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## Example : Weight Ratio Percentage Concentration Calculation

**Question 1.** 10 g of sodium chloride is dissolved in 90 g of water.

Calculate the weight ratio percentage concentration of the solution.
**Solution:**

- Identify the solute and solvent making up the solution:

solute: sodium chloride

solvent: water

- Identify the weights (masses) of solute and solvent and convert to the same units if necessary:

mass solute (sodium chloride) = 10 g

mass solvent (water) = 90 g

- Calculate the weight ratio:

weight ratio = mass solute ÷ mass solvent

weight ratio = 10 ÷ 90 = 0.11

- Calculate the weight ratio percentage:

weight ratio percentage = weight ratio × 100

weight ratio percentage concentration = 0.11 × 100 = 11%

**Question 2.** 250 mg of sodium carbonate is dissolved in 5 g of water.

Calculate the weight ratio percentage concentration of the solution.

**Solution:**

- Identify the solute and solvent making up the solution:

solute: sodium carbonate

solvent: water

- Identify the masses of solute and solvent and convert to the same units if necessary:

mass solute (sodium carbonate) = 250 mg

Convert mass in milligrams (mg) to a mass in grams (g):

mass solute (sodium carbonate)= 250 ÷ 1000 = 0.250 g
mass solvent (water) = 5 g

- Calculate the weight ratio:

weight ratio = mass solute ÷ mass solvent

weight ratio = 0.250 ÷ 5 = 0.05

- Calculate the weight ratio percentage:

weight ratio percentage = weight ratio × 100

weight ratio percentage concentration = 0.05 × 100 = 5%

## Example : Mass of Solute or Solvent Calculation

**Question 1.** An aqueous sucrose solution contains 200 g water and has a weight ratio percentage concentration of 4.2%.

What is the mass of sucrose in grams?

**Solution:**

- Identify the solute and solvent making up the solution:

solute: sucrose

solvent: water

- Identify the known quantities:

mass solute (sucrose) = ? g

mass solvent (water) = 200 g

weight ratio percentage = 4.2%

- Convert the weight ratio percentage to a weight ratio by dividing by 100 :
Weight Ratio Percentage concentration |
= |
weight ratio |
× 100 |

*Weight Ratio Percentage concentration* 100 |
= |
weight ratio |

weight ratio = 4.2 ÷ 100 = 0.042

- Re-arrange the weight ratio equation to find the mass of solute:

weight ratio = mass solute ÷ mass solvent

mass solute = weight ratio × mass solvent

- Substitute in the values and solve:

mass solute = 0.042 × 200 = 8.4 g

**Question 2.** An aqueous potassium chloride solution with a weight ratio percentage concentration of 7.5% contains 312 mg of potassium chloride.

What mass of water in grams is present?

**Solution:**

- Identify the solute and solvent making up the solution:

solute: potassium chloride

solvent: water

- Identify the known quantities:

mass solute (sucrose) = 312 mg

Convert mass in milligrams (mg) to a mass in grams (g)

mass solute (sucrose)= 312 ÷ 1000 = 0.312 g
mass solvent (water) = ? g

weight ratio percentage = 7.5%

- Convert the weight ratio percentage to a weight ratio by dividing by 100 :
Weight Ratio Percentage concentration |
= |
weight ratio |
× 100 |

*Weight Ratio Percentage concentration* 100 |
= |
weight ratio |

weight ratio = 7.5 ÷ 100 = 0.075
- Re-arrange the weight ratio equation to find the mass of solvent:

weight ratio = mass solute ÷ mass solvent

mass solvent = mass solute ÷ weight ratio

- Substitute in the values and solve:

mass solvent = 0.312 ÷ 0.075 = 4.16 g