1. Solutions A solution is formed when a substance is dissolved in a liquid. The concentration of the solution may be expressed as – grams per Litre g L -1 – as a percentage % (g per 100mL) – Moles per litre mol L -1 You need to be able to convert from one to another

2. Concentration by mass Concentration by mass is represented by grams per litre (g L -1 ) it is calculated by dividing the mass of the solute by the volume of the solute

3. If I make up Raro using 100g of powder in 500mL of water, what is the concentration m = 100g V = 0.5L c = ? c = m/V =100g/0.5L = 200gL -1

4. Percentage solutions A percentage solution states how many grams of solute is in 100mL of solution. They may be measured as -weight/weight (w/w) g per 100grams -weight/volume (w/v) g per 100mL -volume/volume (v/v) mL per 100mL

5. What mass of NaCl is required to make up 50ml of a 2% solution? A 2% solution has 2g/100ml or 20gL -1 c = 20g L -1 V = 50mL or 0.05L m = ? m = cV =20 x 0.05 =1g is required in 50ml to make a 2% solution

6. Concentration in moles per litre Chemists usually need to know the amount in mols of a substance that is in a solution. This is measured in mol L -1 A 1mol L -1 solution of CuSO 4 contains 1 mol of CuSO 4 per litre

7. Converting Sometimes concentrations are given in g 100mL -1 To convert to g L -1 multiply by 10 to convert from kg to g multiply by 1000 or 10 3 To convert from mL to L divide by 1000 or multiply by 1/1000