Colligative Properties (11.4)

Question 1

What is colligative properties?

Answer 1

Properties of a solution that depends on the amount of solutes in the solvent. DOES NOT DEPEND ON TYPES OF CHEMICALS. Only depends on the concentration of solution (how many molecules in the solution).

Question 2

What is a mole fraction?

Answer 2

An expression of concentration of a component in a mixture, tells you how many parts of one substance is in a solution/mixture.

Question 3

What is molality?

Answer 3

Measurement ratio of numbers of moles of solute to the mass of solvent in kilograms.

Question 4

Equilibrium Vapor Pressure

Answer 4

When number of solvent molecules that escaped into the air is exactly the same as the number returning to the water.

Question 5

What happens when the air above the water has a certain pressure from the water vapor?

Answer 5

If the pressure doesn’t change, and the temperature stays the same, the pressure will stay consistent.

Question 6

How is vapor pressure measured? Or collected?

Answer 6

It is the force exerted by vapor molecules when they collide with surfaces, which generates the pressure we measure as vapor pressure. That’s why gas gives that “push” towards the container’s surface.

Question 7

What law is the relationship between vapor pressure of solution components and the concentrations of those components?

Answer 7

Raoults law. Partial pressure exerted by any component of an ideal solution is equal to the vapor pressure of the pure component multiplied by its mole fraction in the solution.

Question 8

What happens to the liquids vapor pressure if you are dissolving a non-volatile liquid in a volatile substance?

Answer 8

The vapor pressure will be lowered. The presence of solute molecules decreases the surface area at the top of the liquid thereby reduces the rate of solvent vaporization.

Question 9

How does Rauolts Law apply to distillation processes?

Answer 9

If distilling for a specific liquid, liquid A and B, where liquid A is more volatile. When distilling, there will be a higher mole fraction of liquid A in vapor than liquid A in the solution.

Question 10

What is a good example of real life distillation process?

Answer 10

Oil refineries, they do fractional distillation to separate the components of crude oil. The fractionating column is super heated to collect specific liquids (diesel fuel, kerosene, gasoline).

Question 11

What is boiling point?

Answer 11

Boiling point is the temperature that starts to turn a liquid into gas. The presence of solutes will also raise boiling point to where it takes more energy to reach to the boiling point.

Question 12

What is boiling point directly proportional to?

Answer 12

The molal concentration of solute species.

Question 13

To an extent, so far the lowering of vapor pressure and elevation of boiling point is completely dependent on what?

Answer 13

Completely dependent on the number of particles in the solution and not have to do with mass, size, and identities of chemical particles.

Question 14

What is freezing point?

Answer 14

The temperature of a liquid that becomes a solid under standard atmospheric pressure.

Question 15

Is freezing point depression also directly proportional to molal concentration?

Answer 15

Yes, the boiling point elevation formula applies to the same concepts for freezing point depression. They are just opposites.

Question 16

According to the phase diagram for a solution, why doesn’t solution expand as solution is freezing?

Answer 16

Solutes in the solvent is making it difficult for the pure solvent to spread because solutes are taking up more surface areas in the solution.

Question 17

Why does water expand when freezing?

Answer 17

1. Pure solvents form ice crystal lattices more easily than a solution. Because freezing point depression decreases as more solutes are in pure solvent when freezing, making it difficult for solution to freeze compared to pure solvent.
2. Density of pure solvent is lower than a solution thereby helping the ice form more easily. When water freezes, it floats to the surface instead of sinking. This is due to the structure of the ice.
3. Hydrogen bonding in water is strong and directional because of electromagnetic difference, Oxygen is more electromagnetic than Hydrogens in the bond, so the whole molecule is polar (unequal sharing of electrons). This will result in a partial negative charge on Oxygen and a partial positive charge on the Hydrogens. So these partially charged molecules are attracted to other water molecules that have the same partial charges. In general hydrogen bond is stronger than all of the van der Waals forces, which is why it is considered pretty strong, creating a strong dipole moment.
4. Continuing off from strong dipole moment, strong intermolecular forces means stronger dipole-dipole interactions, which affects a substances ability to boil, freeze, melt, solubility, and other physical properties. Thereby is the reason why water is able to expand so easily when freezing.

+ In conclusion, the less dense, more open structure, water expands as it freezes. It is unusual because most substances contract when they solidify. But because of water’s unique hydrogen bonding causes it to expand.

+ This is off topic, but to be more precise when water freezes, it is the solvent molecules that are freezing, not the solutes. So when the solvent transitions to liquid and gas, the solutes will be left behind because they are non-volatile species.

Question 18

What is a semipermeable membrane?

Answer 18

A type of membrane that allows certain molecules or ions to pass through while blocking others. It selectively permits the passage of solvents such as water, but restricts the movement of solutes.

Question 19

What is osmotic pressure?

Answer 19

The pressure that is needed to stop osmosis, osmotic pressure depends on number of molecules, not mass or size of molecules.

Question 19

What is osmosis?

Answer 19

1. The movement of water through a semipermeable membrane from an area with less solute to a solution with more solute. Water randomly moves due to their kinetic energy, in a solution they are in constant motion, which is why they have the tendency to spread out evenly.
2. Water is naturally attracted to solute particles, if there are more solute particles in one area, water will try to balance itself with the higher concentrated side until both sides of the membrane reaches equilibrium.
3. No energy or carrier is needed because it is a simple diffusion of water.

Question 20

Why is it easier to measure osmotic pressure when osmosis is stopped when adding pressure rather than just measuring the pressure of osmosis?

Answer 20

When continuously applying pressure to stop osmosis, it is now a stable well-defined point where the overall movement of water through the membrane has stopped. It is now at equilibrium and can be measured. It is easier to measure osmosis when it stops rather than trying to measure it while osmosis pressure is still active.

Question 21

What is a triple point in water phase diagram?

Answer 21

1. A unique set of conditions at specific temperature and pressure where three different phases of substance, solid, liquid, and gas coexist in equilibrium.
2. The substance exist as solid, liquid, and gas at the same time, with phases having the ability to transition freely between each other without changing the overall state of the system.

Question 22

What is a hypotonic solution?

Answer 22

A less concentrated solution.

Question 23

What is a hypertonic solution?

Answer 23

A more concentrated solution.

Question 24

What is hemolysis?

Answer 24

Rupture or destruction of red blood cells, surrounding fluids of red blood cells is lower which causes the tendency of water to move inwards towards the cell with higher concentrations.

Question 25

What is crenation?

Answer 25

Shriveling of white blood cells because concentration of surrounding fluids is higher than insides of red blood cells so water has tendency to move outwards of red blood cells causing them to shrink.

Question 26

What is the van’t Hoff factor?

Answer 26

Denoted by i, help’s quantify how the presence of solute particles affect the physical properties of the solution.

i is calculated by number of particles in solution/number of formula units dissolved in solution.

Question 27

Why isn’t the van’t Hoff factor always accurate?

Answer 27

• Because of ion pair formation, especially at higher concentrations, some dissociated ions can recombine to form ion pairs. So some will completely dissociate, and some will just combine back together again.
• These pairs are loosely bound, and are essentially combinations of oppositely charged ions that weakly attracted to each other
• Both of those activities can affect the van’t Hoff factor.

Discovered by Peter Debeye and Erich Huckel