Ch. 12.3 Concentration of a Solution

• The concentration of a solution is a measure of the amount of solute in a given amount of solvent or solution.

• Chemists commonly use several different ways to quantitatively express the concentration of a solution. These include:

Percent Composition by mass Parts per million / Part per billion Molarity (M) Molality (m)

Percent Composition by Mass• Sometimes the amount of solute present in

the solution is expressed as a percent by mass.

grams of solute

• % Composition = ------------------------- x 100

grams of solution

Remember: solution is the solute and solvent together

Percent Composition Sample Problems

1. What is the percent composition of a solution that contains 115 g NaCl dissolved in 500 g of H2O?

2. How many grams of KMnO4 are needed to make 500 g of a 12.0% KMnO4 solution?

Parts per Million (ppm) andParts per Billion (ppb)

ppm =mass of solute in solution

total mass of solution 106

Parts per Million (ppm)

Parts per Billion (ppb)

ppb =mass of solute in solution

total mass of solution 109

What Do You Think?

• A 900.0 g sample of sea water is found to contain 0.0067 g Zn. Express this concentration in ppm.

Molarity (M)• Molarity (M) is the number of moles of solute

per liter of solution.

moles of solute (mol)

• Molarity (M) = --------------------------------

liters of solution (L)

Video

Molarity Sample Problems

1. What is the molarity of a 0.500 L sample of solution that contains 60.0 g of sodium hydroxide (NaOH)?

2. How many grams of sodium chloride (NaCl) are required to prepare 250.0 mL of a 3.00 M solution?

Molality (m)• Molality is the concentration of a solution expressed

in moles of solute per kilogram of solvent.

moles of solute (mol)

• Molality (m) = -----------------------------------

kilogram of solvent (kg)

Molality Sample Problem

1. A solution was prepared by dissolving 17.1 g of glucose, C6H12O6, in 275 g of water. What is the molality (m) of this solution?

Dilutions

• When preparing dilutions, you use the following equation.

–M1V1=M2V2

• As volume goes up, molarity goes down. You have diluted the solution. As volume goes down, the amount of solute in solution increases in concentration.

• Think of diluting your kool aid.

Dilutions practice

1. If I have 340 mL of a 0.5 M NaBr solution, what will the concentration be if I add 560 mL more water to it?

2. If I dilute 250 mL of 0.10 M lithium acetate solution to a volume of 750 mL, what will the concentration of this solution be?

Wrapping It Up• Reflect on what you have learned concerning the today’s

topic.

• Respond to the following…– What is the most important thing you learned today?– What is one question you would still like answered?– What is a way what you have learned today connects with

what you knew before?