Solutions

Question 1

Solute

Answer 1

A substance (e.g. NaCl, NH3, C6H12O6, or CO2) dissolved in a solvent.

Question 2

Solvent

Answer 2

A substance (e.g. H2O, benzene, ethanol) that dissolves a solute. It is the component of the solution that remains in the same phase after mixing.

Question 3

Question:

In a solution, if 2 substances are already in the same phase when mixed, which component is greater in quantity: the solute or the solvent?

Answer 3

The solvent

Question 4

Solvation

Answer 4

The electrostatic interaction exerted when solvent molecules surround solute molecules.

Note: Known as dissolution/hydration when water (H2O) is the solvent

Question 5

Exothermic Solvation (Dissolution)

Answer 5

Occurs when new interactions are stronger than the original ones. This process is favored at low temperatures.

Example:
Dissolution of gases into liquids (e.g. CO2 into H2O)

Question 6

Endothermic Solvation (Dissolution)

Answer 6

Occurs when new interactions are weaker than the original ones. This process is favored at high temperatures.

Ex.
Dissolution of solids into liquids (e.g. [NH4][NO3] or sugar into H2O)

Question 7

Ideal Solution

Answer 7

A solution in which the enthalpy of dissolution is equal to zero. The process is neither exothermic or endothermic.

Question 8

Solutions

Answer 8

Homogenous mixtures of 2 or more substances that combine into a single phase, usually the liquid phase. Consists of a solute dissolved in a solvent.

Question 9

Spontaneous Solvation

Answer 9

Associated with a decrease in Gibbs Free Energy (-G). Solute is said to be soluble.

Question 10

Nonspontaneous Solvation

Answer 10

Associated with an increase in Gibbs Free Energy (+G). Solute is said to be insoluble.

Question 11

Solubility

Answer 11

The maximum amount of solute that can be dissolved in a given solvent at a given temperature.

Question 12

Saturated Solution

Answer 12

A solution in which no more solute can be dissolved. At this point the dissolved solute is in equilibrium with undissolved state. Any additional solute added will not be dissolved.

Question 13

Precipitate

Answer 13

The solid remnants of a solute which remain at the bottom of a solution. Precipitants form because the solution surpassed saturation in which additional solute concentration could not be dissolved.

Question 14

Diluted Solution

Answer 14

A solution in which the proportion of solute to solvent is small.

Note: considered unsaturated if the maximum equilibrium concentration (saturation) has not yet been reached

Question 15

Concentrated Solution

Answer 15

A solution in which the proportion of solute to solvent is large.

Note: considered unsaturated if the maximum equilibrium concentration (saturation) has not yet been reached

Question 16

Soluble Solutes

Answer 16

Solute that have a molar solubility value above 0.1M

Question 17

Insoluble Solutes

Answer 17

Solutes that have a molar solubility value below 0.1M.

Question 18

Aqueous Solution

Answer 18

A solution in which water is the solvent.

Question 19

Water-Soluble Salts

Answer 19

Any salt in combination with an:

• alkali metal (Li+, Na+, K+, Rb+, Cs+, Fr+)
• ammonium (NH4+)
• nitrate (NO3-)
• acetate (CH3COO-)
• halide (Cl-, Br-, I-); except F-
• sulfate (SO4^2-)

Question 20

Basic Salts

Answer 20

Salts that hydrolyze to form hydroxide (OH-) ions.

Question 21

Acidic Salts

Answer 21

Salts that hydrolyze to form hydronium (H3O+) ions.

Question 22

Concentration Units

Answer 22

Expressed as:

• % composition by mass
• mole fraction
• molarity
• molality
• normality

Question 23

Eq.) Percent Composition By Mass

Answer 23

[Mass of solute/Mass of Solution] x 100%

Question 24

Eq.) Mole Fraction

Answer 24

Xa = [moles of A/total moles of all species]

Question 25

Eq.) Molarity

Answer 25

M = [moles of solute/liters of solution]

Question 26

Eq.) Molality

Answer 26

m = [moles of solute/kilograms of solution]