9.3 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

1. • 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
2. 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
3. Turn on the heater
   • Set the heater to supply 10, 000 Joules of energy to the experiment funnel
4. Wait until the reading on the Joulemeter says 10, 000 J
   • Turn the heater off
5. Read and record the mass of each beaker of water on each electronic balance
6. Repeat the experiment at least 3 times and calculate the average mass, m for the water in each beaker 
   • m_A = average mass of water in beaker A
   • m_B = average mass of water in beaker B
7. Calculate the mass of the melted ice and convert into kg
   • Δm = m_A - m_B
   • Mass in g ÷ 1000 = Mass in kg
8. 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
   • Δm = mass of ice

Sample Results Table:

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

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
    • Δm = mass of ice
    • Rearrange the equation
    • So, = 340136 J kg^-1 = 340 000 J