You may use a periodic table, but you may NOT use a calculator. Express all answers as numbers, not words.

*California State Standard: Students know how to calculate the concentration of a solute in terms of grams per liter, molarity, parts per million, and percent composition.*

**Grams per liter** represent the mass of solute divided by the volume of solution, in liters. This measure of concentration is most often used when discussing the solubility of a solid in solution.

**Molarity** describes the concentration of a solution in moles of solute divided by liters of solution. Masses of solute must first be converted to moles using the molar mass of the solute. This is the most widely used unit for concentration when preparing solutions in chemistry and biology. The units of molarity, mol/L, are usually represented by a scripted capital “** M**”.

**Parts per million (ppm)**, is a ratio of parts of solute to one million parts of solution, and is usually applied to very dilute solutions. It is often found in reports of concentration of water contaminants.

To calculate parts per million, divide the mass of the solute by the total mass of the solution. This number is then multiplied by 10^{6} and expressed as parts per million (ppm). In dilute water solutions, we can assume that 1 mL of water-based solution has a mass of 1 gram, so 1 liter of solution has a mass of 1000 grams.

**Percent composition** is the ratio parts of solute to one hundred parts of solution and is expressed as a percent. Determine the mass of solute and solution and then divide the mass of the solute by the total mass of the solution. This number is then multiplied by 100 and expressed as a percent. In dilute water solutions, we can assume that 1 mL of water-based solution has a mass of 1 gram, so 1 liter of solution has a mass of 1000 grams.