Week 2 Day 2 Solutions

Question 1

solute

Answer 1

thing being dissolved

Question 2

solvent

Answer 2

thing doing the dissolving (often water, especially for our purposes)

Question 3

solution

Answer 3

result of dissolving solute in solvent

Question 4

molarity

Answer 4

M = moles (mol) of solute/liter (L) of solution

*molarity uses volume of solution, not solvent

‘molar concentration’

Question 5

molality

Answer 5

m = moles (mol) of solute/kgs (kg) of solvent

*molality uses mass of solvent*

‘molal concentration’

Question 6

Since molarity depends on temperature, as temperature increases, molar concentration will ____________.

Answer 6

Decrease

(most things expand when heated)

Question 7

Is molality temperature dependent?

Answer 7

No, mass does not depend on temp

Question 8

Percent by weight to volume (%w/v)

Answer 8

(%w/v) = grams solute/100 ml solution

Question 9

Percent by weight to weight (%w/w)

Answer 9

(%w/w) - grams of solute/100 g solution

common use in tinctures

Question 10

1 eqiuvalent (Eq) =

Answer 10

1 mole of “reactivity”

i.e. 1 mole of Na+ = 1 Eq of Na+

1 mole of Ca2+ = 2 Eq of Ca2+ (becasue it has a 2+ charge)

Question 11

What is osmolarity?

Answer 11

sum of the molarities of all solutes in a solution

i.e. osmolarity of a 1 M solution of NaCl is 2 Osm

(NaCl is 2 Osm because it is two particles, Na + Cl —-> 1 particle = 1 vote in osmolarity)

Question 12

Solubility

Answer 12

maximum amount of solute that will dissolve in a solvent

aka - saturated solution

units: mass/volume, g/L

Question 13

supersaturated solution

Answer 13

contains more solute than allowed by the solubility

creates unstable system, excess solute will come out of solution crystallizing as a solid, separting as a liquid or bubbling out as gas

Question 14

‘delta Hsoln’

Answer 14

total energy change during dissolving of solute

> 0 needs energy (endothermic) - feels cold

< 0 gives off energy (exothermic) - feels hot

Question 15

Of solids, liquids, and gases, which of the three state’s solubility is most affected by pressure?

Answer 15

Gas

As pressure increases solubility of gaseous solute in a liquid solvent increases

(Because solids and liquids are not very compressible, pressure has very little effect on the solutiblity of solid and liquid solutes)

Question 16

Effect of temperature on solubility of liquids and solids.

Answer 16

Increased temp usually increases solubility of liquids and solids.

Question 17

Effect of temperature on solubility of gases

Answer 17

Increased temp decreases solubility of gases

remember caribbean water (clearer) vs Maine/Alaska ocean (cloudier)

temp increases kinetic energy of particles—>more likely to escape out of solvent into gas particles

Question 18

What are colligative properties?

Answer 18

properties of a solution that depend only on the number of solute particles, and not the identity of the solute particles

Question 19

What are the 4 colligative properties of solution?

Answer 19

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

Question 20

Henry’s Law

Answer 20

effect of pressure on solubility

S = kH * Pgas

S = solubility

kH = Henry’s constant, specific for each gas and is temperature dependent

Pgas = partial pressure for specific gas

Question 21

How do colloids differ from solutions?

Answer 21

particles are larger and are suspended in solvent (not dissolved)

these large particles reflect light, while dissolved molecules don’t

Question 22

ppm

Answer 22

grams of solute/grams of solution X 1 x 10^6ppm

OR

approximately mg of solute/liters of solution