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Concentration of Solutions

Concentration of Solutions. Objectives: 1.Measure the concentrations in terms of molarity, molality, and mole fraction. 2.Differentiate between saturated, unsaturated, and supersaturated solutions. Key Terms:

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Concentration of Solutions

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  1. Concentration of Solutions Objectives: • 1.Measure the concentrations in terms of molarity, molality, and mole fraction. • 2.Differentiate between saturated, unsaturated, and supersaturated solutions. Key Terms: • Concentration, molarity, molality, mole fraction, saturated, unsaturated, supersaturated

  2. Concentration • The concentration of a solution is the amount solute per amount solvent. • 2 classifications: • Dilute … having little dissolved solute compared to carrying capacity (amount at saturation) • Concentrated … having an amount that approaches or is at carrying capacity Dilute Concentrated

  3. Concentration - Molarity • Molarity describes the moles of solute per liter of solvent • Molarity = moles solute / liters solvent • Molarity is expressed with a capital M • ex: 73g of HCl powder is dissolved into 4L of water • Must convert solute to moles 1st • (73g HCl / 4L) x (1 mole HCl /36.5 g HCl) = 2 molHCl • Solve formula • 2 molHCl / 4L = 0.5M HCl • Gas solutions affected by temperature • Changes the volume of the solvent

  4. Concentration - Molality • Molality describes the moles of solute per kilogram of solvent • Molality = moles solute / kilogram of solvent • expressed with a lower case m • ex: 117g of NaCl is dissolved into 1000g of water • (117g NaCl / 1000g) x (1 mole NaCl /58.5 g NaCl) x (1000g / 1kg)= 2 molNaCl / 1kg = 2m NaCl

  5. Making Dilutions • Dilutions/concentrations are manipulated by adding more or less solvent per amount solute • The Molarity is inversely related to the amount of solvent present. • M1V1 = M2V2 or McVc = MdVd • c= concentrated; d = dilute

  6. Percent Solutions • Percent composition problem (part / whole) • % (v/v) = (volume solute / volume solution) x 100% • Useful for liquid or gas solutes • % (m/m) = (mass solute / mass solution) x 100% • Useful for solid solutes • Reported per 100ml or 100g of solution • Which of the following solutions has the lowest %m/m? • Solution 2. (58.5g/mol x 0.10mol) / ((58.5g/mol x 0.10mol) + (1000g))= .0058 • 1ml of H20 = 1g • How much is NaCl is required to make 100g of the same concentration? • 5.85g/1005.85g = x/100g or 585g/1005.85 = .582g NaCl is required

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