William L Masterton Cecile N. Hurley Edward J. Neth University of Connecticut Chapter 10 Solutions

Concentration Units General Vocabulary: Solution – homogeneous mixture of solute and solvent Solute – the substance being dissolved Solvent – the substance doing the dissolving Electrolyte – a substance that conducts electricity when in solution - ionic Nonelectrolyte – a substance that does NOT conduct electricity when in solution - molecular

Concentration Units Molarity – (M) moles of solute per liter of solution Molarity = moles of solute/liters of solution Example: What is the molarity of a solution made by dissolving 12.5g of oxalic acid (H 2 C 2 O 4 ) in 456mL of solution?

Dilution of Solutions M 1 V 1 = M 2 V 2

Example 10.1

Mass Percent Percent by mass = (mass solute/mass solution) * 100

Molality the number of moles of solute per kilogram of solvent Molality (m) = moles of solute/kilograms of solvent

Example

Conversions Between Concentration Units Start with a fixed amount of solution or solvent, see right column When the original concentration is Choose Mass percent100 g solution Molarity (M)1.00 L solution Molality (m)1.00 kg solvent

Example:

Principles of Solubility Factors that determine the extent to which a solute dissolves in a particular solvent: 1. The nature of solvent and solute particles and the interaction between them 2. The temperature at which the solution forms 3. The pressure, in cases of gaseous solutes

Solute-Solvent Interactions “Like dissolves like” = see table in notes Polar solutes dissolve in polar solvents Nonpolar solutes dissolve in nonpolar solvents Nonpolar substances have poor affinity for water Petroleum Hydrocarbons (pentane, C 5 H 12 ) Polar substances dissolve easily in water Alcohols, CH 3 OH Solubility of alcohols decreases as the molar mass of the alcohol increases

Solubility and Intermolecular Forces

Effect of Temperature on Solubility An increase in temperature always shifts the position of an equilibrium to favor an endothermic process heat of solution > 0 heat of solution < 0

Figure 10.4 (Solubility Curves – pg 12)

Effect of pressure on Solubility Pressure has a major effect on the solubility of a gas in a liquid, but little effect on other systems Henry’s Law - At low to moderate pressure, the concentration of a gas increases with the pressure

Solubility Effects of Pressure

Colligative Properties of Nonelectrolytes The properties of a solution may differ considerably from those of the pure solvent Some of these properties depend on the concentration of dissolved particles and not on their nature

Boiling and Freezing Point Boiling point elevation and freezing point lowering are both colligative properties K f is the freezing point lowering constant K b is the boiling point elevation constant

FPL and BPE Constants for Water For water, Kf = 1.86 Kb= 0.52

Example 10.7

Molal Constants

Determination of Molar Masses from Colligative Properties molality = moles of solute/kg of solvent MM solute = grams/moles

Example 10.9

Colligative Properties of Electrolytes When an electrolyte dissolves it breaks apart into ions. NaCl (s)  Na +1 (aq) + Cl -1 (aq) So for every NaCl formula unit 2 aqueous ions are formed The formula is adjusted to reflect the number of ions: ∆T = k m ii = the number of ions formed

Example 10.10

Solution Stoichiometry Example

Solution Stoichiometry Example