20 - Electrode potentials and electrochemical cells

Question 1

Describe the structure of a cell.

Answer 1

• Two half-cells
• Connected by salt bridge
• Each half cell is a metal solid electrode and solution of compound containing that metal eg Cu and CuSO4
• Metal solids are connected by a high resistance voltmeter

Question 2

why does a voltage form in a cell?

Answer 2

• one half-cell has a higher tendency to oxidise to its ion and release its electrons
• so more electrons build up on the metal solid
• a potential difference forms

Question 2

what is the salt bridge?

Answer 2

piece of filter paper soaked in salt solution, usually potassium nitrate

Question 3

describe the components of a standard hydrogen electrode.

Answer 3

H2 gas at 100kPa
Solution containg 1M hydrogen ions (usually HCl)
298K
Pt electrode

Question 4

what potential does a stnadard hydrogen electrode have?

Answer 4

0V

Question 5

what is the shorthand for a cell?

Answer 5

Zn(s) | Zn^2+ (aq) || Cu^2+ (aq) | Cu (s)

solid vertical line between phases
double line is salt bridge
most oxidised goes next to salt bridge

Question 6

what is standard electrode potential?

Answer 6

the potential difference when a half cell is connected to a standard hydrogen electrode

Question 7

What is the EMF formula?

Answer 7

EMF = Ered - Eoxi

Question 8

Which half cell is oxidised, and which is reduced?

Answer 8

the more negative is oxidised so losing electrons
the most positive is reduced so gains electrons