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Solutions

Learn how to calculate molarity and molality of solutions, and apply stoichiometry principles for reactions in solutions. Understand the difference between dilute and concentrated solutions and weak acid versus dilute acid.

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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

  9. Solution concentration and Stoichiometry How many moles of H2O form when 25.0 mL of 0.100 M HNO3 solution is completely neutralized by NaOH? 2.50 x 10-3 mol

  10. Stoichiometry Problems • What volume of 0.500 M HCl(aq) is required to react completely with 0.100 mol of Pb(NO3)2 (aq) forming a precipitate of PbCl2 (s)? 0.400 L • A 238 mL sample of hydrosulfuric acid solution requires 155 mL of a 3.45 M potassium hydroxide for complete neutralization. What is the concentration of the original hydrosulfuric acid solution? 1.12 M

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