SOLUTION PROPERTIES Absolutely pure water conducts electricity very poorly. Some solutes called electrolytes produce water solutions that conduct electricity well. Some solutes called nonelectrolytes produce water solutions that do not conduct electricity. A solution of a strong electrolyte conducts electricity well. A solution of a weak electrolyte conducts electricity poorly. A solution of a nonelectrolyte does not conduct electricity.

ELECTROLYTES STRONG ELECTROLYTES Strong electrolytes form solutions that conduct electricity because they dissociate completely into charged ions when they dissolve. WEAK ELECTROLYTES Weak electrolytes form weakly conducting solutions because they dissociate into ions only slightly when they dissolve. NONELECTROLYTES Nonelectrolytes form nonconducting solutions because they do not dissociate into ions at all when they dissolve.

COLLIGATIVE PROPERTIES OF SOLUTIONS Colligative solution properties are properties that depend only on the concentration of solute particles in the solution. Three colligative properties are boiling point, freezing point, and osmotic pressure. Experiments demonstrate that the vapor pressure of water (solvent) above a solution is lower than the vapor pressure of pure water.

SOLUTION BOILING POINT The boiling point of a solution is always higher than the boiling point of the pure solvent of the solution. The difference between the boiling point of the pure solvent and the solution is represented by the symbol ∆t b. The difference in boiling point between pure solvent and solution depends on the concentration of solute particles, and is calculated using the following equation: ∆t b = nK b M In this equation, ∆t b is the difference between the boiling point of the solution and the boiling point of the pure solvent.

SOLUTION BOILING POINT (continued) The n in the equation is the number of moles of solute particles put into the solution when 1 mole of solute dissolves. For solutes that do not dissociate, n = 1. For solutes that are strong electrolytes, n varies depending on the number of ions formed when the solute dissolves. For example, the dissociation of calcium chloride is represented as: CaCl 2 Ca Cl - Thus, when 1 mole of CaCl 2 dissolves, 3 moles of particles (ions) are put into the solution and n = 3. K b in the equation is a constant called the boiling point constant. K b is characteristic of the solvent used to make the solution. M is the molarity concentration of solute in the solution.

The freezing point of a solution is always lower than the freezing point of the pure solvent of the solution. The difference in freezing point of the solution and pure solvent is ∆t f, which is calculated by subtracting the freezing point of the solution from the freezing point of the pure solvent. The value of ∆t f is calculated by using the following equation: ∆t f = nK f M The symbols in this equation have meaning similar to those given for the boiling point elevation equation. K f is a constant characteristic of the solvent used to form the solution. SOLUTION FREEZING POINT

OSMOTIC PRESSURE OF SOLUTIONS When solutions having different concentrations of solute are separated by a semipermeable membrane, solvent tends to flow through the membrane from the less concentrated solution into the more concentrated solution in a process called osmosis. When the more concentrated solution involved in osmosis is put under sufficient pressure, the net osmotic flow of solvent into the solution can be stopped. The pressure necessary to prevent the osmotic flow of solvent into a solution is called the osmotic pressure of the solution and can be calculated by using the following equation, which is similar to the ideal gas law given earlier: π = nMRT

OSMOTIC PRESSURE OF SOLUTIONS (continued) In this equation, π is the osmotic pressure, n is the number of moles of solute particles put into solution when 1 mole of solute dissolves, M is the molarity of the solution, R is the universal gas constant written as 62.4 L torr/K mol, and T is the solution temperature in Kelvin. The product of n and M is called the osmolarity of the solution.

COLLOIDS Colloids are homogeneous mixtures of two or more components called the dispersing medium and the dispersed phase. The dispersed phase substances in a colloid are in the form of particles larger than those found in solutions. DISPERSING MEDIUM OF A COLLOID The dispersing medium of a colloid is the substance present in the largest amount. It is analogous to the solvent of a solution. DISPERSED PHASE OF A COLLOID The dispersed phase of a colloid is the substance present in a smaller amount than the dispersing medium. It is analogous to the solute of a solution.

COLLOID PROPERTIES In colloids, the dispersed phase particles cannot be seen and do not settle under the influence of gravity. Colloids appear to be cloudy because the larger particles in the dispersed phase scatter light. Colloids demonstrate the Tyndall effect in which the path of the light through a colloid is visible because the light is scattered.

TYPES OF COLLOIDS

STABILIZING COLLOIDS Ions in a dispersing medium are attracted to colloid particles and stick on their surfaces. All colloid particles within a particular system will attract ions of only one charge or the other. The colloid particles all acquire the same charge and repel each other. The repulsion helps prevent the particles from coalescing into aggregates large enough to settle out. Substances known as emulsifying agents or stabilizing agents are used to prevent some colloids from coalescing (e.g. egg yolk in oil and water to form mayonnaise, soap/ detergent ions forming a charged layer around nonpolar oils and greases).

STABILIZING COLLOIDS (continued)

DESTRUCTION OF COLLOIDS Colloid solids are removed from gaseous smoke stack wastes before they are released into the atmosphere in the Cottrel precipitator. The precipitator contains a number of highly charged plates or electrodes. As smoke passes over the charged surfaces, the colloid particles lose their charges. The particles then coalesce into larger particles that settle out and are collected for disposal. Dialysis can be used to separate small particles from colloids (e.g. cleaning the blood of people suffering from kidney malfunction).

DIALYSIS A dialyzing membrane is a semipermeable membrane with larger pores than osmotic membranes that allow solvent molecules, other small molecules, and hydrated ions to pass through. Dialysis is a process in which solvent molecules, other small molecules, and hydrated ions pass from a solution through a membrane.