1. How to calculate the amount of solute in a solution
15.2 Concentration Units
How to calculate the amount of solute in a solution

2. Molarity (M)
The unit of Molarity is often used and often referred to as molar.
Molarity is the moles of solute per liter of solution.
A 1.0 M NaCl solution has a concentration of 1.0 moles of NaCl per liter of solution.
NOT per liter of water, per liter of solution (both solute and solvent).

3. Mass Percent
A common measurement used in less technical environments is mass %.
Mass percent is the mass of the solute divided by the mass of the solution times one hundred.
A 3% hydrogen peroxide solution is 3 grams of H2O2 per 100 grams of solution.
You often times need to know the density of the solution to calculate this.

4. Parts per Million or Billion
The units of ppm and ppb are used when a solute is in very minute concentrations.
ppm is calculated by dividing mass of solute by mass of solution and multiplying by ppb is the same but multiplying by 109.
If Arsenic is present in our water supply at a concentration of 72 ppm, that means that there are 72 grams of As per 1 million grams of drinking water. Not a lot, but enough to cause problems.