Science Club – PH, Acids and Bases

PH: Acids and Alkalis.

Arrival Craft:

Paper volcanos.
Very simple craft. We stuck tissue paper into toilet rolls to make them look like erupting volcanoes.



Start steeping red cabbage.

There are lots of different ways to describe how one thing is different from another.

Apple juice and water are both liquids, but what makes them different?

Apple juice and Vinegar are both brown liquids, but what makes them different?

One of the differences that chemists talk about is PH, that means whether something is acidic or alkaline. Do you know anything that’s acidic? Do you know anything that’s alkaline?

An easy way to test is by using universal indicator paper, it goes different colours depending on the PH of whatever it touches. Colour in your PH table.

Acid or Alkali Guessing Game. Acid comes from the Latin for sour and alkalis taste bitter (you shouldn’t taste everything to find out what it is, though!) Have a selection of liquids, ask the children to guess what colour they will make our universal indicator paper. We used milk, vinegar, bleach, apple juice and coke.


Individual Task:

When we put an acid and an alkaline together they react.

That’s why bath bombs fizz! Baking Soda is alkaline and Citric Acid is acidic, when they dissolve in the water, they mix and fizz.

Children can add a small spoon of cornflour and a small spoon of citric acid to two small spoons of baking soda, then add a flavouring and mix it together with a small spoon of almond oil.


Gather Together for the Conclusion:

Try and remember which was the acid in your bath bomb and which was the base.

Does anyone know the chemical name for water? Look at the molymod kit.

This is what happened: acids ‘donate’ or let loose a hydrogen ion in water, bases ‘donate’ an OH ion. These make water together, and a salt, and carbon dioxide.

I gave the children circles of paper and pegs so they could copy what I was doing with the molymod kit. Lego would work equally well.

Who’s heard of carbon dioxide before? It’s something we breathe out, isn’t it? At room temperature it’s a gas, that’s why we see bubbles when we put our bath bomb in water, the gas is escaping from the liquid.

The strength of the reaction depends on the strength of the acid and the base.

If we want to make a volcano display, which acid should we mix with the baking soda?

Volcano experiment.


Active Science: Act out the neutralisation of Hydrochloric Acid and Sodium Hydroxide.


Optional Extensions:

  • Make red cabbage ph indicator, all you need to do is steep red cabbage in boiling water, then retest our chemicals to see how easy it is to read.
  • Guess what water will be after we dissolve one of our bath bombs in it. Try and see if we were right.


I gave the children some universal indicator paper to take home, because it’s fun to test the pH of various things around the house.


3 thoughts on “Science Club – PH, Acids and Bases

  1. Pingback: Christmas Crafts | frogotter's Blog

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