Redox (R3.2)

Question 1

What does voltaic cells do?

Answer 1

they convert chemical energy to electrical energy by spontaneous redox reaction

Question 2

What does electrolytic cells do?

Answer 2

convert electrical energy to chemical energy by a non-spontaneous redox reaction

Question 3

What’s the purpose of the salt bridge?

Answer 3

neutralise the solutions in two beakers and allow for free flow of ions from one cell to another and

Question 4

In which direction do electrons flow in an electrochemical cell?

Answer 4

from anode to cathode

Question 5

How to recognize the anode from E value?

Answer 5

is less positive

Question 6

How to recognize the cathode from E value?

Answer 6

is more positive

Question 7

Where electrons accumulate in voltaic cell?

Answer 7

where the cathode is

Question 8

What reaction happens at anode?

Answer 8

oxidation

Question 9

What reaction happens at cathode?

Answer 9

reduction

Question 10

What ions are in a salt bridge?

Answer 10

K+ and NO3-

Question 11

What’s the main difference between primary and secondary cells?

Answer 11

primary cells are not rechargable and secondary cells are rechargeable

Question 12

What are the advantages and disadvantages of the primary cells?

Answer 12

+ : inexpensive
- : generate a lot of waste

Question 13

What are the advantages and disadvantages of the secondary cells?

Answer 13

+ : reusable
- : might be dangerous (fire)

Question 14

What are the features of fuel cells?

Answer 14

• use oxygen and hydrogen
• provide continuous supply of energy
• no emissions

Question 15

What is required in electrolytic cells?

Answer 15

a battery for continuous inflow of energy

Question 16

What is electrolysis and what solution is required?

Answer 16

process where compounds are split apart by the passage of electricity through a molten state or aqueous solution

Question 17

What are the common oxidising agents for alcohols?

Answer 17

• Cr2O72- / in acidic environment
• MnO4- / in acidic environment

Question 18

How is oxidation defined in alcohols?

Answer 18

• loss of electrons
• increase in oxidation state
• gain of oxygen/loss of hydrogen

Question 19

What’s the product of partial oxidation of a primary alcohol?

Answer 19

aldehyde

Question 20

What’s the product of a complete oxidation of a primary alcohol?

Answer 20

carboxylic acid

Question 21

What’s the product after the first oxidation of a secondary alcohol?

Answer 21

ketone

Question 22

Why aldehyde has a lower boiling point than carboxylix acid?

Answer 22

aldehyde has weaker intermolecular forces

Question 23

What types of intermolecular forces do aldehydes show?

Answer 23

dipole-dipole

Question 24

What types of intermolecular forces do carboxylic acids show?

Answer 24

hydrogen bonds

Question 25

What type of technique can be used to produce a carboxylic acid (complete oxidation)?

Answer 25

reflux

Question 26

What type of technique can be used to produce a aldehyde (partial oxidation)?

Answer 26

distillation

Question 27

How reduction is defined/recognised?

Answer 27

- gain of electrons - decrease in oxidation state - loss of oxygen/gain of hydrogen

Question 28

What can be a good reducing agent?

Answer 28

hydride ion

Question 29

What is standard hydrogen electrode used for?

Answer 29

it is an electrode that is used as a comparison for other half-cells to establish their standard electrode potential as it is equal to 0.00

Question 30

What does E value mean?

Answer 30

it measures how easily a species gains or loses electrons

Question 31

What does positive E value mean compared to negative?

Answer 31

that it likes to gain electrons

Question 32

What does negative E value mean compared to positive?

Answer 32

that it likes to lose electrons

Question 33

What are the standard conditions for standard hydrogen electrode?

Answer 33

- platinum electrode - solution of 1 mol/dm3 of H ions - 100 kPa of gas

Question 34

How to calculate the overall standard cell potential?

Answer 34

cathode-anode

Question 35

When does the positive value of the overall standard cell potential mean (spontaneity)?

Answer 35

that the reaction is spontaneous

Question 36

When does the negative value of the overall standard cell potential mean (spontaneity)?

Answer 36

that the reaction is non-spontaneous

Question 37

Formula for calculating Gibbs free energy from energy of a cell

Answer 37

from data booklet

Question 38

What's the general rule for electrolysis of solutions with water?

Answer 38

metal ions with a less positive E⦵ value (like Na) than water will NOT be reduced at the cathode

Question 39

What is the product of oxidation of water?

Answer 39

oxygen gas

Question 40

What is the product of reduction of water?

Answer 40

hydrogen gas

Question 41

What happens in electrolysis of diluted aqueous solution of NaCl?

Answer 41

Question 42

What happens in electrolysis of concentrated aqueous solution of NaCl?

Answer 42

Question 43

Which elements are more likely to be oxidised at the anode (E value)?

Answer 43

with more negative E value

Question 44

Which elements are more likely to be reduced at the cathode (E value)?

Answer 44

with more positive E value

Question 45

In electroplating, to which end is the object (e.g. key) connected?

Answer 45

to the negative end of a battery (cathode)

Question 46

What does electroplating system must consist of?

Answer 46

- power supply - cathode - metal anode - electrolyte containing metal ion to the anode

Question 47

How to determine quantity of charge (Q)?

Answer 47

Q=I x t, where I is current in A and t is time in seconds

Question 48

How to get moles from quantity of charge (Q)?

Answer 48

divide Q by F (Faraday's constant)

Question 49

How to correctly annotate standard hydrogen electrode?

Answer 49

Question 50

How to balance redox reactions?

Answer 50

- balance other elements than H and O - balance O by adding H2O - balance H by adding H+ - balance electrons

Question 51

What's the trend for non-metals in redox reactions?

Answer 51

they tend to undergo reduction - are good oxidizing agents

Question 52

What's the trend for the strength of non-metals as oxidising agents in the periodic table

Answer 52

moving up the strength of oxidizing agent increases

Question 53

What's the trend for metals in redox reactions?

Answer 53

tend to lose electrons, they act as reducing agents

Question 54

What's the trend for the strength of metals as reducing agents?

Answer 54

the most reactive metal is the most likely to lose electrons

Question 55

Cathode is attracting positive or negative ions?

Answer 55

positive

Question 56

Anode is attracting positive or negative ions?

Answer 56

negative