Solubility & Concentration CREDIT: D. Scott, CHS

Concentration of Solution Solvent Solute

Concentration of Solution Molarity Parts ratio Mole Fraction Moles of solute Liter of solution Mol L (M) = = amount of solute (g or ml) amount of solution (g or ml) = (102) or (106) or (109) (c) Moles of solute Total moles of solution =

Molarity Example Problem 1 NaCl 12.6 g of NaCl are dissolved in water making 344mL of solution. Calculate the molar concentration.

Molarity Example Problem 2 NaCl How many moles of NaCl are contained in 250.mL of solution with a concentration of 1.25 M? Volume x concentration = moles solute

Molarity Example Problem 3 NaCl What volume of solution will contain 15 g of NaCl if the solution concentration is 0.75 M? moles solute ÷ concentration = volume solution

Mass and volume units must match. % Concentration % (w/w) = % (w/v) = % (v/v) = Mass and volume units must match. (g & mL) or (Kg & L)

% Concentration Example Problem 1 Example Problem 2 (Solid in a Liquid) What is the concentration in %w/v of a solution containing 39.2 g of potassium nitrate in 177 mL of solution? % (w/v) = Example Problem 2 (Liquid in a Liquid) What is the concentration in %v/v of a solution containing 3.2 L of ethanol in 6.5 L of solution? % (v/v) =

What volume of 1.85 %w/v solution is needed to % Concentration Example Problem 3 What volume of 1.85 %w/v solution is needed to provide 5.7 g of solute? % (w/v) = We know: We want to get: g solute ÷ concentration = volume solution

Parts per million/billion (ppm & ppb) or = ppm or = ppb AND For very low concentrations: = ppt parts per trillion Mass and volume units must match. (g & mL) or (Kg & L)

ppm & ppb or Example Problem 1 An Olympic sized swimming pool contains 2,500,000 L of water. If 1 tsp of salt (NaCl) is dissolved in the pool, what is the concentration in ppm? 1 teaspoon = 6.75 g NaCl or

ppm & ppb or Example Problem 2 An Olympic sized swimming pool contains 2,500,000 L of water. If 1 tsp of salt (NaCl) is dissolved in the pool, what is the concentration in ppb? 1 teaspoon = 6.75 g NaCl or

Mole Fraction c A = c B = Mole Fraction (c) moles of A sum of moles of all components A B + c B = moles of B sum of moles of all components B A + Since A + B make up the entire mixture, their mole fractions will add up to one.

Mole Fraction Example Problem 1 In our glass of iced tea, we have added 3 tbsp of sugar (C12H22O11). The volume of the tea (water) is 325 mL. What is the mole fraction of the sugar in the tea solution? (1 tbsp sugar ≈ 25 g) First, we find the moles of both the solute and the solvent. Next, we substitute the moles of both into the mole fraction equation.

Mole Fraction Example Problem 2 Air is about 78% N2, 21% O2, and 0.90% Ar. What is the mole fraction of each gas? First, we find the moles of each gas. We assume 100. grams total and change each % into grams. Next, we substitute the moles of each into the mole fraction equation.