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Date	May 2017	Marks available	2	Reference code	17M.3.sl.TZ2.1
Level	SL	Paper	3	Time zone	TZ2
Command term	Calculate	Question number	1	Adapted from	N/A

Question

There is a link between world energy consumption and carbon dioxide production.

Climate induced changes in the ocean can be studied using measurements such as the Atmospheric Potential Oxygen (APO). Trends in APO concentration from two stations, one in each hemisphere, are shown below.

Trends in atmospheric potential oxygen (APO) based on monthly averages between 1990 and 2010.

[Source: www.ioos.noaa.gov]

The following graph represents world energy consumption by type for the years 1988–2013.

Estimate the percentage of energy consumption which did not directly produce CO₂ in 2013.

[1]

O₂ is consumed in producing CO₂ for electricity generation. The graph shows the relationship between the world’s electricity generation and CO₂ production between 1994 and 2013.

Calculate the mass, in million tonnes, of oxygen gas ultimately found in CO₂ which is consumed in generating 18 $\,$ 000 terawatts of electricity using the equation given for the best fit line. Give your answer to 2 significant figures.

Assume coal is the only energy source.

[2]

The equilibrium expression for O₂ exchange between the atmosphere and ocean is O₂(g) $\rightleftharpoons$ O₂(aq). Identify one factor which shifts the equilibrium to the right.

[1]

c.i.

Factors such as photosynthesis and respiration are excluded so that APO is influenced by oceanic changes only. Suggest why the seasonal cycles from Alert station and Cape Grim observatory are different.

[2]

c.ii.

The change in APO O₂/N₂ ratio, per meg, is measured relative to an O₂/N₂ reference.

$\Delta {\text{(}}{{\text{O}}_{\text{2}}}{\text{/}}{{\text{N}}_{\text{2}}}{\text{)}} = \left( {\frac{{{{({{\text{O}}_2}/{{\text{N}}_2})}_{{\text{sample}}}}}}{{{{({{\text{O}}_2}/{{\text{N}}_2})}_{{\text{reference}}}}}} - 1} \right) \times {10^6}$

Calculate the APO Δ(O₂/N₂) value for an oxygen concentration of 209 $\,$ 400 ppm assuming that any change in N₂ concentration is negligible. Reference values for O₂ and N₂ are 209 460 and 790 190 ppm respectively.

[1]

c.iii.

Suggest a reason for the general negative gradient of the APO curve given in (c).

[1]

c.iv.

Markscheme

« $\frac{{\sum {({\text{renewables}} + {\text{hydroelectricity}} + {\text{nuclear)}}} }}{{{\text{total}}}}$ »

« $\left( {\frac{{8800 - 7200}}{{12600}}} \right) \times 100 =$ » 13 «%»

Accept range of “11–16%”.

[1 mark]

«18000 = 0.54x – 2000»
x = 37037 «million tonnes of CO₂»
« $\frac{{32.00}}{{44.01}}$ x 37037 = 26930»
27000/2.7 x 10⁴ «million tonnes of O₂»

Accept “37000 «million tonnes of CO₂»” for M1.

Award [2] for correct final answer with two significant figures.

Award [1] for non rounded answers in range 26903–26936 «million tonnes of O₂».

[2 marks]

increase in «atmospheric» pressure
OR
increase in [O₂(g)]/concentration of O₂(g)
OR
decrease in [O₂(aq)]/concentration of O₂(aq)
OR
decrease in temperature

Accept “increase in volume of oceans «due to polar ice cap melting»” OR “consumption of O₂ in oceans/O₂(aq)
«by living organisms»”.

State symbols required for oxygen concentration.

[1 mark]

c.i.

summer in one station while winter in other
OR
stations are at different latitudes

oxygen dissolves better in colder water

Accept “opposite seasons «in each hemisphere»”.

Do not accept “different locations with different temperatures” OR “stations are in different hemispheres”.

[2 marks]

c.ii.

« ${\text{(}}\frac{{209400}}{{209460}} - 1{\text{)}} \times {10^6}$ =» − 286.5 «per meg»

The nitrogen cancels so is not needed in the calculation.

Negative sign required for mark.

[1 mark]

c.iii.

decrease in [O₂]/concentration of O₂
OR
increasing combustion of fossil fuels «consumes more O₂ so [O₂]/concentration of O₂ decreases»
OR
warmer oceans/seas/water «as oxygen dissolves better in colder water»
OR
deforestation