Chapter 13 - Solutions

Types of Mixtures

Solutions

soluble - definition

dissolving sugar; sugar disappears but can be tasted; uniformly distributed in the water

solution - definition

same composition and properties throughout - homogeneous mixture

Components of Solutions

solvent - definition

solute - definition

solute sometimes is the component of the solution that is there in the lesser quantity e.g. gas in a gas or liquid in a liquid

for a solid in a liquid, the solute particles are so small they cannot be seen and they will remain dissolved and uniformly mixed as long as the conditions do not change e.g. the solvent evaporating or the temperature changes

figure 13-2a page 396 - filter the solution through filter paper and both solute and solvent will pass through - the solute particles are that small - 0.01 to 1 nm in diameter

figure 13-2b page 396


Types of Solution

different types list in table 13-1 page 396 - note that you must specify which is solute and which is solvent

figure 13-3 alloy of silver/gold

Suspensions

suspension - definition

e.g. muddy water

size of particles is greater than 1000 nm

can filter the solute particles using filter paper

Colloids

colloids - definition

particle size is between 1 nm and 1000 nm

mud that settles out of water still leaves a cloudy mixture because a colloid has formed

colloids pass through a paper filter

in a colloid the particles do not settle out because of the constant movement of the surrounding molecules

dispersed phase

dispersing medium

table 13-2 page 398 - examples of colloids

foam, aerosol, gel

Homework: 13.1

Tyndall Effect

colloids may appear homogeneous

particles, however, are large enough to scatter light e.g. headlights on a foggy night

Tyndall effect: need colloid, transparent medium, a strong beam of light, view the path of the light at right angle

solution does not display this effect

figure 13-4 page 398

table 13-3 page 398 - properties of solutions, colloids, and suspensions

Brownian motion - can detect motion of particle in a colloid under a microscope; view bright light across specimen at right angles; movement due to rapidly moving molecules.

Solutes: Electrolytes vs. Nonelectrolytes

solutes can be classified according to the type of particles they form in solutions: molecules/atoms or ions

ionic compound

electrolyte - definition

includes soluble ionic compounds and some polar covalent compounds, e.g. HCl produces H3O+ + Cl-

solution with neutral covalent molecules does not conduct electricity and is called an nonelectrolyte

nonelectrolyte - definition

figure 13-5a page 400

figure 13-5b page 400

figure 13-5c page 400

not all electrolytes conduct to the same extent

Homework: 13.2

The Solution Process

Factors Affecting the Rate of Dissolution

Increasing the Surface Area of the Solute

molecules or ions of the solute are attracted by the solvent and the dissolving process occurs at the surface of the solute e.g. cube of sugar in warm water

the more surface area the faster the dissolving process

figure 13-6 page 401


Agitating a Solution

Stirring or shaking brings the solute and solvent into better contact and increases the rate of dissolving

Heating a Solvent

at higher temperatures the average K.E. of the solvent increases and the collisions between solute and solvent are more frequent and, thus, the rate of dissolving increases for most solvents.

Homework: 13.3


Solubility

When you add solute to solvent you eventually reach a point at which no more solute will dissolve in the solvent and the excess falls to the bottom of the container -- you have exceeded the solubility of the solvent.

When you have reached the solubility of the solvent you can have solution equilibrium -- saturated solution.

solution equilibrium - definition

the solubility of the solvent and therefore where solution equilibrium occurs depends on
a) the nature of the solvent; b) the nature of the solute; c) the temperature.

Saturated vs. Unsaturated Solutions

saturated solution - definition

figure 13-7 page 402

unsaturated solution - definition

figure 13-8 page 403

adding more solute to a saturated solution

adding more solvent to a saturated solution

how do you recognize a saturated solution?

Supersaturated Solutions

Saturating a solution at a temperature above room temperature and cooling it to room temperature -- what would you expect to happen?

supersaturated solution - definition

disturbing a supersaturated solution and the results

seeding a supersaturated solution

Solubility Values

solubility - definition

units are usually grams of solute/100 grams of water (or solvent)

temperature dependent for all solutions

for gases need pressure also

Table 13-4 page 404

rate of dissolving is not related to solubility

Solute-Solvent Interactions

like dissolves like
bonding and polarity
intermolecular forces between solute and solvent

Dissolving Ionic Compounds in Aqueous Solution

water is polar vs. ionic compounds

solvent pulls and surround solute therefore need attraction between the two

hydration - definition

figure 13-9 page 405

solute is said to be hydrated

solvation

hydrates (water of hydration) e.g. copper (II) sulfate penta hydrate

figure 13-10 page 405

water molecule is incorporated into the crystal structure

heating gently drives off the water and leaves you with the anhydrous form of the compound

Nonpolar Solvents

ionic compounds and nonpolar solvents e.g. carbon tetrachloride and benzene and toluene

Liquid Solutes and Solvents

immiscible - definition

toluene and water

figure 13-11 page 406

miscible - definition

e.g. benzene and carbon tetrachloride - nonpolar

e.g. ethanol and water - polar

figure 13-12 page 406

ethanol is intermediate between water and carbon tetrachloride

Effects of Pressure on Solubility

only important in dealing with gases

gas + solvent = solution

if equilibrium is undisturbed, the solubility of the gas in the liquid is unchanged at a given temperature

increasing the pressure increases the solubility of the gas in the solvent e.g. carbonated beverages

new equilibrium is established with more gas molecules dissolved in the solvent

Henry's Law

Henry's Law - statement

assumption is that the gases do not react with each other; each gas would dissolve to the same extent as if it were the only gas present

effervescence - definition

figure 13-13 page 407

Effects of Temperature on Solubility

for gases, increasing the temperature generally decreases the solubility

figure 13-14 page 408

at new equilibrium have fewer gas molecules in solution

for solids in liquids - can be either an increase or decrease in solubility

figure 13-15 page 408

each substance is affected differently by a change in temperature

Homework: 13.4


Heats of Solution

always have an energy change when a solution is formed

KI in water - outside of the container feels cold

LiCl in water - outside of the container feels hot

energy is required to separate solute molecules and solvent molecules and energy is involved when the solvent surrounds the solute particles - 3 energy factors in the dissolving process

solvated - definition

figure 13-9 page 405

figure 13-16 page 409 Solvation process

heat of solution - definition

sign convention - tables only

table 13-5 page 410

Homework: 13.5


Concentrations of Solutions

concentration - definition

molarity and molality

dilute vs concentrated

not related to saturation of solution

Molarity


molarity - definition
need to know molar mass to calculate molarity
symbol is M
M= amount of solute in moles/volume of solution in liters
use volumetric flask to prepare molar solutions
figure 13-17 page 413
for NaOH the molar mass is 40 g/mol
thus 40 g ( one mole ) of NaOH added to a one liter volumetric flask and then add enough water to bring the total volume to one liter ---> 1 M solution ( 1 mol/1L = 1 M )
OR 20 g ( 0.5 mole ) of NaOH added to a one-half liter volumetric flask and then add enough water to bring the total volume to one-half liter ---> 1 M solution ( 0.5 mol/0.5 L = 1 M )
OR 20 g ( 0.5 mole ) of NaOH added to a one liter volumetric flask and then add enough water to bring the total volume to one liter ---> 0.5 M solution ( 0.5 mol/1 L = 0.5 M )
First type of molarity problem - given grams and volume and asked to calculate molarity:
Sample Problem 13-1

sample problem 13-1

Second type of molarity problem

sample problem 13-2

Homework: 13.6

Molality


molality - definition

figure 13-18 page 416

For NaOH, molar mass is 40 g;
40 g of NaOH added to exactly 1 kg of water produces a 1 molal ( 1 m ) solution of NaOH.

molality = moles of solute/1kg of solvent or
molality = moles of solute/1000 g of solvent

e.g. 80 g of NaOH dissolved in 1 kg of water would produce a 2 m solution -- 80 g of NaOH is 2 mol of NaOH in 1 kg of water is 2 mol/kg or 2m

Sample Problem 13-4

sample problem 13-4

Sample Problem 13-5

sample problem 13-5

Homework: 13.7

end of notes

Molality is the concentration of a solution expressed in moles of solute per kilogram of solvent.

Soluble means capable of being dissolved. back

A solution is a homogeneous mixture of two or more substances in a single phase. Back

The solvent is the dissolving medium in a solution. Back

The solute is the substance dissolved in the solution. Back

A suspension is a mixture in which the particles of the solvent are so large that they settle out unless the mixture is constantly stirred or agitated. Back

A colloid or a colloidal dispersion is a mixture that contains particles that are intermediate in size between those in solutions and suspensions. Back

An electrolyte is a substance that dissolves in water to give a solution that conducts electric current. Back

A nonelectrolyte is a substance that dissolves in water to give a solution that does not conduct an electric current. Back

 

Solution equilibrium is the physical state in which the opposing processes of dissolution and crystallization of a solute occur at equal rates. Back

A saturated solution is a solution that contains the maximum amount of dissolved solute. Back

An unsaturated solution is a solution that contains less solute than a saturated solution under the existing conditions. Back

A supersaturated solution is a solution that contains more dissolved solute than a saturated solution contains under the same conditions. Back

Solubility of a substance is the amount of that substance required to form a saturated solution with a specific amount of solvent at a specified temperature. Back

 

Hydration is the solution process with water as the solvent. Back

Immiscible indicates that liquid solutes and solvents are not soluble in each other. Back

Miscible indicates that liquid solutes and solvents freely dissolve in one another in any proportion. Back

Henry's law states that the solubility of a gas in a liquid is directly proportional to the partial pressure of that gas on the surface of the liquid. Back

Effervescence is the rapid escape of a gas from a liquid in which it is dissolved. Back

Solvated means that a solute particle is surrounded by solvent molecules. Back

Heat of solution is the amount of heat energy absorbed or released when a specific amount of solute dissolves in a solvent. Back

The concentration of a solution is a measure of the amount of solute in a given amount of solvent or solution. Back

Molarity is the number of moles of solute in one liter of solution. Back