Solution Concentration

Calculations of Solution Concentration: Mass Percent Mass percent Mass percent is the ratio of mass units of solute to mass units of solution, expressed as a percent

A Simplifying Assumption 1 ml of water = 1 gram of water1 ml of water = 1 gram of water 1000 ml of water = 1 liter = 1000 grams1000 ml of water = 1 liter = 1000 grams Assume that solutions with water as the solvent have the density of pure water (1 mL = 1 gram)Assume that solutions with water as the solvent have the density of pure water (1 mL = 1 gram) –It’s not true, but it’s close enough –It’s not true, but it’s close enough

Calculations of Solution Concentration Mole fraction Mole fraction – the ratio of moles of solute to total moles of solution

Calculations of Solution Concentration: Molarity Molarity Molarity is the ratio of moles of solute to liters of solution

Preparation of Molar Solutions Problem: How many grams of sodium chloride are needed to prepare 1.50 liters of M NaCl solution?  Step #1: Ask “How Much?” (What volume to prepare?) L  Step #2: Ask “How Strong?” (What molarity?) mol 1 L  Step #3: Ask “What does it weigh?” (Molar mass is?) g 1 mol = 43.8 g

Calculations of Solution Concentration Molality Molality – moles of solute per kilogram of solvent

Serial Dilution Problem: What volume of stock (11.6 M) hydrochloric acid is needed to prepare 250. mL of 3.0 M HCl solution? M stock V stock = M dilute V dilute (11.6 M)(x Liters) = (3.0 M)(0.250 Liters) x Liters = (3.0 M)(0.250 Liters) 11.6 M = L