Metals, bases, certain metal hydroxides and certain metal carbonates, are insoluble in water.
You add the base/carbonate/metal to the warm acid until no more will dissolve and you have some of the insoluble solute left over – this is called an ‘excess’.
For metals and metal carbonates, an additional sign that the reaction has stopped is that the reaction stops fizzing. You filter the mixture to remove the excess base/carbonate/metal to obtain the pure salt solution.
The pure solution can drip through the filter paper into the beaker below, leaving the insoluble solids behind.
To obtain the pure salt from the solution, we need to remove some of the water. The method used is called evaporation.
We can evaporate some of the water by using a Bunsen burner (as shown below).
Another way to evaporate some of the water is by placing the solution near a radiator/window ledge. This will evaporate the water much more slowly and will result in larger crystals.
Warm the salt solution to evaporate some of the water. You get larger crystals if you evaporate the water slowly.
Obtaining the salt from the solution