Suggest another advantage and one disadvantage of solar energy.

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.

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

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

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

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

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»”.

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”.

high viscosity ✔

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

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.

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»”.

CO₂ (g) + H₂O (l) $\rightleftharpoons$ H⁺ (aq) + HCO₃^– (aq)

OR

CO₂ (g) $\rightleftharpoons$ CO₂ (aq) AND CO₂ (aq) + H₂O (l) $\rightleftharpoons$ 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) $\rightleftharpoons$ CO₂ (aq) equation only for M1.

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