electrochemistry

Question 1

what is a fuel cell

Answer 1

a galvanic cell that requires hydrogen and oxygen to function - can continuously turn chemical energy into electrical energy as long as there is a constant supply of hydrogen/oxygen

Question 2

what is a galvanic cell

Answer 2

• converts chemical energy into electrical energy
• 2 electrolytes (separate)
• spontaneous reaction (doesnt require an external source to drive the reaction)

As the cell given below operates, the strip of silver gains mass (only silver) and the concentration of silver ions in the solution around the silver strip decreases, while the strip of lead loses mass and the concentration of lead increases in the solution around the lead strip

Question 3

what is a dry cell

Answer 3

several of them placed in series to form battery

- once run out of electrons, the cell/battery is dead

Question 4

what is a rechargeable cell

Answer 4

• electrolytic cell (converts electrical energy into chemical energy)
• external supply of electricity forces electrons into the cathode + pulls electrons away from anode

Question 5

what is an electrolytic cell & electrolysis

Answer 5

• converts electrical energy into chemical energy
• electrolysis = process where electrons transferred to cathode from external source and electrons pulled from anode
• cathode = neg. (due to forced charge)
• anode = pos
• non-spontaneous

Question 6

what is corrosion

Answer 6

when a metal oxidises and degrades (loses electrons) when exposed to oxygen and water

• eg. iron is oxidised, oxygen is reduced
• redox reaction (transfer of electrons)

Question 7

how does fractional distillation work

Answer 7

crude oil heated in gas chamber at very high temp.

• different fractions each at different temperature
• each alkane/hydrocarbon has a different boiling point (due to molecular structure + no. of bonds)
• bigger molecule = higher boiling point
• separated when each hydrocarbon reaches its boiling point + forms a gas
• each separate gas cools to a diff. oil/fuel (eg. diesel)

Question 8

what are all the different uses of electrolytic cells

Answer 8

electroplating

purifying metals

recharging batteries

Question 9

how can corrosion be prevented

Answer 9

1. impervious layer
   - less reactive metal coating (prevents exposure): eg. paint, grease
2. sacrificial anode
   - more reactive metal (will corrode instead)

Question 10

what is a redox reaction

Answer 10

transfer of electrons between 2 species (oxidising agent to reducing agent)

Question 11

Advantages of fuel cells

Answer 11

• no greenhouse gases emitted (water is the only product)
• fuel used is abundant (ie. hydrogen and oxygen?)
• efficient (more efficient than fossil fuels)

Question 12

disadvantages of fuel cells

Answer 12

• catalyst is expensive
• hydrogen is flammable (dangerous)
• contamination of electrodes may occur

Question 13

what is the electrolysis equation for oxidation

Answer 13

2 H2O(l) → O2(g) + 4 H+(aq) + 4e

Question 14

what is precipitation

Answer 14

2 salt solutions mix to form an insoluble solid

Question 15

explain variation in voltage diff. for different metal combinations in galvanic cells

Answer 15

• higher diff. in reactivity = higher voltage
• due to higher reactive metal anode losing electrons to cathode more easily which means there is a larger voltage
• will be negative if the role switches (ie. if Mg connected to pos electrode & Cu to neg. electrode =&raquo_space; they will switch)

Question 16

what speeds up rusting

Answer 16

• a more reactive metal (ie. iron reacts faster than Al)

- salt in water = electrolyte and conducts electricity so iron can lose electrons more easily