Download - Chapter 14
Chapter 14Solutions
“how things dissolve” – homogeneous mixtures of
2 or more substances◦ – does the dissolving (H2O is the
universal solvent) ◦ – what gets dissolved
3 things happen when dissolving occurs:1. solvent molecules split up2. solute units split up3. Form solvent/solute attractions
Rules for solutions “likes dissolve like”~ water is highly polar, dissolves polar
solutes and ionic solutes fairly well
– solvent/solute attraction H2ONaCl(s) Na+
(aq) + Cl-(aq)
electrolytes dissociate into ions
__________ – molecules split up b/c of the weak attraction into smallest molecule unit
H2O
C12H22O11 C12H22O11
Non-electrolytes undergo __________ __________
Ex. oil/water vs. oil/benzene
~ liquid in liquid – often volumes are not additive, called __________.
Why? intermolecular attractions 50 mL H2O + 50 mL methanol ≈ 97 mL
total
gas in liquid – same attractiongases tend to be less soluble at higher
temps. The __________ the pressure, the __________
soluble, b/c the gas is forced into the solution more. If pressure __________ the gas is ________ soluble
Finely divided solids dissolve much more rapidly than large crystals◦Granulated sugar vs. sugar cubes
__________ _______– a sol’n that is capable of dissolving more solute. (ex. 15.0g NaCl in 100g of H2O at room temp.) There are no un-dissolved solutes remaining.
__________ ______– a sol’n has its maximum amount of solute dissolved in it. You always see un-dissolved solute. (ex. 40.0g NaCl in room temp. water) When a sol’n is saturated, the solute is still dissolving – it’s just that the solute is also re-crystallizing out of the sol’n at the same rate, so there is no apparent change.
__________ ______– by heating a saturated sol’n and carefully cooling it, you can get more solute dissolved then theoretically possible. It is an unstable condition that is the basis for rock candy.
Spontaneity of the Dissolution ProcessAssume solvent is a liquidMajor factors that affect dissolution
of solutes (dissolving of solutes) ◦change of energy content, DHsolution
exothermic favors dissolution endothermic does not favor dissolution
◦change in disorder, or randomness, DSmixing increase in disorder favors dissolution increase in order does not favor dissolution
Best conditions for dissolution◦__________ __________ __________
Molarity: M= n/Vn = moles of solute V = Liters of
solution
Molality: m = n/kgn = same kg = mass of solvent
Mole fraction (x) number of moles of one part per moles of all parts of the solution
xa = na xb = nb etc…
ntotal ntotal
Ex. 1) What is the molality and mole fraction of 50.0 g potassium chloride in 425 g water?
Colligative properties__________ __________ of solutions
that depend only on the number of particles dissolved and not the kinds of particles dissolved.
__________ ◦Vapor Pressure◦Boiling Point Elevation◦Freezing Point Depression◦Osmotic Pressure
1. Vapor pressure-- Pvap goes down with increase in concentration.
Water vs. water + sugar *more sugar higher Pvap vs. lower Pvap
In solns, fewer molecules have the chance to turn into vapor
__________ – the vapor pressure of an ideal solution is directly proportional to the mole fraction of the solvent in the solutionPvap = (Pvap
o)(xsolvent) ~ ideal gases obey PV = nRT very well ~ Raoult’s Law is close to ideal when the solute and
solvent have very similar I.F.
Effect of Pressure on SolubilityPressure changes have ________ or
__________ on solubility of liquids and solids in liquids
Pressure changes have __________ effects on the solubility of gases in liquids◦ why carbonated drinks fizz when opened◦ cause of several scuba diving related
problems including the “bends”
2. & 3. Boiling Point Elevation & Freezing Point Depression
__________ exist as liquids over a wider temp. range
solutions move the __________ ______of a substance further down the curve.
pg. 563 & next slide show a phase diagram comparison between pure solvent and a solution
Why? __________– more attractions need to
be overcome before boiling can occur. __________ _____– ions get in the way of freezing.
Phase Diagram
Dissociation of Electrolytes & Colligative Properties
_____________ have larger effects on boiling point elevation & freezing point depression than soluble ____________________
one mole of sugar dissolves in water to produce one mole of aqueous sugar molecules
one mole of NaCl dissolves in water to produce 1 mole of Na+ & 1 mole of Cl- ions
colligative properties depend on number of __________ particles◦expect twice the effect for NaCl than for sugar
Ex. for F. P & B.P.Salt in water for pasta raises the B.P.Which of the following raises the B.P. more?
◦0.1 M HF vs. 0.1 M HCl Weak electrolyte vs. strong electrolyte
(s.e. dissociates thus higher B.P.)
◦0.1 M CH3OH vs. 0.1 M CH3COOH Nonelectrolyte vs. weak electrolyte
(w.e. slightly soluble so higher B.P.)Salt on the road ~ often CaCl2 (3 particles
dissolved) is chosen over NaCl (2 particles dissolved) CaCl2 lowers F.P. more
Homemade ice-cream ~ Yummy!
B.P & F.P. EquationsBoiling point elevation∆Tb = imkb
∆T = change in temp. m = molality k = constant
i = van’t hoff factor ~ measures the extent of ionization (number of dissolved particles)
Freezing point depression ∆Tf = imkf pg 564. table 14-2
Ex. 2) 15.0 g of ethanol is dissolved in 750. g of formic acid. The freezing point of the solution is 7.20oC. The freezing point of pure formic acid is 8.40oC. What is kf for formic acid?
4. Osmotic pressurethe pressure produced on the surface of a
semipermeable membrane by osmosis. ◦__________ – net flow of solvent between two
solns separated by a semipermeable membrane◦Solvent passes from __________ concentration
soln. into __________ concentration soln.◦Ex. of semipermeable membranes ~ skin, cell
membranes, cellophane, and saran wrap
π = MRTπ = symbol for osmotic pressureM = molarity T = temp R = 0.082057 L atm/mol K
Ex. 3) What is the molar mass (grams/mole) of 30.0 mL of an unknown substance if 0.300 g of that substance has an osmotic pressure of 0.400kPa at room temperature?
ColloidsMixtures that have particle sizes
between those of true solutions and suspensions (suspensions have particles that are very large, they will settle out unless the mixture is constantly stirred).◦Fog, smoke, paint, milk
The _______________ – colloids scatter light when its shined on them.
Hydrophilic & Hydrophobic Colloids
________________ – water loving colloids◦Blood plasma, some biological proteins
________________ – water hating colloids, require emulsifying agents to stabilize in water (emulsion helps keep two things together that normally would not mix)◦__________ – emulsion of fat and proteins mixed in
water, casein is the emulsifier◦__________ – oil and eggs with water, lecithin from
egg yolk is the emulsifier◦__________ and __________ are excellent
emulsifying agents ~ hard water reacts with soap anions and precipitates making bathroom scum
Hydrophilic & Hydrophobic Colloids
Medicines that are injected into humans such as shots must be at the same concentration as the existing chemical in our blood. These solutions are called isotonic. For example, if the medicine contains potassium ions, they must be the same concentration as the potassium ions in our blood. Why do medicines have to be made that way?