Lecture 5_190613

Question 1

Solute

Answer 1

thing being dissolved

Question 2

Solvent

Answer 2

thing doing the dissolving (often water)

Question 3

Molarity

Answer 3

M = moles of solute / liters of solution
* volume of solution

density of H2O is 1.000 g/ml at 4˚C (temp H2O is most dense)

Question 4

Molality

Answer 4

m = moles of solute / kgs of solvent

* mass of solvent

Question 5

Percent by Weight to Volume

Answer 5

%(w/v) = grams of solute / 100 ml of solution
*see 6/13 lecture example in notes!

NOTE: mg% = mg of solute / 100 ml of solution
mg% = mg/dL

Question 6

Percent by Weight to Weight

Answer 6

%(w/w) = grams of solute / 100 g of solution\

Question 7

Parts Per Million

Answer 7

grams of solute / million grams of solution = mass fraction (1 ppm = 1 mg/L; liquids)

moles of solute / million moles of solution = mole fraction (gases)

Question 8

1 equivalent (Eq)

Answer 8

= 1 mole of “reactivity”

Example:
1 mole of Na+ = 1 equivalent of Na+
1 mole of Ca++ = 2 equivalents of Ca++ (because it has +2 charge)

Question 9

1 normal solution (N)

Answer 9

1 equivalent / 1 liter of solution

Question 10

Osmolarity

Answer 10

sum of the molarities of all solutes in a solution

Example:
The osmolarity of a 1 M solution of NaCl is 2 Osm (Na = 1 and Cl = 1)

increased Osm = decreased concentration

Question 11

Solubility

Answer 11

Maximum amount of solute that will dissolve in a solvent

mass / volume

Like dissolves like – polar solvents dissolve polar solutes. non-polar solvents dissolve non-polar solutes.

Example: solubility (in H2O) of CH4 is 23 mg/l, solubility (in H2O) of CH3F is 2.4 kg/l (~100,000 times more soluble)

Question 12

Heat of solution

Answer 12

ΔHsoln = ΔHsolute + ΔHsolvent + Δhmix

ΔHsolute = energy to break up solute (usually > 0)
ΔHsolvent = energy to break up solvent (usually > 0) ΔHmix = energy back by new arrangement (usually < 0)
ΔHsoln = total energy change during dissolving of solute
> 0 needs energy (endothermic) – feels cold
< 0 gives off energy (exothermic) – feels hot

Examples:
Acid + water is very exothermic and generates lots of heat.
Dissolving ammonium chloride (NH4Cl) in water is endothermic and it can be used as a cold pack.

Question 13

Henry’s Law (pressure & solubility)

Answer 13

The solubility of a specific gas can be stated as,
S = k_H * Pgas

Increased pressure causes more gas to dissolve into solution.

where S is solubility, k_H is Henry’s constant, Pgas is partial pressure for specific gas

*k_H is specific for each gas and is temperature dependent

Question 14

Temperature & solubility

Answer 14

Increased temperature

1) usually increases solubility of liquids and solids, but
2) decreases solubility of gases

*warm H2O = increased gas in H2O = increased life

Question 15

As more solute is dissolved in a solution, the physical properties of the solution change

Answer 15

1) vapor pressure decreases with increasing solute concentration
2) boiling point increases with increasing solute concentration
3) freezing point decreases with increasing solute concentration
4) osmotic pressure increases with increasing solute concentration

For (2) and (3), think “anti-freeze” in a car. Anti-freeze increases the boiling point, preventing boiling over in summer, and decreases freezing point, preventing coolant freezing in winter.

if (2) is true then (1) is true (THINK SHIFTING TO RIGHT OF PHASE DIAGRAM)

Question 16

Vapor Pressure Raoult’s law

Answer 16

Ps = Χs * P˚s

Where Ps is the vapor pressure exerted by solute s, Χs is the mole fraction of s in the solution and P˚s is vapor pressure of pure s.

The vapor pressure of a solute in a solution depends on the concentration

Ptotal = Χs1 * P˚s1 + Χs2 * P˚s2 + Χs3 * P˚s3 + …

Any solute that has no vapor pressure (P˚ = 0) will cause a decrease in vapor pressure compared to a solution without it. This results in an increase in boiling point.

Question 17

Osmotic Pressure

Answer 17

∏ = M * R * T
where ∏ is osmotic pressure, M is molar concentration, R is universal gas constant, and T is temperature (in Kelvin).

high concentration to low

Question 18

Colloids vs Solutions

Answer 18

Colloids contain particles larger than molecules suspended in a solvent.

These large particles reflect light, while dissolved molecules don’t.

Question 19

Miscible

Answer 19

2 liquids are miscible if theyare soluble in each other in all proportions.