1. 8.3 The Concentration of Solutions

2. What is Concentration?
Concentration tell us the amount of solute per quantity of solvent.

3. Concentration Units
There are many units of measurement for concentration.
Mass/volume
Mass/mass
Volume/volume
Parts per million
Parts per billions
Molar Concentration
Solubility Concentration

4. 1. Mass/Volume (m/v)
This quantity gives the mass of the solute dissolved in a volume of solution expressed as a percent.
Mass/volume Percent = Mass of solute (g) x 100%
Volume of Solution (mL)

5. Example
A pharmacist adds 2.00 mL of distilled water to 4.00 g of a powder drug. The final volume of the solution is 3.00 mL. What is the concentration of the drug in g/100mL of solution. What is the (m/v) of the solution?
% m/v = Mass of solute (g) x 100%
Volume of Solution (mL)
= 4.00 g / 3.00 mL X 100%
= 133%

6. 2. Mass/mass (m/m)
Gives the mass of solute dissolved in a mass of solution and is expressed as a percent.
This is used for alloys, example stainless steel
Fe (78%), Cr (15%), Ni (7%)
Mass/mass Percent = Mass of solute (g) x 100%
Mass of Solution (g)

7. Example
Calcium chloride, CaCl2 can be used instead of road salt to melt ice. A student collected a sample g sample of slush and allowed it to melt. The residue that was left had a mass of 4.58 g (assume its only CaCl2). What is the mass/mass percentage of calcium chloride in the slush?
X g = g
100 g g
X = 19.5 g or 19.5 % CaCl2

8. 3. Volume/volume (v/v)
When mixing 2 liquids together to form a solution, it is easier to measure their volumes rather than their masses.
Volume/volume %= Volume of solute (mL) x 100%
Volume of Solution (mL)

9. Example
Rubbing alcohol is commonly used as an antiseptic for small cuts. It is sold as 70% v/v solution of isopropyl alcohol in water. What is the volume of isopropyl alcohol used to make 500 mL of rubbing alcohol?
v/v %= Volume of solute (mL) x 100%
Volume of Solution (mL)
70 % = Volume of solute (mL) x 100%
500 mL
Volume of solute (mL) = 70% 500mL = 350 mL is needed
100%

10. 4. Parts per million (ppm) and 5. Parts per billion (ppb)
The concentration of a very small quantity of a substance in the human body or the environment is usually expressing in ppm (or ppb, next slide)

11. ppm Calculations Or ppm = Mass of solute x 106 Mass of Solution
Mass of solute = x (g)
Mass of Solution g of solution

12. ppb Calculations ppb = Mass of solute x 109 Mass of Solution Or
Mass of solute = x (g)
Mass of Solution g of solution

13. 6. Molar Concentration The most useful and widely used in chemistry
Molar concentration is the number of moles of solute that can dissolve in 1L of solution

14. Is this a molar solution?
Ouch!!

15. Completing the Bermuda Triangle