Electrode Potentials And Electrochemical Cells

Question 1

How do we get electricity?

Answer 1

By the movement of electrons

Question 2

What type of cells make electricity

Answer 2

Electrochemical cells make electricity

Question 3

How are electrochemical cells made?

Answer 3

• Made from two different metals dipped in salt solutions of their own ions and connected by a wire (the external circuit)

Question 4

How many reactions are in an electrochemical cell?

Answer 4

• Oxidation
• Reduction
• Redox processes

Question 5

How do electrons flow in an electrochemical cell?

Answer 5

Electrons flow through the wire from the more reactive metal to the less reactive one

Question 6

What is the use of a voltmeter

Answer 6

• Found in the external circuit
• Used to measure the voltage between the two half-cells
• Finds the cell potential or electromotive force known as Ecell

Question 7

What other variations of half-cells are possible?

Answer 7

• Half cells involving solutions of two aqueous ions of the same element.

Question 8

Why is a platinum electrode used?

Answer 8

Platinum is an inert gas so it does not react with ions

Question 9

What type of reaction happens at each electrode

Answer 9

Reversible reactions

Question 10

What does the reversible arrow show?

Answer 10

That both reactions of each electrode can go in either directions (the flow of electrons)

Question 11

How are half-equations for electrochemical cells written

Answer 11

• They’re always written with the reduction reaction going forward direction (with the electrons on the left-hand side)

Question 12

What is the condition dependent on which direction the reaction will go in

Answer 12

• The reaction depends on on how easily each metal looses electrons ( how easily it’s oxidised)

Question 13

What is the function of electrode potentials

Answer 13

• Measure how easily metals are oxidised
• A metals that’s easy to oxidise has a very negative electrode potential. One that’s harder to oxidise has a less negative (or positive) electrode potential

Question 14

What are the guideline for wiring the overall equation for a cell

Answer 14

• Reduced means the half equation goes forward
• Oxidised means the half equation goes backwards

Question 15

List the conditions that affect cell potentials

Answer 15

• Temperature
• Pressure
• Concentration

Question 16

What is the standard electrode potential of a half cell?

Answer 16

The standard electrode potential of a half cell is the voltage measured under standard conditions when the half-cell is connected to a standard hydrogen electrode

Question 17

What are the standard conditions for a half-cell?

Answer 17

• Any solutions must have a concentration of 1.00mol dm-3
• The temperature must be 298K (25C)
• The pressure must be 100kPa

Question 18

Note

Answer 18

Is standard conditions are maintained, the reading in the voltmeter when a half-cell is connected to the standard hydrogen electrode will be the standard electrode potential of that half-cell

Question 19

What is the function of the salt bridge

Answer 19

• Connects the solutions
• Made from filter paper soaked in KNO3(aq)
• Allows ions to flow through and balance out the charges

Question 20

What is the function of the electrochemical series

Answer 20

It shows you what elements are reactive and which are not

Question 21

What is an electrochemical series

Answer 21

An electrochemical series is basically a list of standard electrode potentials for different electrochemical half-cells

Question 22

What can be calculated from the electrochemical series

Answer 22

Standard cell potentials

Question 23

What is the function of a standard electrode potential

Answer 23

Standard electrode potential values can be used to calculate the standard cell potential Ecell or (EMF: electromotive force) when two half-cells are joined together.

Question 24

Give the equation for the EMF of a cell

Answer 24

Ecell= Ereduced - Eoxidised

Question 25

What is the first step in calculating the EMF

Answer 25

L First write the two half equations down as reduction reactions and write their E/V value from the electrochemical series

Question 26

Describe the shorthand way of drawing electrochemical cells

Answer 26

• The half cell with a more negative potential goes on the left • The oxidised forms go in the centre of the cell diagram

Question 27

What do electrode potentials predict?

Answer 27

Whether a reaction will happen

Question 28

What do the vertical lines on n a shorthand electrochemical cell show?

Answer 28

Double lines show a salt bridge

Question 29

The more negative the electrode is, the more…..

Answer 29

Reactive the metal will be

Question 30

What happens to metals when they react?

Answer 30

They loose electrons, they become oxidised

Question 31

Give one advantage and one disadvantage of non-rechargeable batteries

Answer 31

• They are cheaper however, • They cannot be recharge

Question 32

Name a metal that is used in the electrodes in an alkaline hydrogen-oxygen fuel cell

Answer 32

Platinum containing electrodes

Question 33

What electrolyte is used in an alkaline hydrogen-oxygen fuel cell?

Answer 33

Aqueous alkaline solution (OH-)

Question 34

How is a lithium battery recharged vs a non-rechargeable battery

Answer 34

• To recharge these batteries, a current is supplied to force electrons to flow in the opposite direction around the circuit • And reverse the reactions • The reactions that take place in non-rechargeable batteries are difficult or impossible to reverse in this way

Question 35

What happened to the half equations in a rechargeable batteries

Answer 35

The reactions are reversed

Question 36

Give one type of electrochemical cells which provide electricity

Answer 36

Batteries

Question 37

Give some types of batteries, their advantages and disadvantages

Answer 37

•Non-rechargeable batteries: can only be used until they run out. They are cheaper. • Rechargeable batteries: Last longer and are cheaper in the long-run

Question 38

What type of cells are used in mobile phones and laptops

Answer 38

Lithium cells

Question 39

Describe how lithium cells provide electricity

Answer 39

• Lithium cell is made up of a lithium cobalt oxide (LiCoO2) and a graphite electrode • The electrolyte is a lithium salt in an organic solvent • Half equations: Check digital flashcards 🔴 • The Li+/ Li half cell has the more negative E value so goes in the direction of oxidation (backwards) • The reaction that happens at the battery supplies, positive and negative electrode: Check did vital flashcards for answers🔴🔴

Question 40

How do fuel cells generate electricity and give examples

Answer 40

• Chemicals that generate electricity are contained in the electrodes and the electrolyte that form the cell • Chemicals are stored separately outside the cell and are fed in when electricity is needed • alkaline hydrogen-oxygen fuel cell, used to power electric vehicles • Hydrogen and oxygen gases are fed into two separate platinum-containing electrodes • The electrodes are separated by an anion-exchange membrane that allows (OH-) and water to pass through it but not hydrogen and oxygen gases • The electrolyte is an aqueous alkaline KOH solution • Electrons flow from the negative circuit through an external circuit to the positive electrode • The OH- ions pass through the anion-exchange membrane towards the negative electrode

Question 41

Why do fuel cells have big advantages?

Answer 41

• using fuel cells in cars is more efficient • able to convert more of their available energy into kinetic energy to get the car moving • Internal combustion engines waste a lot of their energy producing heat • Fir fuel cells the only waste product is water so no nasty toxic chemicals to dispose of and no carbon emissions • Fuel cells don’t need to be recharged like batteries. As long as hydrogen and oxygen are supplied the cell will continue to produce electricity

Question 42

What are some disadvantages of fuel cells

Answer 42

• Energy is needed to supply hydrogen and oxygen • They can be produced from the electrolysis of water e.g. • Re-using the waste product from the fuel cell but this requires electricity • This electricity is generated by burning fossil fuels • The whole process isn’t usually carbon neutral • Hydrogen is also highly flammable, it needs to be handled carefully when it is stored or transported

Question 43

What is the overall effect of alkaline hydrogen-oxygen fuel cell

Answer 43

Hydrogen and oxygen react to make water

Question 44

Agents on the left hand side of the electrochemical series are more easily?

Answer 44

Reduced, so oxidising agents