Question

How can understanding change of state help you to seprate a salt water solution

Answer 1

Because if you wanted to separate the salt from the solution, you will have to know the boiling point of the water. Since one way is to evaporate water from salt, which means you boil the water and leave all the salt behind, you have a solid left, which is the salt. You had to know that water can be evaporated because it is a liquid.

The three states of matter are:
-Solid
-Liquid
-Gas
There is one more that doesn't appear often, Plasma
 

Answer 2

Answer: You can apply the fact that water changes from liquid to gas when heated to its boiling point.

Explanation:

Salt solution contains salt dissolved in water. The water can be separated from the salt by evaporation of the solution to dryness. This exploits the fact that water changes from liquid to gas at it's boiling point. This is an example of change of state. When heated strongly, all the water present will be converted to vapour and the solid salt reappears.