Solution is a homogeneous mixture of 2 or more substances ...



Solution is a homogeneous mixture of 2 or more substances in a single state.

Solution Properties:

1. Comprised of small particles ( atoms, molecules, ions)

2. Particles are evenly distributed on a

molecular level

3. Particles don’t settle or separate from solution

Two Components:

Solute – substance dissolved (broken down)

Solvent – substance doing the dissolving

seawater:

solute – salt

solvent – water

Solutions Terms:

Soluble –

a substance dissolves in another substance

Salt and sugar are soluble in water

Insoluble –

a substance that does not dissolve in another

Mercury and oil are insoluble in water

Miscible –

Liquids soluble in each other at all proportions

Water and ethanol are miscible

Alloys – Solid solutions of metals

Bronze = ( Cu + Sn + Zn )

Gold Jewelry = ( Au + Cu)

Types of Solutions:

Solute Solvent Example

Gas Gas Air ( O2 in N2)

Gas Liquid Soda ( CO2 in H2O )

Liquid Liquid Antifreeze (ethylene glycol in water)

Solid Liquid Ocean water (salt in H2O)

Gas Solid Charcoal filter

( gas in carbon )

Liquid Solid Dental Filling

( Hg in Ag )

Solid Solid Sterling Silver

( Cu in Ag )

Mixture Types: Solution, Suspension, Colloid

Suspensions

Heterogeneous mixture of a solvent – like substance, particles slowly settle out; ( Soil + Water); Scatters Light = “Tyndall Effect”

Colloids / Colloidal Dispersions

Mixture with particle size between solutions and suspensions

(Muddy water, inks, Foams, Fog, Smoke, liquid - liquid emulsion)

Classify the following:

• Sand + water mixture = Suspension

• Brass door knob = Solution ( alloy)

• Atmospheric Cloud = Colloidal dispersion

Aqueous Solutions – Solutions with water as the solvent

Water called the “ Universal Solvent “ It can dissolve so many substances

2 types of substances dissolve in water

1. Electrolytes

2. Non-electrolytes

Electrolytes – ionic compounds dissolved in water that yield ions.

Mobile ions in solution carry electrons (current) NaCl is an electrolyte

Nonelectrolyte – substance dissolved in water that does not conduct electricity

No mobile ions

Sugar is a nonelectrolyte or neutral solute

Solution Formation

1. Dissolving occurs at solid surface

2. Water molecules separate or dissociate the NaCl into ions

3. Water molecules surround the ions

Dissociation:

NaCl(s) + H2O(l) → Na + (aq) + Cl – (aq)

Solvation – Solvent – Solute interaction

Hydration – Water – Solute interaction

Heat of Solution

NaCl solution formation breaks attractions among solute particles

Energy absorbed to separate solute particles

Endothermic Process;

Solution Temperature decreases

NH4NO3(s) + H2O(l) + Heat → NH4+(aq) + NO3 –(aq)

“Cold Pack” reaction

Formation of attractions between solute – solvent particles

Energy released ;

Exothermic process

Solution Temperature increases

NaOH(s) + H2O(l) → Na+(aq) + OH –(aq) + Heat

Solubility

Amount of solute dissolved in a specific solvent under given conditions

Units: grams of solute per 100 grams of solvent at a specific temperature and pressure

g solute / 100 g solvent at ( T, P )

Factors affecting solubility:

1. Nature of solute and solvent

2. Temperature

3. Pressure for gases

Polar vs. NonPolar Nature of solvent

Polar molecules have polar bonds

Charge separation due to electronegativity difference

Water is a Polar molecule

Nonpolar Molecules have:

o Nonpolar bonds with comparable electronegativites

o No net Dipole Moment

Polar substances NonPolar substances

Water Hydrocarbons (Benzene)

Alcohols Carbon tetrachloride (CCl4)

Acids Chloroform (CHCl3)

Acetone Oils, Waxes, Greases

Ionic Compounds Gasoline

“ Like dissolves Like” Rule

Two substances dissolve in each other if their molecules are alike in polarity

Water + Grease = Insoluble

(Polar) + (NonPolar) = Insoluble

Turpentine + Grease = Soluble

(Nonpolar) + (Nonploar) = Soluble

Like dissolves Like

Solute Polar Solvent Nonpolar Solvent

Polar Soluble Insoluble

NonPolar Insoluble Soluble

Ionic Soluble Insoluble

Affect of Pressure on Gas Solubility

Solid & Liquid solubility not affected by pressure

Increase in Pressure = Increase in Gas Solubility

(over a solvent) (in any solvent)

Increase in pressure = increase in gas molecule’s strike rate at solvent surface to enter the solution

Pressurized liquid has more gas dissolved in it

Closed soda bottle Pressure > 1 atm;

Increase solubility of CO2

Henry’s Law

Gas solubility increases with the partial pressure of that gas on the liquid surface at a constant temperature.

Factors Affecting Dissolving Rate :

1. Surface Area

2. Temperature

3. Stirring

Increase surface area by decreasing particle size

Compare two solids of equal masses,

Fine Powder vs. Large granules

(Large surface Area) (small surface area)

(small particle size) (large particle size)

Increase surface area = increased dissolving rate

Increase stirring = increase dissolving rate

• Solvation occurs at solid surface

• Stirring provides fresh solvent at solute surface

Higher Temperature = Increase Solvent Kinetic energy

• Increase # of solvent particles in contact with solute

• Increase Temperature = faster dissolving rate

Types of Solutions:

Saturation

Saturated solution contains a maximum amount of solute as can be dissolved under existing conditions

Saturation not the same as concentration

Unsaturated solution contains less than the maximum amount of solute than can be dissolved

Supersaturated solution contains a greater amount of solute than that needed to form a saturated solution

Supersaturated solutions are very unstable, solute crystallizes out of solution

Examples: Rock Candy, Sodium Acetate

Solution Concentration

Amount of solute in a given amount of solvent or solution

Concentrated solution – a large amount of solute in the solvent

Dilute solution – a small amount of solute in the solvent

Units of Solution Concentration:

• Percent by mass

• Molarity

• Molality

Percent by Mass

Number of solute grams dissolved in 100 g of solution.

% by Mass = __Solute Mass______ __ x 100

Mass solute + Mass solvent

10 g of sodium hydroxide is dissolved in 90 g H20

% mass of solute = 10 g NaOH_______ x 100

10 g NaOH + 90 g H2O

(10 g / 100 g ) x 100 = 10 % solute by mass

A solution of sodium chloride prepared by dissolving 5 g of salt in 550 g water.

% solute by mass = ?

5 g NaCl / (5 g NaCl + 550 g H2O) x 100 = 0.9% NaCl

Molarity ( M )

Number of moles of solute in one liter of solution

Molarity = moles solute

Liter solution

M = n / V

1 molar solution of HCl contains one mole of HCl in every liter of solution.

( 1 M HCl)

10.0 g NaOH dissolved in solvent to make a 0.100 L solution.

What is the molarity of the solution?

Molality (m)

Solute moles per kilogram of solvent

Molality = moles solute

mass solvent (kg)

1 kg = 1,000 g

1 molal solution contains 1 mol solute in exactly 1 kg of solvent

35.0 g ammonia (NH3) dissolved in 1 Kg water. Molality of solution =?

35.0 g NH3 = 2 mol

Molality = 2 mol NH3 = 2 m NH3

1 kg H2O

Colligative Properties of Solutions

• Vapor-Pressure Lowering

• Boiling-Point Elevation

• Freezing-Point Depression

Colligative properties depend on the

# solute particles, not their chemical nature

Vapor Pressure reduction occurs as nonvolatile solute prevents solvent particles from escaping at the surface.

Boiling - Point Elevation:

At BP, VPeq = AP

Therefore, decrease VP = Increase BP

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