# Concentration of Solutions Objectives: 1.Measure the concentrations in terms of molarity, molality, and mole fraction. 2.Differentiate between saturated,

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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

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

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 1 st – (73g HCl / 4L) x (1 mole HCl /36.5 g HCl) = 2 mol HCl Solve formula – 2 mol HCl / 4L = 0.5M HCl – Gas solutions affected by temperature Changes the volume of the solvent

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 mol NaCl / 1kg = 2m NaCl

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. – M 1 V 1 = M 2 V 2 or M c V c = M d V d c = concentrated; d = dilute

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 H 2 0 = 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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