Solution Concentration• A measure of how much solute is dissolved

in a specific amount of solvent or solution.

• Described qualitatively using “dilute” and “concentrated”

• Can be calculated quantitatively by mass (molarity) or by volume (molality)

• Can also be expressed as a percent – either percent by mass or percent by volume

Solution Concentration

• If the solute is a solid being dissolved in a liquid, usually use molarity or % by mass

• If the solute is a liquid being dissolved in a liquid, usually use molality or % by volume

Percent Concentration•Percents are a ratio of the amount of solute over the total amount of solution times 100%•The amount can be measured in mass or volume but both measurements must be the same unit

Try It

• A salt water aquarium must maintain a sodium chloride solution similar to ocean water which is 3.6 g NaCl per 100.0 g of water. What is the % by mass of NaCl in the solution?

3.6 / (3.6 + 100.0) X 100%

= 3.5%

Try It

• Isopropyl rubbing alochol is usually 70% alcohol and 30% water. If you have 750 ml of rubbing alcohol, how much is isopropyl alcohol and how much is water?

.70 x 750 ml = 525 ml of alcohol

.30 x 750 ml = 225 ml of water

Molarity

• One of the most common ways to describe concentration quantitatively

• Also called molar concentration

• Abbreviated with a capital M (yes, just like Molar Mass)

• Calculated by dividing the moles of solute by the liters of solution

• Label is moles per liter or M

Try It

• You have a 100 ml sample of an aqueous solution that contains .085 moles of KCl. What is it’s molarity?

100 ml x 1l / 1000 ml = .100 L

.085 molKCl / .100 L = .85 mol/L or .85M

Preparing a Molar Solution

• How many grams of sucrose (C12H22O11) is needed to prepare one liter of a 1.50 M solution?

• You’ll need the molar mass of sucrose:

1.5 mol 342 g_____________ X ___________ = 513 g / liter 1 liter 1 mol

Preparing a Molar Solution• How many grams of sucrose (C12H22O11) is

needed to prepare 100 mL of a 1.50 M solution?

1.5 mol 342 g_____________ X ___________ = 513 g / liter 1 liter 1 mol

1 L 513 g

100 mL X __________ X _____________ = 51.3 g

1000 mL 1 L