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Solution Concentration: Mass Percent, Molality and Mole Fraction. 14.2: 480 - 488. Main Idea. Concentration can be expressed in terms of percent or in terms of moles. Methods for Showing Concentration. Molarity Percent by mass Percent by Volume Molality Mole Fractions.
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Solution Concentration: Mass Percent, Molality and Mole Fraction 14.2: 480 - 488
Main Idea • Concentration can be expressed in terms of percent or in terms of moles
Methods for Showing Concentration • Molarity • Percent by mass • Percent by Volume • Molality • Mole Fractions
Percent Solution • Two percentage methods to show how concentrated a solution is: • Percent by volume = volume of solute x 100% volume of solution • Percent by (m/v) = mass of solute x 100% solution volume(mL)
Percent Solution • Examples: • If 10. mL of pure acetone is diluted with water to a total solution volume of 200. mL, what is the percent by volume of the acetone solution? Percent by volume = volume of solute x 100% volume of solution Percent by volume = 10 x 100% = 50.% 200
Percent Solution • Examples: Calculate the grams of solute needed to make 250. mL of a 0.10% MgSO4 solution. Percent by (m/v) = mass of solute x 100% volume of solution (mL) = 0.10%= ___?__ x 100% 250mL ? = 0.25g MgSO4
Molality • Another way to express solution concentration is Molality (m)
Examples • How many grams of sodium fluoride are needed to prepare a 0.40m NaF solution that contains 750.0g of water?
Examples • Calculate the molality of a solution prepared by dissolving 10.0g of NaCl in 600.g of water. m = 0.290 m
Mole Fraction • Solution concentration can also be expressed by using the mole fraction Mol solute Mole Fraction Total moles in solution
Examples • What is the mole fraction of each component in a solution made by mixing 1.25 mol ethylene glycol and 4.00 mol water?
Examples What is the mole fraction of each component in a solution made by mixing 300.g of ethanol (C2H5OH) and 500.g water? Moles of ethanol = 6.51mol Moles of water = 27.8mol Mole fraction of ethanol = 6.51/(27.8+6.51) =0.190 Mole fraction of water = 27.8/(27.8+6.51) =0.810
Honors: Before you go… • Calculate the mass of calcium cyanide needed to make a 0.25m calcium cyanide solution using 450g of water.