Chapter 13
13.1 What is a solution?
• mixture
– two or more subs. that are physically
combined
– no form./any proportion
– subs. retain properties
– easily separated by physical means
• solution – homogeneous mixture
– solute – subs. being dissolved(sugar)
• particles are 0.1 to 2 nm in size
– solvent – subs. doing the dissolving(water)
Solution
Solute
Solvent
salt water
radiator fluid
pop/cola
salt(s)
antifreeze(l)
CO2 (g)
water(l)
water(l)
water(l)
dental filling
brass
filter on gas mask
Hg (l)
Cu (s)
poisonous gas(g)
Ag, Sn, Cu (s)
Zn (s)
charcoal(s)
air
?????
?????
O2 (g)
??? (l)
??? (s)
N2 (g)
??? (g)
??? (g)
• suspension – a two phase heterogeneous
mixture that separates upon standing
• particles are >1000 nm in size
– clay in water
– dust in air
• colloid – a two phase heterogeneous
mixture that remains mixed(usually due to
like charged particles)
• particles are 2 to 1000 nm in size
– milk – fat and casein dispersed in whey
– glue water – glue dispersed in water
• Tyndall effect – scattering of light caused
by undissolved particles
– gaseous or liquid solutions = dissolved - no
Tyndall effect
– suspensions or colloids = undissolved –
positive for Tyndall effect
• separation techniques for mixtures
– filter/decant - colloids and suspensions
– evaporation – remove liquids from solids
– chromatography – separates solutions by
molecular size
– distillation – separates solutions by boiling
• fractional distillation – separation by boiling point
differences
13.2 Concentration and Molarity
• concentration – the ratio of solute to
solvent
– qualitative
• dilute
• concentrate
• quantitative
1) parts per million(ppm)
•
•
# of solute particles to solution particles
1 ppm = 1 solute particle to 1,000,000 total
particles
• 1 drop of food coloring in 40 gal H2O
• for aqueous solutions = mg solute/L solution
What is the concentration in ppm for a solution that
has 0.0380 grams of lead in 300.0 mL of tap
water solution?
X ppm = 1000 mg x 0.0380 g Pb x 1000 mL
1g
x 300.0 mL sol x 1L
X ppm = 127 mg/L or ppm
http://planetforlife.com/co2history/index.html
• Atmospheric carbon dioxide during the last four ice ages.
(http://planetforlife.com/co2history/index.html)
2) parts per billion(ppb)
– micrograms/L (µg/L)
– 1 ppb =
•
•
1 mL of water in an Olympic swimming pool
7 people in the world at current population
• Sixteen pesticides have been detected in eight brand-name baby
foods, according to a study by the Environmental Working Group
and the National Campaign for Pesticide Policy Reform, two public
interest groups based in Washington, DC.
• In their study, the EWG and the NCPPR collected a random
sampling of 76 jars of baby food from grocery store shelves in
Denver, Philadelphia, and San Francisco. The group chose fruits
and vegetables babies most commonly eat during their first year of
life. Of these, 53% harbored traces of one pesticide, and 18% had
two or more pesticides. Plums contained the highest amounts at 46
parts per billion and peaches contained 29 parts per billion.
Pears had the highest number of multiple pesticides overall (five).
3) molarity(M)
•
•
# of particles to volume of solution
M = mol solute/L solution
– vinegar is composed of 5.00 grams of acetic
acid(HC2H3O2) in 100.0 mL of solution.
What is the M of vinegar?
M = 1 mole acetic acid x 5.00 g acetic acid
60.06 g acetic acid x 0.1000 L solution
M = 0.833 mol/L or M
4) molality (m)
–
–
# particles solute to mass solvent
moles of solute to kilograms of solvent
•
used in calculating freezing point depressions and boiling
point elevations
5) karat (k)
–
concentration of Au in alloys
• 24 k gold = pure Au
• 12 k gold = 50% Au & 50% other metal(s)
6) mass % (% m/m)
–
–
mass of solute per mass solution
used in industry
In a regular Coke there is 39 grams of sugar in 355
grams of pop, what is mass %?
% m/m = 39 grams sugar/355 grams pop
% m/m = 11% sugar
7) volume % (%v/v)
– volume solute per volume solution
13.3 Solubility and the Dissolving Process
• solubility – the ability of a subs. to dissolve
@ specific T and P conditions
– hydrophilic
•
•
•
•
•
“water loving”
dissolve in water
vitamin C
most ionic compounds
polar molecules
– hydrophobic
• “water fearing”
• insoluble in water
• soluble in fats or oils
– vitamin A
– wax
– styrofoam
• general rule of solubility
– “like dissolves like”
– soaps/detergents dissolve in both
laundry ball
• polar end of soap – attaches to water
• nonpolar end of soap – attaches to dirt/oil/fat
– miscible – mutually soluble
– immiscible – does not dissolve
• dissolving
– the breaking up of a solute to the smallest
particles that make up the solute
• particles 0.1 to 2 nm
• NaCl breaks apart to Na+ & Cl- ions
• sugar break apart to C12H22O11 molecules
– occurs at surface of solute (anim)
– methods utilized to increase dissolving rate of
a solid in a liquid
• powdering/crushing
– more surface area
• stirring
– fresh solvent in contact with solute
• heating
• dissolving mechanisms and NRG changes
1) solute(s)  solute(l)
•
•
•
NRG is added to solute for phase change
dissociation – separation in to ions/molecules
endothermic
2) solvent moves apart to allow solute to enter
•
•
•
solvent makes room for solute
NRG needed to move solvent apart
endothermic
3) solute and solvent attract
•
•
•
solvation/hydration
decrease entropy – release NRG
exothermic
• if dissolv. mech. 1 & 2 > 3
– dissolving is endothermic
– heating increases dissolving
– solution feels cold during dissolving
– temp. of solution increases during crystallizing
• cold pack
• most solutes
• if dissolv. mech. 1 & 2 < 3
– dissolving exothermic
– heating decreases dissolving
• cooling increases dissolving
– not very common
• NaOH
• solubility of ionic compounds
– vary due to many factors
• soluble – more than 1 g/100 g H2O
• slightly soluble – 0.1 to 1 g/100 g H2O
• insoluble – less than 0.1 g/100 g H2O
• equilibrium – two opposing processes
occurring simultaneously
– melting and freezing
– dissolving and crystallizing
• if a solution is at equilibrium
– undissolved solute remains in solvent
• crystals in bottom of container
– saturated solution – solvent is “holding” the
maximum amount of solute at those
conditions
– saturated solutions contain undissolved solute
• if dissolving is occurring faster than
crystallizing(not at equillibrium)
– no undissolved solute
– all solute dissolves
– unsaturated solution – solvent is holding less
than the maximum amount of solute
• dissolving > crystallizing
• each substance has different solubility @ different
temperatures
– solubility curve – figure 12, page 472
• supersaturated solution
– a unique phenomena
– solvent holds more than the maximum
amount of solute @ the specified conditions
• more solute than a saturated solution
– not common
– very easily disturbed
• honey
• liquid hand warmers
• solubility of gases in liquids
– different than solids/liquids
– T affect solubility of gases
• solubility increases as T of solvent decreases
– less molecular motion
– gas particles remain isolated
– cold liquids dissolve more gases
» cloudy ice
– hot liquids dissolve less gases
» thermal pollution
– P affect solubility
• Henry’s law
– solubility of a gas in a liquid is directly related to the P of
that gas above the liquid
– fizz keeper
13.4 Physical Properties of Solutions
• electrolyte
– substance that when dissolved or molten
conducts electricity
• carry e-‘s
• ions need to be present
– ionic compounds dissociate when dissolved
NaCl(s)  Na+(aq) + Cl-(aq)
– acid ionization
HCl(l)  H+(aq) + Cl-(aq)
– What are the electrolytes in Gatorade?
– In Gatorade, the key electrolytes are the minerals
sodium, potassium and chloride. When athletes
sweat, they lose electrolytes such as sodium,
potassium, and chloride that are essential to
hydration and muscle function. Unlike water and other
beverages that are not scientifically formulated,
Gatorade is lab-tested to ensure it helps replenish the
electrolytes lost in sweat and stimulates thirst so
athletes will ingest an adequate amount of fluid and
electrolytes to stay better well-hydrated compared to
when using beverages without electrolytes,
particularly sodium.¹²³
http://www.gatorade.com/frequently_asked_questions/default.aspx
• strong electrolyte
– completely ionize/dissociate
– lots of ions
10 NaCl(s)  10 Na+(aq)+ 10 Cl-(aq)
• weak electrolyte
– partially ionize/dissociate
– few ions
10 HC2H3O2(l)  H+(aq) + C2H3O2-(aq) + 9 HC2H3O2(aq)
• nonelectrolyte
– no ionization/dissociation
– no ions
– molecules(not acids)
• colligative properties
– any prop. that affects the solvents physical
prop. because of the number of solute
particles
– adding solute to solvent changes the prop. of
the solvent
1) vapor pressure
•
•
•
decreases when solute is added to solvent
vapor P = P created when a confined liquid evap.
less solvent part. at surface to evap.
–
–
–
less evap. = less P
tap water evap. slower than distilled water
sim lab
2) freezing point
– decreases when solute is added to solvent
– freezing pt. – T at which the vapor P of the
solid = vapor P of liquid
– since vapor P of liquid is reduced the Tf is
reduced
– solutions freeze at lower T than pure
solvents
•
more solute particles = lower freezing points
•
(simulated lab)
• freezing pt. depression calculation
ΔTf = m x Kf x i
m = molality(mol solute/kg solvent)
Kf = freezing pt constant(water = 1.86o
C/m)
i = van’t Hoff factor = # particles
dissoc./ionized
• freezing pt depression sample problem
– What T does 175 grams of water freeze if
22.5 grams of sodium chloride is added?
ΔTf = m x Kf x i
ΔTf = 1 mol NaCl x 22.5 g NaCl x 1.86o C x 2
58.44 g NaCl x 0.175 Kg H2O x
ΔTf = 8.18o C
normal Tf = 0o C
- ΔTf = 8.18o C
new Tf = - 8.18o C
m
• How many grams of calcium chloride are
needed to lower the freezing point of 750.0
grams of water to -6.55o C?
ΔTf = 6.55o C
X m = 6.55o C____
1.86o C/m x 3
X m = 1.17 m
X g CaCl2 = 110.98 g CaCl2 x 1.17 mol CaCl2 x 0.7500 Kg
1 mol CaCl2 x
X g CaCl2 = 97.4 g CaCl2
Kg
3) boiling point
– increases when solute is added to solvent
• boiling point = T at which the vapor P of the
liquid is equal to atmospheric P
•
•
•
Tb – H2O = 100o C @ 1 atm
solute reduces vapor P of solvent
more NRG added to get same vapor P
•
•
T of liquid will be higher to attain vapor P = atm. P
solutions have higher boiling points than
pure solvents
•
more solute particles = higher boiling points
ΔTb = m x Kb x i
m = molality
Kb = boiling point constant (H2O = 0.510o C/m)
i = van’t Hoff factor
My mom always adds salt to the water when she
cooks noodles so the noodles cook faster. She
adds about 2.0 grams of salt to 1.0 liter of water.
What T does her water boil?
ΔTb = 1 mol NaCl x 2.0 g NaCl x 0.510o C x 2
58.44 g NaCl x 1.0 Kg
x
m
ΔTb = 0.035o C
normal Tb = 100o C
+ ΔTb = 0.035o C
new Tb = 100.035o C
• How many grams of sugar(C12H22O11)
would need to be added to 500.0 grams of
water to increase the boiling point to
105.0o C?
ΔTb = 5.0o C
X m = 5.0o C________
0.510o C/m x 1
X m = 9.8 m
X g = 342.34 g x 9.8 mol x 0.5000 Kg
1 mol
x 1 Kg
X g = 1700 g sugar
• surfactants – substance that concentrates
at the interface between two phases
– solid-liquid, liquid-liquid, liquid-gas
– detergent – synthetic surfactant(not natural)
• generally made from vegetable oil and sulfuric acid
• often liquid
– soap – natural surfactant
• generally made from sodium/potassium salts of
natural animal fatty acids
• often solid
– emulsifying agent - substance, such as soap
or eggs, that allows two immiscible liquids to
remain dispersed in one another
• Sodium Lauryl Sulfate – SLS – An Industrial
Detergent
•
SLS is an Engine Degreaser! And it’s in nearly every cleansing product we
use from toothpaste to beauty soap. SLS is generally made from petroleum
oil and sulfuric acid, and may still contain traces of both. It makes personal
products foamy, and is a strong detergent that strips away the skin’s
precious oils in addition to removing dirt. Ironically, the FDA actually uses it
as a skin irritant to test the anti-irritation properties of various drugs.
• Sodium Laureth Sulfate
•
Sodium Laureth Sulfate (SLES) is one of the most common shampoo
ingredients. In fact most personal hygiene products contain this specific
ingredient. SLES is a washing surfactant, in other words a washing
detergent. Imagine it as a car polish that returns the shine by removing the
top layer of the paint.