| Date | May 2017 | Marks available | 2 | Reference code | 17M.3.sl.TZ1.15 |
| Level | SL | Paper | 3 | Time zone | TZ1 |
| Command term | State | Question number | 15 | Adapted from | N/A |
Question
Vegetable oils, such as that shown, require conversion to biodiesel for use in current internal combustion engines.
State two reagents required to convert vegetable oil to biodiesel.
Deduce the formula of the biodiesel formed when the vegetable oil shown is reacted with the reagents in (a).
Explain, in terms of the molecular structure, the critical difference in properties that makes biodiesel a more suitable liquid fuel than vegetable oil.
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.
Markscheme
methanol
OR
ethanol
strong acid
OR
strong base
Accept “alcohol”.
Accept any specific strong acid or strong base other than HNO3/nitric acid.
[3 marks]
CH3(CH2)16COOCH3 / CH3OCO(CH2)16CH3
OR
CH3(CH2)16COOC2H5 / C2H5OCO(CH2)16CH3
Product must correspond to alcohol chosen in (a), but award mark for either structure if neither given for (a).
[1 mark]
lower viscosity
weaker intermolecular/dispersion/London/van der Waals’ forces
OR
smaller/shorter molecules
Accept “lower molecular mass/Mr” or “lower number of electrons”.
Accept converse arguments.
[2 marks]
Specific energy: «» = 40.1 «kJ g−1»
Energy density: «= 40.1 kJg−1 x 0.850 gcm−3» = 34.1 «kJcm−3»
Award [1] if both are in terms of a unit other than kJ (such as J or MJ).
[2 marks]
Examiners report
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.
-
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.
-
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.
