Properties of Solutions

Chemical reactions often occur in _________ – a homogeneous mixture of two or more substances.

The solute is the substance preset in a smaller amount, and the _______ is the substance present in a larger amount. In __________________, the solvent is always water.

solutions

solvent

aqueous solutions

Properties of Solutions

Solutions are not just a solid mixed in a liquid. That’s just one of many options.

Solid in Liquid

Liquid in _____

Liquid in _____

Gas in _____

Solid in ____Solid in ____Gas in _____Liquid in ____Gas in _____

Liquid

Solid

Liquid

Solid

GasSolid

Gas

Gas

Spontaneous !2nd law of Thermodynamics

In order for ANYTHING to happen spontaneously ANYWHERE in the universe, the entropy of the universe must _________!

Entropy is ________ or __________

--Which is more likely – your room to be neat or messy?

**Messy is HIGH Entropy

increase

disorder randomness

Aqueous Ionic Solution Properties

_________– process in which an ion is surrounded by water molecules.

For example:

NaCl (s) Na+ (aq) + Cl- (aq)

CaCl2 (s) _______________

H2

O

H2

O

Hydration

Ca2+ (aq) + 2 Cl- (aq)

Hydration

Ion-Dipole Forces________________ are the electrostatic

attraction between an ion and the oppositely charged end of a _____molecule.

Example:

Ions in water

 

Interaction releases energy = (_______) of hydration = Hhyd

Cl-

OHH

O H

H

O

H

H

OHH

O H

H

OHH

K+

Ion-dipole Forces

polar

enthalpy

Electrolytes

Electrolyte - a substance that dissolves in water to form ions & make a solution that conducts _____________.

Exp. Ionic like Na + Cl-

or ______________ molecules• Non electrolyte- _________ conduct electric

current. Exp. Sugar and _________ molecules

electric current

highly polardoes NOT

non polar

Energetics of SolutionsIntermolecular forces/interactions:

1)   solute-solute

2)   solvent-solvent

3)   solute-solvent (_______ or _______)

 To form a solution, you must pull apart some of 1 and 2 (endo) but gain 3 (exo)!

 Hsoln = H1 + H2 + H3

 Hsoln overall can be endo or exo.

solvation hydration

Energetics of Solutions

Exothermic – feels ______Solute + solvent solution +_____

Endothermic – feels _____Solute + solvent + heat solution

HOTheat

cold

Energetics of Solutions If exo, new IMF will allow for the

solution to be at __________ (energy is ______) solution will form! Feel: ___

If endo, it ___________ form solution . If too endo, the solute _____ dissolve. solute-solvent interactions not strong enough to break up 1, 2 interactions!

Why do processes that are endo allow for solvation anyways? Can happen if the level of disorder ________ enough! Feel: ____

lower energyreleased hot

may or may notwon't

increases cold

Liquid Solutes in Solvents“Like dissolves _____” is a useful rule to

predict whether or not one substance dissolves in another

So polar would dissolve with _____

Miscible: Substances that are soluble together in ____ proportions

 Immiscible: Substances that are ____ soluble with each other _____________

 

Like

polar

ALL

NOTno matter what

Will it dissolve?“Like dissolves Like” is a useful rule to predict

whether or not one substance dissolves in another

How about water & oil?

Water & vinegar?

Water & grease?

Gasoline & grease?

 Polar & nonpolar?

Non polar & non polar?

Immiscible

Miscible

Immiscible

Miscible

Immiscible

Miscible

How does it look?

Oil & Vinegar Water & Vinegar

Non-polar & polar

Immiscible

Polar & Polar

Miscible

Energetics of SolutionsSolid solutes:

When a solid is added to a liquid ______, molecules in solid phase overcome ____ and escape into solution, called __________ or __________.

Opposite can also happen: molecules in solution collide with undissolved solid and come out of solution, called ______________.

solventIMF

hydration. solvation.

crystallization

Energetics of SolutionsSolid solutes:

 

Dynamic equilibrium is when rates of solute coming into and out of solution ___________.

pure solventpure solid(to becomethe solute)

solution: solid particles dissolve in solvent

and

crystallization: soluteparticles become part of the solid phase

+

are equal

Factors affecting the rate of Dissolution

- -Increasing __________________   

--_________ a Solution  

-- _________ a solvent

surface area of solute

Agitating

Heating

3 Types of Solutions1. Saturated solution

Solution in equilibrium w/ undissolved solid. (there can be no increase in the # of dissolved solute particles)

_______ measures the amount of _____ that is required to reach __________ for a given quantity of _______ (the max amount that can be dissolved!)

 e.g., NaCl in water: X g/100 ml H2O

Solubility solutesaturation

solvent

3 Types of Solutions2. Unsaturated solution

Has less solute than the ________ limithttp://www.wwnorton.com/chemistry/overview/ch5.htm#precipitate

3. Supersaturated solution

Under some conditions, you can get ____ solid dissolved than the solubility limit (_______, easy to get crystallization!) Examples: Honey & sodium thiosulfate

solubility

more

unstable

Temp and Solubility

For most solids, solubility with __T

For most gases, solubility with __T

Solutes that are Gases:

• Gases dissolve in liquids

• Solubility of a gas as Pext __

Note: ______________ solubility largely independent of Pressure!

solid and liquid

Temp and Solubility

Temp and Gas SolubilityAs a gas heats up, due to _______ law

its volume will __________

The volume is now ______ dense and will _______ & ________ liquid

HEAT

Escape!!

CharlesEXPAND

LESSRise escape

The opposite will happen if you cool liquid – more can enter

Gas in atmosphere is in dynamic equilibrium w/ gas in solution:

 

 

 

Rate at which gas particles strike solution surface is ______ at P

solvent

= gas particleincreased pressure

Pressure and Gas Solubility

greater so more enter

Pressure and SolubilityHenry's Law: the solubility of a gas

in a liquid is ________ proportional to the partial pressure of that gas on the surface of the liquid.

_____________- the rapid escape of dissolved gas from its liquid solvent.

So if you double pressure, you __________ solubility !

Think soda pop !

directly

DOUBLE

Effervescence

Solution ConcentrationMolarity – the number of moles of

______ in one liter of ________.

Molarity (M) = amount of solute (mole) volume of solution

(L)

Ex. 0.50 mole NaOH = 0.50 M NaOH 1.00 L

solute solution

Solution ConcentrationMolality – the number of moles of

solute in one kg of solvent.

Molality (m) = amount of solute (mol)kg of solvent (kg)

Ex. 0.12496 mol NaOH = 0.0625 m NaOH 2.00 kg H2O

Solution ConcentrationMole fraction – the moles of component

A divided by the total moles.

Mole fraction(X) = moles component Atotal moles

component

Ex. 0.12496 mol NaOH 0.12496 mol NaOH + 110.98 mol H2O

= 0.00112 mol fraction NaOH

Solution ConcentrationWeight % = mass %

Weight % = mass component A x 100total mass solution

5.00 g NaOH = 0.249 % NaOH

5.00 g NaOH + 2000 g H2O

Weight % usually reported in parts by mass (ppm, ppb, ppt, etc.)

Solution Concentrationppm = parts per million

ppb = parts per billion

A sample with 1.0 g of a substance in a sample with a total mass of 1.0 x 106 g would have a concentration of 1 ppm. one in a million!

Ex. 5000 mg NaOH = 0.00248 = 2.49 ppm

2.01 L

Colligative PropertiesColligative properties depend only on

the number of solute molecules in a solution.

Adding solute to a pure solvent cause:

• Decreased vapor pressure

• Boiling point (BP) elevation

• Freezing point (FP) depression

• Osmotic pressure

Vapor Pressure

Vapor pressure of a solution is lower than that of pure solvent.

Both liquids are in equilibrium w/ gas phase; particles escape more easily out of pure solvent. It has a higher vp! 

pure solvent solution

time

solutionpure solvent

Vapor Pressure

Reduction in vp is determined mainly by the decrease in # of solvent particles at surface of a solution that can escape into the gas phase.

• This will be determined by mole fraction of the solvent.

The amount by which vp is reduced in solution is proportional to the concentration of solute particles!

Vapor Pressure

pure solvent solution

= solvent particle

Consider a pure solvent and a solution:

Vapor Pressure In the pure solvent (mole fraction = 1)

all surface particles are solvent particles.

In the solution only some of the particles at the surface are solvent particles.

High conc of solute or low mole fraction solvent

low vp

  Dilute conc of solute orhigh mole fraction solvent vp is

less reduced

Vapor Pressure

Boiling Point ElevationBoiling point (bp) occurs when vp = Pext

Addition of of solute will vp, and bp will occur at higher T for solution.

  why do we put salt in spaghetti water?

let Tbp = increase in bp (it’s elevation!)

Tbp = Tbp(f, solution) – Tbp(i, pure solvent)

bp (solution) = bp (pure solvent) + Tbp

Boiling Point Elevation Tbp = kbp m

where kbp = molal bp elevation constant

  m = molality of solution

depends on the solvent!

Solvent norm FP (oC) kfp (oC/m) norm BP kbp

(oC/m)

Water 0.00 1.86 100.00 0.52

Benzene 5.5 5.12 80.1 2.53

Ethanol-117.3 1.99 78.4 1.22

BP Elevation PracticePure H2O bp 100.0oC and kbp = 0.52

oC/m

What is bp elevation for a solution of 3.2 m CH3OH? What is the new bp?

-> Tbp = (0.52 oC/m)(3.2 m) = 1.664 oC

Tbp final = Tbp (pure) + Tbp

= 100.0oC + 1.664 oC

= 101.7 oC

Freezing Point DepressionFreezing point (fp) is also prop to

molality.

At the interface between liquid and solid (where solvent must solidify), there is less solvent, causing the system to release more heat to get the solvent particles to solidify.

It has to get colder to actually freeze!

s

liq

Tfp = kfp m

kfp = molal fp depression constant

Tfp is the decrease in fp

Tfp = Tfp(i, pure solvent) – Tfp(f, solution)

fp (soln) = fp (pure solvent) - Tfp

Freezing Point Depression

FP Depression Practicefor water kfp = 1.86 oC/m

Tfp (pure) = 0.0 oC

  What is the fp depression for a solution that is 3.2 m CH3OH?

-> Tfp = (1.86 oC/m)(3.2 m) = 5.952 oC

Tfp (soln) = Tfp (pure) – Tfp =

0.0 oC – 5.952oC = -6.0 oC

OsmosisOsmosis is the net movement of

solvent molecules from a less concentrated solution into a more concentrated one across a semi-permeable membrane. 

Colligative PropertiesColligative properties depend on # of

particles. If solute is an electrolyte, must consider all of its aqueous ions!

When performing calculations, multiply the concentration by the van't Hoff factor (i) i = the # of ions after dissociation/formula unit.

NaOH (aq) Na+ (aq) + OH- (aq) i = 2

MgCl2 (aq) Mg2+ (aq) + 2Cl- (aq) i = 3

Colligative Properties Tbp = ikbp mTfp = ikfp m = iMRT

The result is that, for example:

  1.0 M CH3OH (aq) = 1.0 M particles

0.5 M NaOH (aq) 0.5 M Na+ (aq) + 0.5 M OH- (aq)

= 1.0 M particles

Both solutions have same reduction in vapor pressure!

BP Elevation Practice401.2 g solute were dissolved in 2.0 kg

of water. The bp elevation of the solution is 2.3 oC. What is the molar mass of the solute? hint: Tbp = kbp m -> 2.3 oC = (0.52 oC/m)(m) -> m =

4.423 m

 4.423 m = (4.423 mol /kg solvent)(2.0 kg) = 8.846 mol solute

 molar mass: 401.2 g /8.846 mol solute = 45.35 g/mol

Solution types

Homogenous Solution – looks the same through-out, cannot separate by filtering

Heterogenous Solution – CAN separate out by filtering. May settle out.

Suspensions: A heterogenous mixture in which droplets or particles are suspended in a liquid

ColliodsSolutions containing suspensions of

particles that will not "settle out"

(intermediate between solution and suspension) particles are large, have large surface area.

ColliodsColloids in water can be …

Hydrophobic = water "fearing;“ usually nonpolar or polar w/ weak attractions to water.

Hydrophilic = water "loving;“ usually polar (e.g., proteins)

ColliodsEmulsions are colloidal dispersions of

one liquid in another that would normally be immiscible (e.g., mayonnaise, hand lotion)

  Usually contain an emulsifying agent

(soap or a protein – bridges between the different types of molecules)

ColliodsSurfactant/detergent are used as soaps

that have polar and nonpolar ends – can "bridge" between polar aqueous solution and nonpolar grease/dirt.

Energetics of Solutions Liquids solutes:

Liquids are called miscible if they mix in any proportions (water and ammonia) and immiscible if they will not mix in any proportions (water and oil).

“Like dissolves like“

• Polar solutes dissolve in polar solvents.

• Nonpolar solutes dissolve in nonpolar solvents. (grease in gasoline)