14 - redox 2

Question 1

what type of electrode is used as a reference?

Answer 1

hydrogen
(the standard hydrogen electrode)

Question 2

what is a standard hydrogen electrode?

Answer 2

hydrogen gas at standard conditions bubbling over a piece of platinum foil dipper into a solution of hydrochloric (or sulfuric) acid
surface of the platinum foil is covered in porous platinum
porous platinum has a large surface area and allows an equilibrium between hydrogen ions in solution and hydrogen gas to be established quickly

Question 3

what are the standard conditions?

Answer 3

• 1 atm
• 298K
• 1 mol dm-3

Question 4

how do we measure a standard electrode potential?

Answer 4

connect the two half cells via a circuit containing a high resistance voltmeter
two half cells create a complete cell

Question 5

what does a salt bridge likely contain?

Answer 5

conc solution of potassium nitrate in the form of liquid or gel
functions by allowing the movement of ions

can contain any ionic salt but the ions present must not interfere with the components of the half cells

Question 6

why should the voltmeter have infinite resistance?

Answer 6

so there is no flow of electrons around the external circuit

Question 7

what do + and - signs indicate with respect to the hydrogen electrode?

Answer 7

• indicates the metal electrode is negative
  + indicates the reverse

Question 8

what do E⦵ values tell us?

Answer 8

method of comparing the positions of equilibria (- is left + is right)

Question 9

what is the potential difference called when measures whilst no electrons are flowing (no current)?

Answer 9

electromotive force (emf)
can be positive or zero
(emf of a cell with a hydrogen electrode as the positive electrode will be negative and when hydrogen electrode is the negative electrode the emf will be positive)