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CHP 12 solutions
Concentration • There are numerous ways to measure concentration • (amount of solute/amount of solvent or soln) • Molarity, M • Molality, m (also cm) • Mole Fraction, XA • Mass Percent • Parts per million (ppm)
Concentration • Molarity, M This one should be very familiar. It is the measure of concentration in Chemistry 121. • Molality, m (also see written as cm)
Molality Example • What is the molality of a solution that contains 5.67 g of glucose (180.2 g/mol) dissolved in 25.2 g of water? Glucose is C6H1206.
Concentration • Mole Fraction, XA
Mole Fraction Example • A solution is made by dissolving 5.67 g of glucose, C6H12O6, in 25.2 g of water. a. What is the mole fraction of C6H12O6 in this solution? b. What is the mole fraction of water in this solution?
Concentration • Mass Fraction • Mass Percent (Percent by Mass) • ppm • ppb
Mass Fraction Examples • 22.5 g of NaCl are dissolved in 237.5 g of water. • What is the mass fraction of NaCl in this solution? • What is the % NaCl (by mass)? • What is the ppm NaCl? • What is the ppb NaCl?
Once Concentration is Known, It Serves as a Conversion Factor • You want to prepare 36.00 g of a solution that is 5.00 % KBr (by mass). Explain how you would do this.
Converting Concentration • An aqueous solution is 0.120 m in glucose, C6H1206. What are the mole fractions of each component in the solution? • An aqueous solution is 0.150 mole fraction glucose, C6H1206. If glucose is the only solute, what is the molality of glucose in the solution?
Converting Concentrations • An aqueous solution is 0.273 m KCl. What is the molar concentration of potassium chloride, KCl? The density of the solution is 1.011 x 103 g/L. • An aqueous solution is 0.907 MPb(NO3)2. What is the molality of lead Pb(NO3)2, in this solution? The density of the solution is 1.252 g/mL.
Colligative Properties Some properties of the solvent are changed by the addition of the solute -vapor pressure -boiling point -freezing point -Osmotic pressure
Colligative Properties Some properties of the solvent are changed by the addition of the solute How much property is changed doesn’t really depend on what solute is, but just on how much solute there is
Vapor-Pressure Lowering Raoult’s Law PBsoln = XBPBo
Vapor-Pressure Lowering • Calculate the vapor pressure and the vapor pressure lowering of water when 5.78 g of glucose (a nonvolatile solute), C6H12O6, are dissolved in 25.2 g of water at 25 0C, where the vapor pressure of water is 23.8 mmHg.