Concentration Concentration of of

SolutionsSolutions

ConcentrationConcentration

• measurementmeasurement that describes that describes

how much solutehow much solute in in given amount of given amount of

solvent or solutionsolvent or solution

• express concentration using many, express concentration using many, many different units many different units – pick the unit according to task at handpick the unit according to task at hand

PercentPercent

• by mass

• by Volume

% = part x 100

whole

Twists in Word Problems

• sometimes ask for part or whole, not percent

• sometimes give volume/mass of solution

• sometimes give volume/mass of solvent and volume/mass of solute

mass solution = mass solute + mass solvent

ppm (parts per million)ppm (parts per million)

• used when solute is present in very small used when solute is present in very small amountsamounts

(Regents board doesn(Regents board doesn’’t follow this rule)t follow this rule)

ppm (parts per million)ppm (parts per million)

ppm = ppm = grams solutegrams solute x 1,000,000 x 1,000,000

•ppm is ratio between mass solute & mass soln

•like % except the whole is 1,000,000 instead of 100

grams solutiongrams solution

About 0.0043 g of O2 can be dissolved in 100 mL of water at 20oC. Express in ppm.

[memorize: 1 mL water has mass of 1 g][memorize: 1 mL water has mass of 1 g]

• ppm = 0.0043g x 1,000,000

100.0043

= 43 ppm

CO2 gas has solubility of 0.0972 g/100 g water at 40oC. Express in parts per million.

ppm = 0.0972 g solute x 1,000,000 100.0972 g solution

= 971 ppm

What is the concentration in ppm of a solution with 30.0 g NaNO3 in 70.0 g water?

ppm = 30.0 g NaNO3 x 1,000,000

100.0 g solution

= 300,000 = 3.0 X 105 ppm

How many grams of KOH are needed to be dissolved in water to make 2000.0 grams of a 10.0 ppm solution?

10 ppm = ? grams KOH X 1,000,000 2000.0 g solution

? = 0.02 grams KOH