Reaction of vinegar with bicarbonate of soda

Bicarbonate of soda (or baking soda) is a chemical called sodium bicarbonate. Vinegar contains acetic acid.
Last week
we tested these two chemicals with red cabbage indicator, and found that a solution of bicarbonate of soda was alkaline, but vinegar was acidic.

This week we made another solution of sodium bicarbonate with some indicator - it was blue just like before. But when we added a few drops of vinegar, the solution turned purple - neutral! The vinegar had reacted with the sodium bicarbonate and neutralised it.

We did an experiment to find out more about what happens when the acetic acid in vinegar reacts with sodium bicarbonate.

Vinegar, bicarb, bottle and balloon

Our experiment

We used:

  • A small plastic bottle
  • A balloon
  • Some sodium bicarbonate (1 or 2 teaspoons)
  • Some white vinegar (50ml or 100ml)
  • A cardboard cone

We all wore safety glasses to make sure nothing could splash in our eyes.

filling the balloon
  1. We put the cardboard cone in the neck of the balloon and tipped the sodium bicarbonate carefully through the cone into the balloon.
    The first group used 1 teaspoon of sodium bicarbonate, the second group used 2 teaspoons of sodium bicarbonate.
  2. We poured vinegar into the bottle. The first group used 50ml of vinegar, the second group used 100ml of vinegar.
  3. Very carefully we stretched the mouth of the balloon right over the mouth of the bottle, being careful not to spill any of the sodium bicarbonate into the bottle.
  4. Then we lifted the balloon completely upright so that the sodium bicarbonate inside the balloon poured into the vinegar.


What happened?

The sodium bicarbonate and vinegar fizzed and we saw lots of bubbles. We could see that a reaction was happening. Then the balloon blew up! The bottle felt really cold around the mixture. After a while the mixture stopped fizzing and the balloon stopped expanding.

The second group used double the amount of sodium bicarbonate and double the amount of vinegar, and their balloon blew up more.



When sodium bicarbonate and vinegar mix, they react with each other and one of the things that is made is carbon dioxide gas. The reaction needs heat to make it happen, so it takes heat from its surroundings, leaving the bottle feeling cold.

The gas couldn't escape because it was trapped by the balloon. As more and more gas was made, the balloon blew up. Carbon dioxide gas kept on being produced until there was no vinegar or bicarbonate of soda left to react.

As we had captured the carbon dioxide inside the balloon, we could see how much space it took up.
The gas took up much more space than the vinegar and sodium bicarbonate did!

The group who used twice as much sodium bicarbonate and vinegar made twice as much gas, so their balloon blew up to twice the volume.

What is carbon dioxide?

Carbon dioxide is a gas that is found in the air. You cannot see it or smell it. When you add an acid to a carbonate, carbon dioxide is produced.

Composition of air

Carbon dioxide is not poisonous - it is the gas that is used to make the 'fizz' in lemonade and cola. People breathe carbon dioxide out.
All the people on earth are breathing it out all the time... BUT only a tiny fraction - just or 0.04% - of the air around you is carbon dioxide! This is mainly because plants and algae use it up in photosynthesis.

The picture on the right shows that most of the air is made up of two other gases - nitrogen and oxygen.


Making a volcano

At the end of this week's Science Club we made a volcano erupt!


Our volcano was built out of playdough around a small bottle. In the bottle was a little warm water, a teaspoon of sodium bicarbonate, a few drops of food colouring, and a few drops of washing up liquid.

When we poured vinegar into the top, the volcano erupted and lots of lava came out! It was great fun but rather messy!

More science to try at home

You can make your own volcano at home exactly as described above. You will need a small bottle, one with a fairly narrow neck works best. If you do this inside, make sure you build your volcano on a large tray, or in a sink, or over several sheets of newspaper! The food colouring, water and dishwashing liquid are optional, they just make the volcano look a bit more impressive. You can experiment with the quantities of volcano ingredients to see what makes the best eruption.

You could use a cardboard cone or some sand to build a volcano shape around your bottle, but why not make your own playdough? This is a brilliant easy playdough recipe (especially if you have little brothers or sisters - it will keep them entertained for ages).

Recipe for 'no-cook' playdough:

  • 150g salt
  • 125g plain flour
  • 2 tsp cream of tartar
  • 1 tbsp cooking oil
  • 230ml boiling water
  • Food colouring

Mix together the salt, flour and cream of tartar in a large bowl, stir in the cooking oil.

Get an adult to add 230ml of boiling water and give the mixture a good stir. It will be very hot! Once it has cooled down a bit, knead the dough well until it has a nice consistency.

Add some food colouring and knead it in carefully - this can make beautiful patterns, but be warned food colouring can stain fingers!

If you store the playdough in a sealed bag in the fridge it should keep for ages.