If the solute you’re using is a liquid, then you can also calculate the mass using the density formula, where density D = m/V, where m is the mass of the liquid and V is the volume. To find the mass, multiply the density of the liquid by the volume.

If you aren’t measuring the volume yourself, you may need to convert the mass of the solute into volume using the density formula. For example, if you’re finding the concentration of 3. 45 grams of salt in 2 liters of water, you would find the volume of salt using the density formula. Look up the density of salt either in a textbook or online and solve the formula for m. In this case, the density of salt is 2. 16 g/mL. The formula would read 2. 16 g/mL = (3. 45 g)/V. Multiply each side by V to get V(2. 16 g/mL) = 3. 45 g. Then divide the each side by 2. 16 to find the volume, or V = (3. 45 g)/(2. 16 g/mL) = 1. 60 mL. Add the volume of the solute to the volume of your solvent, ma. So in this example, 2 L + 1. 6 mL = 2,000 mL + 1. 6 mL = 2,001. 6 mL. You can either leave the measurement in milliliters or convert it back to liters to get 2. 002 L.

In our example for the concentration of 3. 45 grams of salt in 2 liters of water, your equation would be C = (3. 45 g)/(2. 002 L) = 1. 723 g/L. Certain problems may ask for your concentration in specific units. Be sure to convert the units before putting them in your final formula.

If your solute is a liquid, you may need to calculate the mass using the formula D = m/V, where D is the liquid’s density, m is the mass, and V is the volume. Look up the density of the liquid in a textbook or online and then solve the equation for the mass.

For example, if you want to find the concentration of 10 g of cocoa powder mixed with 1. 2 L of water, you would find the mass of the water using the density formula. The density of water is 1,000 g/L, so your equation would read 1,000 g/L = m/(1. 2 L). Multiply each side by 1. 2 L to solve the mass in grams, so m = (1. 2 L)(1,000 g/L) = 1,200 g. Add the mass of the cocoa powder to get 1,210 g.

In our example, C = (10 g)/(1,210 g) = 0. 00826.

In this example, the percent concentration is (0. 00826)(100) = 0. 826%.

In our example, the ppm = (0. 00826)(1,000,000) = 8,260 ppm.

For example, if your solute is potassium hydroxide (KOH), find the atomic masses for potassium, oxygen, and hydrogen and add them together. In this case molar mass = 39 +16 + 1 = 56 g/mol. Molarity is used mainly in chemistry when you know the chemical makeup of the solute you’re using.

For example, if you want to find the number of moles in 25 g of potassium hydroxide (KOH), then the equation is mol = (25 g)/(56 g/mol) = 0. 45 mol Convert the mass of your solute to grams if it isn’t already listed in grams. Moles are used to represent the number of atoms in the solution.

In this example, if you’re using 400 mL of water, then divide it by 1,000 to convert it to liters, which is 0. 4 L. If your solvent is already listed in liters, then you can skip this step.

In this example, M = (0. 45 mol)/(0. 4 L) = 1. 125 M.