2.43 describe experiments to investigate the effect of light on net gas exchange from a leaf, using hydrogen-carbonate indicator

Experiment

Hydro-carbonate indicator:

Normal CO2 = Orange

Increased CO2 = Yellow

Decreased CO2 = Purple

1. Take 4 test tubes and put add the same volume of hydro-carbonate indicator to each of them
2. Then take 3 similar sized leaves, roll them up and trap the leaf stem with the bung so they're sitting above the indicator
3. Wrap aluminium around 1, baking paper and leave the 3rd. 
4. Place them in bright light and leave them for an hour. Then check the colour of the indicator

The 4th tube is the control. If the indicator changes in that one there is something wrong with the experiment.

2.32 describe an experiment to investigate the energy content in a food sample.

Finding the amount of energy in food

This is also called calorimetry.

Experiment

1. Obtain a dry food sample that will burn easily
2. Weigh the food and skewer it on a needle
3. Add 25cm3 of water to a boiling tube
4. Measure the temperature of the water
5. Light a bunsen away from the water
6. Put the food in the bunsen burner and then place the lit food under the test tube. 
7. Once the foods gone out relight it and repeat this until the food will not light again.
8. Measure the final temperature of the water

Calculations:

To find the energy in Joules:

Energy in Food (J) = Mass of Water (g) x Temperature Change (C) x 4.2

• The mass of the water is the same as the volume (1g of water = 1cm3 of water)
• The 4.2 is the Specific Heat Capacity of Water. You will have learnt about this in Chemistry but it just is the amount of energy needed to raise 1g of water by 1 degree.

To find the energy per gram:

Energy per gram (J/g) = Energy in food (J) / Mass of food (g)

NB - This means you can compare food stuffs fairly.

To increase the accuracy

• Insulate the boiling tube with foil to reduce heat loss would improve accuracy
• Use a calorimeter will improve the accuracy of your results.