Question 18N.3.hl.TZ0.15
| Date | November 2018 | Marks available | [Maximum mark: 9] | Reference code | 18N.3.hl.TZ0.15 |
| Level | hl | Paper | 3 | Time zone | TZ0 |
| Command term | Deduce, Determine, Formulate, Identify, Outline, State | Question number | 15 | Adapted from | N/A |
Chemical energy from redox reactions can be used as a source of electrical energy.
Outline how a rechargeable battery differs from a primary cell.
[1]
«redox» reaction in rechargeable battery is reversible «but not in a primary cell»
OR
secondary cells need to be charged before use
OR
secondary cells have greater rate of self-discharge ✔
Accept “primary cells cannot be recharged/reused”, “primary cells can be used only once” OR “lithium batteries may explode”.
Formulate half-equations for the reactions at the anode (negative electrode) and cathode (positive electrode) during discharge of a lithium-ion battery.
[2]
Anode (negative electrode):
Li (graphite) → Li+ (electrolyte) + e–
OR
LiC6 (s) → 6C (s) + Li+ (electrolyte) + e– ✔
Cathode (positive electrode):
Li+ (electrolyte) + e– + MnO2 (s) → LiMnO2 (s)
OR
Li+ (electrolyte) + e– + NiO2 (s) → LiNiO2 (s)
OR
Li+ (electrolyte) + e– + CoO2 (s) → LiCoO2 (s)
OR
2Li+ (electrolyte) + 2e– + 2CoO2 (s) → Co2O3 (s) + Li2O (s) ✔
Accept “polymer” for “electrolyte”.
Award [1 max] if electrodes are reversed.
Do not accept “CO” for “Co”.
A voltaic cell consists of a nickel electrode in 1.0 mol dm−3 Ni2+ (aq) solution and a cadmium electrode in a Cd2+ (aq) solution of unknown concentration.
Cd (s) + Ni2+ (aq) → Cd2+ (aq) + Ni (s) EΘcell = 0.14 V
Determine the concentration of the Cd2+ (aq) solution if the cell voltage, E, is 0.19 V at 298 K. Use section 1 of the data booklet.
[2]
«E = EΘ − lnQ»
OR
0.05 = –0.01283 ln [Cd2+]
OR
ln[Cd2+] = – 3.897 ✔
[Cd2+] = 0.020 «mol dm–3» ✔
Award [2] for correct final answer.
The chemical structure of a photosensitive dye found in blueberries and a schematic diagram of a solar cell are shown.
Identify the structural feature of the dye that allows the conversion of solar energy into electrical energy.
[1]
«extensive» conjugation
OR
«extensive» alternate single and double bonds ✔
Accept “delocalization”.
Outline the effect of sunlight on the dye in the solar cell.
[1]
electrons excited/released «from dye» ✔
Accept “photooxidation/oxidizes dye”.
State the purpose of TiO2.
[1]
transfers e– to external circuit ✔
Accept “provides large surface area”.
Deduce the reduction half-equation at the cathode.
[1]
I3– (aq) + 2e– → 3I– (aq) ✔
Accept “3I2 (aq) + 2e– → 2I3– (aq)”.