CH3.1 Redox and standard electrode potential

Question 1

what is a redox reaction

Answer 1

A redox reaction is a combination of oxidation and reduction.

Question 2

what is oxidation in turms of electrons and oxidation number

Answer 2

Oxidation is lose of electrons meaning a more positve oxidation number.

Question 3

what is reduction in terms of electrons and oxidation number

Answer 3

reduction is gain of electrons resulting in a more negative oxidation number.

Question 4

why does oxidation and reduction have to hapen at the same time

Answer 4

Because the electrons that are lost in the reduction are the same electrons that are gained in the oxidation.

Question 5

oxidation agent

Answer 5

Is a substance that takees electrons from another substance and so it is reduced.

Question 6

reducing agent

Answer 6

Is a substance that gives electrons to another substance and so it is oxidised.

Question 7

what does the half equation of a reaction represent

Answer 7

wither the oxidation or reduction reaction (one of the redox equations)

Question 8

What is the point of a half cell

Answer 8

the point of setting up a half cell is so that the reduction and oxidation can occur at two different places seperatly.

Question 9

salt bridge

Answer 9

The salt bridge is a piece of apparatus that connects the solutiongs in two half-cells so that the circuit can be complete and the current can flow without the solution mixing.

Question 10

what is a salt bridge made of

Answer 10

gel soaked in a solution of potassium nitrate, or filter paper soaked in potassium nitrate.

Question 11

what must be at both hald cells

Answer 11

The reactants and the products of that half equation, as well as a metal that allows electrons to flow into or out of the half cell.

Question 12

what are the three main different types of half cells

Answer 12

metal/ metal ions
a gas in contact with a solutiong of non-metal ions
A soultion containing ions of metal in two different oxidation states using an inert metal electrode

Question 13

metal/metal ions half cell

Answer 13

This is when the electrode is the metal that is needed for the half eqaution which is submerged in 1 moldm-3 solution of the metal ion.

Question 14

gas in contact with a solutiong of non-metal ions half-cell

Answer 14

gas is bubbled over the inert electrode which is dipping into a solution of the ions

Question 15

What is a inert electrode used for

Answer 15

When there is not a metal for the electrons to move across, (non metals are not conductors) The platinum half cell allows the electrons to flow in or out o the half-cell

Question 16

soution containing ions of the metal in two different oxidation states half cell

Answer 16

uses inert metal platinum electrode. because there are no conductors, typically used for tanisition metals as they have several oxidation states.

Question 17

which half cell always produces a colour change

Answer 17

solution containg ions of metal with different oxidation state wiht a platinum inert metal electrode.

Question 18

which half cell sometimes produces a colour change

Answer 18

metal/ metal ions

Question 19

which half cell never produces a colour change

Answer 19

A gas in contact with a solution of non-metal ions with an inert platinum metal electrode.

Question 20

when representing a half cell what do the lines represent

Answer 20

chagne in state

Question 21

standar electrode potential

Answer 21

a measuer of the ability of the half cell to gain or lose electrons.

Question 22

what is hydrogens standard electrode potential

Answer 22

0

Question 23

what does a negative standard electrode potential mean

Answer 23

The species is easier to reduce then hydrogen

Question 24

what does a positive standard electrode electrode potential mean

Answer 24

The substance is easier to oxides

Question 25

what is another name for the hydrogen half-cell

Answer 25

the standard hydrogen electode

Question 26

what type of half cell is the standard hydrogen electrode/hydrogen half cell

Answer 26

A gas in contact with a solution of non-metal ions witha n inert metatl electrode

Question 27

what electrode is used in the hdyrogen half-cell

Answer 27

inert platinum black electrode

Question 28

exsplain the hydrogen half cell

Answer 28

inert platinum black electrode

H2 gas pupem over electrode, at standard conditions, electrode dipped in solution of 1 moldm-3 H+ ions

Question 29

how is the standard electrode potential for half-cell measuerd

Answer 29

it is done by joining it to the standard hydrogen electrode.

Question 30

standard hydrogen electrode drawn eqaution

Answer 30

Pt(s) l H2(g) l H+(aq) ll (the secound electrode that you want to find the standard electrode potential of)

Question 31

which electrode has the more positive standard electrode potentiala

Answer 31

The positve electrode has a more positive eectrode potentials

Question 32

which way do the electrons flow

Answer 32

The electrons flow towards the more positive standard electrode potential.

Question 33

how does reactiveity of the metals and non metals , and electrode potential relate

Answer 33

The more reactive metals have the most negative electrode potential, with the most reactive non-metals having the most positive value for standard electrode potential.

Question 34

how is the e.m.f. worked out using the standard electrode potential

Answer 34

The e.m.f of an electrochemical cell is worked out by the difference in the standard electrode potential of the two half cells. it is always a postive value.

Question 35

feasible reaction

Answer 35

A reaction that can occur spontanuosly

Question 36

finding the feasiblity of two half equations using standard electrode potentital values.

Answer 36

use the anticlockwise rule
write both the half equations in order of increasing standard electrode potentials, with the most negative value first
start from the top right hand conrner and move anticlockwise around the equation. This means that in the feasible reaction the top reaction goes in reverse and the bottom goes in the direction it is written.

Question 37

EMF standard electrode potential equation

Answer 37

E.M.F. of reaction = standard electrode potential of reductino - standard electrode potential of oxidation

if this value is negative then the reaction is feasible

Question 38

what are fule cells being developed as

Answer 38

a method of releasing energy very effeciently fom fuels such as hydrgoen methane or methanol.

Question 39

how does the fuel cell work

Answer 39

The fuel cell system passes the fuel over a platinum metal which acts as both a catalys and electrode. The electrons are removed from the hydrogen at one electrode. The protons (H+) diffuse through a semi permeable membrance to the other electrode where they recive electrons and oxygen molecules to form water molecules.

Question 40

equations for the fuel cell and voltage produced

Answer 40

H2 –> 2H+ + e-
O2 + 4H+ + 4e- –> 2H2O
2H2 + O2 –> 2H2O
1.23v

Question 41

benefits of fule cell 3

Answer 41

1. convinient way of storing and relasing energy
2. energy efficiey is much high than standard fuel system (35-45% compared to 22% of disel)
3. emission ffrom fuel cells is less damaging than the carbon dioxide from traditional energies.

Question 42

drawbacks of fuel cell 3

Answer 42

1. The hydrogen fuel must be generated elsewhere and this is likely to use fossil fuel energy sources which will cause their own carbon dioxde emission
2. an energy loss compared to liquid fuels
3. fule cells operate at lower temperatures so need very efficient catalysts which use expensive metals.