Concentration of Concentration of SolutionsSolutions

ConcentrationConcentration

• A measurement that describes how A measurement that describes how much solute is in a given amount of much solute is in a given amount of solvent or solution.solvent or solution.

• Many, many different units to express Many, many different units to express concentration. Pick the unit by the concentration. Pick the unit by the task at hand.task at hand.

PercentPercent

• By mass

• By Volume

• Part over Whole times 100%.

Twists• Sometimes they ask for the part or the

whole, not the percent.

• Sometimes they give you the volume/mass of the solution; sometimes they give you the volume/mass of the solvent and the volume/mass of the solute.

• Mass solution = Mass solute + Mass solvent

Molarity (M)Molarity (M)

Molarity (M) = Molarity (M) = moles of solutemoles of solute

liters of solutionliters of solution

Movie on Preparing Solutions

Recall the mole map!

# of grams

# of moles

X F.M.X F.M. by F.M.by F.M.

Twists

• Sometimes they give moles of solute; sometimes they give grams of solute. Grams must bemust be converted to moles.

• Sometimes they give mL of solution instead of Liters. Milliliters must bemust be converted to liters.

• Sometimes they ask for the grams or moles of solute or the volume, rather than the molarity.

Rearranging …

Molarity (M) = Molarity (M) = # moles of solute# moles of solute

liters of solutionliters of solution

Liters of solution = Liters of solution = # of moles solute# of moles solute MolarityMolarity

# of moles of solute = Molarity X Liters # of moles of solute = Molarity X Liters

PPM (parts per million)PPM (parts per million)

• PPM = PPM = grams solutegrams solute X 1,000,000 X 1,000,000

• Usually used when the solute is Usually used when the solute is present in very small amounts.present in very small amounts.

• (The Regents don’t follow this rule.)(The Regents don’t follow this rule.)

grams solutiongrams solution

PPM (parts per million)PPM (parts per million)

• PPM = PPM = grams solutegrams solute X 1,000,000 X 1,000,000

• PPM is a ratio between the mass of the solute & the mass of the solution.

• Kind of like % except you multiply by 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.• Remember 1 mL of water has a mass of 1 g.

• PPM = (0.0043g / 100.0043) X 1,000,000.

• PPM = 43 ppm

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

PPM = (0.0972 g / 100.0972 g solution)

X 1,000,000.

PPM = 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 / 100.0 g solution)

X 1,000,000.

PPM = 300,000 = 3.0 X 105

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 / 2000.0 g solution)

X 1,000,000.

Divide both sides by 1,000,000.

1 X 10-5 ppm = (? grams KOH / 2000.0 g soln.)

Multiply both sides by 2000.

0.02 = grams KOH