Electrode potentials

Question 1

What happens when a metal is placed in a solution of its ions?

Answer 1

An equilibrium is established between the ions in solution and the metal atoms

Question 2

Represent the equilibrium by a half equation

Answer 2

M^n+(aq) + ne- ⇌ M(s)

Question 3

What are the half equations always written as

Answer 3

Reductions, Electrons on LHS

Question 4

What are two half cells combined called?

Answer 4

A cell

Question 5

What is the standard electrode potential?

Answer 5

The potential difference measured when a half cell is connected to the standard hydrogen electrode under standard conditions 1moldm-3 and 298K

Question 6

What are electrode potentials represented by and what are they measured in?

Answer 6

Represented by E⦵ and measured in Volts

Question 7

What is the electrode potential?

Answer 7

A measure of the feasibility of the reduction occurring

Question 8

What does a negative E⦵ suggest?

Answer 8

That the reduction will not occur unless a more feasible oxidation takes place

Question 9

What is emf?

Answer 9

The potential difference measured when two half cells are connected

Question 10

What does a positive emf indicate?

Answer 10

A feasible reaction

Question 11

What does a negative emf indicate?

Answer 11

Unfeasible reaction

Question 12

What does the emf always relate to?

Answer 12

The overall redox equation, oxidation and reduction combined

Question 13

What are the five features of the standard hydrogen electrode?

Answer 13

1. Platinum electrode
2. 1.00 moldm-3 hydrogen ions in solution
3. H2 gas at 100kPa
4. Temperature 298K
5. Standard electrode potential = 0.00V

Question 14

How do you combine two half cells?

Answer 14

Combined using a salt bridge and an external circuit using a high resistance voltmeter to produce a cell

Question 15

How do you make the salt bridge?

Answer 15

Filter paper soaked in potassium nitrate solution which dips into both solutions

Question 16

What is the purpose of the salt bridge?

Answer 16

Allows electrical connection between the two half cells without them having to mix

Question 17

What usually are the left and right hand cells?

Answer 17

Left hand cell is the one in which oxidation occurs and is the negative electrode of the cell
Right hand cell is the one in which the reduction occurs. It is the positive electrode of the cell

Question 18

How do you remember where oxidation occurs

Answer 18

NEGATOX

Negative electrode is the one at which oxidation occurs

Question 19

Draw the diagram of a standard hydrogen half cell and a zinc half cells

Answer 19

in book

Question 20

How do you calculate the emf of a cell?

Answer 20

The emf of a cell is calculated by simply adding the two values together where you have switched the sign of the most negative so it is an oxidation

Question 21

Describe non standard conditions in a cell

Answer 21

Two identical cells will show no overall charge, however, two cells that are the same except for concentration of ions will show a reduction where the ion in solution is at a higher concentration

Question 22

What is an ammeter used in a non standard conditions in a cell?

Answer 22

The ammeter allows current to flow

Question 23

What will you observe in non standard conditions?

Answer 23

The mass of the ion in the solution of greater concentration will increase as the metal is made

Question 24

How are conventional cells representations written?

Answer 24

Oxidation at left hand half-cell⎮⎮ Reduction at right hand half-cell

Question 25

Give an example of the conventional cell representation of Zn2+ + 2e- → Zn E⦵ = -0.76V Cu2+ + 2e- → Cu E⦵ = +0.34V

Answer 25

``` Rewrite as: Zn → Zn2+ +2e- E⦵ = +0.76 Cu2+ +2e- → Cu E⦵ = +0.34 Then in conventional cell representation Zn⎟Zn2+ ⎟⎟Cu2+ ⎟Cu ``` Overall emf = +0.74 + +0.34 = +1.10V therefore feasible

Question 26

What are the three things about phase boundaries

Answer 26

1. ⎟is used when two species are in different states 2. , is used when two species are in the same state 3. Pt should be included if it is used as the electrode for gaseous electrodes

Question 27

What does a positive emf mean?

Answer 27

The reaction is feasible

Question 28

What does the oxidation emf of a metal give?

Answer 28

The reactivity of the metal, the more positive the oxidation the more reactive the metal.

Question 29

What happens to the reactivity of the halogens down the group?

Answer 29

Decreases, as you go down the halogens they are less easily reduced

Question 30

Describe oxidising and reducing agents

Answer 30

on page

Question 31

What are the three main types of cells

Answer 31

Primary cells - Non rechargeable Secondary cells - Rechargeable Fuel cells - continually produce electric current as long as they're supplied with a fuel

Question 32

Which way do the electrons flow in a battery

Answer 32

From the negative end (where oxidation occurs and electrons are lost) to the positive end (where reduction occurs and electrons are gained)

Question 33

Draw a typical primary cell

Answer 33

in book

Question 34

What is the overall ionic equation for a primary cell

Answer 34

Zn + 2MnO2 + 2H2O → Zn2+ + 2MnO(OH)2 + 2OH-

Question 35

What is the purpose of the carbon rod?

Answer 35

The carbon rod carries eletrons back to the MnO2 paste

Question 36

Write the reduction of ammonium ions

Answer 36

2NH4+ + 2e- → 2NH3 + H2

Question 37

What is the overall equation for the old type of cells ?

Answer 37

Zn + 2NH4+ → Zn2+ +2NH3 +H2

Question 38

In the nickel cadmium, lead-acid and lithium ion cell give: 1. What happens at the negative electrode 2. What happens at the positive electrode 3. The overall ionic equation

Answer 38

on page

Question 39

What is the conventional cell representation of the lithium ion cell

Answer 39

Li⎟Li+⎮⎮Li+ , CoO2 ⎟LiCoO2⎟Pt

Question 40

What do fuel cells do?

Answer 40

Convert chemical energy into electrical energy

Question 41

What are the different types of fuel cells?

Answer 41

Acidic hydrogen fuel cell, alkaline hydrogen fuel cell, Ethanol fuel cell

Question 42

Hydrogen fuel cell alkaline 1. Negative electrode 2. Positive electrode 3. Overall equation

Answer 42

1. Oxidation: H2 + 2OH- → 2H2O + 2e- 2. Reduction: O2 + 2H2O + 4e- → 4OH- 3. 2H2 + O2 →2H2O

Question 43

What is the conventional cell representation for the hydrogen fuel cell alkaline?

Answer 43

Pt ⎮H2⎮OH- , H2O⎟⎟O2 ⎮H2O , OH- ⎟Pt

Question 44

What are environmental issues of all the different cells?

Answer 44

1. Primary cells - source of waste 2. Secondary cells - Finite lifespan 3. Fuel cells - Constantly producing current while fuel is supplied

Question 45

Why are phones bad

Answer 45

Contain precious metals and so should be recycled

Question 46

What is the con of hydrogen fuel cells

Answer 46

Theyre carbon neutral but EXTREMELY hard to maintain