S OLUTION C ONCENTRATION : M ASS P ERCENT, M OLALITY AND M OLE F RACTION 14.2:

M AIN I DEA Concentration can be expressed in terms of percent or in terms of moles

M ETHODS FOR S HOWING C ONCENTRATION 1. Molarity 2. Percent by mass 3. Percent by Volume 4. Molality 5. Mole Fractions

P ERCENT S OLUTION 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)

P ERCENT S OLUTION 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

P ERCENT S OLUTION Examples: Calculate the grams of solute needed to make 250. mL of a 0.10% MgSO 4 solution. Percent by (m/v) = mass of solute x 100% volume of solution (mL) = 0.10%= ___?__ x 100% 250mL ? = 0.25g MgSO 4

M OLALITY Another way to express solution concentration is Molality ( m )

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

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

M OLE F RACTION Solution concentration can also be expressed by using the mole fraction Mole Fraction Mol solute Total moles in solution

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

E XAMPLES What is the mole fraction of each component in a solution made by mixing 300.g of ethanol (C 2 H 5 OH) and 500.g water? Moles of ethanol = 6.51mol Moles of water = 27.8mol Mole fraction of ethanol = 6.51/( ) =0.190 Mole fraction of water = 27.8/( ) =0.810

H ONORS : B EFORE YOU GO … Calculate the mass of calcium cyanide needed to make a 0.25 m calcium cyanide solution using 450g of water.