Concentration of Solutions : Concentration: Amount of a substance per . defined space. Percent by mass: Is the ratio of the solute’s mass to the solution’s mass expressed as a percent. Percent by mass = (solute) (solution or solvent) X 100

Example # 1: Calculate the percent by mass of solute in 55 g of solution with 15 g of potassium nitrate dissolved in water. Data: 15 g Solute’s mass = % by mass = X 100 Solution’s mass = 55 g % by mass = ?   = X 100 = 27 % of KNO3

Example # 2: Calculate the percent by mass of solute in a solution made by 25 g of sodium chloride & 50 g of water. Data: 25 g Solute’s mass = 50 g Solvent’s mass = 50 g + 25 g = 75 g Solution’s mass = % by mass = ? X 100 % by mass = = X 100 = 33 % of NaCl

Solution Concentration: Example: Calculate the percent by volume of alcohol in 95 mL of solution which contains 30 mL of alcohol. % by volume = X 100 Data: Solute = 30 mL % by volume = X 100 95 mL Solution = = X 100 % by volume = ? = 32 % of alcohol

Mole Fraction: Is the ratio between the # of moles of each component & the total # of moles in the solution. ΧA = ΧA = Mole fraction of A nA = Moles of A nB = Moles of B

x NaOH + x H2O = 1 20.0 g = 0.500 mol = 4.99 mol ÷ 40.0 g/mol   20.0 g ÷ 40.0 g/mol = 0.500 mol NaOH= 90.0 g ÷ 18.02 g/mol = 4.99 mol H2O=   = Χ NaOH = = 0.0911 NaOH   = Χ H2O = = 0.909 H2O x NaOH + x H2O = 1

Example # 2: Calculate the mole fraction of a solution made by 37.5% HCl and 62.5% water. HCl= 37.5 % = 37.5 g ÷ 36.46 g/mol = 1.03 mol H2O= 62.5 % = 62.5 g ÷ 18.02 g/mol = 3.47 mol Χ HCl = = = 0.229 HCl = Χ H2O = = 0.771 H2O x HCl + x H2O = 1 x H2O = 1 - x HCl = ;