Calculating Percent by Mass/Volume

The concentration of a solution can be expressed as a percent – the ratio of solute to solution. This calculation is commonly performed based on the mass of a substance (m/m) or on the volume of substances (v/v). A solution that is composed of 5 g of salt for every 95 g of water will have a mass percent of 5%.

5 g NaCl5 g+95 g solution

x 100=5.0%

Example: A solution made from 35 mL of ethanol and 65 mL of water will have a percent by volume?

% by volume = volume of solute

volume of solution x 100 =

35 mL of solute65 mL+35 mL solution

x 100 = 35%

1. What is the percent by mass of 5.0 g of iron (II) sulfate dissolved in 75.0 g of water?

2. A solution is made by adding 25 mL of benzene to 80 mL of toluene. What is the

percent by volume of benzene?

3. A solution is formed by adding 35 g of ammonium nitrate to 250 g of water. What is the percent by mass of ammonium nitrate?

4. What is the percent by volume of a solution formed by mixing 25 mL of isopropanol

with 45 mL of water?

5. What is the mass percent of each component in the mixture formed by adding 12 g of calcium sulfate, 18 g of sodium nitrate, and 25 g of potassium chloride to 500 g of water?

6. A solution is made by dissolving 125 g of sodium chloride in 1.5 kg of water. What is the

percent by mass?

7. What is the percent by volume of a solution formed by added 15 L of acetone to 28 L of water?

8. An experiment requires a solution that is 80% methyl alcohol by volume. What volume

of methyl alcohol should be added to 200 mL of water to make this solution?

Useful Equations:

Percent by Mass= mass of solute

mass of solution x100

Percent by Volume=volume of solute

volume of solution x 100

Solution = Solute + Solvent

1000 mL = 1 L and 1000 g = 1 kg

Calculating Percent by Mass/Volume

Solutions are comprised of two parts – the solute and the solvent. The solute is the substance that gets dissolved, and is present in a smaller amount. The solvent is the substance that does the dissolving and is present in a greater amount. A solution that has a lot of solute per solvent is described as concentrated, while a solution with a small amount of solute is called dilute. The concentration of a solution is commonly given a number value by dividing the moles of the solute by the liters of the solution. This measurement is known as the molarity of a solution and it has units of mol/L or M. To find the molarity of a solution, you must know the moles of solute and the liters of solution. Recall the grams can be converted to moles using the molar mass. Also remember that the volumes in milliliters can be converted to liters.

1. A solution has a volume of 2500 mL. How many liters is this? 2. Convert 50 g of calcium carbonate, CaCO3, into moles. 3. A solution contains 0.42 moles of solute in 0.75 L. Calculate the molarity of the solution. 4. What is the molarity of a solution that contains 15.0 g of NaOH per 500.0 mL of

solution? 5. A 250.0 mL solution contains 4.6 g of copper (II) chloride, CuCl2. Find the molarity of this

solution. 6. How many moles of hydrochloric acid, HCl, are present in 0.085 L of a 3.0 M solution? 7. A 37.5 mL solution contains 0.181 g of potassium chromate, K2CrO4. What is the

molarity? 8. What is the molarity of a solution that contains 0.85 g of ammonium nitrate, NH4NO3,

dissolved in a solution with volume 100.0 mL? 9. Calculate the mass of lead (II) nitrate, Pb(NO3)2, necessary to make 50.0 mL of a 0.100

M solution. 10. What volume of a 0.35 M solution of sodium chloride could be formed with 25 g of

NaCl?

Useful Equations:

Molarity = mol of soluteL of solution

1 L = 1000 mL