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Why is lemonade fizzy?

Have you ever baked a cake? Eaten an apple and watched it go brown? Seen rust on a car? Lit a fire? Seen a plant grow? If you have, you’ve seen chemical reactions at work, they are around us all the time and while some are pretty safe others can be very dangerous!

Chemical changes happen when two or more substances (reactants) are mixed together causing the materials to change completely. With a chemical reaction the original materials, the reactants, are used up and new materials, called products, are made.

I love lemonade, and other sparkling drinks, nothing quite beats an ice cold fizzy drink on a sunny day. But why is Lemonade fizzy? Such a great question for my Explorers to learn about this week, along with some other activities getting them interacting with simple chemical changes.

One of my favourite kitchen devices is my Soda Stream which pumps water (a liquid) full of carbon dioxide (a gas)- these two substances have a different state of matter and understanding these properties helps us answer the question of why lemonade is fizzy.

It’s all about states of matter

Gases are less dense than liquids, the molecules move freely and spread out to fill the space available, like inside a bottle, but as soon as we open the lid the gas will escape to fill the room. Meanwhile the molecules in a liquid are joined together but flexibly, in a way that allows a liquid to fill a container, like a cup but the molecules won’t spread out beyond the container.

This is important to helping us get to grips with why lemonade is fizzy. Commercial lemonade producers will use gas canisters, like my soda stream uses but on a much larger scale, to pump carbon dioxide into water flavoured with lemons. Once the carbon dioxide gas is trapped inside the water it needs to be quickly sealed in a bottle to stop it from escaping.

Have you ever shaken up a bottle of fizzy drink and then opened it? What happens?

It fizzes everywhere, you can hear the gas escaping and the liquid is taken with it. You can see the bubbles of gas rising through the liquid and popping at the surface. This is because gases are less dense than the liquid it’s trapped in, gases can’t be contained within a liquid once we open the bottle- it wants to escape beyond the container it’s in.

But how do the bubbles get in?

So, that’s how commercially produced lemonade works, so how do you make lemonade at home without a canister of carbon dioxide?

This is where chemical changes come into play, to produce carbon dioxide we can create a simple chemical reaction between an acid (the lemon juice) and a base (the bicarbonate of soda). This reaction is known as a neutralisation reaction, it produces carbon dioxide as a byproduct of the reaction between the two substances. The gas bubbles produced are trapped inside the liquid until they can all rise through the lemonade and escape out of the glass. This gives us a fizzy drink we can enjoy at home really easily.

  • Lemons / lemon juice
  • Sugar
  • Baking Soda
  • Spoon
  • Cup
  • Water
  1. Stir two tablespoons of sugar into a cup of warm water (or boiled water with adult supervision)
  2. Keep stirring until all the sugar has dissolved- you will not be able to see the sugar crystals anymore.
  3. Squeeze the juice from your lemon into a cup
  4. Add some of your sweetened water (taste it to see if you like it!)
  5. Now add ¼ teaspoon of bicarbonate of soda into your cup- watch the fizzing and taste your lemonade!

To begin with you added sugar into warm water, it looked like the sugar crystals had disappeared. In fact, they had just dissolved. Dissolving is where the solute (in this case sugar) is broken down into really small pieces and spreads throughout a solvent (the water). This was a physical change but not a chemical one, we know the sugar is still there because the water tastes sweet.

Lemon juice is an acid and bicarbonate of soda is a base (or alkali). The chemical reaction we create by mixing these two substances is called a neutralisation reaction. It releases lots of carbon dioxide which we see as fizzy bubbles and the new liquid we are left with, the lemonade is PH neutral- it is neither an acid nor a base. We have changed the composition of the mixture, so we know it’s a chemical change.

What happens is we make another glass of lemonade but add ice this time? What happens to the reaction time?

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