chpt 14 electrolysis

Question 1

What is discharged at the anode for inert electrode in both dilute and conc solutions ?

Answer 1

1. dilute -> OH-
   4OH- (aq) -> 2H2O (l) + O2 (g) + 4e-
2. concentrated
   anion -> anion + e-

Question 2

What is discharged at the anode in both dilute and conc solutions ?

Answer 2

The ion that is less reactive is selectively discharged as it it more ready to leave its salt

Question 3

What happens at the anode for a reactive copper electrode ?

Answer 3

1. Anode oxidises other release cu2+ ions into the solution
   Cu (s) -> Cu2+ (aq) + 2e-
   impurities will fall to the bottom of the electrolyte, causing anode to shrink in size
   (anode sludge)

Question 4

What happens at the cathode for a reactive copper electrode ?

Answer 4

1. cation lower in the reactivity series is selectively discharged
2. if copper in solution is selectively discharged (mostly the case)
   Cu2+ (aq) -> Cu (s)
   red brown solid copper will form a red brown layer over the copper cathode

Question 5

How can reactive electrodes be used for electroplating ?

Answer 5

1. object to be plated os made the cathode
2. metal for electroplating is made the anode
3. anode will dissolves to form ions in the solution
4. electrolyte must have the same metal as the electroplating metal to allow it to be discharged on the cathode and form an insoluble layer

Question 6

How does a simple cell work ?

Answer 6

1. two electrode with differing reactivities
2. less rxtive electrode is made the cathode and more rxtive electrode is made the anoe
3. electros flow from the reactive metal to the less rxtive metal due to the diff in ability to lose electrons
4. Anode is negative electrode (gives electrons back to Voltmeter)
5. more reactive anode undergoes oxidation and shrinks in size
6. less reactive cathode selectively discharges less reactive anion

Question 7

What does the hydrogen fuel cell do ?

Answer 7

1. only water and potentially useful heat is created as by products
2. in alkali electrolyte,
   anode : 2h2(g) +4oh- -> 4h20 +4e-
   cathode : o2 (g) + 2h20 + 4e- > 4oh-
3. in acid electrolyte,
   anode : 2h2(g) -> 4h+ +4e-
   cathode : o2(g) + 4h+ + 4e- -> 2h20
4. disadvantage is that the electrodes need to be mada of expensive materials
   eg platinum ad palladium
5. hydrogen in the fuel cell are mostly derived from cracking of hydrocarbons, but if not, might be obtained from a process that contributes to global warming