20 Electrode Potential and Electrochemcial Cells

Question 1

Zinc and copper cell

Answer 1

Daniel cell = emf of 1.1v
Used to provide the electricity for old fashioned telegraph
Not practical for a portable device = liquid

Question 2

Zinc and carbon cell

Answer 2

Positive electrode is made of carbon
When the cell discharges the zinc is used up so the wall thin
Ammonium chloride paste in water (corrosive)

Zinc chloride cell - better an supping high currents
(Potassium hydroxide) hydrogen oxides to make water
Ammonium dissolves in water of the paste

Question 3

Rechargeable batteries

Answer 3

Lead-acid battery
Two plates - positive plate lead coated in lead oxide
- negative lead plate
Lithium ion
Light weight
Cant leak (solid polymer so can be bended and folded)
Charge can be topped up

Question 4

Standard conditions

Answer 4

298k
1.00 moldm^-3
100Kpa

Question 5

Different potentials have different charges why?

Answer 5

Compared to hydrogen

How easily they give out electrons

Question 6

Negative value of Eo

Answer 6

Better at realising electrons than hydrogen

reducing agent is the most negative

Question 7

Some half equations do not contain a material that can be used as an electrode

Answer 7

Use another solid (usually metal) electrode

Using platinum

Question 8

Explain how an electric current can be generated

Answer 8

Hydrogen relesed electrons and oxygen gained electrons

Question 9

Why a fuel cell does not need to be charged

Answer 9

The reactants are supplied continuously

Question 10

Main advantage of using hydrogen in a fuel cell

Answer 10

More energy efficient

Question 11

One major hazard if using hydrogen

Answer 11

Highly flammable

Question 12

Explain why rechargeable cells are connected to these solar cells

Answer 12

Store electricity

Solar cells only work when light is shoring on it

Question 13

Why many waste disposal centres contain separate section for batteries

Answer 13

Contain heavy metals and toxic chemicals

Question 14

Why is the electrode is rubbed with sandpaper

Answer 14

Expose the pure metal for the chemical recatin by removing the oxidation layer

Question 15

Function of the carbon rods in the cell

Answer 15

Allows electrons to flow

Question 16

One essential property of the non-reactive porous separator

Answer 16

Unreactive and allows ions to pass

Question 17

One environmental advantage of this rechargeable cell

Answer 17

Less metal is used

Question 18

Oxidising agent

Answer 18

Gain of electrons

Question 19

Function of a salt bridge

Answer 19

Allows ions to flow so that the charge can flow which completes the circuit

Question 20

Why can a cell not be recharged

Answer 20

Reaction isn’t reversible

Question 21

Feasible

Answer 21

If the negative equations is realising electrons

if the emf is positive then the reaction is feasible

Question 22

the two cells will have different potentials what is the significance in the charge and size?

Answer 22

how easily they give out electrons

compared to hydrogen

Question 23

negative E

Answer 23

electrons with negative E are better releasing electrons than hydrogen 
reducing agent (most negative)

Question 24

true or false

the number of electrons has no effect on value of E

Answer 24

true

Question 25

some half equations do not contain a material that can be used as an electrode

Answer 25

platinum (pt) is used are electrode

Question 26

portal batteries

nickel and cadmium

Answer 26

more expensive to buy
recharged up to 500 times

2Ni(OH) (s) + Cd(s) + 2H2O(l) ——- 2Ni(OH)2 (s) + Cd(OH)2(s)

reaction goes from left to right on discharge (electrons flowing from Cd to Ni ) and right to left on charging

Question 27

lithium ion

Answer 27

rechragable lithium ion cell is used in laptops, tablet an smartphones
light (lithium is a light material)
can’t leak = solid
negative electrode = Li+ + e- —- Li
postive electrode = Li+ + CoO2 +e- —— Li+(CoO2)-

Question 28

alkaline hydrogen-oxygen fuel cell

Answer 28

doesn’t need to be electrically recharged
2H2 (g) + O2(g) —– 2H2O(l)
cell has two electrode of porous platinum based material
type of fuel cell is used to generate electricity on spacecraft because the only by product of water

Question 29

hydrogen economy

Answer 29

seems green as only by-product is water
most hydrogen is made from crude oil
hydrogen is high flammable
(one way of storing hydrogen safely is by absorbing it into solid compounds called metal hydroxides. the hydrogen is absorbed under pressure and reassign by gentle heating)

Question 30

use of electrochemical cell

Answer 30

Electrochemical cells can be used as a commercial source of electrical energy

Question 31

Lithium cell

Answer 31

Positive electrode: Li+ + CoO + e– → Li+[CoO ]– 2 2
Negative electrode: Li → Li+ + e–
Cells can be non-rechargeable (irreversible), rechargeable
or fuel cells.