Chapter 20: Electrochemistry

Question 1

Electrolysis

Answer 1

Decomposition of a compound into its elements by an electric current

Question 2

Electrolyte

Answer 2

Compound that is decomposed either molten ionic compound or conc aq solution of ions

Question 3

Electrodes

Answer 3

Rods of carbon(graphite)/metal conduct electricity to and from an electrolyte

Question 4

Redox at cathode

Answer 4

Gain electrons, always reduction, metal layer or molten layer in the cell, gas bubbles off

Question 5

Redox at the anodes

Answer 5

Anions. Lose electrons. Oxidize.

Question 6

Mass of substance proportionality

Answer 6

Strength of current and time over which a constant electric current passes

Question 7

Faraday definition

Answer 7

Quantity of electricity charge carried by 1 mol of electrons or singly charged ions.

Question 8

Faraday value

Answer 8

96 500 C mol^-1

Question 9

Steps to calculate mass using F

Answer 9

Write half-equation
Find number of electrons E, multiply by F
Calculate Q=It
Calculate M = Q/ EF * Ar

Question 10

Calculating volume(at rtp)

Answer 10

Write half-equation
Find number of electrons E, multiply by F
Calculate Q=It
Calculate M = Q/ EF * 24.0

Question 11

Avogadro constant

Answer 11

L= F/C

Question 12

Redox equilibrium

Answer 12

Exists between 2 chemically related species that are in different oxidation states
Rate of electrons = rate of electron loss

Question 13

Finding the charge on 1 mole of electrons steps

Answer 13

Weigh the electrodes separately
Pass constant current over period of time
Remove, wash and dry electrodes with distilled water and propanone
Reweigh electrodes: cathode increases, anode decreases

Question 14

Calculation for finding the charge on 1 mol of electrons

Answer 14

Mass of anode at the start and end 
Mass removed at anode 
Charge transfer 
Calculate 1 mol in grams of substance 
Mole/weight x charge =X
How many electrons for one mole= Y
X x Y = Z 
L = Z/electrons

Question 15

Electric potential(voltage)

Answer 15

The relationship established when a metal is put into a solution of its own ions, between the metal and metal ion system in solution

Question 16

Electrons Potential E

Answer 16

Difference between 2 systems

Cannot be measured because of electrical double layer when an element is placed in a solution of its ions

Question 17

Standard cell potential

Answer 17

E cathode - E anode

Question 18

Flow of electrons using E standard

Answer 18

More positive pole attracts the negative electrons

Question 19

Predicting reaction using E standard

Answer 19

More positive, forward direction, easier to reduce

Less positive, reverse direction, easier to oxidize

Question 20

Feasibility

Answer 20

Feasible if likely to occur, standard cell potential value is positive, forward reaction is feasible not reverse, doesn’t determine rate

Question 21

Direction of reaction

Answer 21

Clockwise pattern

More positive to less positive: reactant to product of more positive to reactant and product of less positive

Question 22

Will It oxidize?

Answer 22

1. Write half reactions(more positive on top)
2. Identify stronger oxidizing and reduction agent: more positive is oxi because more likely to accept. Less positive is red, more likely to release
3. Do they react
4. More positive reaction goes forward, less positive goes reverse
5. Combine half-equations

Question 23

Why is platinum used in the standard hydrogen electrode

Answer 23

Inert, doesn’t take part in the reaction, surface allows electron transfer from one species to another, ensures electrical contact

Question 24

What do E standard values represent

Answer 24

Indicates how easy it is to reduce or oxidize

Question 25

What does a more positive or less negative E standard value indicate

Answer 25

It’s easier to reduce ions on the left. Metal on the right is relatively I reactive and is a relatively poor reducing agent

Question 26

Standard electrode potential

Answer 26

Voltage of the half cell, relative to hydrogen cell under standard conditions