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Published byMaude Mitchell Modified over 4 years ago

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Solutions Concentrations of Solutions

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Solutions Objectives Given the mass of solute and volume of solvent, calculate the concentration of solution Given the concentration of a solution, determine the amount of solute in a given amount of solution Given the concentration of a solution, determine the amount of solution that contains a given amount of solute

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Solutions Concentration The concentration of a solution is a measure of the amount of solute in a given amount of solvent or solution Concentration is a ratio: any amount of a given solution has the same concentration The opposite of concentrated is dilute These terms are unrelated to the degree to which a solution is saturated: a saturated solution of a solute that is not very soluble might be very dilute

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Solutions Concentration Units

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Solutions Molarity Molarity is the number of moles of solute in one liter of solution For example, a “one molar” solution of sodium hydroxide contains one mole of NaOH in every liter of solution The symbol for molarity is M. The concentration of a one molar NaOH solution is written 1 M NaOH

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Solutions Molarity To calculate molarity, you must know the amount of solute in moles and the volume of solution in liters. When weighing out the solute, this means you will need to know the molar mass of the solute in order to convert mass to moles. Example: One mole of NaOH has a mass of 40.0 g. If this quantity of NaOH is dissolved in enough water to make 1.00 L of solution, it is a 1.00 M solution.

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Solutions Molarity The molarity of any solution can be calculated by dividing the number of moles of solute by the number of liters of solution: Note that a 1 M solution is not made by adding 1 mol of solute to 1 L of solvent. In such a case, the final total volume of the solution might not be 1 L Solvent must be added carefully while dissolving to ensure a final volume of 1 L

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Solutions Molarity Sample Problem You have 3.50 L of solution that contains 90.0 g of sodium chloride, NaCl. What is the molarity of that solution?

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Solutions Molarity Sample Problem Solution Given: solute mass = 90.0 g NaCl solution volume = 3.50 L Unknown: molarity of NaCl solution

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Solutions Molarity Sample Problem You have 3.50 L of solution that contains 90.0 g of sodium chloride, NaCl. What is the molarity of that solution?

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Solutions Molarity Sample Problem Solution Given: solute mass = 90.0 g NaCl solution volume = 3.50 L Unknown: molarity of NaCl solution

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Solutions Molarity Sample Problem You have 0.8 L of a 0.5 M HCl solution. How many moles of HCl does this solution contain?

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Molarity Sample Problem Solution Given: volume of solution = 0.8 L concentration of solution = 0.5 M HCl Unknown: moles of HCl in a given volume Solutions

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Molarity Sample Problem To produce 40.0 g of silver chromate, you will need at least 23.4 g of potassium chromate in solution as a reactant. All you have on hand is 5 L of a 6.0 M K 2 CrO 4 solution. What volume of the solution is needed to give you the 23.4 g K 2 CrO 4 needed for the reaction?

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Molarity Sample Problem Solution Given: volume of solution = 5 L concentration of solution = 6.0 M K 2 CrO 4 mass of solute = 23.4 K 2 CrO 4 mass of product = 40.0 g Ag 2 CrO 4 Unknown: volume of K 2 CrO 4 solution in L Solutions

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Molality Molality is the concentration of a solution expressed in moles of solute per kilogram of solvent. A solution that contains 1 mol of solute dissolved in 1 kg of solvent is a “one molal” solution. The symbol for molality is m, and the concentration of this solution is written as 1 m NaOH

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Solutions Molality The molality of any solution can be calculated by dividing the number of moles of solute by the number of kilograms of solvent: Unlike molarity, which is a ratio of which the denominator is liters of solution, molality is per kilograms of solvent Molality is used when studying properties of solutions related to vapor pressure and temperature changes, because molality does not change with temperature

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Solutions Molal Solutions

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Solutions Molality Sample Problem A solution was prepared by dissolving 17.1 g of sucrose (table sugar, C 12 H 22 O 11 ) in 125 g of water. Find the molal concentration of this solution.

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Molality Sample Problem Solution Given: solute mass = 17.1 C 12 H 22 O 11 solvent mass = 125 g H 2 O Unknown: molal concentration Solutions

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Molality Sample Problem A solution of iodine, I 2, in carbon tetrachloride, CCl 4, is used when iodine is needed for certain chemical tests. How much iodine must be added to prepare a 0.480 m solution of iodine in CCl 4 if 100.0 g of CCl 4 is used?

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Molality Sample Problem Solution Given: molality of solution = 0.480 m I 2 mass of solvent = 100.0 g CCl 4 Unknown: mass of solute Solutions

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