In chemistry, knowing which substances are "acids," and which are "bases," is key. Setting molecular science aside, acids and bases are best thought of as opposites of each other, and the two kinds of substances can "neutralize" one another, rendering such dangerous substances as hydrochloric acid meek as a lamb. But beware! Both acids and bases can cause dangerous chemical burns if not neutralized, so knowing which is which is imperative!
So, how to test for acids and bases? Chemists use "indicators" to test whether a substance is an acid or a base. Indicators work by turning a distinctive colour in the presence of an acid or a base. In this activity you and your child can make your own indicator from red cabbage, which contains a chemical that turns from its natural deep purple colour to bright red in acids and greenish in bases.