How do we express the concentration of a solute in a solution? We use Mass Percentage.
Mass Percentage is one of the way of representing the concentration of a solute in a solution. Mass percentage is calculated as the mass of a solvent divided by the total mass of the solution, multiplied by .
So it is easy to find out the formula:
A beer contains alcohol. So, the mass percentage of alcohol in the beer is:
Some other notes:
The mass percentage does not change with the temperature and air pressure.
There are other ways to express the concentration of a solute in a solution such as volume percentage, molality and amount-of substance concentration.
Some reference books express mass percentage as . However, try not to use that to prevent a confusion with Solubility.
Now, there is an example:
I want to dilute a , to a solution. How much water should I add in grams to do this?
is the mass of solution.
is the mass percentage before adding water.
is the mass percentage after adding water.
Note that the mass of does not change before and after the water added.
So, let the fixed mass of be and the mass of water should add be
Before adding water,
After adding water,
Compare the two equations we have,
So, the amount of water we should add is .