For hundred’s of years farmers have worked at the top of the Black Mountain to remove the grey rock that can be found there.

When the rock is loose they then burn it in a kiln at an extremely high temperature.

But why did farmers need this grey stone so much?

Limestone

Limestone was burnt in the kilns to make quicklime. Quicklime was spread on fields and water was added to make slaked lime. Spreading lime on the fields helped to neutralise acidic soil to that crops would grow better.

Slaked lime is an alkaline.

Many household items are either acids or alkalis too but are not hazardous.

Some acids and alkalis are stronger and must be handled with care. The strength of an acid or alkali is measured on the pH scale. Neutral chemicals are pH 7, those measuring less than 7 are acid, whilst those measuring more than 7 (up to 14) are alkaline.

Adding an acid to and alkaline (and vice versa) will neutralise it. Did you know that the liquid in your stomach is an acid. The acid in your stomach helps you digest your food.

The pH Scale

What did you observe?

1. What colour did the litmus paper/solution turn?

2. What is the pH number of the item?

3. Is the item acid, alkaline or neutral?

Hydrochloric acid is used in the stomach to help _______. If we eat too many “rich” foods our stomachs create too much ____ – this is called ______. This acid needs to be neutralised by taking indigestion tablets.

Soil is naturally acidic, mainly due to acid ____. This can have bad effects on ____ and vegetable growth, so the excess acid may need to be neutralised with an _____ or suitable fertiliser.

Fill in the blanksWrite the following into your books and fill in the blanks using the words in red

plant, digestion, indigestion, alkali, rain, acid