1 Concentration Day 2: Chapter 14

CONCENTRATION The amount of solute present in a set amount of solvent or total solution. The amount of solute present in a set amount of solvent or total solution.

CONCENTRATION Molarity (M or mol/L) Molarity (M or mol/L) Molality (m or mol/Kg) Molality (m or mol/Kg) Weight percent (%) Weight percent (%) mole fraction (c) mole fraction (c)

4 Weight Percent

CONCENTRATION Weight Percent Weight Percent % = mass solute (g) x 100 % = mass solute (g) x 100 total mass solution (g) total mass solution (g) What percent of Soda is sugar? 43 g sugar/355g total =.12 (100) = 12% What percent of Yogart is sugar? 25 g/ 170 g total =.15 (100) = 15%

CONCENTRATION parts per million (ppm) 7ppm is = 7 grams of solute One million grams total Used to measure small levels of trace solutes in water (dissolved oxygen)

CONCENTRATION Molarity (M) is measurement of concentration. Molarity (M) is measurement of concentration. Molarity is the number of moles solute dissolved in one liter of solution. Molarity is the number of moles solute dissolved in one liter of solution. M = mol solute total L solution total L solution

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Molarity Example What is the molarity of a solution that contains 1.8 mol of HCl in 500. mL of total solution M = mol of HCl X M = 1.8 mol M = mol of HCl X M = 1.8 mol liters solution L liters solution L = 3.60 M or 3.6 mol/L 0f HCl = 3.60 M or 3.6 mol/L 0f HCl

Molarity Example How many moles of solute are present in 1.5 L of 0.20 M NaCl solution? M = mol of NaCl 0.20M = X mol liters solution 1.5 L liters solution 1.5 L = 0.30 moles of NaCl = 0.30 moles of NaCl

Molarity Example How many grams of CuCl 2 should be used to prepare.250 L of a 0.40 M solution? How many grams of CuCl 2 should be used to prepare.250 L of a 0.40 M solution? M = moles of CuCl 2.40 M = x moles M = moles of CuCl 2.40 M = x moles liter solution.250 L liter solution.250 L =.10 moles of CuCl 2 =.10 moles of CuCl 2 Change moles to grams: Moles X Molar mass = Mass.10 moles x 134 grams CuCl 2 = 13.4 g 1 mole CuCl 2

13 An IDEAL SOLUTION is one where the properties depend only on the concentration of solute. Need conc. units to tell us the number of solute particles per solvent particle. The unit “molarity” does not do this! Concentration Units

14 Concentration Units MOLE FRACTION, X For a mixture of A, B, and C MOLE FRACTION, X For a mixture of A, B, and C What fraction of Soda is sugar? 43 g sugar: 300.g water = 0.13 mol: 17 mol = X = 0.13/17.13 = X water = 17/17.13 = 0.99

15 MOLALITY, m What molal of sugar (342 g/mol) is in Soda ? 43 g sugar & 300.g water 0.13 mol & kg m = 0.13 mol / 0.30 Kg = 0.43m

16 Calculating Concentrations Dissolve 62.1 g (1.00 mol) of ethylene glycol in 250. g of H 2 O. Calculate mol fraction, molality, and weight % of glycol.

17 Calculating Concentrations 250. g H 2 O = 13.9 mol Dissolve 62.1 g (1.00 mol) of ethylene glycol in 250. g of H 2 O. Calculate X, m, and % of glycol. X glycol =

18 Calculating Concentrations Calculate molality Dissolve 62.1 g (1.00 mol) of ethylene glycol in 250. g of H 2 O. Calculate X, m, and % of glycol. Calculate weight %