8.8 Concentration and Consumer Products

Recap: The amount concentration of a solution is the amount of solute per unit volume of solvent: c= n V where the units are mol/L.

Concentration and Consumer Products In general: concentration = quantity of solute quantity of solution NOT solvent

Percent Concentration Percent Concentration: Involves volumes of solutes and solutions, their masses or both volume and mass

a) Percent Volume by Volume (%V/V) Eg. “5% v/v” means “5 mL of solute in 100 mL of sol n ” Commonly used when both solute and solution are liquids

b) Percent Mass by Volume (%W/V) Eg. “5% w/v” means “5 g of solute in 100 mL of sol n ” The term weight on a product label refers to mass

Percent Mass by Mass (%W/W) Eg. “5% w/w” means “5 g of solute in 100 g of sol n ” % W/W is often used for mixtures of solids in liquids or other solids

Extremely Low Concentrations Scientists working in medical or environmental fields often measure concentrations that are extremely low. Instead of using percent concentrations, extremely low concentrations are expressed in ppm, ppb or ppt.

a) Parts per million ppm = parts per million (1 ppm = 1 mg/1L OR 1mg/1kg)

Water Bottle Label

b) Parts per billion ppb = parts per billion [1 ppb = 1 /1000 (1ppm)]

c) Parts per trillion ppt = parts per trillion [1 ppt = 1 /1000 (1ppb)]

Some tips when working with concentration problems: All measured quantities must have the same unit (except for %W/V) The density of an aqueous solution= the density of water  1 mL= 1 g 1 t= 1000 kg; 1 kg= 1000 g; 1 kg= mg; 1 L = 1000 mL (see page 409 for more units)

Homework Read pp. 406 – 411 Answer # p. 411 #