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Solutions

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  1. Solutions Concentration of Solutions

  2. Objectives • Define molarity and calculate its value. • Define molality and calculate its value. • Apply the principles of stoichiometry to reactions that occur in solution.

  3. Concentration Dilute vs. Concentrated Weak acid vs. dilute acid Concentration – a measure of the amount of solute in a given amount of solvent or solution

  4. Molarity Molarity – the number of moles of solute in 1 liter of solution. • Dissolving 2 moles of NaOH (80.0g) in enough water to make 1 Liter of solution would yield a 2 M solution of NaOH

  5. Sample Problems • What is the molarity of a 2.0 L solution that is made from 14.6 g of NaCl? 0.12 M • What is the molarity of a HCl solution that contains 10.0 g of HCl in 250 mL of solution? 1.1 M • How many moles of NaCl are in 1.25 L of 0.330 M NaCl? 0.413 mol • How many moles of HCl exist in 500. mL of 0.50 M solution of HCl? 0.25 mol

  6. Sample Problems • What is the molarity of a solution composed of 6.25 g of HCl in 0.300 L of solution? 0.571 M • How many moles of KI are present in 0.250 L of a 2.30 M solution? 0.575 mol • What volume of a 0.500 M solution of HBr is needed for a reaction that requires 32.5 g of HBr? 0.803 L

  7. Molality Molality – concentration in moles of solute per kilogram of solvent. To make a 2.00 m solution of NaOH: • Measure 2 moles of NaOH (80.0 g) and dissolve in 1.00 kg of distilled water.

  8. Sample Problems • What is the molality of a solution composed of 255 g of acetone (CH3)2CO) dissolved in 200. g of water? 22.0 m • What quantity in grams of methanol (CH3OH) is required to prepare a 0.244 m solution in 400. g of water? 3.12 g • How many grams of AgNO3 are needed to prepare a 0.125 m solution in 250 mL of water? 5.3 g • What is the molality of a solution containing 18.2 g HCl and 250. g of water? 1.99 m

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