You might recognise the drinks in the images (hot chocolate, fizzy drinks and tea) but how much do they know about them? Hot chocolate powder is a mixture of different ingredients, including powdered cocoa and sugar. The materials in the mixture have not changed, they are just mixed together. The powder is added to water or milk to make hot chocolate. The sugar dissolves in water but the powdered cocoa, a mixture of substances, just spread through the water.
Fizzy drinks, such as cola, are made by dissolving a gas (carbon dioxide) in liquid water. Substances such as sugar, salt, flavourings and colourings are also dissolved in the water. While the drink is kept under pressure inside a bottle or can, the carbon dioxide stays dissolved. As soon as the drink is opened, the dissolved carbon dioxide begins to come out of solution and change back into gas. Bubbles of gas rise to the surface and escape. These bubbles also form in our mouths and travel up into our noses, producing the different sensations of a fizzy drink. Eventually, all the gas comes out of the solution and the drink goes flat.
Tea is made by adding tea leaves to water. Different substances in the tea leaves dissolve into the water. A tea bag or strainer helps us to separate the tea leaves from the tea.
The Big Question
Does hot chocolate have to be hot?
Planning your investingation and think like a scientist. How will you find out if hot chocolate has to be made with hot water?
Work with your parent to answer a big question. Tweet or post your video to share your results and what you think. What do you already know or think you know about why hot chocolate is always ‘hot’?
Discuss with your parent the different ways you can approach the question. To help you, break down the question, here are some prompts:
How will you and your parent explore the question? Explain your ideas, justify them with what you already know and refine them based on views expressed by other people. What is your plan for the investigation? Here are some tips:
Imagine you had to present your investigation at school assembly or to your family, how would you show your action plan? Plan the various ways this could work. Why not try out your investigation? If you intend to carry out a taste test as part of their investigation, work in a food preparation area rather than a science area.
Hot chocolate powder is a mixture of different ingredients, including powdered cocoa and sugar. Cocoa powder is a bitter substance left over after cocao butter is extracted from roasted cacao beans.
It’s the sugar in the mixture that makes hot chocolate taste sweet. The sugar dissolves in water because it is soluble. Heat can make things dissolve more quickly. The amount of a substance that can be dissolved also increases with the temperature of the water but there is a limit to how much of a substance (solute) can dissolve in a liquid. When the maximum amount of a solute is dissolved in the liquid, we say the solution is saturated. You'll notice that you've reached saturation when sugar no longer dissolves and remains as crystals. (Tip: if you're experimenting with dissolving sugar in class use demerara so the children can see it really easily).
The powdered cocoa in the hot chocolate mixture does not completely dissolve because it is a mixture of soluble substances and insoluble particles. As the hot chocolate is stirred, the insoluble particles spread through the water to form a suspension. If the hot chocolate is left for a while, most of these particles will sink to the bottom of the container. That's why you often find a sludgy bit a the bottom of your mug of hot chocolate after drinking it.