St Mary's C of E (Aided) Primary School, Pulborough

Science - Colour-changing potions

Years 5 and 6 have been enjoying themselves during Science Week - here's a report on their work on acid and alkaline substances:

We chopped a red cabbage into pieces and placed it into a jug, along with some boiling water, then waited ten minutes for the water to cool. Next, we poured the cabbage water through a sieve into another jug. We added cold water and noticed that the liquid was a dark purple. Then we poured the potion into three glasses. We added drops of white vinegar to one glass and watched it turn bright pink! We then stirred some bicarbonate of soda into another glass and saw that it turned blue. The liquids changed colour because of the amount of acid in them. Acidity is measured using the pH scale. Strong acids have a pH of around 1, while strong alkalines (the opposites of acids) have a pH of around 14. Cabbage juice contains anthocyanin, which changes colour if something is an acid or alkaline. Acids such as vinegar turn the cabbage juice pink, while bases such as bicarbonate of soda turn it blue or green.