# Solutions and Their Properties

Solutions and Their Properties Chapter 13 Learning Objectives Students understand The energetics of the solution process The basis of the like dissolves like rule

How changes in pressure and temperature affect solubility Learning Objectives Students will be able to

Use the units of solution concentration Calculate the enthalpy of a solution Use Henrys law Use Le Chateliers principle Solutions and Their Properties

A solution is a homogenous mixture of two or more substances in a single phase. solute vs. solvent The changes that occur when a substance is dissolved in a pure liquid are called colligative

properties. 13.1 Units of Concentration Molarity (mole solute/liter solution) does not work when dealing with colligative properties solute molecules take up some volume

Four units that can be used to calculate concentration of solute per solvent are molality, mole fraction, weight percent, parts per million Mole Fraction The mole fraction, X, of a solution is

defined as the amount of a given component of a mixture divided by the total amount of all the components of the mixture. XA = nA / (nA + nB +)

Practice Problem If you dissolved 10.0 g of sugar, C12H22O11 in 250. g of water, what is the mole fraction, molality, and weight percent of sugar? 13.2 Solution Process

Unsaturated Saturated Supersaturated Solubility is the

concentration of solute in equilibrium with undissolved solute in a saturated solution. Liquids Dissolving in Liquids

If two liquids mix to form a solution, they are miscible. Immiscible liquids do not mix and exist as separate layers. Like dissolves like! Solids Dissolving in Liquids Once an ion has entered a solution and is surrounded by water

molecules, then they are hydrated. Heat of solution may be endothermic or exothermic depending upon how much energy is absorbed or lost by the reaction. Enthalpy of Solution Heat of solution can be calculated by

taking the sum of the standard heat of formation of the products minus the sum of the heat of formation of the reactions. Practice Problem Use the data in Table 13.1 (p. 478) to calculated the enthalpy of solution

for NaOH. Homework After reading sections 13.1-13.2, you should be able to do the following P. 505 (1-21 odd) 13.3 Factors Affecting Solubility

Solubility of a gas in a liquid is directly proportional to the gas pressure. Sg = kHPg where S is the gas solubility, P is the partial pressure of the gaseous solute, and k is the Henrys Law constant carbonated soft drinks; SCUBA tanks

(narcosis and the bends) Henrys Law What is the concentration of CO2 in water at 25oC when the partial pressure is 0.33 bar? Temperature Effects

Solubility of solids in water increases with increasing temperature Solubility of gases in water decreases with increasing temperature Fish seek lower depths in summer Thermal pollution Practice Problem

Case Study p. 482 Henrys Law and Exploding Lakes Le Chateliers Principle States that a change in any of the factors determining an equilibrium causes the system to adjust by shifting in the direction that reduces or counteracts the effect of the change

gas + liquid solvent saturated solution + energy Temperature Effects Le Chateliers Principle States that a change in any of the factors determining an equilibrium causes the system to adjust to reduce or counteract the effect of the change.

Gas + liquid solvent saturated solution + heat increasing temperature shifts reaction left 13.5 Colloids Colloids are intermediate between a solution and a suspension. (Jello, milk, fog)

Tyndall effect: colloids scatter visible light when dispersed in a solvent, making the mixture appear cloudy Colloids Hydrophilic and hydrophobic Emulsions are colloidal dispersions of liquid in liquid (mayo, milk)

emulsifying agents keep colloids from settling out Surfactants Soaps and detergents are emulsifiers. These substances affect the properties of surfaces are called surfactants; ones used

for cleaning are called detergents. Homework After reading Section 13.3-13.5, you should be able to do the following P. (19-24, 51-52)

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