20 Electrode Potential and Electrochemcial Cells Flashcards
Zinc and copper cell
Daniel cell = emf of 1.1v
Used to provide the electricity for old fashioned telegraph
Not practical for a portable device = liquid
Zinc and carbon cell
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
Rechargeable batteries
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
Standard conditions
298k
1.00 moldm^-3
100Kpa
Different potentials have different charges why?
Compared to hydrogen
How easily they give out electrons
Negative value of Eo
Better at realising electrons than hydrogen
reducing agent is the most negative
Some half equations do not contain a material that can be used as an electrode
Use another solid (usually metal) electrode
Using platinum
Explain how an electric current can be generated
Hydrogen relesed electrons and oxygen gained electrons
Why a fuel cell does not need to be charged
The reactants are supplied continuously
Main advantage of using hydrogen in a fuel cell
More energy efficient
One major hazard if using hydrogen
Highly flammable
Explain why rechargeable cells are connected to these solar cells
Store electricity
Solar cells only work when light is shoring on it
Why many waste disposal centres contain separate section for batteries
Contain heavy metals and toxic chemicals
Why is the electrode is rubbed with sandpaper
Expose the pure metal for the chemical recatin by removing the oxidation layer
Function of the carbon rods in the cell
Allows electrons to flow
One essential property of the non-reactive porous separator
Unreactive and allows ions to pass
One environmental advantage of this rechargeable cell
Less metal is used
Oxidising agent
Gain of electrons
Function of a salt bridge
Allows ions to flow so that the charge can flow which completes the circuit
Why can a cell not be recharged
Reaction isn’t reversible
Feasible
If the negative equations is realising electrons
if the emf is positive then the reaction is feasible
the two cells will have different potentials what is the significance in the charge and size?
how easily they give out electrons
compared to hydrogen
negative E
electrons with negative E are better releasing electrons than hydrogen reducing agent (most negative)
true or false
the number of electrons has no effect on value of E
true
some half equations do not contain a material that can be used as an electrode
platinum (pt) is used are electrode
portal batteries
nickel and cadmium
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
lithium ion
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)-
alkaline hydrogen-oxygen fuel cell
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
hydrogen economy
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)
use of electrochemical cell
Electrochemical cells can be used as a commercial source of electrical energy
Lithium cell
Positive electrode: Li+ + CoO + e– → Li+[CoO ]– 2 2
Negative electrode: Li → Li+ + e–
Cells can be non-rechargeable (irreversible), rechargeable
or fuel cells.
