Ch. 10 - Properties of Solutions

n_u , m_u

solute (u)

n_v , m_v

solvent (v)

Molarity (M)

Normality (N)

N = M * (# equivalent)

• # equivalent:

1 HCl ——→ 1 H⁺ + 1 Cl^-     # equiv = 1

1 H₂SO₄ ——→ 2 H⁺ + SO₄^2-   # equiv = 2

Mole Fraction (X)

Mass Percent (P)

Molality (m)

Mass of solution

m_solution = m_u + m_v

Density of Solution

be careful with units…

Can be g/mL or g/cm³

Concentration Conversion

M —→ assume 1 L

m -→ assume 1 Kg

X —→ assume 1 mole

m% —→ assume 100 g

Make denominator 1 or 100 if other information not given

To solve concentration questions….

1. Identify Key Words

2. Write out Question (Q)

3. Write out what you know - Data (D)

Solution Formation

ΔH_solution = ΔH_solute + ΔH_solvent + ΔH_mix

ΔH_solute + ΔH_solvent

hydration energy

ΔH_mix

lattice energy

hydration E > lattice E

ΔH_solution < 0

EXOTHERMIC

T increases

hydration E < lattice E

ΔH_solution > 0

ENDOTHERMIC

T decreases

Liquid-liquid solution

Like dissolves like

hydrophilic: NH, OH

hydrophobic: C, H, halides (F, Cl, Br, I, At)

Solid-liquid solution

polar solid dissolves in H₂O

Factors that affect solubility

Temperature and Pressure

Temperature affect on solubility

Solid: T increases, solubility increases

Gas: T increases, solubility decreases

Pressure affect on solubility

Gas: P increases, solubility increases

Henry’s Law

C_g = K_H * P_g

C_g = conc. of dissolved gas

K_H = constant

P_g = partial pressure of gas solute above the soln.

Colligative Properties

boiling point elevation, freezing point depression, vapor pressure lowering, and osmotic pressure

Vapor pressure lowering (colligative property)

• the colligative property where the vapor pressure of a solvent decreases when a non-volatile solute is added

• The amount of vapor pressure lowering is directly proportional to the mole fraction of the solute and can be calculated using Raoult's Law:

P_solution = X_solvent * P°_solvent

Raoult’s Law

P_solution = X_solvent * P°_solvent  For NON-VOLATILE

P_solution = ∑ (X_solvent * P°_solvent) For VOLATILE

P_solution - vapor pressure of solution

X_solvent - mole fraction of solvent

P°_solvent - vapor pressure of pure solvent

Freezing Point Depression (colligative property)

ΔT_f = i*K_f*m_solute

m = MOLALITY

Boiling Point Elevation (colligative property)

ΔT_b = i*K_b*m_solute

m = MOLALITY

T_{bp =} T_{normal bp} + ΔT_b (ALL IN KELVIN)

Osmotic Pressure (colligative property)

Π = iMRT

R = 0.082 L*atm/mol*K

T = KELVIN

Π = in ATM

As [solute particle] ↑

v.p and f.p ↓

b.p and o.p ↑

i

van hoff’s coefficient

CH₃OH —→ i = 1 (non-electrolyte)

NaCl —→ i = 2

CaCl₂ —→ i = 3

n_{solute particles} (other)

n_{solute particles} = n_solute * i