Half cells

Question 1

PD cannot be measured directly, how is the circuit completed? Why is this done?

Answer 1

• through a salt bridge
• compare value between 2 half cells

Question 2

What is a salt bridge?

Answer 2

• piece of filter paper soaked in a solution of salt

Question 3

What salt solution is soeaked into the salt bridge? WHat must be considered when choosing the salt bridge?

Answer 3

• saturated potassium nitrate
• doesn’t react w/ beaker contents

Question 4

Why is a wire not used?

Answer 4

• avoid further metal/ion potentials in the circuit

Question 5

Why is the voltmeter connected high resistance?

Answer 5

• ideally infinitely high resist
• avoid any flow of current through circuit

Question 6

Why is current flow avoided?

Answer 6

• electrons would flow from most -ve electrode to the positive
  
  • region of high e- to low e-
• voltage measured drops
• to make comparisons, maximum possible volatage must be recorded
  
  • this is emf

Question 7

What does a -ve E^ϴ value tell us?

Answer 7

• more readily gives up electrons than the SHE
• form ions more readily
  
  • leave more e- behind on the metal,
  • making it mre -ve
• eqm lies further to left
• more likely to release electrons than the SHE