1. Environmental Chemistry Lesson # 1
Measuring Solutions

2. Definitions
Solution – a homogeneous mixture of two or more substances.
Solvent – the substance in which substances are dissolved
Solute – the substance(s) being dissolved

3. Concentration
Concentration is the quantity of a given solute in a solution. The more solute, the more concentrated the solution. A solution with little solute is said to be dilute.
Concentration can be expressed as a percent or in moles.
Concentration = Quantity of Solute
Quantity of Solution

4. Percentage Concentration
Percentage concentration means the percentage of solute compared to the total volume of the solution, where the solute can be measured by volume (mL) or weight (g).
Volume by volume is %V/V, and weight by weight is % W/W, and weight by volume is % W/V.
c = vsolute x 100% or c = msolute x 100% or c = msolute x 100%
vsolution msolution vsolution

5. Example 1
A mixture contains 140 mL of pure acetic acid in a 500 mL bottle of solution. What is the percentage by volume concentration of acetic acid?

6. Example 2
A hydrogen peroxide solution contains 3 g of H2O2 in every 100 mL of solution. Calculate the percentage weight by volume concentration of the solution.

7. Example 3
A sterling silver ring has a mass of 12.0 g and contains 11.1 g of pure silver. What is the percentage weight by weight concentration of silver in the metal?

8. Molar Concentration
Molar concentration is the amount of solute, in moles, dissolved in one litre of water.
C = amount of solute (in moles)
amount of solution (in litres)
*Note that C is capitalized to denote a molar quantity, just as molar mass is M, whereas mass is m.

9. Example 4
A stoichiometric calculation produced mol of sodium hydroxide in L of solution. Calculate the molar concentration of sodium hydroxide

10. Example 5
A solution contains 5.85 g of sodium chloride dissolved in 5.00 L of solution. Calculate the molar concentration of sodium chloride.

11. Example 6
In a solution containing 21.2 g sodium carbonate in 1.50 L of solution, calculate the concentration of the solution.

12. Example 7
What mass of potassium hydroxide is required to prepare 600 mL of a solution with a concentration of mol/L?

13. Dilution A concentrated standard solution is called a stock solution.
Adding water to this solvent decreases the concentration to a desired level, and is known as dilution.
For example, hydrochloric acid as a stock solution normally has a concentration of 10 mol/L, whereas what you use in the lab is usually a diluted 1 mol/L solution.
Calculating the new concentration or volume required to make a certain solution is straightforward, as the mass or amount of solute does not change, even with the addition of water.
Concentration is inversely related to the solution’s volume (concentration decreases with increasing volume, and vice versa).
CiVi = CfVf
*Where i is the initial concentration and volume (of the stock solution), and f is the final concentration and volume (of the dilute solution)

14. Example 8
Water is added to L of 2.40 mol/L NH3 (aq) cleaning solution, until the final volume is 1.00 L. Find the molar concentration of the final, diluted solution.

15. Example 9
A student is instructed to dilute some concentrated hydrochloric acid (36%) to make 4.00 L of 10% solution. What volume of hydrochloric acid solution should the student initially measure to do this?