1. Chapter 16: Mixtures & Solutions

2. Heterogeneous Mixtures
Mixture: a combination of two or more pure substances in which each pure substance retains its individual chemical properties
Can be homogeneous and heterogeneous
Heterogeneous mixture: a mixture that does not have a uniform composition and in which the individual substances remain distinct.
Suspensions: a mixture containing particles that settle out if left undisturbed
Particles are large enough for gravity to cause the particles to settle
Ex. Muddy water (particles can be separated when poured through a filter)
Ex. Latex paint
Colloid: heterogeneous mixtures of intermediate sized particles (between 1 nm and 1000 nm) and do not settle out.
Ex. Milk

3. The most abundant substance in a mixture is the dispersion medium.
Colloids are categorized according to the phases of their dispersion particles and dispersing mediums.

4. Tyndall effect: when dispersed colloid particles scatter light.
Brownian motion: the jerky, random movements of particles in a liquid colloid, from the results of particle collisions.
Robert Brown ( )
Noticed random movements of pollen grains dispersed in water
Results from a collision of particles of the dispersion medium with the dispersed particles  prevents settling
Tyndall effect: when dispersed colloid particles scatter light.
Example: headlights in fog

5. Homogeneous Mixtures
Solution: a homogeneous mixture of two or more substances
2 Parts of a simple solution:
Solute: the component that is dissolved (least abundant part)
Solvent: the dissolving agent (most abundant part)
Aqueous Solution: a substance (solute) is dissolved in water (solvent)
Complex Solutions: More than one solute

7. Common Solution Formation Terms
A substance that dissolves in a solvent is soluble.
Substances that form a solution
Ex. Salt and water
A substance that does not dissolve in a solvent is insoluble.
Ex. Sand and gasoline
Two liquids that are soluble in each other in any proportion are miscible.
Ex. Water and ethanol  alcoholic beverages
Two liquids that can be mixed but separate shortly after are immiscible.
Ex. Oil and Vinegar

8. Solvation
Solvation: the process of surrounding solute particles with solvent particles to form a solution.
Solvent particles break their interactions to form interactions with the solute particles
Oil does not form a solution with water because there is little attraction between polar water molecules and nonpolar oil molecules.
Hydration: solvation with water as the solvent
During solvation, the solute must separate into particles and move apart, which requires energy.
The overall energy change that occurs during solution formation is called the heat of solution.

9. Factors That Affect Solvation
Agitation: brings fresh solvent into contact with the solute
Temperature: the solvent particles have more kinetic energy, increasing the force and frequency of solvent-solute collisions
Particle Size: smaller solute particles have greater surface area and therefore more solvent-solute collisions occur

10. Solubility
Solubility: maximum amount of substance that dissolves in a given quantity of a solvent at a certain temperature
Depends on the nature of the solute and solvent
Saturated solutions: contains the maximum amount of solute that can be dissolved at a given temperature
Unsaturated solution: a solution that contains less solute than a saturated solution
Supersaturated solution: under suitable conditions, the solution contains a greater amount of solute than a saturated solutions
To form a supersaturated solution, a saturated solution is formed at high temperature and then slowly cooled
Supersaturated solutions are unstable

11. Factors that Affect Solubility
Nature of the solute/solvent
“Like dissolves like”
Nonpolar solvents (carbon tetrachloride) dissolve nonpolar solutes (grease)
Polar solvents (water) dissolve ionic compounds (salt) and polar solute
Temperature
Solid dissolving in a liquid  solubility tends to increase as temperature increases
Gas dissolving in a liquid  solubility tends to decrease as temperature decreases
Pressure
Gas solubility increases as the pressure above the solution increases
Ex. Carbonated beverages: bottled under high pressure to increase the CO2 solubility in the water

12. Henry’s Law: at a given temperature, the solubility of a gas in a liquid is directly proportional to the pressure of the gas above the liquid
Example: The solubility of a gas in water is 0.22g/L at 20.0kPa of pressure. What is the solubility at 115 kPa?

13. Solution Concentration
Concentration: a measure of the amount of solute that is dissolved in a specific quantity of solvent
Qualitative Descriptions:
Dilute solutions: contains a small amount of solute
Concentrated solution: contains a lot of solute

14. Percent by mass Usually describes a solid dissolved in a liquid
Expressed as a percentage
Ratio of the solute quantity to the total solution quantity
Example: What is the mass percent of a solution with g of CaCl2 dissolved in 450g of water?

15. Percent by Volume
Usually describes solutions with both parts as liquids
Expressed as a percentage
Ratio of the solute quantity to the total solution quantity
Example: What is the percent by volume of a solution with 45.1 mL of ethanol mixed with mL of water?

16. Molarity Number of moles of solute dissolved in 1L of solution
Example 1: What is the concentration when 35.4 g of LiOH is added to enough water to form a solution with a volume of 450mL?
Example 2: How would you prepare mL of 1.2 M Na2CO3?

17. Molality The ratio of moles of solute dissolved in 1 kg of solvent
Useful to eliminate volume changes due to temperature
1m is a molal solution
Example: What is the molal concentration of a solution made by dissolving 67.2 g Mg(NO3)2 in mL of water

18. Mole Fraction
Ratio of the number of moles of solute to the total number of moles of solute and solvent
Example: Calculate the mole fraction when 34.5 g of NaCl is dissolved in 250 g of water.
XA = mole fraction
n = number of moles
A/B = substances

19. Making Dilutions
Chemicals are shipped and stored in high concentrations
We dilute these concentrated solutions for use in experiments
To dilute an acid:
Add acid to the required amount of water
This generates the least amount of heat
Example: How would you prepare mL of 3.0 M H2SO4 from a stock solution that is 18.4 M?
M1V1 = M2V2

20. Colligative Properties
Colligative Properties: physical properties of solutions that are affected by the number of particles but not by the identity of dissolved solute particles.
Electrolytes: an ionic compound whose aqueous solution conducts electricity
Ions separate (dissociate) during the hydration process
Increases the number of dissolved particles in solution
Ex. 1 mole of NaCl breaks into 1 mol Na+ and 1 mol Cl-
3 mole CaBr2  3 mol Ca2+ and 6 mol Br-
Nonelectrolytes: many molecular compounds dissolve in water but do not dissociate
Ex. Sugar C12H22O11
These solutions do not conduct electricity
No separation = less of an impact on colligative properties

21. Vapor Pressure Lowering
Vapor Pressure: pressure exerted in a close container by liquid particles that have escaped the liquid’s surface and entered the gas state
Adding a nonvolatile solute to a solvent lowers the solvent’s vapor pressure
Solute particles occupy some of the surface area (fewer particles enter the gaseous state)
Solute particles interact with the solvent particles therefore requiring more energy for the solvent to escape
The greater the number of solute particles, the lower the vapor pressure

23. Boiling Point Elevation
Boiling occurs when: vapor pressure = atmospheric pressure
More heat is needed to supply additional kinetic energy to raise the vapor pressure to atmospheric pressure.
The amount of increase is dependent upon the amount of solute
The boiling point of a solution is higher than the boiling point of a pure solvent
ΔTb = Kbm
ΔTb is the boiling point elevation
Kb is the molal boiling point elevation constant
m represents molality

25. Freezing Point Depression
Solute particles interfere with the solvent particle attractive forces
This prevents the solvent from freezing at its normal temperature
The freezing point of a solution is always lower than that of the pure solvent
Amount of decrease is dependent on amount of solute
ΔTf = Kfm
ΔTf is the freezing point depression
Kf is the freezing point depression constant
m is molality

27. What is the boiling and freezing temperature of the solution of 23
What is the boiling and freezing temperature of the solution of g NaI in 345 g of water.

28. Osmotic Pressure
Osmosis: the diffusion of a solvent through a semipermeable membrane
Water molecules diffuse across the membrane from the dilute solution to the concentrated solution
Osmotic pressure: the amount of additional pressure caused by water molecules that moved into the concentrated solution