Question 19M.3.hl.TZ1.17
| Date | May 2019 | Marks available | [Maximum mark: 7] | Reference code | 19M.3.hl.TZ1.17 |
| Level | hl | Paper | 3 | Time zone | TZ1 |
| Command term | Deduce, Outline, State, Suggest | Question number | 17 | Adapted from | N/A |
E10 is composed of 10% ethanol and 90% normal unleaded fuel.
Ethanol has a Research Octane Number (RON) of 108.6.
Outline how higher octane fuels affect engine performance.
[1]
increased AND fuels can be compressed more «before ignition» [✔]
Note: Accept “engines can be designed with higher compression ratio” OR “less chance of pre-ignition/auto-ignition/knocking occurring”.
One G2 respondent was concerned that “Research Octane Number” was used instead of “Octane Rating”, but most candidates correctly outlined how higher octane fuels affect engine performance.
Ethanol can be used in a direct-ethanol fuel cell (DEFC) as illustrated by the flow chart.
Deduce the half-equations occurring at electrodes A and B.
Electrode A:
Electrode B:
[2]
Electrode A: C2H6O (aq) + 3H2O (l) → 12H+ (aq) + 12e– + 2CO2 (g) [✔]
Electrode B: 3O2 (g) + 12H+ (aq) + 12e– → 6H2O (l) [✔]
Note: Accept balanced equations with integer or fractional coefficients.
Penalize equilibrium arrows once only.
Some candidates did very well and deduced the half-equations occurring in a DEFC as illustrated in a flow chart. A few used equilibrium arrows and lost a mark. Some candidates failed to balance the half-equations.
State the name and function of X in the diagram in (b)(i).
Name:
Function:
[2]
Name:
PEM/proton-exchange membrane/polymer exchange membrane/polymer electrolyte membrane [✔]
Function:
allows the passage of protons/H+ ions «from anode to cathode but not electrons or molecules» [✔]
Was answered well.
Outline why aqueous ethanol, rather than pure ethanol, is used in a DEFC.
[1]
Any one of:
water is a reactant/allows the cell to operate at a higher concentration of protons/H+ ions
OR
water is a stronger electrolyte and thus produces higher electric current [✔]
less dangerous/flammable [✔]
Few candidates could outline why aqueous ethanol is used in a DEFC.
Biodiesel containing ethanol can be made from renewable resources.
Suggest one environmental disadvantage of producing biodiesel from renewable resources.
[1]
use of «farm» land «for production»
OR
deforestation «for crop production for fuel»
OR
can release more NOx «than normal fuel on combustion» [✔]
Note: Ignore any reference to cost.
Most could suggest one environmental disadvantage of producing biodiesel from renewable resources.