# How much water should be evaporated from 20 L of a 20% salt solution to increase it to a 25% salt solution?

##### 1 Answer

#### Explanation:

The idea here is that you're dealing with a *mass by volume* solution, presumably, which means that you get **for every**

In this particular case, your solution will contain a total of

#20 color(red)(cancel(color(black)("L solution"))) * (10^3color(red)(cancel(color(black)("mL"))))/(1color(red)(cancel(color(black)("L solution")))) * "20 g salt"/(100color(red)(cancel(color(black)("mL solution"))))#

# = " 4,000 g salt"#

Now, you can **increase** the concentration of this solution by *removing* some of the solvent, i.e. by evaporating some of the water.

The amount of salt present in the solution **does not change**, which means that you can use the target concentration to figure out what is the *final volume* of the solution

#"4,000" color(red)(cancel(color(black)("kg salt"))) * (100 color(red)(cancel(color(black)("mL solution"))))/(25 color(red)(cancel(color(black)("g salt")))) * "1 L"/(10^3color(red)(cancel(color(black)("mL"))))#

#= " 16 L solution"#

Therefore, you can make this target solution by evaporating a total of

#color(green)(bar(ul(|color(white)(a/a)color(black)(V_"evaporated" = "20 L" - "16 L" = "4 L")color(white)(a/a)|)))#