Mix It Up!
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flagWhat you'll discover
- arrow_forwardPredict whether something will dissolve, float, sink or spread before you add it
- arrow_forwardExplain why salt seems to vanish in water but sand never does
- arrow_forwardShow that oil always floats on top of water
- arrow_forwardUse stirring to speed up dissolving and diffusion
Four things can happen
When you add something to water, only a few things can happen. It can dissolve and seem to disappear, like salt or sugar. It can float on top, like oil. It can sink to the bottom, like sand. Or it can slowly spread out, like a drop of food colouring.
Scientists call spreading out diffusion. Try every ingredient in the beaker and watch which of the four things happens!
Where does the salt go?
Salt does not really disappear — it just breaks into pieces far too small to see. Water particles surround each tiny piece of salt and carry it away into the liquid. That is what dissolving means.
Here is the proof it is still there: taste sea water (yuck, salty!) or let salty water dry in the sun. The water leaves, and the salt comes back as white crystals. Nothing was lost!
Sand is stubborn
Sand never dissolves, no matter how hard you stir. Its particles hold on to each other too tightly for water to pull them apart. So sand just sinks to the bottom and sits there.
A mixture like sand in water is easy to separate again — you can pour it through a filter or just wait for the sand to settle. A dissolved mixture like salt water is much trickier!
Stirring is a speed boost
Stirring does not make impossible things happen — it only makes possible things happen faster. Salt dissolves quicker when you stir because fresh water keeps rushing past each salt grain. Food colouring spreads in seconds instead of minutes.
But stir sand all day and it still will not dissolve. Stirring is a speed boost, not a magic wand!