Stir salt into water. The salt dissolves. Now you have a solution. It looks the same all the way through.

Oil and vinegar are not like that. They do not stay mixed. They split into two layers.

Sometimes mixing makes something new. Bubbles of gas can be a sign of that. You can see the bubbles.

Not every change needs a mix. Iron turns to rust in air and water.

Vinegar has an acid. Baking soda is a base. Mix them and they react. They bubble up with gas.

Cooks use this in cake batter. Baking soda reacts with a sour thing, like lemon juice. The batter rises. Bread rises because of gas bubbles inside it, too.

Baking powder is baking soda with a dry acid. Add water and it fizzes.

Red cabbage juice shows one color in an acid. It shows a different color in a base.

The juice can change color when you add something. That makes it an indicator.

Try it with a grown-up. Add a little vinegar to some red cabbage juice. Watch to see the color. Does it change? Write down what you see.

Words to know

• solution: an even mix
• react: change together
• batter: cake mix
• indicator: a color clue