Testing solutions with indicator paper
A fair test follows steps. A grown-up helps, and everyone wears goggles. First put one blue strip and one red strip side by side on a clean white plate. Second, dip a clean spoon or dropper into the liquid and put one drop on each strip. Third, watch the colours and write the result in a table. Fourth, rinse the spoon with water and dry it before the next liquid, so one liquid never mixes with another. Why do we need two strips? A blue strip stays blue for both neutral and alkaline liquids, and a red strip stays red for both neutral and acidic ones. Together the two strips give a clear answer. If you have no litmus paper, red cabbage water also works as an indicator: a grown-up soaks chopped cabbage in warm tap water and strains it, and it turns pink or red with an acid and blue-green with an alkali.
| Liquid | Blue strip | Red strip | Group |
|---|---|---|---|
| lemon juice | turns red | stays red | acidic |
| soapy water | stays blue | turns blue | alkaline |
| sugar water | stays blue | stays red | neutral |
| Drop added to cabbage water | Colour |
|---|---|
| vinegar | pink |
| soapy water | blue-green |
Home test. With a grown-up, test three liquids from your kitchen with indicator paper or red cabbage water. Draw a table with the liquid, the colour you saw and the group. Rinse the spoon every time. Put the liquids back in a safe place afterwards, and never mix them or taste them.