Acid rain

Your pupils may have heard of acid rain. This can damage rivers, lochs, and thereby affect plant and animal life. Atmospheric pollution occurs when gases such as sulphur dioxide and nitrogen oxides are released into the atmosphere. This can be from natural sources, such as volcanoes and rotting vegetation or by human activity, such as industrial processes or the burning of fossil fuels. These gases can dissolve in the water vapour in clouds and fall as very dilute sulphuric and nitric acid rain.

Figure 20 - Looking at the effects of vinegar, lemon juice and water on three samples of chalk.

You can use the following activity to demonstrate the weathering effect of dilute acids on rocks such as limestone (calcium carbonate). Some white blackboard chalk is made of the same material. Coloured and some makes of white chalk are made of calcium sulphate and will not work.

Set up three containers (e.g. plastic cups, Fig. 20). Label each cup, water W, lemon juice L and vinegar V and fill each about a third full of the appropriate liquid. Put a stick of chalk in each one and observe what happens. You should see bubbles forming in the vinegar and lemon juice cups, which shows that there is a chemical reaction taking place. There will be an observable change to the stick of chalk after quite a short time   (Fig. 21). Lemon juice and vinegar, although weak acids, are considerably stronger than acid rain but they will show a speeded up version of what happens to rocks subjected to acid rain over a long period of time.

Figure 21 - Results 
Flushed away