| Date | May 2019 | Marks available | 1 | Reference code | 19M.3.sl.TZ2.12 |
| Level | SL | Paper | 3 | Time zone | TZ2 |
| Command term | State | Question number | 12 | Adapted from | N/A |
Question
This question is about biofuel.
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.
Evaluate the use of biodiesel in place of diesel from crude oil.
Strength:
Limitation:
Markscheme
large/extensive «electronic» conjugation
OR
«contains» many alternate single and double bonds
OR
extended system of alternating double and single bonds [✔]
Note: Student response must indicate a large or extended system to award mark.
Strength
Any one of:
less flammable «than diesel» [✔]
recycles carbon «lower carbon footprint»
OR
lower greenhouse gas emissions [✔]
easily biodegradable «in case of spill» [✔]
renewable
OR
does not deplete fossil fuel reserves [✔]
economic security/availability in countries without crude oil [✔]
Limitation
Any one of:
more difficult to ignite inside the engine «than diesel» [✔]
more viscous «than diesel» [✔]
lower energy content/specific energy/energy density [✔]
uses food sources
OR
uses land that could be used for food [✔]
«production is» more expensive [✔]
less suitable in low temperatures [✔]
increased NOx emissions for biodiesel [✔]
greenhouse gases still produced [✔]
Note: Accept “«close to» carbon neutral”, “produce less greenhouse gases/CO2”.
Accept “engines have to be modified if biodiesel used” as limitation.
Do not award marks for strength and limitation that are the same topic/concept.
Examiners report
This question was not well answered as many students missed the idea of the system being a large/extensive/extended or containing many alternating single and double bonds. Although fewer students than expected received a mark, examiners did note there were more student who wrote about conjugation or alternating single and double bonds (but were missing the idea of the system being large) which is an improvement from previous sessions.
This question was well answered, and many candidates received one or both marks. Some candidate who did not receive marks were too vague, especially with the limitation.
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.
-
19M.3.hl.TZ1.17c:
Biodiesel containing ethanol can be made from renewable resources.
Suggest one environmental disadvantage of producing biodiesel from renewable resources.
-
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.
-
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.
