| Date | May 2019 | Marks available | 1 | Reference code | 19M.3.hl.TZ1.17 |
| Level | HL | Paper | 3 | Time zone | TZ1 |
| Command term | Suggest | Question number | 17 | Adapted from | N/A |
Question
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.
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:
State the name and function of X in the diagram in (b)(i).
Name:
Function:
Outline why aqueous ethanol, rather than pure 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.
Markscheme
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”.
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.
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» [✔]
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 [✔]
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.
Examiners report
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.
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.
Was answered well.
Few candidates could outline why aqueous ethanol is used in a DEFC.
Most could suggest one environmental disadvantage of producing biodiesel from renewable resources.
Syllabus sections
-
18M.3.sl.TZ1.11a.ii:
State the formula of a fuel that might be produced from the vegetable oil whose formula is shown.
-
18M.3.hl.TZ1.13b:
State the formula of a fuel that might be produced from the vegetable oil whose formula is shown.
- 16N.3.sl.TZ0.14a: State the equation for the complete transesterification of the triglyceride given below with...
- 18N.3.sl.TZ0.11c.ii: Describe how vegetable oils can be converted to a more suitable fuel.
- 18N.3.sl.TZ0.11c.i: State a physical property of vegetable oils that makes them very difficult to use as fuel in...
- 18N.3.sl.TZ0.11b: Light can be absorbed by chlorophyll and other pigments. Consider molecules A and B...
- 18N.3.hl.TZ0.14b.i: State a physical property of vegetable oils that makes them very difficult to use as fuel in...
- 18N.3.hl.TZ0.14b.ii: Describe how vegetable oils can be converted to a more suitable fuel.
-
17M.3.sl.TZ1.15d:
Determine the specific energy, in kJg−1, and energy density, in kJcm−3, of a particular biodiesel using the following data and section 1 of the data booklet.
Density = 0.850 gcm−3; Molar mass = 299 gmol−1;
Enthalpy of combustion = 12.0 MJmol−1.
- 17N.3.sl.TZ0.15b: Vegetable oils are too viscous for use as liquid fuels. Describe, using an equation, how a...
-
18M.3.hl.TZ1.13a:
Outline the major technical problem affecting the direct use of vegetable oils as fuels in internal combustion engines and the chemical conversion that has overcome this.
-
17M.3.sl.TZ1.15b:
Deduce the formula of the biodiesel formed when the vegetable oil shown is reacted with the reagents in (a).
- 17N.3.sl.TZ0.15a: State the structural feature of chlorophyll that enables it to absorb visible light.
-
17M.3.sl.TZ2.12b:
Coloured molecules absorb sunlight. Identify the bonding characteristics of such molecules.
-
19N.3.sl.TZ0.14a:
Write the equation for the complete combustion of ethanol.
-
16N.3.sl.TZ0.14b:
Outline why the fuel produced by the reaction in (a) is more suitable for use in diesel engines than vegetable oils.
-
18M.3.sl.TZ2.14b:
Outline why the ester product of this reaction is a better diesel fuel than pentyl octanoate.
-
19M.3.sl.TZ1.13c:
Biodiesel containing ethanol can be made from renewable resources.
Suggest one environmental disadvantage of producing biodiesel from renewable resources.
-
18M.3.sl.TZ2.14a:
Deduce the equation for the transesterification reaction of pentyl octanoate, C7H15COOC5H11, with methanol.
-
17M.3.sl.TZ1.15c:
Explain, in terms of the molecular structure, the critical difference in properties that makes biodiesel a more suitable liquid fuel than vegetable oil.
-
19N.3.sl.TZ0.14c:
Explain, including a suitable equation, why biofuels are considered to be carbon neutral.
- 19N.3.sl.TZ0.14d: State the type of reaction that occurs when ethanol reacts with vegetable oil to form biodiesel.
-
19M.3.sl.TZ2.12a:
The structure of chlorophyll is given in section 35 of the data booklet.
State the feature of the chlorophyll molecule that enables it to absorb light in the visible spectrum.
-
17M.3.sl.TZ1.15a:
State two reagents required to convert vegetable oil to biodiesel.
-
20N.3.sl.TZ0.9d:
A mixture of gasoline and ethanol is often used as a fuel. Suggest an advantage of such a mixture over the use of pure gasoline. Exclude any discussion of cost.
-
19M.3.sl.TZ2.12b:
Evaluate the use of biodiesel in place of diesel from crude oil.
Strength:
Limitation:
-
18M.3.sl.TZ1.11b:
Outline why biofuels are considered more environmentally friendly, even though they produce more carbon dioxide per kJ of energy than petroleum based fuels.
- 20N.3.hl.TZ0.11d: A mixture of gasoline and ethanol is often used as a fuel. Suggest an advantage of such a...
-
18M.3.sl.TZ1.11a.i:
Outline the major technical problem affecting the direct use of vegetable oils as fuels in internal combustion engines and the chemical conversion that has overcome this.
-
19M.3.hl.TZ2.17:
This question is about biofuel.
Evaluate the use of biodiesel in place of diesel from crude oil.
- 20N.3.sl.TZ0.9e: Contrast the molecular structures of biodiesel and the vegetable oil from which it is formed.
