1. Chemistry 20 - Chapter 5 Solutions 5.3 Concentration of a Solution

2. Concentration is defined as the quantity of solute per volume of solution is defined as the quantity of solute per volume of solution quantity of solute can be communicated as a mass, as a quantity in moles, or sometimes as a volume quantity of solute can be communicated as a mass, as a quantity in moles, or sometimes as a volume many ways of communicating concentration many ways of communicating concentration

3. Concentrations using mass ppm (parts per million or 1 drop in a full bathtub) = mg/L ppm (parts per million or 1 drop in a full bathtub) = mg/L ppb (parts per billion or 1 drop in a full swimming pool) = mg/kL ppb (parts per billion or 1 drop in a full swimming pool) = mg/kL %W/V = g/100 mL %W/V = g/100 mL mass per litre = g/L mass per litre = g/L

4. Concentrations using moles molar concentration = mol/L molar concentration = mol/L this is by far the most common way of expressing concentration of solutions in chemistry courses this is by far the most common way of expressing concentration of solutions in chemistry courses

5. Concentrations using volumes % by volume = mL of solute per 100 mL of solution % by volume = mL of solute per 100 mL of solution eg. 5% acetic acid (by volume) means that there are 5 mL of acetic acid for every 100 mL of solution eg. 5% acetic acid (by volume) means that there are 5 mL of acetic acid for every 100 mL of solution can also be measured in L of solute/100L of solution can also be measured in L of solute/100L of solution

6. Calculations for concentrations using mass use: C=m/v for concentrations using mass use: C=m/v for molar concentrations use: for molar concentrations use:C=n/v for concentrations using volume use: C=v (solute) /v (solution) for concentrations using volume use: C=v (solute) /v (solution)

7. Dilution the process of decreasing the concentration of a solution by adding more solvent. the process of decreasing the concentration of a solution by adding more solvent. eg. making orange juice from frozen concentrate eg. making orange juice from frozen concentrate during a dilution the volume increases and the concentration decreases during a dilution the volume increases and the concentration decreases

8. Dilution Problems four variables: four variables: C 1, v 1, C 2, v 2 C 1, v 1, C 2, v 2 use the formula: use the formula: C 1 v 1 =C 2 v 2

9. Example What volume of concentrated hydrochloric acid is required to prepare 1.0 L of 6.0 mol/L HCl (aq) ?

10. Example C 1 =11.6 mol/L (from data sheet) v 1 = ??? C 2 = 6.0 mol/L v 2 = 1.0 L

11. Solution

12. Concentration of Ions to calculate the concentration of an ion: to calculate the concentration of an ion: –first write a dissociation equation –set up a ratio between the coefficient of the reactant and the concentration of the reactant and the coefficient of the cation and the conc. of the anion

13. Example Calculate the concentration of the cations and anions in a 0.25 mol/L solution of Na 3 PO 4(aq).

14. Example Na 3 PO 4(aq) ---> 3Na + (aq) + PO 4 -3 (aq) 0.25 mol/L 0.75 mol/L 0.25 mol/L

15. Communicating H + ion Conc. acids turn blue litmus red acids turn blue litmus red acids have low pH’s (below 7) acids have low pH’s (below 7) bases turn red litmus blue bases turn red litmus blue bases have high pH’s (above 7) bases have high pH’s (above 7) a pH of 7 is neutral a pH of 7 is neutral pH = -log [H + ] pH = -log [H + ] eg. pH 7 = 1.00x10 -7 mol/L eg. pH 7 = 1.00x10 -7 mol/L

16. Assignment Read pages 203-214 Read pages 203-214 Do # 1-3 on pg 205 Do # 1-3 on pg 205 Do #4-6 on page 206 Do #4-6 on page 206 Do #7-12 on page 208 (By end of class) Do #7-12 on page 208 (By end of class) Do #13-16 on page 210 Do #13-16 on page 210 Do #17-19 on page 212 Do #17-19 on page 212 Section Review page 214 Section Review page 214