Electrochemical Cells

Question 1

What is standard electrode potential of a half cell

Answer 1

Pd of a half cell compared with a standard hydrogen half cell, measured at 298K, solution concens of 1moldm-3 and gas pressure of 1atm

Question 2

What measures potential difference

Answer 2

Voltmeter

Question 3

What is a salt bridge

Answer 3

Filter paper soaked in potassium nitrate stoppered with porous plug (as potassium/nitrate salts soluble so will not interfere with reaction) to allow ions that have built up on either side to move to other side, completes circuit as even with high resistance some electrons do flow, if circuit not complete current would cease

Question 4

Why use high resistance voltmeter

Answer 4

Stops current flowing from where there are a lot of them to where there are less, means cannot make proper comparison

Question 5

What happens when metals in contact with their ions in aqueous solution

Answer 5

Once equilibrium established metal atoms lose their electrons leaving them behind on piece of metal equal to rate of zinc ions gaining electrons from the piece of metal and become atoms, here there is a pd between the piece of metal which has negative charge and solution which contains positive ions

Question 6

What does cell potential indicate

Answer 6

Indicated how it will react either in oxidation or reduction reaction

Question 7

How are electrodes with very negative standard electrode potential likely to react and where is equilibrium in reduction equation

Answer 7

Indicate strong reducing agents so are oxidised themself, further to the left so to ion and electrons

Question 8

How is electrode with very positive standard electrode potential likely to react and where does equilibrium lie for reduction equation

Answer 8

Indicates strong oxidising agents, reduced themself, equilibrium further to right than hydrogen so to element

Question 9

What is standard electrode potential compared to and what is its value

Answer 9

Hydrogen
H+ + e- —-> 1/2 H2
0V

Question 10

What happens if piece of wire used as salt bridge

Answer 10

It would set up its own equilibria and only allow electrons to pass not ions

Question 11

What would happen if used silver in salt bridge

Answer 11

Would form precipitate with halogens, interfere with reaction

Question 12

Where is flow of electrons from

Answer 12

From anode to cathode, more negative standard electrode potential to less

Question 13

Which blocks undergo oxidation reactions

Answer 13

S/d and some p

Question 14

Which block undergoes reduction

Answer 14

P

Question 15

How to represent standard electrode potential

Answer 15

E circle with line through

Question 16

How to use gas in electrode

Answer 16

Flow of gas directed down and through surface of water where inert platinum electrode used to catalyse the reaction

Question 17

Do you inverse electrode potential value when going in other direction for reaction

Answer 17

No

Question 18

What is conventional cell representation

Answer 18

-half cell with most negative potential goes on the left
-the most oxidised species from each half cell goes next to the salt bridge
-salt bridge shown as double line
-state symbols included

Question 19

How to calculate overall cell emf

Answer 19

Emf (cell) = E circle(right) - E circle (left, more negative)

So minus negative to give positive

Question 20

How to represent gas/aqueous ions on both sides in cell notation

Answer 20

Comma between the two and line then Pt (s)

Question 21

What occurs on the right and what electrode

Answer 21

Reduction, cathode

Question 22

What occurs on the left and what electrode

Answer 22

Oxidation, anode

Question 23

Where do electrons move in cell

Answer 23

From anode to cathode

Question 24

Do you put numbers in front of atoms in cell notation

Answer 24

Yes to balance charges on overall redox reaction

Question 25

What does very positive electrode potential indicate

Answer 25

Better oxidising agent, will oxidise species more negative than themself

Question 26

What does very negative electrode potential indicate

Answer 26

Better reducing agent, will reduce species less negative than themself

Question 27

What do single lines show in cell notation

Answer 27

Boundary between phases