Yr7 Module 5 lesson 7

Finding the energy in vegetable Oil

Brief

Find out how much energy there is in 100g of vegetable oil.

Safety

Make sure you hair is tied back and that you are wearing safety glasses.

Method

1/ Weigh a spirit burner filled with vegetable oil with the lid on and record this in your results table.

2/ Using a 100cm3 measuring cylinder, measure 100cm3 of tap water and place this into a 250cm3 conical flask.

3/ Clamp the conical flask in a retort stand and measure the starting temperature of the water. Record this in your results table.

4/ Place the spirit burner under the conical flask to leave a 4cm gap between the wick and the bottom of the flask, then light the burner.

5/ Stir the water slowly until the temperature has increased by 50oC above the starting temperature. Then snuff out the spirit burner using the lid, allow to cool the re-weigh the used spirit burner with the lid on. Record this in your results table.

6/ Use the calculation you have been given on your worksheet to find the number of kJ in 100g of vegetable oil.

Results

Mass of spirit burner at start / g
Mass of spirit burner at end / g
Temperature of water at start / oC
Temperature of water at end / oC

Calculations

1/ Find the mass of vegetable oil used.

mass of burner at start - mass of burner at end = mass of oil used

______- ______=

2/ Work out the number of Joules used to heat up the water

mass of water x temp rise x specific heat capacity of water

100g x 50oC x 4.2J.g-1.oC-1 = ______

3/ Work out how many Joules would be transferred if 100g of oil were combusted.

number of joules to heat up water x 100g / mass of oil used = energy in 100g of Oil

______x 100g / ______=

4/ Convert the number of Joules into kJ by dividing your answer by 1000.

______/ 1000 = kJ.100g-1

Evaluation

The label on the bottle of oil states that 100g of vegetable oil has an energy value of 3700kJ. How does your value compare to the nutritional information on the bottle?

Discuss why you think your result was less than the one on the bottle.

·  Was all the heat going into the water?

·  What else was being heated up that you did not include in your calculation

·  How could you improve your method?

Homework

Plot a graph of the following energy values remember to choose the correct type of graph..

Type of oil / kJ.100g-1
Maize Oil / 3700
Olive Oil / 4000
Rape seed Oil / 3800
Diesel Oil / 3500

Q1 Give two reasons why vegetable oil is better than diesel to fuel cars and lorries.