CHAPTER 17 and 18 WATER AND AQUEOUS SOLUTIONS

 Water 1. Structure of water (H 2 O) a. two atoms of hydrogen b. One atom of oxygen c. Bent structure d. Bond angles °

e. O has a sp 3 hybridization f. Polar covalent g. Has hydrogen bonds

 Properties 1. Surface tension a. an inward force that tends to minimize the surface area of a liquid b. Gives the spherical shape c. Gravity helps flatten the shape

d. higher the surface tension the more spherical the shape 2. Surfactant a. Wetting agent (soap or detergent) b. Reduces surface tension (flattens shape) c. Soap interferes with hydrogen bonds

3. Vapor pressure a. Caused by molecules that escape the surface of the water and enter the gas phase b. Hydrogen bonds hold molecules together escape is low c. Gives water unusually low vapor pressure

4. Specific heat capacity a. The quantity of heat, in joules or calories, required to raise the temperature of 1 g of a substance 1 °C b. Water’s = J/g°C (helps moderate daily air temp.)

5. At 1 atm (101.3 kPa) pressure: a. Water freezes and melts at 0 °C b. Expands 11% in volumes as it freezes c. Density is g/cm 3 (floats in water) d. Most dense at 4 °C e. Boils at 100 °C

 Types of mixtures 1. Solutions Characteristics a. Homogeneous mixture of two or more substances in a single phase b. Solvent – the part that causes the dissolving c. Solute – the part that dissolves

d. electrolyte: a substance dissolved in water that conducts an electrical current e. Nonelectrolyte: a substance dissolved in water that does not conduct an electrical current f. Soluble: able to dissolve

Types of solutions

2. Suspensions a. A heterogeneous mixture of a solvent- like substance with particles that slowly settle out b. Can be separated by a filter

3. Colloid: a. Particles that are intermediate in size between those in solutions, and suspensions b. Can not be filtered

Class of colloidPhases SolSolid dissolved in liquid GelSolid network extending throughout liquid Liquid emulsionLiquid dispersed in liquid FoamGas dispersed in liquid Aerosol* *smokeSolid dispersed in gas *fogLiquid dispersed in gas *SmogSolid an liquid dispersed in gas Solid emulsionLiquid dispersed in solid Colloidal Suspensions

4. Tyndall Effect (Tyndall Scattering) Scattering of light by the particles in a colloid or fine suspensions 5. Brownian Motion Deals with the movement of solids from an area of high concentration to low concentration over a permeable membrane

Review of Properties of Solutions, Colloids, and Suspensions SolutionsColloidssuspensions HomogeneousHeterogeneous nm solute particles nm dispersed particles Over 1000 nm suspended particles Does not separate on standing Particles settle out Cannot be separated by filtration Can be separated by filtration No light scatteringScatters light (Tyndall effect) May scatter light, but not transparent

The Solution Process A. Factors Affecting the Rate of Dissolving 1. Increasing the surface area of the solute 2. Agitating the solution 3. Heating the solvent

B. Solubility 1. Solution equilibrium a. The physical state in which the opposing processes of dissolving and crystallizing of a solute occur at the same rate b. solute + solvent solution

c. Saturated solution a solution that contains the maximum amount of dissolved solute d. Unsaturated solution a solution that contains less solute than a saturated solution under existing conditions

e. Supersaturated solution a solution that contains more dissolved solute than a saturated solution under the same condition f. Solubility a substance is the amount of that substance required to form a saturated solution with a specific amount of solvent at a specific temperature

g. Solubility curve A graph showing the concentration of a substance in its saturated solution in a solvent as a function of temperature

 Factors Affecting Solubility 1. Types of solvents and solutes (like dissolves like) a. Polar dissolves in polar b. Ionic dissolves in ionic and polar c. Nonpolar dissolves in nonpolar d. Immiscible: substances that are not able to dissolve in each other (ex. Oil and water)

e. Miscible: two substances that are mutually soluble 2. Pressure a. Effects gases b. Henry’s Law: The solubility of a gas in a liquid is directly proportional to the partial pressure of that gas on the surface of the liquid.

*Effervescence of soda (Effervescence: the rapid escape of a gas from a liquid in which it is dissolved) How does Henry’s Law apply?

3. Temperature a. Gases Increasing temperature decreases gas solubility b. Solids Most often, increasing temperature increases solubility

Heats of solution 1. The amount of heat energy absorbed or released when a solute dissolves in a specific amount of solvent 2. endothermic = + 3. exothermic = -

4. solvated: a solute molecule or ions surrounded by solvent molecules a. Solute-solute attraction is broken up ( endothermic) b. solvent-solvent attraction is broken up (endothermic)

c. Solute-solvent attraction is formed (exothermic)  Concentration of solutions 1. concentration: a solution is a measurement of the amount of solute in a given amount of solvent or solution

a. Percent by mass 1. the number of grams of solute dissolved in 100 g of solution 2. % mass = mass of solute 100 mass of solute + mass of solvent

3. Ex. A solution of sodium chloride is prepared by dissolving 5 g of salt in 550 g water. What is the concentration of this solution given as percent by mass?

b. Molarity (M) 1. the number of moles of solute in 1 liter of solution 2. molarity = number of moles of solute number of liters of solution

3. Ex. What is the molarity of 3.50 L of solution that contains 90.0 g of sodium chloride? 4. How many moles of HCl are present in 0.8 L of a 0.5 M HCl solution?

c. Molality (m) 1. the concentration of a solution expressed in moles of solute per kilogram of solvent 2. molality = no. of moles solute mass of solvent (kg)

c. Ex. A solution contains 17.1 g of sucrose (C 12 H 22 O 11 ) dissolved in 125 g water. Find the molal concentration of this solution. d. Ex. A solution of iodine in tetrachloride is needed for certain chemical tests. How much iodine must be added to prepare a m solution of iodine in CCl 4 if g of CCl 4 are used?

Colligative Properties of Solutions A. Colligative property: A property that depends on the number of solute particles but is independent of their nature B. nonvolatile: has little tendency to become a gas under existing condition

C. Types of Colligative Properties 1. Freezing-point depression (Δt f ) a. Molal freezing point constant (K f ) b. the freezing point depression of the solvent in a 1 molal solution of a nonvolatile molecular solute c. Δt f = K f m

d. Example: What is the freezing-point depression of water in a solution of 17.1 g of sucrose (C 12 H 22 O 11 ) and g of water?

2. Boiling-point elevation (Δt b ) a. Boiling point constant (K b ) b. The difference between the boiling points of the pure solvent and a nonelectrolyte solution in that solvent, and is directly proportional to the molal concentration of the solution c. Δt b = K b m

d. Example: What is the boiling point elevation when 11.4 g of ammonia (NH 3 ) is dissolved in g of water? (K b for water is 0.52 C°/ m)