How Much Will Dissolve?
- Chemistry
- Ages 8–11 · Grades 3–5
- Hands-on experiment
What you’ll find out
- Dissolving spreads a substance through a liquid; it does not destroy it.
- There is a limit to how much will dissolve, and warmth raises it.
- Evaporating the liquid brings the dissolved substance back.
No sign-up and no real names. In the lesson you check your understanding as you read, run the experiment yourself, and practise until it sticks.
Water gets full
Stir a spoon of sugar into a glass of water and it seems to vanish. Stir in another, and that goes too. Keep adding spoonfuls and eventually something changes: the sugar stops disappearing and starts settling on the bottom instead. The water is full. Scientists call this saturated. Every liquid has a limit like this, and the limit is different for different substances — water takes far more sugar than it takes salt.
Warm water takes more
Now try the same thing with warm water instead of cold. The warm water takes noticeably more sugar before it fills up. This is why sugar disappears so quickly into hot tea, and why a glass of iced drink often has undissolved sugar sitting at the bottom. The heat has not changed the sugar in any way. It has made the water better at holding it.
Getting it back again
Here is the part that matters most. The sugar never went away. Leave a dish of sweet water somewhere warm and the water slowly evaporates into the air. The sugar cannot do that, so it is left behind in the dish, and you can see it and taste it again. This is exactly how sea salt is made: shallow pools of sea water are left in the sun, the water leaves, and the salt stays.
Curriculum links: NGSS 5-PS1-1 · NGSS 5-PS1-4