Summary: Observe reversible change by melting and solidifying chocolate, and eat your results!
Set-up: 5 mins
Play: 30 minutes initially, with the checking and tasting coming later!
Complexity: Easy, but fun for all ages
- A chocolate bar (or Easter Egg), cooking chocolate, or chocolate drops, a saucepan or microwave, molds (an ice cube tray or a takeaway container will do). Optional extras: mini marshmallows, sprinkles, frozen raspberries, desiccated coconut, food essences such as peppermint.
What to do
Younger children can get stuck into watching the chocolate melt (below). You might preface the activity for older children by asking them: Do you know what reversible change is? Explain some materials can be changed, for example by being melted (a solid becomes liquid) or frozen (a liquid becomes solid). A reversible change is when the material can be returned to its original state, it is a physical change that can be undone. We are going to see this with chocolate.
Melt the chocolate on a very low heat in the saucepan (or in a microwave, although the saucepan enables children to observe the changes occurring). Don’t use too much heat, as there is a danger of burning the chocolate or your child! (If you don’t have a low enough setting, use the microwave please!). Encourage your child to watch and to describe what is happening. When the chocolate is melted, transfer it to another dish and allow your child to stir it and ladle it in a spoon. What words would they use to describe the chocolate now? (smooth, syrupy, drippy etc.) Explain that you have changed the chocolate from solid to liquid, but now you are going to reverse that change. Would your child like to create some mini chocolates in a chocolate mould or an ice cube tray, or would they like to try to create another chocolate bar (a flat rectangle of chocolate can be produced in an empty and clean takeaway container)? Pour the chocolate into your chosen container (note: ask your child could you pour the chocolate before it was melted?). How does your child think we can return the chocolate to its usual solid state? Use the fridge or freezer to re-set the chocolate.
Try re-setting different containers of chocolate in the fridge, in the freezer, and on the kitchen bench. Which does your child think will set first? You might check every hour, and record your results.
Challenge your child to redesign the chocolate before re-setting it. Use the optional extras to create a new flavour of chocolate!
Try a similar reversible change recipe for frozen blueberry yoghurt bark at https://realfood.tesco.com/recipes/frozen-blueberry-yogurt-bark.html. This time you will start with a liquid and freeze it solid. Before eating it, see how it turns back into yoghurt as it melts.
What learning does this activity promote?
Observation, scientific behaviour, predictions, hypothesising, theorising, sensory exploration.
By Dr Vicki Hargraves