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
Second type of molarity problem
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 13-5
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