CHAPTER 13

Mixtures and Concentrations

Types of Mixtures

• Solutions

• Suspensions

• Colloids

Solutions• Soluble

– Capable of being dissolved

• Solution– Homogenous mixture – thoroughly

mixed

• Solvent– Dissolving medium – “doing” the

dissolving– Often Water = the universal solvent

• Solute– Substance being dissolved

• Example – Sugar Water

Solutions

• Electrolyte– Conducts electric current when in solution– Example – NaCl – IONICS, Acids, Bases

• Nonelectrolyte– Does NOT conduct electricity– Example – Sugar – MOLECULAR

SUBSTANCES

Solutions• Types of solutions

– Gas solutions• Gas with gas – quickly intermingle – air• Constant motion

– Liquid solutions• Liquid with gas – Soda (CO2 in sugar water)• Liquid with liquid – Vinegar (acetic acid + water)

– Solid solutions• Alloy – two or more metals are mixed

– Sterling silver (Cu + Ag)– Brass (Cu + Zn)– Bronze (Cu + Sn)

Solutions

• Evidence that it is a solution– Cannot be filtered– NO light scattering

Suspensions

• Heterogeneous mixture with particles that settle out– Water particles are not strong enough to keep

other particles from settling out– Example - Muddy water

• Evidence that it is a suspension– Can be filtered– Particles settle– May scatter light– Not transparent

Colloids

• In-between a solution and a suspension– Medium size particles– Small enough to be kept in “permanent”

suspension

• Dispersed phase– Solute-like particles

• Dispersing phase– Solvent-like particles

Colloids

• Evidence that it is a colloid– Scatters light– Does not settle

• Tyndall Effect– Light scattered by colloidal

particles

Examples – Jello; Cool Whip Time: 5:39-6:26

Making Solutions• Factors affecting rate of dissolving – ways

to speed up dissolving– Increase surface area of solute

• More solute touches solvent• Ex – crush, spread out

– Agitate solution• Spreads out already dissolved solute to bring in

more fresh solvent in contact with solute• Ex – stir, shake

– Heat solvent• Particles move faster as energy increases• More collisions between solute and solvent

Solubility

• Solution equilibrium – opposing rates of dissolving and crystallizing are equal– Unsaturated

• Contains less than maximum amount of solute

– Saturated• Contains maximum amount of solute• More will NOT dissolve

– Supersaturated• Has more solute than a saturated solution at same

conditions

Supersaturated solutions

• Steps to make– Heat saturated solution– Add more solute– Cool slowly

– Addition of one more crystal?• Will crystallize entire solution!!• Video

Factors affecting solubility

• Solubility = Ability to dissolve

• Type of solute/solvent– “like dissolves like”– Immiscible – Liquids NOT soluble in each

other• Water and oil

– Miscible – Liquids are soluble in each other• Vinegar

Factors affecting solubility

• Pressure– Increase pressure = increase amount of gas

dissolved– Example – Soda– Henry’s Law

• Increase pressure = Increase solubility of a gas

Factors affecting solubility

• Temperature– If solute is gas

• Increase temp = Decrease solubility

– If solute is solid usually…• Increase temp = Increase solubility

Heat of Solution

• Amount of energy released/absorbed when solute dissolves in solvent (kJ/mol)– Endothermic

• Absorbs heat• Positive (+) heat of solution

– Exothermic• Releases heat• Negative (-) heat of solution

– Solvated – solute particles surrounded by solvent

Bond changes during solution formation

• Solute-solute attractions broken– REQUIRES ENERGY

• Solvent-solvent attractions broken– REQUIRES ENERGY

• Solute-solvent attractions formed– RELEASES ENERGY

Compare energies

• Process is ENDOTHERMIC if:– Steps 1 + 2 > Step 3

• Process is EXOTHERMIC if:– Step 3 > Steps 1 + 2

Concentrations

• Percent by Mass

• Mole Fraction (needs to be added)

• Molarity (M)

• Molality (m)

Percent by mass

• % Mass = Mass solute x 100%

Mass total solution

Solution = solute + solvent !!!!

Examples

Mole Fraction

• Mole Fraction (X) = Moles substance A

Total moles solution

Examples

Molarity

• Molarity (M) = Moles solute

Liters solution

Examples

Molality

• Molality (m) = Moles solute

kg solvent

Examples

Colligative Properties

• A property that depends of number of solute particles– Vapor-Pressure Lowering– Boiling Point Elevation– Freezing Point Depression

• Nonvolatile – a substance that does NOT evaporate very much

Vapor-Pressure Lowering

• Adding a nonvolatile substance lowers the vapor pressure– Increase solute = Decrease VP

• SIMPLIFIED Reason – Less solvent at the surface

Boiling Point Elevation

• Increase solute = Increase BP– Boiling occurs when VP = Patm

– If VP is lowered by adding a solute, it will take more energy to make VP = Patm, so the temperature will be higher

– Ex – Add salt to cook (not enough to notice, though)

Boiling Point Elevation

• ∆T = Kb * m

– Kb = Boiling point elevation constant

– Kb of water = 0.51°C/m

• Examples

Freezing Point Depression

• Increase solute = Decrease FP– When freezing occurs, the solvent solidifies– Adding solute, you must cool the solution to a

lower temp to freeze– Ex – antifreeze, salt on roads (most now also give off heat),

homemade ice cream - http://science.howstuffworks.com/question58.htm

Freezing Point Depression

• ∆T = Kf * m

– Kf = Freezing Point Depression Constant

– Kf of water = 1.86°C/m

• Examples

Molar Mass Calculations

Steps:

1. Use ∆T = K * m to find m

2. Use m equation to find moles solute

3. Use MM = mass solute / moles solute to find MM

Examples: