Chemistry Question

CHM210 Assignment 6Due Dec 7, 5 pm
1. The principal cause of anthropogenic climate change is the extraction of fossil fuels from the
geological domain, and the redistribution of CO2 into the atmosphere, hydrosphere,
biosphere, and surface soils. Typically, this issue is discussed in terms of the emission of CO2
into the atmosphere, however, it is well known that carbon in the “above-ground” domain
cycles freely between environmental compartments at the surface. For this question, you will
consider the partitioning of carbon between the atmosphere and the ocean.
a) Calculate the mass of carbon as CO2 in the Earth’s atmosphere to 2 significant figures, using
the contemporary CO2 mixing ratio of 416 ppm. (2 marks)
For the purposes of this question, you can assume that the average pressure at Earth’s surface
is 0.98 atm, and that the radius of the Earth is 6370 km. You may also need the average
molar mass of air (28.96 g/mol) and you may find it useful to recall that the SI units of
𝑁
pressure are 𝑃𝑎 = 𝑚2 =
𝑘𝑔 𝑚 𝑠−2
𝑚2
)
b) Calculate the mass of inorganic carbon in the top 100 m of Earth’s oceans that is in
equilibrium with this mixing ratio of atmospheric CO2. (2 marks)
Assume that the equilibrium between atmospheric CO2, and the dissociation of carbonic acid
are the only significant factors controlling the inorganic carbon content of the top 100 m of
ocean. For this question, you may disregard the influence of CaCO3 on the solubility of CO2.
The following data may be useful for your calculations:
Salinity = 35%; Temperature = 15 oC; Pressure at sea level = 1 atm, Ocean pH = 8.1;
KH = 3.811 x10-2 M atm-1; Ka1 = 1.148 x10-6 M and Ka2 = 7.516 x10-10 M for H2CO3
c) Imagine that in 2100, the mixing ratio of CO2 in the atmosphere has increased to 600 ppm.
Calculate the increase in inorganic carbon mass dissolved in the ocean, using the same
assumptions as in part b). (2 marks)
d) Assuming the surface ocean and the atmosphere are the only significant reservoirs of CO2 in
the surface environment, calculate the mass of fossil carbon that was burned to account for an
increase in atmospheric mixing ratio from 416 ppm to 600 ppm, and also the increase in
inorganic carbon dissolved in the surface ocean, as calculated from parts c) and b). (2 marks)
e) Using your favourite software (R, Excel) or drawing by hand, generate a speciation diagram
for carbonic acid like Figure 10.6 but using the equilibrium constants in Q1b. Label the axes
and indicate the two pKa values. (3 marks)
2. Decarbonizing the energy supply is desirable from a climate mitigation perspective, but
alternative energy sources can also cause environmental issues. Site C is a dam and
hydroelectric generating station on the Peace River in northeast B.C. Once operational, the
site will provide 1000 megawatts (MW) of capacity and about 5100 gigawatt hours (GWh) of
energy each year (https://www.sitecproject.com/about-site-c/project-overview).
a) If this dam provides power that replaces electricity produced by coal combustion, what
amount of annual CO2 emissions (in kg of carbon) can be avoided by the Site C project?
State your assumptions in performing this calculation. (2 marks)
b) In the early phase of the excavation for the Site C dam, significant amounts of sulphide were
measured in the bedrock and in the nearby surface waters, whereas later the majority of
sulphur was in the form of sulphate. Write the balanced redox half-reaction that represents
the conversion of sulphide to sulphate (2 marks)
c) Briefly explain why this is expected to cause additional leaching of heavy metals from the
bedrock. (1 mark)
There is a separate concern about the
mobilization of mercury in the Site C
region and the consequences for the
exposure of local First Nations
communities to mercury in their diet. In
anticipation of these issues, an analysis
has been carried out to predict the
expected peak concentrations of
methylmercury in fish in the dam
reservoir waters compared to baseline
measurements in the river (see graph).
d) Briefly explain why the flooding of the region behind the hydroelectric dam is expected to
increase the concentration of methylmercury in the reservoir water compared to the
concentrations in the Peace River. (2 marks)
e) If a local community member typically eats three portions of 200 g of Bull trout per week,
how much more methylmercury will they be ingesting in their diet on an annual basis (in g),
at the time of peak impact compared to before the construction of the dam? (2 marks)
Due December 19 at 11:59 PM
This assignment is intended to give you skills in expressing your own professional and scientific
opinions, supporting them with scientific arguments and references, and a further chance to
explore the intersection of chemistry with society.
You will write a paper of 1500-2000 words on the topic of “my favourite chemistry-society
connection.” You will include both your personal opinions and will also include a mix of scholarly
references and lay materials that illuminate and support your arguments. For scholarly (peerreviewed) references, primary references are preferred over reviews. For lay references (non-peerreviewed), things that have a permanent presence are preferred over web links that are
impermanent. You should have ≥10 items of source material.
This is not your usual term paper, and you won’t find a suitable paper in an online term paper bank.
Papers on topics that are highly technical and/or that are not focused on a connection of chemistry
to society (i.e. papers that are mostly a literature review of a technical area with little of your own
personal opinion) are inappropriate and will receive a grade of zero. If you’re unsure, please ask if
your topic is appropriate before you get started on writing your paper.
You will create your own figures, decide upon and implement a cohesive presentation style, and you
will also apply the writing lessons that you have learned through the term. Submit as a pdf through
this assignment page.
Rubric:
Content (50%)
– Motivating introduction, significant # of topics, number and variety of references/source
material, integration of material from multiple sources within a single paragraph, flow and
linkages between topics, meaningful concluding section.
Personal opinion (25%)
– Personal opinions, scholarly comparisons, thoughtful analysis of multiple sides of an issue,
some evidence that you have integrated knowledge into your own conclusions, rather than just
listing a set of ideas and conclusions from elsewhere.
Quality of presentation (25%)
– Strong topic sentence and paragraph structure, clear sentence structure, grammar, personally
made, effective Figures, formatting, style.
Late submissions will have 10% of the term paper value deducted per day. Given the long time
horizon, medical extensions will only be provided where justified by a correspondingly long-term
inability to work.