P2: Electrochemistry

Question 1

What is a displacement reaction?

Answer 1

When one element takes the place of another

The one that takes over displaces, is the stronger reducing agent

Question 2

What is the order of reducing agent power from strongest to weakest?

Answer 2

Li
K
Ca
Mg
Zn
Ni
Pb
Cu
Ag

Question 3

What is the electrochemical series?

Answer 3

Ranks the reducing power of half equations

Question 4

Forwards is…

Answer 4

oxidising agent

Question 5

Backwards is…

Answer 5

metal reducing agent

Question 6

What is a half-cell?

Answer 6

Metal dipped in a solution of its own ions (an electrode)

Question 7

What is a cell?

Answer 7

Two half cells connected together

Question 8

What is a battery?

Answer 8

Two or more cells connected together

Question 9

Which way do electrons flow?

Answer 9

Left to right
Negative to Positive

Question 10

What is the electromotive force ‘E’?

Answer 10

The maximum voltage possible between the 2 electrodes

Question 11

What do we use as a comparison fro all oxidising and reducing agents?

Answer 11

The hydrogen electrode

Question 12

What does the hydrogen electrode consist of?

Answer 12

-Strip of platinum dipped in a solution containing H+ ions
-Hydrogen gas bubbled through

Question 13

What are the standard conditions?

Answer 13

298K
100kPa
1 mol dm-3

Question 14

What does E (and standard symbol) stand for?

Answer 14

Standard electrode potential

Question 15

What is the EMF?

Answer 15

Electromotive force

Question 16

How do you calculate EMF?

Answer 16

‘E’ of cell= ‘E’ right - ‘E’ left

Question 17

What does a negative EMF value tell us?

Answer 17

Negative electrode on right

Question 18

What side is the positive electrode normally on?

Answer 18

Right

EMF is +

Question 19

What happens is + charge builds up in the left hand solution, and - charge builds up in the right solution?

Answer 19

Reactions come to a halt, voltage drops

Question 20

What is the purpose of a salt bridge?

Answer 20

Prevents build up of charge by allowing the movement of ions

Question 21

What is required for a salt bridge?

Answer 21

-Salt should not react with the ions in solution in either electrodes

Question 22

How do you represent cells?

Answer 22

1. Salt bridge is ll
2. • electrode on right
3. Ignore spectator ions
4. Most oxidised substances next to the salt bridge
5. Separate substances in different states with a l
6. Separate multiple substances in the same state with a comma

Question 23

What are some examples of non-rechargeable cells?

Answer 23

Zinc chloride
Zinc carbon
Alkaline
Button

Question 24

What is in a Daniell Cell?

Answer 24

Zinc and Copper

Question 25

What is a separator?

Answer 25

Used when the the + and - electrode are very close together, prevents them from reacting directly. Porous, allows transfer of ions.

Question 26

What is a dry cell?

Answer 26

Have no free liquid, only paste

Question 27

What is an electrolyte?

Answer 27

Substance that contains ions that are free to move, completing an electrical circuit

Question 28

What is in an alkaline battery?

Answer 28

-Zinc is powdered, increase SA -Next to a brass pin -Electrolyte is KOH paste

Question 29

How does recharging work?

Answer 29

Works in an equilibrium, so applying a strong electrical force pushes the electrons back towards the negative terminal

Question 30

Why do cars have rechargeable batteries?

Answer 30

To start their internal combustion engines

Question 31

Describe the positive electrode of a Lead-acid battery

Answer 31

-Lead IV oxide -Dipped in sulphuric acid -Becomes coated in lead sulphate as battery discharges

Question 32

Describe the negative electrode of a Lead-acid battery

Answer 32

-Lead -Dipped in sulphuric acid -Becomes coated in lead sulphate as battery discharges

Question 33

Describe how lithium ion cells work

Answer 33

1. Lithium starts at the negative electrode, with its support medium of powdered graphite 2. As lithium gives up electrons at the negative electrode, it migrates through the electrolyte to the positive electrode (cobalt IV oxide)

Question 34

Give the overall reaction that occurs in a lithium ion cell

Answer 34

Li (s) + CoO2 (s) ----> LiCoO2 (s)

Question 35

What are the advantages of lithium ion cells?

Answer 35

-Li is the lightest metal -Strongest reducing agent (so a high voltage) -Constructed without any moisture

Question 36

What do fuel cells require?

Answer 36

Continuous supply of reactants

Question 37

How do alkaline fuel cells work?

Answer 37

1. H2 is oxidised to H+ at the negative electrode 2. O2 is reduced to OH- at the positive electrode 3. H2O is produced at the negative electrode as the OH- migrates to the - electrode and combines with H+

Question 38

What is the overall equation for an alkaline fuel cell?

Answer 38

2 H2 + O2 -----> 2 H2O

Question 39

Do hydrogen fuel cells produce fossil fuels?

Answer 39

Not directly, but producing H2 does

Question 40

Why are hydrogen fuel cells dangerous?

Answer 40

Hydrogen is a hazard as it is explosive