1. Solution Concentrations

2. Ways of expressing concentration
Fingers of whiskey
Teaspoons of sugar
Molarity
Grams per L [dm3]
% (W/V) [weight per volume]
% (V/V) [volume per volume]
% (W/W) [weight per weight]
ppm (mg L-1) [Parts Per Million]

3. Molarity Moles are a chemists measure Moles per Litre i.e mol L-1
A 1 molar (1M) solution contains 1 mole of solute in 1 litre of solution.

4. Making a 1 molar [1M] solution
Weigh out 1 mole of solute and dissolve it in some deionised water.
Transfer the solution to a volumetric flask [with washings]
Make up the solution to the one litre mark with deionised water.
Long narrow neck makes it accurate
Must mix it to make it homogeneous

5. We rarely make up a litre of solution [school is too mean to spend the money]
500 cm3 or 250 cm3 is much more usual
Rarely make up 1 Molar solution
might be 0.1 M or 0.02 M etc.
Some examples

6. Problems What is the molarity of these solutions?
8 g NaOH in 200 cm3 of solution
5 g KMnO4 in 600 cm3 of solution
18 g K2Cr2O7 in 400 cm3 of solution
20 g HNO3 in 100 cm3 of solution
25 g CuSO4.5H2O in 50 cm3 of solution.

7. Grams per litre [dm3] Less scientific
grams of solute per litre of solution
Concentration = Molarity * Molar Mass

8. Example What is the concentration of 0.2 M NaCl?
0.2 mole = 0.2 of 58.5
= 11.7 g L-1
Conc. = Molarity * RMM

9. Problems
What is the concentration of the following solutions in grams per L ?
0.1 M NaOH
0.5 M H2SO4
0.05 M KMnO4
10 M NH4OH
2.5 M HNO3

10. Percentage weight / volume
% (W/V)
Grams of solute per 100 cm3 of solution.
E.g. what is the % (W/V) of 0.1 M NaOH
0.1 M NaOH = 0.1 of 40g per litre
= 4 g per litre
= 4 g per 1000 cm3
= 0.4 g per 100 cm3 = 0.4 % (W/V)

11. Percentage volume / volume
% (V/V)
Volume of solute per 100 cm3 of solution
10% (V/V)
10 cm3 Orange juice /100 cm3 solution
Whiskey 40% (V/V)
40 cm3 Ethanol in 100 cm3 whiskey

12. How much alcohol?? Beer = 4% - Pint = 600 ml
Wine = 12% - Glass = 140 ml
Whisky = 40 % - Shot = 50 ml
Volume of alcohol
Beer = 4 * 6.0 = 24 ml
Wine = 12 * 1.4 = 17 ml
Whisky = 4 * 5.0 = 20 ml

13. Percentage weight per weight
% (W/W)
Grams of solute per 100 g of solution.
When a powdered solid is dissolved in a powdered solid.
Not common
Self raising flour - Flour and baking soda
Sensodyne 5%(W/W) KNO3

14. Parts per Million - ppm Measuring very dilute solutions
e.g. pesticide residues in water or hardness
mg per litre [milligrams per litre]
a litre of water contains 1000g which is milligrams
So it tells us how many milligrams of solute there are in a million milligrams of solution

15. Problem
A solution contains g of calcium carbonate in 500 cm3. What is its hardness in p.p.m.?
0.035g is mg
35 mg in cm3
70 mg in 1000 cm3
= 70 ppm.