Solutions

1. Solutions

2. Overview • Solution formation • Types of solution • Solubility and the solution process • Effect of temperature and pressure on solubility • Colligative properties • Ways of expressing concentration • Vapor pressure of a solution • Boiling-point elevation and freezing point depression. • Osmosis • Colligative properties of ionic solutions • Colloid Formation • Colloids

3. Types of Solution • Solution – homogeneous mixture of two or more substances of ions or molecules. E.g. NaCl (aq) • Solvent = component which is the component in greater amount. • Solute = component which is present in the smaller amount. • Gaseous = gases are completely miscible in each other. • Liquid = gas, liquid or solid solute dissolved in solute. • Solid = mixture of two solids that are miscible in each other to form a single phase. • Colloid – appears to be a homogeneous mixture, but particles are much bigger, but not filterable. E.g. Fog, smoke, whipped cream, mayonnaise, etc. • Suspension: larger particle sizes, filterable. E.g. mud, freshly squeezed orange juice.

4. Solubility and the Solution Process • The solid dissolves rapidly at first but as the solution approaches saturation the net rate of dissolution decreases since the process is in dynamic equilibrium. • When the solution has reached equilibrium the amount of solute does not change with time; • At equilibrium: the rate of dissolution = rate of solution Fig. 12.2 Solubility Equilibrium

5. Solubility and the Solution Process II • Saturated solution: maximum amount of solute is dissolved in solvent. Trying to dissolve more results in undissolved solute in container. • Solubility: Amount of solute that dissolves in a solvent to produce a saturated solution. (Solubility often expressed in g/100 mL.) E.g. 0.30 g of I2 dissolved in 1000 g of H2O. • Unsaturated solution: less than max. amount of solute is dissolved in solvent. E.g. 0.20 g of I2 dissolved in 1000 g of H2O. • Supersaturation = more solute in solution than normally allowed; we call this a supersaturated solution.

6. Units of Concentration • Physical properties of solutions are often related to the concentration of the solute in the solution.Molarity • Mole fraction: The same quantity we have used in fractional abundances as well as with gases (Dalton’s law). A unitless number.Weight (mass) Percent (wt%) – similar to mole fraction except use mass of each. • E.g. determine the wt% of a solution prepared by dissolving 1.44 g of NaCl in 100.0 mL of water. Assume that the density of water is 1.00 g/mL • Other units: parts per million (ppm) and parts per billion (ppb) for small concentrations.

7. Units of Concentration2 • Molality(m): defined as the mol of solute per kg of solvent. Unlike Molarity this unit is temperature independent. E.g. determine the molality of a solution prepared by dissolving 1.44 g NaCl into exactly 100.0 mL of water. Assume the density of water is 1.00 g/mL. E.g.2 Determine mass % of solution made from dissolving 30.0 g H2O2 with 70.0 g H2O. E.g.3 Determine molality of 30% H2O2(aq) E.g.4 Determine the mole fraction of the compound in E.g. 3 E.g.5 Concentrated ammonia is 14.8 M and has a density of 0.900 g/mL. What is the molar volume and the molality?

8. 0.5L of water to make a 1.5 M solution