Solubility

Question 1

Solubility of a solute (S)

Answer 1

maximum amount that dissolves in a fixed quantity of solvent at a specific temperature.

Question 2

saturated solution

Answer 2

one in which the solvent has dissolved all the solute it can at that temperature

Question 3

Like dissolves like

Answer 3

-solute particles must separate
-solvent particles make room for solute
-solute and solvent particles must mix together, and attract each other
Some energy must be absorbed to allow particles to separate
Some energy is released when they mix & attract each other

Question 4

Water reasoning

Answer 4

hydrogen bonds in water would have to break and can only be replaced by London forces between solute and water (not favourable)Like dissolves like, i.e. match intermolecular forces of solvent & solute

Question 5

Charged species don’t dissolve in non-polar solvents.

Answer 5

When salts dissolve in water, they dissociate and are “hydrated” (surrounded by water molecules)c) Ionic solutes dissolve in very polar solvents

Question 6

For an ionic compound to dissolve

Answer 6

hydration energy > lattice energy

Question 7

Solid-Solid mixtures

Answer 7

Solids diffuse very little and usually form heterogeneous mixtures

Question 8

Gas-Solid solutions

Answer 8

When a gas dissolves in a solid, it occupies the spaces between closely packed particles

Question 9

Solid-Solid solutions

Answer 9

Alloys are made by melting solids, mixing them and allowing them to freeze.

Question 10

Substitutional alloys

Answer 10

atoms of another element take the place of atoms of the main element in the structure

Question 11

Interstitial alloys

Answer 11

atoms of another element fillsome of the spacesbetween atoms of the main element

Question 12

Energy changes in Solution Formation

Answer 12

Step 1: Solute particles separate from each other. This process is endothermic.
Solute (aggregated) + heat→solute (separated) ΔHsolute> 0
Step 2: Solvent particles separate from each other. This process is endothermic.
Solute (separated) + solvent (separated) → solution + heatΔHmix< 0
Step 3: Solute and solvent particles mix and form a solution. This step is exothermic.
Solvent (aggregated) + heat→solvent (separated) ΔHsolvent> 0Energy changes in Solution Formation

Question 13

Heat of Solution

Answer 13

The overall solution process may be either exothermic or endothermic.

Question 14

Exothermic Process

Answer 14

Hsoln< 0 because the sum of the endothermic processes (Hsolute+ Hsolvent) is smaller than the exothermic term (Hmix).

Question 15

Endothermic process:

Answer 15

Hsoln> 0 because the sum of the endothermic processes (Hsolute+ Hsolvent)is larger than the exothermic term (Hmix).

Question 16

Solvation and Hydration

Answer 16

Solvation is the process of surrounding a particle with solvent particles. In water, solvation is called hydration.

Question 17

Hydration of Ions

Answer 17

The hydration of an ion is always exothermic because ion-dipole forces are very strong (stronger than H-bonds)

Question 18

Trends in Hhydr for Ions

Answer 18

The heat of hydration for an ion depends on the charge density, the ratio of charge to volume

The higher the charge of the ion and the smaller its radius, the closer the ion can be to the oppositely charged pole of the H2O molecule, and the stronger the attraction.The heat of hydration for an ion depends on the charge density, the ratio of charge to volume

Question 19

Lattice energy

Answer 19

Energy to separate an ionic solute (Hsolute) into gaseous ions is the energy required to overcome the intermolecular forces in the solid(Hlattice) This is highly positive!

Question 20

Solutions and Entropy

Answer 20

The entropy(S) of a system is related to the number of ways a system can disperse its energy and therefore to the freedom of motion of the particles (disorder).
Gases have the highest entropy of the three states of matter.
A solution usually has higher entropy than the pure solute and pure solvent.
An increase in entropy is favored in both physical and chemical processes

Question 21

Solubility as an Equilibrium Process

Answer 21

A saturated solution contains the maximum amount of dissolved solute at a given temperature in the presence of undissolved solute.
Undissolved solute is in equilibrium with dissolved solute.
Solute (undissolved) -> solute (dissolved)
An unsaturated solution contains less than the equilibrium concentration of dissolved solute. If more solute is added, it will dissolve.

Question 22

Factors that affect Solubility

Answer 22

Temperature affects solubility. Most solids are more soluble at higher temperatures. Gases become less soluble as temperature increases.
Pressure affects the solubility of gases –they become more soluble at higher pressure. Factors that affect Solubility

Question 23

Gas solubility in water decreases with rising temperature

Answer 23

Gases have weak intermolecular forces
weak interactions between gas and solvent.
*KE overcomes intermolecular forces
gas solute molecules leave the solution

Question 23

Henry’s Law

Answer 23

The solubility of a gas (Sgas) is directly proportional to the partial pressure of the gas (Pgas) above the solution.

Question 24

Pressure and solubility

Answer 24

A change in pressure does not affect the solubility of liquid or solid solutes as they are almost incompressible.
Pressure has a major effect on gas solubility;;;;;;

Question 25

The effect of pressure on gas solubility.

Answer 25

P increases, and more gas particles collide with the liquid surface. More gas particles dissolve until equilibrium is re-established. Gas + solvent (dynamic equi) saturated solution

Question 26

Molarity

Answer 26

Molarity is no. of moles of solute in 1.0 L of solution

Question 27

Molality

Answer 27

Depends on mass, the no. of moles solute dissolved in 1.0 kg of solvent

Question 28

interconverting concentration terms

Answer 28

To convert a term based on amount (mol) to one based on mass, you need the molar mass. (g/mol)
To convert a term based on mass to one based on volume, you need the solution density(g/L or g/mL)
Molality involves the quantity of solvent, whereas the other concentration terms involve the quantity of solution.

Question 29

Colligative Properties of Solutions

Answer 29

The presence of solute particles alters the solution properties, but not as expected…
The number of solute particles, not their chemical identity is what makes the difference!

Question 30

The magnitude of Colligative Property

Answer 30

Calculate a number of particles in the solution. This depends on the molecular formula and the type of solute strong electrolyte weak electrolytenonelectrolyte

Question 31

Vapour Pressure Lowering

Answer 31

The vapour pressure of a solution of a nonvolatile nonelectrolyte is always lower than the pure solvent.
Why?Opposing rates and change in entropy