Solutions and Electrochemistry

Question 1

TRUE or FALSE: for gases, solubility decreases with increasing temperature.

Answer 1

TRUE

Question 2

What does Henry’s Law state? What is the formula?

Answer 2

increasing pressure of a gas increases its solubility in a liquid (i.e. even if there is a lot of pressure, very little gas will dissolve)

C = kP (note: C = concentration, k = Henry’s constant, P = pressure)

Question 3

Oxidation reaction entails a ___________ of electrons.

a) gain
b) loss

Answer 3

b) loss

Question 4

Reduction reaction entails a ___________ of electrons.

a) gain
b) loss

Answer 4

a) gain

Question 5

TRUE or FALSE: reduction reactions and oxidation reactions always occur together.

Answer 5

TRUE

Question 6

If a species is oxidized, its oxidation number:

a) increases
b) decreases

Answer 6

a) increases

hint: LEO –> lose electrons

Question 7

If a species is reduced, its oxidation number:

a) increases
b) decreases

Answer 7

b) decreases

hint: GER –> gain electrons

Question 8

TRUE or FALSE: oxidizing agents are oxidized, and reducing agents are reduced.

Answer 8

FALSE: oxidizing agents are REDUCED, and reducing agents are OXIDIZED

Question 9

What should the sum of all oxidation numbers for all atoms in a molecule equal to?

Answer 9

the overall charge of the molecule (see page 311 for rules for assigning oxidation numbers)

Question 10

TRUE or FALSE: When calculating potential of a reaction, multiply the reduction or oxidation potential by the coefficients in the reaction.

Answer 10

FALSE –> do NOT multiply the potentials by the coefficients in the reaction (because reduction potentials are an INTENSIVE PROPERTY, independent of the amount of material present)

Question 11

What is the oxidative potential for the H2 (g) –> 2H+ + 2e- half reaction? What is the name for this electrode?

Answer 11

E = 0 V; Standard Hydrogen Electrode (SHE)

Question 12

When calculating the potential of the entire cell (anode and cathode), where the anode is associated with the standard hydrogen electrode (SHE) half-reaction, how do you calculate the answer for the potential of the entire cell/reaction?

Answer 12

E rxn = E reduction (at the cathode)

E rxn = E red + E ox, but E ox = 0 because of the SHE half-reaction

Question 13

Positive E indicates a:

a) spontaneous redox reaction and positive delta G
b) nonspontaneous redox reaction and negative delta G
c) spontaneous redox reaction and negative delta G
d) nonspontaneous redox reaction and positive delta G

Answer 13

c) spontaneous redox reaction and negative delta G

Question 14

The anode always undergoes a(n):

a) oxidation half-reaction
b) reduction half-reaction

Answer 14

a) oxidation half-reaction

hint: LEO –> anode has electrons to LOSE

Question 15

The cathode always undergoes a(n):

a) oxidation half-reaction
b) reduction half-reaction

Answer 15

b) reduction half-reaction

hint: GER –> cathode (+) can GAIN electrons

Question 16

What are the 3 main differences between galvanic/voltaic cells and electrolytic cells?

Answer 16

galvanic:

1. spontaneous redox reaction
2. cell produces energy and electric current
3. anode is (-) and cathode is (+)

electrolytic:

1. nonspontaneous redox reaction
2. external energy required
3. anode is (+) and cathode is (-)

Question 17

Using the terms, anode reactant, anode product, cathode reactant, and cathode product, write the shorthand cell notation. What are 5 things to keep in mind when writing this notation?

Answer 17

anode reactant | anode product || cathode reactant | cathode product

1. specify states (s, l, g)
2. do NOT specify stoichiometric coefficients
3. concentrations SOMETIMES specified
4. single bar | = difference in state
5. double bar || = salt bridge

Question 18

Is the standard cell potential (E) for an electrolytic cell negative or positive?

Answer 18

NEGATIVE E for electrolytic cell because NONSPONTANEOUS rxn

Question 19

What is Faraday’s First Law of Electrolysis?

Answer 19

mass of material produced at an electrode from electrolysis is directly PROPORTIONAL to the amount of electricity being transferred (Coulombs)

Question 20

What is Faraday’s Second Law of Electrolysis?

Answer 20

equivalent amounts of electricity will produce different amounts of material proportional to the material’s weight

Question 21

What is the formula used to calculate number of moles of electron (n), using Faradays law?

Answer 21

n = I x t x 1/F

note: n = number of moles of electrons, I = current, t = time, F = Faraday’s constant ~ 100,000 C/mol

Question 22

What is the Nernst Equation?

Answer 22

E = E° - (RT/nF) ln(Q)

note: don’t need to use for calculation, but for predicting concentration cells???? …idk lol im confused what this is used for (pg. 326 chem cc)

Question 23

a solution is a heterozygous mixture - true or false

Answer 23

false it is a homogenous mixture

Question 24

what is the term referring to a solution where the solute particles are too small to be filtrated

Answer 24

colloids

Question 25

what is the Tyndall effect

Answer 25

light scattering by the particles in a colloid

Question 26

what are some examples of non polar solvents

Answer 26

hexane, diethyl ether and benzene

Question 27

ionic compounds dissolve in ___ solvents

polar or nonpolar

Answer 27

polar

Question 28

what is the formula for molality

Answer 28

moles of solute / solvent in kg

Question 29

what is the formula for mass percentage

Answer 29

(mass of solute/mass of solvent ) x100%`

Question 30

the vapor pressure of a liquid depends on _____

a) temp
b) volume
c) pressure

Answer 30

temperature

Question 31

as the temperature of a liquid ____, the average kinetic energy _____ and the vapor pressure _____

fill in with increase or decrease

Answer 31

increases… increases…increases

Question 32

at the normal boiling point, what is the pressure

Answer 32

1 atm (atmospheric)

Question 33

bond breaking is _____ and bond forming is _____

fill in with exothermic or endothermic

Answer 33

endothermic… exothermic

Question 34

what is Raoult’s law

Answer 34

????

Question 35

rules for solubility

Answer 35

?????