Chapter 6

Solutions and Colloids

Chemistry B11

Mixture: is a combination of two or more pure substances.

Homogeneous: uniform and throughout

Air, Salt in water

Heterogeneous: nonuniform

Soup, Milk, Blood

Mixtures

Solution

Solutions

Gas in gas (air) solid in solid (alloys) liquid in liquid (alcohol in water)

Gas in liquid (cokes) solid in liquid (sugar in water)

Solutions

Well-mixed (uniform) – single phase

homogenous

transparent

cannot be separated by filtration

cannot be separated on standing

sugar in water

Solutions (liquid in liquid)

Solvent: greater quantity (water)

Solute: smaller quantity (sugar)

Immiscible: two liquids do not mix.

miscible: two liquids can mix. alcohol in water (in any quantities)

for liquid in liquid

Solutions

Saturated: solvent contains or holds all the solute it can (at a given T).

maximum solute that solvent can hold (Equilibrium).

Unsaturated: solvent can hold more solute (at a given T).

Is not the maximum solute that solvent can hold.

Supersaturated: solvent holds more solute that it can normally hold (at a given T).

(more than an equilibrium condition)

Temperature and Solutions

Solubility: the maximum solute that will dissolve in a given amount of a solvent (at a given T).

T Solubility

T Crystal is formed

Temperature and Solutions

T Solubility

Seeding

A surface on which to being crystallizing.

Supersaturated solution

gas in liquid: T ↑ Solubility ↓

Global Warming

Pressure and Solutions

P Solubility (gas in liquid)Henry’s law

Concentration

Concentration: amount of a solute dissolved in a given quantity of solvent.

1. Percent concentration:

Weight / volume (W / V)% =Weight solute

Volume of solution (mL)× 100

Weight / Weight (W / W)% =Weight solute

Weight of solution× 100

Volume / volume (V / V)% =Volume solute (mL)

Volume of solution (mL)× 100

2. Molarity (M): number of moles solute dissolved in 1 L of solution.

Concentration

Molarity (M) =moles solute (n)

volume of solution (L)

Molarity × V = number of moles (n)

prepare the solution: M, V → n (mol) → m (g)

Prepare the solution

prepare the solution: M, V → n (mol) → m (g)

m (g)

Volumetric flask

3. Parts per Million (ppm):

Concentration

ppm =g soluteg solvent

× 106

Parts per billion (ppb):

ppb =g soluteg solvent

× 109

Dilution

Concentrated solution(Stock solution)

Dilute solution

Dilution

M1V1 = moles(n) before dilution

M2V2 = moles(n) after dilution

M1V1 = M2V2

% V1 = % V2

Equivalent

Number of Equivalents (Eq) in 1 mole of each ion is number of charges of that ion.

Ion Charge # of Equivalents in 1 mole

Na+ 1+ 1 Eq

Ca2+ 2+ 2 Eq

Fe3+ 3+ 3 Eq

Cl- 1- 1 Eq

SO42- 2- 2 Eq

Equivalent

Ex. 1: How many equivalents of CO32- are in 1 mole of Al2(CO3)3?

The charge of CO32- is 2- → 1 mole Al2(CO3)3 has 2 Eq CO3

2-.

Ex. 2: How many equivalents of Fe3+ are in 5 mole of Fe2O3?

The charge of Fe3+ is 3+ → 1 mole Fe2O3 has 3 Eq.

5 moles: 5 × 3 = 15 Eq

Water in our body

1. About 60% of our body.

2. Most of the reactions occur in aqueous solution.

3. Participates in many biochemical reactions.

4. Transports reactants and products from one place in our body to another.

5. Eliminates the waste materials from cells and our body (urine).

Solvent and Solute

polar dissolves polar

Nonpolar dissolves nonpolarlike dissolves like

Ions Hydrated by H2O

Hydration

Solvent and Solute

Most chlorides (Cl-) and sulfates (SO42-) are soluble in water.

(except AgCl, BaSO4, and …)

Most carbonates (CO32-), phosphates (PO4

3-) and hydroxides (OH-) are insoluble in water.

(except NaOH, LiOH, KOH, and NH4OH)

All nitrates (NO3-) and acetate (CH3COO-) are soluble in water.

Electrolytes

+ -

electrolyte

Electrolyte: conducts an electric current.

strong electrolytes: molecules dissociate completely into ions (NaCl).

weak electrolytes: molecules dissociate partially into ions (CH3COOH).

nonelectrolytes: molecules do not dissociate into ions (DI water).

NaCl → Na+ + Cl-

Na+Cl-

bulb

Ionization (Dissociation)

Colloids

Solutions: diameter of the solute particles is under 1 nm.

Colloids: diameter of the solute particles is between 1 to 1000 nm.

non transparent, non uniform, large particles, cloudy (milky)

but a stable system

Colloids

Tyndall effect:

You can see the pathway of the light passes through a colloid. (particles scatter light.)

emulsion: a mixture of immiscible substances (liquid-liquid). (milk and mayonnaise)

suspension: system does not stays stable and settle (> 1000 nm). (sand in water)

Suspension

Brownian motion

Random motion of colloid particles.

Dust

Why do colloidal particles remain in solution and do not stick together?

1. Surrounding water molecules prevent colloidal molecules from touching and sticking together.

2. A charged colloidal particle encounters another particle of the same charge, they repel each other.

Freezing and boiling point

If we dissolve a solute in a solvent: bp fp

ΔT = ikMΔT: change of bp or fp (T2 - T1)i: number of particlesK: constant (depend on solute) – Kb Kf

M: molarity

NaCl Na+ + Cl- i = 2

C2H6O2 i = 1

K2SO4 2K+ + SO42- i = 3

osmotic pressure

Osmotic Pressure

Semipermeable membrane

Higher concentration → Higher osmotic pressure

Osmotic Pressure

Water flows from low concentration

tohigh concentration.

Osmotic Pressure

Osmolarity (osmol) = M × i

M: molarityi: number of particles

Osmolarity ↑ → Osmotic pressure ↑

Hemolysis Crenation

Isotonic solution Hypotonic solution Hypertonic solution

The most typical isotonic solutions

0.9% (m/v) NaCl

5% (m/v) Glucose

0.9 g NaCl/100 mL of solution

5 g glucose/100 mL of solution

Higher than these numbers → Hypertonic solution

Lower than these numbers → Hypotonic solution

Dialysis

Dilute solution