CHAPTER 17 and 18

WATER AND AQUEOUS SOLUTIONS

Water

1. Structure of water (H2O) a. two atoms of hydrogen

b. One atom of oxygen

c. Bent structure

d. Bond angles 104.5 °

e. O has a sp3 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 = 4.184 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 0.917 g/cm3 (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 colloid Phases

Sol Solid dissolved in liquid

Gel Solid network extending throughout liquid

Liquid emulsion Liquid dispersed in liquid

Foam Gas dispersed in liquid

Aerosol*

*smoke Solid dispersed in gas

*fog Liquid dispersed in gas

*Smog Solid an liquid dispersed in gas

Solid emulsion Liquid 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

Solutions Colloids suspensions

Homogeneous Heterogeneous Heterogeneous

0.01-1 nm solute particles

1-1000 nm dispersed particles

Over 1000 nm suspended

particlesDoes not separate

on standingDoes not separate

on standingParticles settle out

Cannot be separated by

filtration

Cannot be separated by

filtration

Can be separated by filtration

No light scattering Scatters 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 curveA 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 (C12H22O11) 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 0.480 m solution of iodine in CCl4 if 100.0 g of CCl4 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 (Δtf) a. Molal freezing point constant (Kf)

b. the freezing point depression of the solvent in a 1 molal solution of a nonvolatile molecular

solute

c. Δtf = Kfm

d. Example: What is the freezing-point depression of

water in a solution of 17.1 g of sucrose (C12H22O11) and 200.0

g of water?

2. Boiling-point elevation (Δtb) a. Boiling point constant (Kb)

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. Δtb = Kbm

d. Example: What is the boiling point elevation when

11.4 g of ammonia (NH3) is dissolved in 200.0 g of water? (Kb for water is 0.52 C°/ m)