Following our free-style potions session, this week we played with dissolving solids in water. Our focus this time was on exploring rather than scientific accuracy – I wanted the kids’ imaginations and curiosity to be sparked.

Set up

* bowls containing a variety of solids, including instant coffee, gravy granules, salt, caster sugar, sand, flour, sprinkles (two types) and gummy bears (guaranteed to elicit interest)

* large jug of hot water

* large jug of cold water

* glass jars & glasses

* teaspoons

I also printed off a chart for C(9) and J(8) to record their results if they wanted to.

What we did

Before I gave them the chart, I invited the children to use their senses to guess what each of the substances was. The gravy granules evoked a lot of interest here, the smell reminding them of their favourite snacks. (I wonder if they’ll be more excited next time I serve gravy.)

We talked about the scientific method and I suggested that before they added each substance to water, they make a guess which they needn’t share out loud as to whether or not it would dissolve. (The secret hypothesis is a safeguard against my perfectionist child melting down mid-experiment.)

They then took turns putting a teaspoon of each substance into water (first cold then hot), observing, stirring and then recording their results.

Highlights

* The sprinkles were interesting. First they lost their colour, turning the water cloudy. Then after a few minutes they dissolved. C(9) guessed that the colouring was very soluble, and that the sprinkles were made of sugar so also dissolved, but more slowly.

* They loved watching the coffee granules dissolve rapidly in the hot water.

* The gummy bears prompted a couple of spin-off experiments of their own. Firstly the children noticed that they gave off little flecks in the hot water. Then they observed that after being in water for a while, they lost the colour around their edges and expanded slightly, so it was decided to leave them overnight. (I put them in the fridge, anticipating a future taste-test request.) More on this in a separate post.

* They liked watching the gravy vortex created by rapid stirring.

What we might do differently next time

* Both children added every substance to both hot and cold water, which involved a lot of me running around washing out jars. Next time I would suggest they take turns doing the hot or cold water. Or have more jars.

* More importantly, while I was busy washing up jars, the children decided salt wasn’t soluble! They hadn’t given it enough time to dissolve. We repeated this part of the experiment later and talked about how we don’t see and feel bits of salt around us when we swim in the sea!

* I might provide a measuring beaker and spoon, so they could use the same amounts of solid and water each time. We could time how long the solids take to dissolve in hot water compared with cold.

The science

When a solid dissolves, it breaks into tiny pieces, so small that you can’t see them in the water. We call the mixture of solid and water a “solution”. Solutions may be coloured (like coffee), but they are always transparent.

We also talked about how hot water molecules move more quickly so come into contact with solid particles more often, which is why solids dissolve more quickly in hot water than cold.

What next?

Over our next few “potions” session we’ll be experimenting with ways of separating mixtures and solutions.