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Date November 2018 Marks available 1 Reference code 18N.3.sl.TZ0.11
Level SL Paper 3 Time zone TZ0
Command term Identify Question number 11 Adapted from N/A

Question

Solar energy, which is freely available, is indispensable to life on earth.

Suggest another advantage and one disadvantage of solar energy.

[2]
a.

Light can be absorbed by chlorophyll and other pigments.

Consider molecules A and B represented below.

Identify, with a reason, the molecule that absorbs visible light.

[1]
b.

State a physical property of vegetable oils that makes them very difficult to use as fuel in internal combustion engines.

[1]
c.i.

Describe how vegetable oils can be converted to a more suitable fuel.

[1]
c.ii.

Contrast the importance of carbon dioxide and methane as greenhouse gases.

[2]
d.

Explain, using an equation, the effect of increased carbon dioxide in the atmosphere on the pH of lake water.

[2]
e.

Markscheme

Advantage:

renewable «energy source»

OR

does not produce greenhouse gases

OR

can be installed «almost» anywhere

OR

low maintenance costs ✔

 

Disadvantage:

widely dispersed/not concentrated «form of energy»

OR

geography/weather/seasonal dependent

OR

not available at night

OR

energy storage is difficult/expensive

OR

toxic/hazardous materials used in production

OR

concerns about space/aesthetics/local environment where installed

OR

need to be «constantly» cleaned ✔

 

Accept “can be used for passive/active heating”, “can be converted to electric energy”.

Accept any specific greenhouse gas name or formula for “greenhouse gases”.

Accept “solar cells require large areas”, “solar cell manufacture produces pollution/greenhouse gases”, “higher cost of solar cells «compared with traditional sources such as fossil fuels or hydroelectric»”.

a.

B AND larger/more extensive «electronic» conjugation

OR

B AND «contains» more alternate single and double bonds ✔

 

Accept more specific statements, such as “sp3 carbon in A prevents conjugation between aromatic rings”.

b.

high viscosity ✔

 

Accept “low volatility”, just “viscous/viscosity” OR “does not flow easily”.

c.i.

convert to esters of monoatomic alcohols

OR

react with short-chain alcohols «in the presence of acid or base» ✔

 

Accept “convert to shorter «carbon chain» esters” OR “transesterification”.

Accept specific alcohols, such as methanol or ethanol.

c.ii.

carbon dioxide/CO2 more/most abundant «GHG than methane/CH4»

OR

carbon dioxide/CO2 has «much» longer atmospheric life «than methane/CH4» ✔

 

methane/CH4 «much» better/more effective at absorbing IR radiation «than carbon dioxide/CO2»

OR

methane/CH4 has a greater greenhouse factor «than carbon dioxide/CO2»

OR

methane/CH4 has a greater global warming potential/GWP «than carbon dioxide/CO2» ✔

 

Accept “carbon dioxide/CO2 contributes more to global warming «than methane/CH4»”.

d.

CO2 (g) + H2O (l) H+ (aq) + HCO3 (aq)

OR

CO2 (g) CO2 (aq) AND CO2 (aq) + H2O (l) H+ (aq) + HCO3 (aq) ✔

«increasing [CO2 (g)]» shifts equilibrium/reaction to right AND pH decreases ✔

 

Accept “H2CO3 (aq)” for “CO2 (aq) + H2O (l)”.

Equilibrium arrows required for M1.

State symbols required for CO2 (g)  CO2 (aq) equation only for M1.

Accept “concentration of H+/[H+] increases AND pH decreases” for M2.

e.

Examiners report

[N/A]
a.
[N/A]
b.
[N/A]
c.i.
[N/A]
c.ii.
[N/A]
d.
[N/A]
e.

Syllabus sections

Options » C: Energy » C.4 Solar energy
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