solubility

Question 1

Define solubility

Answer 1

Solubility is an intrinsic property of a material. It is the maximum amount of solute that will dissolve in a given quantity of a solvent, at a given temperature.

Question 2

Describe polar solvents and properties affecting solubility

Answer 2

Polar solvents dissolve polar solutes. Solubility of these depends on structural features including:

• ratio of polar:non-polar groups of molecules
• Straight chain alcohols, aldehydes and ketones are slightly soluble in water
• additional polar groups increase solubility
• branching of chains increases solubility

Question 3

Describe non-polar solvents and give an example

Answer 3

Dissolves non-polar solutes through weak intermolecular attractions and vdW forces.
example: oil in benzene

Question 4

Describe semipolar solvents and give an example

Answer 4

Intermediate solvents that induce miscibility in polar and non-polar liquids. This can induce a degree of polarity
example: acetone increases solubility of ether in water.

Question 5

What is a solvation mechanism? What is the universal solvent?

Answer 5

Solvation mechanisms are the way in which a solvent dissolves a solute.
Water is regarded as a universal solvent, where it has a high dielectric constant and is amphiprotic.

Question 6

What is a dielectric constant?

Answer 6

The extent to which a material can store charge. Increasing polariy is proportional to the dielectric constant.

Question 7

What is dipole interaction in terms of being a solvent mechanism?

Answer 7

This is the attraction between partial charges of solvents and solutes. Solutes must be polar to compete for bonds of solvent molecules.

Question 8

Describe H bond formation as a solvation mechanism

Answer 8

Water dissolves phenols, alcohols and other O and N containing compounds that can form hydrogen bonds with water.

Question 9

How do amphiprotic substances interact as solvents?

Answer 9

Amphiprotic substances are able to break covalent bonds of strong acids and bases, being both a proton donor and acceptor, being an effective solvent for these substances.

Question 10

Describe solvent-solute interactions of weak acids and bases in water.

Answer 10

weak acids/bases are not completely ionised (solubilised) in water due to hydrogen bonds formed. Addition or a conjugated acid/base will increase the solubility of the substance.

Question 11

What factors affect gas-in-liquid solutions?

Answer 11

pressure
temperature
electrolytes
chemical reactions

Question 12

Describe how pressure affects a gas-in-liquid solution and what law governs this

Answer 12

This can be observed using Henry’s law, where the concentration of dissolved gas is proportional to the partial pressure of undissolved molecules times the solubility coefficient.
This is only applicable to dilute solutions at a constant temperature.

Question 13

Explain the effects of temperature on solubility in a gas-in-liquid solution

Answer 13

As temperature increases, the solubility of gas decreases due to the tendency of gas to expand.

Question 14

Explain how electrolytes affect the solubility of gas-in-liquid solutions

Answer 14

Gases are released by the introduction of salts due to a greater affinity of electrolytes towards water resulting in a weakening of gas-solvent interactions. This decreases the solubility of gases in liquids.

Question 15

Describe a liquid-in-liquid system and

the categories of these

Answer 15

These are preparations involving the mixing of 2 or more liquids, and are divided into completely and partially miscble systems.

Question 16

what is complete miscibility of a liquid-liquid system?

Answer 16

Adhesive forces between molecules is greater than cohesive forces. This creates no solubility issues

Question 17

What forces are involved in a partially miscible liquid-liquid system?

Answer 17

Adhesive forces between two liquids is less than cohesive forces between molecules of the same phase. Non-polar molecules will be squeezed out by powerful attractive forces in a polar liquid.

Question 18

How does temperature affect liquid-liquid systems?

Answer 18

There is a upper and lower critical temperature at which above and below these (repsectfully) two liquids are miscible in all proportions.
When there is no critial temp for a solution, the two liquids are partially miscible over all temperatures.

Question 19

How does the addition of a foreign substance affect the solubility of a liquid-liquid system?

Answer 19

If the added material’s solubility is significantly different in either of the components, this causes the solubility between the liquid pair to be decreased (salting out).
When the material added is soluble in both liquids to the same extent, the mutual solubility of the liquid pair increases (blending)

Question 20

What factors affect the solubility of a solid-in-liquid solution?

Answer 20

temperature
molecular structure of solute
nature of solvents
crystal characteristics
acid/base properties.

Question 21

How is solute distributed in immiscible solvents?

Answer 21

Solute is distributed according to the partition coefficient. This gives a ratio of concentration of substance in each solvent, at equilibrium, at a given temperature.

Question 22

what does log P indicate?

Answer 22

When log P is greater than 1, the solution is lipophilic

when log P is smaller than 1, the solution is hydrophilic.