Redox and electrode potential

Question 1

whats a redox reaction

Answer 1

where reduction and oxidation happen simultaneously

Question 2

whats a half equation

Answer 2

an equation that shows oxidation or reduction - one half of a full redox equation

Question 3

whats a redox titration

Answer 3

a titration that can be performed to determine how much reducing agent is need exactly to react with a known quantity of oxidising agent, or vice versa

Question 4

5 steps of calculating concentration of a reagent from a titration

Answer 4

1) write balanced equation or redox reaction
2) decide what you know and what you need to know
3) calculate moles present n=vxc
4) use molar ratios from equation to find moles of other reagent
5) calculate unknown conc c=n/v

Question 5

state the balanced overall redox titration equation for the oxidation of Fe2+ to Fe3+ by manganate(VII) ions in solution

Answer 5

MnO4- + 8H+ + 5Fe2+ -> Mn2+ + 4H2O + 5Fe3+

Question 6

state the balanced overall redox titration equation for the oxidation of Zn to Zn2+ by Dichromate(VI) in solution

Answer 6

CrO72- + 14H+ + 3Zn -> 2Cr3+ + 7H2O + 3Zn2+

Question 7

state the balanced overall redox titration equation for Potassium Manganate(VII) reacted with acidified iron(II) Sulphate

Answer 7

MnO4- + 8H+ + 5Fe2+ -> Mn2+ + 4H2O + 5Fe3+

Question 8

State the 2 equations that occur when titrating iodine with Sodium Thiosulphate.

1) oxidise iodide ions to iodine
2) titrate iodine solution with sodium thiosulphate

Answer 8

1) IO3- + 5I- + 6H+ -> 3I2 + 3H2O

2) I2 + 2S2O32- -> 2I- + S4O62-

Question 9

Which way do electrons flow

Answer 9

from more reactive metal to less reactive metal

Question 10

A metal thats easily oxidised has a very negative or potential electrode potential

Answer 10

negative

Question 11

whats standard electrode potential

Answer 11

voltage measured understand conditions whena half cell is connected to a standard hydrogen electrode

Question 12

whats a standard hydrogen electrode

Answer 12

an electrode where hydrogen gas is bubbled through a solution of aqueous H+ ions under standard conditions

Question 13

what are standard conditions when measuring electrode potentials using the standard hydrogen electrode

Answer 13

• ion solution 1 mol dm-3
• temp 295k (25°C)
• pressure 100kPa

Question 14

whats an electrochemical series

Answer 14

a list of electrode potentials written in order from most negative to most positive

Question 15

The more reactive a metal is, the more/less it wants to lose electrons to form a positive ion. (Oxidised)
More reactive metals have more negative/positive electrode potentials.

Answer 15

more

Negative

Question 16

The less reactive a metal is, the more/less it wants to lose electrons to form a positive ion. (Reduced)
Less reactive metals have more/less positive standard electrode potential

Answer 16

less

More

Question 17

whats standard cell potential (e.m.f)

Answer 17

voltage between 2 half cells in an electrochemical cell

Question 18

Whats the formula for E⦵cell

Answer 18

E⦵reduction - E⦵oxidation

Question 19

How do you know if a reaction is feasible or not

Answer 19

feasible direction of reaction will give positive overall E⦵ value. Reaction will not happen other way round.

Question 20

what are the 2 problems with predicting reactions

Answer 20

• conditions not always standard, change in temp or conc may change electrode potential
• reaction kinetics not favourable, rate of reaction may be so slow it wont appear to happen. Ea may be too high

Question 21

How do rechargeable storage cells work

Answer 21

• reactions that occur within them are reversible
• current is supplied to force electrons to flow in the opposite direction around circuit and reverse reactions
• possible because none op the substances escape or are used up

Question 22

-equations for reactions occurring during recharging are what

Answer 22

same equations for storage cells in reverse

Question 23

name 2 positive and 2 negatives of electrochemical cells

Answer 23

+cheap to make
+relatively high power density
-production uses toxic chemicals, need to be disposed of at end of lifespan
-chemicals used to make cells=very flamable , dangerous production

Question 24

whats a fuel cells

Answer 24

device that converts the energy of a fuel into electricity through an oxidation reaction

Question 25

describe the 4 steps of an acidic hydrogen-oxygen fuel cell

Answer 25

1) at anode, platinum cat splits H2 into H+ and e-
2) PEM only allows H+ across, forces e- to travel around circuit to cathode
3) electric current created in circuit, sued to power something e.g. bike or car
4) at cathode, O2 combines with H+ from anode + e- from circuit to make H2O. This is the only waste product

Question 26

Whats the PEM

Answer 26

polymer electrolyte membrane

Question 27

what makes a hydrogen-oxygen fuel cell acidic

Answer 27

H+ ions crossing PEM to balance half-reactions at each electrode makes it an acid fuel cell

Question 28

whats the overall redox reaction of an acidic + alkaline hydrogen-oxygen fuel cell

Answer 28

1/2O2 + H2 -> H2O

both acidic and alkaline are the same