Solution Stoichiometry Topic 8.3

Expressing Concentration

• a solution can be described as concentrated or dilute .

• concentration is a ratio of the quantity of solute to the quantity of solution

• most calculations that involve solutions require quantitative of concentration.

• thus a solution with a concentration of 50 g per litre of solution is more dilute than a solution with 52 g of the same solute per litre of solution

Calculating Percent Concentrations

There are three common methods for expressing percent concentration:• mass/volume percent, or percent (m/v)• mass percent, or percent (m/m)• volume percent, or percent (v/v)

Mass/Volume Percent

Expresses the mass of solute dissolved in a volume of solution as a percent:

Percent(m/v) = mass of solute [in grams] X 100% mass of solution [in millilitres]

Read pgs 371 -373 of text (MHR chemistry 11) and look at worked examples and practice problems

Mass Percent

Expressed as a percent ratio of the mass of the solute to the mass of the solution:

Percent(m/m) = mass of solute X 100% mass of solution

Read pgs 374 -376 of text (MHR chemistry 11) and look at worked examples and practice problems

Very Small Concentrations

Expressed in terms of parts per million or parts per billion:Both are fractions with the mass of solute divided by mass of the solution

ppm = mass of solute ppb= mass of solute

Read pgs 374 -376 of text (MHR chemistry 11) and look at worked examples and practice problems

mass of solutionX 106

mass of solutionX 109

Solutions

Concentration is expressed in terms of the mass or amount of solute dissolved in 1 dm3 of solution

g/dm3 or mol/dm3

• Molarity is a term used to express concentration. The units of molarity are moles per liter (It is abbreviated as a capital M)

mL 1000

moles

Liter

moles M = mol/dm3

gram/dm3 or g/dm3

Practice Problems