Concentrations and Colligative Properties SOLUTIONS II Concentrations and Colligative Properties

Solution Concentrations Always: concentration = amount of solute_____ amount of solvent or solution Expressed as relative amounts: dilute or concentrated unsaturated or saturated Most often expressed with specific amounts of each component CHM 1010 PGCC Barbara A. Gage

Percent Solution By volume: By mass: By mass/volume: (volume must have the same units) By mass: (mass must have the By mass/volume: (generally grams and mL) CHM 1010 PGCC Barbara A. Gage

Percent Solution What is the % m/v of a solution containing 35 g of sodium sulfate in 500 mL of water solution? What would the % be if the solute was potassium acetate? 2. Since the nature of the substance does not play a part in the calculation the % value does not change. CHM 1010 PGCC Barbara A. Gage

Percent Solution How many grams of copper (II) chloride are required to make 345 mL of a 25% solution (m/v)? CHM 1010 PGCC Barbara A. Gage

Molarity (again) Because many reactions happen between substances in solution, it is important to have a concentration based on moles. CHM 1010 PGCC Barbara A. Gage http://fuelcell.com

Molarity How many grams of sodium phosphate are required to make 250 mL of a 0.140 M solution? CHM 1010 PGCC Barbara A. Gage

Reactions with Solutions How many mL of 0.30 M NaCl are needed to react with 20.0 mL of 0.12 M Pb(NO3)2? 2 NaCl (aq) + Pb(NO3)2 (aq)  PbCl2 (s) + 2 NaNO3 (aq) CHM 1010 PGCC Barbara A. Gage

Converting a concentrated solution to a dilute solution. Figure 3.11 Converting a concentrated solution to a dilute solution. CHM 1010 PGCC Barbara A. Gage

Dilution Calculations For dilutions use the formula: Ci x Vi = Cf x Vf Where Ci = initial concentration Vi = initial volume Cf = final concentration Vf = final volume You can use any type of concentration or volume unit as long as they are the same. CHM 1010 PGCC Barbara A. Gage

Dilution Calculations How many mL of 0.50 M KCl are required to make 1.5 L of 0.20 M KCl? CHM 1010 PGCC Barbara A. Gage

Colligative Properties Properties that change depending on the number of particles dispersed in a solvent Vapor pressure lowering CHM 1010 PGCC Barbara A. Gage

The effect of a solute on the vapor pressure of a solution. Figure 13.11 The effect of a solute on the vapor pressure of a solution. CHM 1010 PGCC Barbara A. Gage

Colligative Properties Properties that change depending on the number of particles dispersed in a solvent Vapor pressure lowering Boiling point elevation Freezing point depression CHM 1010 PGCC Barbara A. Gage

Phase diagrams of solvent and solution. Figure 13.12 Phase diagrams of solvent and solution. CHM 1010 PGCC Barbara A. Gage

Boiling and Freezing Point Changes ΔTb = Kb x m where m= moles solute kg solvent Kb = boiling pt constant ΔTf = Kf x m Kf = freezing point constant Applications… CHM 1010 PGCC Barbara A. Gage

Table 13.5 Molal Boiling Point Elevation and Freezing Point Depression Constants of Several Solvents Boiling Point (0C)* Melting Point (0C) Solvent Kb (0C/m) Kf (0C/m) Acetic acid 117.9 3.07 16.6 3.90 Benzene 80.1 2.53 5.5 4.90 Carbon disulfide 46.2 2.34 -111.5 3.83 Carbon tetrachloride 76.5 5.03 -23 30. Chloroform 61.7 3.63 -63.5 4.70 Diethyl ether 34.5 2.02 -116.2 1.79 Ethanol 78.5 1.22 -117.3 1.99 Water 100.0 0.512 0.0 1.86 *at 1 atm. CHM 1010 PGCC Barbara A. Gage

Colligative Properties Properties that change depending on the number of particles dispersed in a solvent Vapor pressure lowering Boiling point elevation Freezing point depression Osmotic pressure – movement of solvent particles across a semipermeable membrane CHM 1010 PGCC Barbara A. Gage

The development of osmotic pressure. Figure 13.13 The development of osmotic pressure. Applied pressure needed to prevent volume increase osmotic pressure pure solvent solution semipermeable membrane net movement of solvent CHM 1010 PGCC Barbara A. Gage

Osmotic Pressure Remember PV = nRT? P V = n R T P = n R T V Π = M RT Where Π = osmotic pressure M = molarity CHM 1010 PGCC Barbara A. Gage

Osmosis and cells When a cell is placed in a solution with a hypertonic (higher solute concentration but less water) water flows out of the cell and the cell shrinks (crenation). When a cell is placed in a hypotonic solution (less solute but more water), water flows into the cell and the cell swells and may burst (hemolysis). CHM 1010 PGCC Barbara A. Gage

i = Colligative Properties of Electrolyte Solutions For electrolyte solutions, the compound formula tells us how many particles are in the solution. The van’t Hoft factor, i, tells us what the “effective” number of ions are in the solution. van’t Hoff factor (i) i = measured value for electrolyte solution expected value for nonelectrolyte solution For vapor pressure lowering: P = i(solutex P0solvent) For boiling point elevation: Tb = i(bm) For freezing point depression: Tf = i(fm) For osmotic pressure :  = i(MRT) CHM 1010 PGCC Barbara A. Gage