors in the reading
• Repeat the experiment at least 3 times

#### Safety Considerations

• Ensure no water gets on the electronic balance
• Wipe up any spillages immediately and turn off the balance
• Do not touch the heating element with your fingers, as it could be hot and burn your skin
• Do not handle ice with your bare hands, use a spoon to measure it into the beaker

#### Worked example

A student conducts an experiment to find the latent heat of fusion for ice

They obtain the following table of results:

Calculate the latent heat of fusion.

Step 1: Complete the average mass row in the table

•     The average mass is calculated by adding all 3 masses together and then dividing by 3

Step 2: Calculate the average mass in kg

• Mass in g ÷ 1000 = Mass in kg

Step 3: Calculate the latent heat of fusion

• Calculate the specific latent heat of fusion of ice to water using the equation ΔE = LΔm
• ΔE = Energy supplied by the heater = 10, 000 J
• L = Specific latent heat of fusion
• Δ= mass of ice
• Rearrange the equation
• So, = 340136 J kg-1 = 340 000 J

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