SOLUTION CONCENTRATION: MASS PERCENT, MOLALITY AND MOLE FRACTION14.2: 480 - 488

MAIN IDEA

Concentration can be expressed in terms of percent or in terms of moles

METHODS FOR SHOWING CONCENTRATION

1. Molarity2. Percent by mass3. Percent by Volume4. Molality5. Mole Fractions

PERCENT SOLUTION

Two percentage methods to show how concentrated a solution is: Percent by volume = volume of solute x 100%

volume of solution Percent by (m/v) = mass of solute x 100%

solution volume(mL)

PERCENT SOLUTION

Examples: If 10. mL of pure acetone is diluted with water to

a total solution volume of 200. mL, what is the percent by volume of the acetone solution?

Percent by volume = volume of solute x 100% volume of solution

Percent by volume = 10 x 100% = 50.% 200

PERCENT SOLUTION

Examples:Calculate the grams of solute needed to make 250.

mL of a 0.10% MgSO4 solution.

Percent by (m/v) = mass of solute x 100% volume of solution (mL)

= 0.10%= ___?__ x 100% 250mL

? = 0.25g MgSO4

MOLALITY

Another way to express solution concentration is Molality (m)

solvent kg 1

solute of moles )(molality m

EXAMPLESEXAMPLES

How many grams of sodium fluoride are How many grams of sodium fluoride are needed to prepare a 0.40needed to prepare a 0.40mm NaF solution that NaF solution that contains 750.0g of water?contains 750.0g of water?

solvent kg 1

solute of moles )(molality m

EXAMPLESEXAMPLES

Calculate the molality of a solution prepared Calculate the molality of a solution prepared by dissolving 10.0g of NaCl in 600.g of water.by dissolving 10.0g of NaCl in 600.g of water.

solvent kg 1

solute of moles )(molality m

m = 0.290 m

MOLE FRACTION

Solution concentration can also be expressed by using the mole fraction

BA

AA nn

nX

Mole Fraction

Mol solute

Total moles in solution

EXAMPLESEXAMPLES

What is the mole fraction of each component in a What is the mole fraction of each component in a solution made by mixing 1.25 mol ethylene glycol solution made by mixing 1.25 mol ethylene glycol and 4.00 mol water?and 4.00 mol water?

EXAMPLES

What is the mole fraction of each component in a solution made by mixing 300.g of ethanol (C2H5OH) and 500.g water?

Moles of ethanol = 6.51molMoles of water = 27.8molMole fraction of ethanol =

6.51/(27.8+6.51) =0.190Mole fraction of water =

27.8/(27.8+6.51) =0.810

HONORS: BEFORE YOU GO…

Calculate the mass of calcium cyanide needed to make a 0.25m calcium cyanide solution using 450g of water.