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Test Your Knowledge

The Air Up There

1. How many grams of carbon monoxide can be formed from the photochemical oxidation (reaction 1.0) of 175.2g of carbonyl sulfide (COS)?
 
2. Describe several sources of carbonyl sulfide.
 
3. How do aerosols impact global temperatures?
 
4. How do volcanic eruptions impact atmospheric temperatures?
 
5. Why do the atmospheric aerosols differ geographically?

More About Aerosols

6. Compare and contrast natural aerosols with anthropogenic aerosols.
 
7. How do desert dust aerosols impact climate?

Biogeochemical Cycles

1. How many moles of pyrite are required to produce 342.15g of iron (III) oxide? (use reaction 1.1)
 
2. In the absence of oxygen and nitrate, sulfate will serve as an electron acceptor in the oxidation of organic matter. The equation below illustrates this process. Determine if the equation is balanced; if it is not, then balance it.

SO42- (aq) + H3O+ (aq) + 8e- → HS- (aq) + H2O
 
3. How is the carbon cycle connected to the nitrogen cycle?
 
4. The bacteria nitrospira converts NH3 to NO2-, and then converts NO2- to NO3-. The conversion of NO2- to NO3-, is shown in this equation: NO2- + H2O → NO3- + 2H+ + 2e-.

a. What process in the nitrogen cycle does the bacteria nitrospira perform?
 
b. Assuming no other reactions occur, what effect would this reaction have on soil pH?

5. Nitrogen is included in most commercial fertilizers because plants need nitrogen to grow. 78% of the atmosphere is nitrogen, so why isn't the earth overpopulated with giant plants?

More About Biogeochemical Cycles

6. Compare and contrast ammonification and nitrification.

7. Your little brother is sitting at the table blowing bubbles in his cup of water. You decide to play a trick on him and surreptitiously drop a piece of blue calcite in the water. To your chagrin, your trick backfires and your precious calcite seems to be dissolving. What is happening?

More About Ozone

1. How is smog formed?
 
2. How is tropospheric ozone formed?
 
3. In the reaction of NO with ozone, what mass of NO would be required to form 61.3g of NO2?
 
4. Why does smog affect visibility?
 
5. Compare and contrast stratospheric and tropospheric ozone.
 
6. What role do PANs play in the long-range transport of NOx?
 
7. If there is a dearth of oxygen, how is destruction of ozone accomplished?
 
8. What role does the chlorine in SSA play in the formation of the ozone hole?

More About Tropospheric Ozone

1. What is the mole of charge for an ammonium ion?
 
2. What weight of Ca2+ is required to replace 6 mols of K+?
 
3. How does acid deposition affect plants?
 
4. A large forest fire burns for several days in Monterey County, California. How is this likely to affect the rain in the area?
 
5. To complete a lab assignment, Marco collects water samples from several locations. The composition of each sample is shown in the table below. Based on these numbers, which of the following choices matches each sample with its most likely location?

Concentration (μmol / L) Mg2+ Na+ SO42- NO3-
Sample 1 0.02 0.15 3.21 2.18
Sample 2 0.12 0.25 0.36 0.42
Sample 3 0.06 0.04 5.21 3.99

A. Sample 1: inland city with a lot of heavy industry
Sample 2: city in Southeast US with little heavy industry
Sample 3: coastal city with a lot of heavy industry

B. Sample 1: coastal city with little heavy industry
Sample 2: coastal city with a lot of heavy industry
Sample 3: city in Southeast US with a lot of heavy industry

C. Sample 1: coastal city with a lot of heavy industry
Sample 2: city in Southeast US with little heavy industry
Sample 3: inland city with a lot of heavy industry

D. Sample 1: inland city with no heavy industry
Sample 2: inland city with little heavy industry
Sample 3: city in Southeast US with little industry

6. Professor Humic collects soil samples from two geographically distant locations. Sample A is collected from a tropical rainforest in Belize, while Sample B is collected from a temperate forest in New Jersey. Water with a pH of 5.2 is added to both samples. Assuming the soil will react in the lab as it would in its natural location, describe the chemical reactions for buffering that will take place in each sample. Will each sample undergo the same chemical reactions?

7. Describe two processes that neutralize the acidity of the rain.

8. A water sample from a lake in Pennsylvania contains the following concentrations of ions:
Concentration (μmol / L)
NH4+ 0.8
Ca2+ 16.4
SO42- 3.4
HCO3- 3.4

Calculate the total charge in the water using what you know about molc and concentrations.

More About Rain

1. How do indirect greenhouse gases differ from direct greenhouse gases?
 
2. Why is methane an important greenhouse gas?
 
3. If the concentration of NO in the atmosphere increased, what might happen to the concentration of CO in the atmosphere?
 
4. Using only residence times, put the greenhouse gases listed below in order of 100 year GWP, from smallest expected GWP to largest GWP:

Greenhouse gas Residence time (yr)
A 17,000
B 8
C 296
D 120
E 12

5. A new greenhouse gas is discovered that absorbs radiation with wavelengths between 8.5 and 12.8 μm. It has a lifetime of 2 years and a radiative forcing of 35 W/m2. Compared to other greenhouse gases, how much of a "threat" is this new greenhouse gas?
 
6. If the concentration of methane in the troposphere increased by 50%, what might happen to the concentration of OH in the troposphere?
 
7. What is the relationship between formaldehyde and methane?

Answers

The Air Up There

1. How many grams of carbon monoxide can be formed from the photochemical oxidation (reaction 1.0) of 175.2g of carbonyl sulfide (COS)?

This question spirals back to the chapter on the mole. The first step is to determine how many mols of COS we have. To do this, you simply add up the molecular weights of carbon, oxygen, and sulfur. (Hint: look on the periodic table.) Depending on the periodic table you use, your numbers might be slightly different.

12.01g + 16.00g + 32.07g = 60.02g

So one mol of COS = 60.02g.

To determine how many mols 175.2g is, we do some simple math:

175.2 g COS × 1 mol_COS__ = 2.919 mols COS 60.02 g COS

Looking at the coefficients in the equation, COS + hv → S + CO we can tell that 1 mol of COS yields 1 mol of carbon monoxide.

Now that we know the reaction yields 2.919 mols CO, we can determine the mass.

1 mol of CO = 12.01 g + 16.00 g = 28.01 g

2.919 mols CO × __28.01 g CO __ = 81.76 g CO
1 mol CO

2. Describe several sources of carbonyl sulfide.
Soil, salt marshes, and trees are all sources of carbonyl sulfide.

3. How do aerosols impact global temperatures?

Light colored aerosols tend to decrease temperatures, while dark colored aerosols tend to increase temperatures.

4. How do volcanic eruptions impact atmospheric temperatures?

In the troposphere, volcanic eruptions tend to decrease temperatures. In the stratosphere, however, they tend to increase temperatures because they absorb solar radiation that is reflected from the earth's surface. It's somewhat like clouds in that depending on the location they either heat or cool the earth.

5. Why do the atmospheric aerosols differ geographically?

Aerosols can be from the ocean, the soil, pollen, pretty much anything that can be blown around by the wind. Aerosols differ geographically because different "stuff" is found in different locations. SSA aerosols, for example, tend to have more chlorine, magnesium, and calcium. Aerosols near urban areas might include nitrates and sulfates. The aerosols from a tropical jungle will be vastly different that the aerosols found over Alaska.

More About Aerosols

6. Compare and contrast natural aerosols with anthropogenic aerosols.

Natural aerosols lead to fewer, but larger droplets in clouds. Anthropogenic aerosols, by contrast, lead to more, but smaller droplets in clouds. Anthropogenic aerosols also tend increase the reflectivity of clouds. Both types of aerosols can be either dark or light, and thus can either increase or decrease albedo. Both types of aerosols have geographic patterns of distribution and both help clouds form. We could go on and on about aerosols, but this should suffice.

7. How do desert dust aerosols impact climate?

Desert dust aerosols tend to warm the atmosphere and can decrease rainfall by preventing storm clouds from forming.

Biogeochemical Cycles

1. How many moles of pyrite are required to produce 342.15g of iron (III) oxide? (use reaction 1.1)

Pyrite is FeS2. Using the equation for the weathering of pyrite, we can see that two 4 mols of pyrite yields 2 mols (or ½ the amount) of Iron (III) oxide.

Reaction 1.1: 4FeS2 + 15O2 + 8H20 → 2Fe2O3 + 8H2SO4

First, we should calculate how many mols of Iron (III) oxide have a mass of 342.15 g. Using the periodic table, we can determine that the molar mass of Fe2O3 is

55.85 (2) + 16.00 (3) = 159.7g

342.15g Fe2O3 × (1 mol Fe2O3 /159.7 g ) = 2.142 mols Fe2O3

We know there are twice as many mols of pyrite, so we multiply the moles of Fe2O3 by 2:

2.142 mols Fe2O3 × (2 mols FeS2 / 1 mol Fe2O3) = 4.282 mols FeS2

2. In the absence of oxygen and nitrate, sulfate will serve as an electron acceptor in the oxidation of organic matter. The equation below illustrates this process. Determine if the equation is balanced; if it is not, then balance it.

SO42- (aq) + H3O+ (aq) + 8e- → HS- (aq) + H2O

3. How is the carbon cycle connected to the nitrogen cycle?

The first step is to determine if the equation is balanced. We can ignore all the extraneous information, like the number of electrons, the ionic charges, and whether the species are aqueous or gases. It might help to rewrite the equation without the information you don't need:

SO4 + H3O → HS + H2O

The easiest way to determine if it is balanced is it set up a chart and count each element on both sides of the equation. In this equation, you could probably also just glance at it and determine that it is not balanced based on oxygen.

# left side Element # right side 1 S 1 5 O 1 3 H 3

Now comes the fun (or torturous) part. You need to balance the O's, but you can't do so without also changing the S's or the H's. It would be easier to change the H's, because if you change the S's, the H's change as well.

Since there is only one H on the left side, and it is H3, you know that the total number of H's on each side has to be a multiple of 3, such as 6, 9, 12, 15, 18, 21, 24, 27. Now you can just start putting in numbers and seeing what works. When you do so, you should find that:

SO4+ 9H3O → HS + 13H2O

You can check your answer by making another chart # left side Element # right side 1 S 1 13 O 13 27 H 27

Nitrates can be the oxidizing agents for the decomposition of organic matter. These reactions produce ammonium ions or nitrous oxide, which are part of the nitrogen cycle.

4. The bacteria nitrospira converts NH3 to NO2-, and then converts NO2- to NO3-. The conversion of NO2- to NO3-, is shown in this equation: NO2- + H2O → NO3- + 2H+ + 2e-.

a. What process in the nitrogen cycle does the bacteria nitrospira perform?

In the first step, the bacteria converts NH3 to NO2-, or changes ammonia to nitrite. We know this is nitrification.

b. Assuming no other reactions occur, what effect would this reaction have on soil pH?

b. The process of nitrification leads to the release of H+ ions. Acids have excess H+ ions, so a release of H+ ions will acidify the soil meaning it decreases soil pH.

5. Nitrogen is included in most commercial fertilizers because plants need nitrogen to grow. 78% of the atmosphere is nitrogen, so why isn't the earth overpopulated with giant plants?

The nitrogen in the atmosphere is not in a form that plants can use. Before the plants can use the nitrogen, it has to be fixed by soil bacteria.

More About Biogeochemical Cycles

6. Compare and contrast ammonification and nitrification.

In nitrification, the ammonium ion is a reactant; in ammonification, the ammonium ion is a product. Nitrification takes ammonium and produces nitrates. Ammonification takes organic nitrogen, kicks out the carbon, and we end up with ammonium, carbon dioxide, and water.

7. Your little brother is sitting at the table blowing bubbles in his cup of water. You decide to play a trick on him and surreptitiously drop a piece of blue calcite in the water. To your chagrin, your trick backfires and your precious calcite seems to be dissolving. What is happening?

When your brother was blowing into the water, he was adding carbon dioxide to it and forming carbonic acid. When calcite reacts with carbonic acid, it forms calcium bicarbonate, as seen in the reaction below. This is the same process that causes stalactites and stalagmites to form.

Reaction 1.3c: CaCO3 + H20 + CO2 → Ca(HCO3)2

More About Ozone

1. How is smog formed?

The simple version is this: smog is formed from the reactions between VOCs, hydrocarbons, NO, and ozone. We could rewrite all the equations, but that would just waste space.

2. How is tropospheric ozone formed?

Light dissociates NO2, resulting in an oxygen atom. This single oxygen atom then reacts with diatomic oxygen, forming ozone. CIRES scientists are researching if oil and gas wells are contribute to the formation of tropospheric ozone.

3. In the reaction of NO with ozone, what mass of NO would be required to form 61.3g of NO2?

A good first step is write out the equation (4.1)

NO + O3 → NO2 + O2

Using the coefficients, we can tell that for every mole of NO2 produced, we need 1 mol of nitric oxide.

Now we need to determine how many mols of nitrogen dioxide are 61.3g.

The molar mass of nitrogen dioxide is: 14.01 + 32.00 = 46.01 g

61.3 g ×l (1 mol / 46.01 g) = 1.33 mols

That means we need 1.33 mols of nitric oxide to produce 1.33 mols of nitrogen dioxide.

4. Why does smog affect visibility?

Smog affects visibility because the aerosols it contains scatter visible radiation.

5. Compare and contrast stratospheric and tropospheric ozone.

Besides the obvious difference of location, the personalities of these two types of ozone could not be more different. Stratospheric ozone is like a nurturing older sister (we know, probably a figment of our chemistry-laden imagination), protecting us humans from the malevolent rays of the evil older sister Sun. Tropospheric ozone, by contrast, is like a pesky younger sister, wreaking havoc wherever it goes. It damages plants (didn't one of your sisters ruin your science fair project on the effect of singing Heavy Metal songs to plants?), reduces visibility, irritates the lungs and eyes, and decreases property values due to its horrid, dung color.

6. What role do PANs play in the long-range transport of NOx?

PANs decompose to form NOx and are fairly table at low temperatures. This combination means PANs can travel long distance and then decompose to produce NOx far from the original source.

7. If there is a dearth of oxygen, how is destruction of ozone accomplished?

If there isn't an abundance of oxygen, ozone is broken down via two catalysts. The basic process is this: each catalyst reacts with ozone, forming an oxygenated version of the catalyst and diatomic oxygen. Then these newly oxygenated catalysts react with one another. This forms each catalyst on its own and diatomic oxygen.

8. What role does the chlorine in SSA play in the formation of the ozone hole?

While the chlorine in CFCs plays a significant role in the formation of the ozone hole, the chlorine from SSA barely makes a cameo. SSAs tend to have short residence times and so do not mix into the stratosphere. Some of the chlorine produced by marine algae does mix into the stratosphere, but only sticks around for a brief time and so only plays a minor role in the destruction of stratospheric ozone.

More About Tropospheric Ozone

1. What is the mole of charge for an ammonium ion?

An ammonium ion has the formula: NH4+. The mole of charge is equal to the oxidation number. Oxidation # = 1, so molc = 1.

2. What weight of Ca2+ is required to replace 6 mols of K+?

A molc is a molc is a molc. 6 molc of Ca2+ are needed to replace 6 molc of K+. That is the easy part, now here comes the hard part. Only 3 moles of Ca2+ are needed, because each mol of Ca2+ is 2 molc.
1 molc Ca2+ = ½ mol Ca2+ 1 molc K+ = 1 mol K+
6 molc Ca2+ = 3 mol Ca2+ 6 molc K+ = 6 molK+

Now, using the periodic table, or our encyclopedic of molar masses, we know that one mol of calcium is 40.1 g. Since we're using 3 mols of calcium, we multiply that number by 3 and get 120.3 g or 120. g.

40.1g / mol Ca2+ × 3 moles Ca2+ = 120.g

3. How does acid deposition affect plants?

Acid deposition can leach nutrients from the soil, mobilize heavy metals like aluminum, damage plants, and make pink hydrangeas blue.

4. A large forest fire burns for several days in Monterey County, California. How is this likely to affect the rain in the area?

The forest fire will release sulfur dioxide, which will decrease the pH of the rain. The equation for the reaction is from the "desperate to know more section."

5. To complete a lab assignment, Marco collects water samples from several locations. The composition of each sample is shown in the table below. Based on these numbers, which of the following choices matches each sample with its most likely location? Concentration (μmol / L) Mg2+ Na+ SO42- NO3- Sample 1 0.02 0.15 3.21 2.18 Sample 2 0.12 0.25 0.36 0.42 Sample 3 0.06 0.04 5.21 3.99

A. Sample 1: inland city with a lot of heavy industry
Sample 2: city in Southeast US with little heavy industry
Sample 3: coastal city with a lot of heavy industry


B. Sample 1: coastal city with little heavy industry
Sample 2: coastal city with a lot of heavy industry
Sample 3: city in Southeast US with a lot of heavy industry


C. Sample 1: coastal city with a lot of heavy industry
Sample 2: city in Southeast US with little heavy industry
Sample 3: inland city with a lot of heavy industry


D. Sample 1: inland city with no heavy industry
Sample 2: inland city with little heavy industry
Sample 3: city in Southeast US with little industry


We know that for areas on the coast, the ratio of magnesium ions to sodium ions hovers near 0.12. A good first step, then, would be to calculate the ratio of Mg to Na for each sample to determine if it is from a coastal area:

Sample 1: ratio = 0.02 /0.15 = 0.13 → this one is likely to be from a coastal area

Sample 2: ratio= .12/.25 = 0.48 → this matches the ratio found in the Southeast US

Sample 3: ratio = 0.06/0.04 = 1.5 → probably not a coastal area or the Southeast US.

Sample 1 most likely comes from the coast, eliminating (A) and (D).

The next step is to look at the concentrations of SO42- and NO3-. Areas with a lot of heavy industry will have higher concentrations of these two anions. This means that sample 1 and sample 3 are located near industry. This leaves us with (C) as the correct response.

6. Professor Humic collects soil samples from two geographically distant locations. Sample A is collected from a tropical rainforest in Belize, while Sample B is collected from a temperate forest in New Jersey. Water with a pH of 5.2 is added to both samples. Assuming the soil will react in the lab as it would in its natural location, describe the chemical reactions for buffering that will take place in each sample. Will each sample undergo the same chemical reactions?

The question asks us to describe the chemical reactions for buffering. We know that temperate soils, like sample B, tend to have greater CECs than tropical soils (sample A). Temperate soils rely on cation exchange to buffer the soil. This means that H+ ions swap out with cations.

Tropical soils, like sample B, by contrast rely on aluminum to buffer the soil. The reaction is Al(OH)3 + 3H+ → Al3+ + H20.

7. Describe two processes that neutralize the acidity of the rain.

NH3, emitted by livestock and fertilizers, neutralizes rain acidity by scavenging H+ ions: NH3 (aq) + H+ → NH4+. Soil dust, containing calcium carbonate, can also neutralize rain acidity use a similar process: CaCO3 (s) → Ca2+ + CO32- then CO32- + 2H+ → CO2 (g) + H2O.

8. A water sample from a lake in Pennsylvania contains the following concentrations of ions: Concentration (μmol / L) NH4+ 0.8 Ca2+ 16.4 SO42- 3.4 HCO3- 3.4

Calculate the total charge in the water using what you know about molc and concentrations.

To answer this question, a good first step would be to rewrite the table and add a third column for charge: Concentration (μmol / L) Charge (μmol / L) NH4+ 0.8 × 1 0.8 Ca2+ 16.4 × 2 32.8 SO42- 3.4 × -2 -6.8 HCO3- 3.4 × -1 -3.4

Remember, molc = oxidation # In this case, we can take the concentration and multiply it by the oxidation #. This is shown in the table above.

The final step is to add up all the charges:

0.8 + 32.8 – 6.8 – 3.4 = charge of 23.4 μmol / L

In real life, the positive and negative charges would balance one another out (electroneutral), so we can assume there are negative charges that were not measured.

More About Rain

1. How do indirect greenhouse gases differ from direct greenhouse gases?

Indirect greenhouse gases, such as carbon monoxide, do not absorb infrared/longwave radiation emitted by the earth. They do, however, control the abundances of direct greenhouse gases. This means they indirectly affect the greenhouse effect. Direct greenhouse gases, such as methane, contribute to the greenhouse effect directly because they absorb radiation emitted by the earth.

2. Why is methane an important greenhouse gas?

Methane is an important greenhouse for many reasons. First, its atmospheric concentration has increased by 1% annually in recent years. Second, it has a GWP 22 times greater than that of carbon dioxide. Three, and perhaps most importantly, it absorbs the wavelengths of radiation that both water vapor and carbon dioxide miss.

3. If the concentration of NO in the atmosphere increased, what might happen to the concentration of CO in the atmosphere?

NO converts HO2 to OH, so it increases the amount of OH in the troposphere. If the amount of NO in the atmosphere increases, the amount of OH increases. But the question asks about CO, not OH. OH works to remove CO from the atmosphere (CO + OH → CO2 + H), so more OH means less CO.

This is a very simplistic version of atmospheric chemistry because it only takes into account a few of the thousands of reactions that take place in the atmosphere at any given time.

4. Using only residence times, put the greenhouse gases listed below in order of 100 year GWP, from smallest expected GWP to largest GWP: Greenhouse gas Residence time (yr) A 17,000 B 8 C 296 D 120 E 12

Only considering residence time, the shorter the residence time, the smaller the value for 100-yr GWP. In order to answer this question, then, we just need to put them in order from shortest to longest residence time: B, E, D, C, A

5. A new greenhouse gas is discovered that absorbs radiation with wavelengths between 8.5 and 12.8 μm. It has a lifetime of 2 years and a radiative forcing of 35 W/m2. Compared to other greenhouse gases, how much of a "threat" is this new greenhouse gas?

In some ways, this fictitious greenhouse gas is on par with methane. It's large radiative forcing makes it a serious threat, but it's relatively short residence time somewhat nullifies the threat. The most threatening property of the ghg is that it absorbs in the window that carbon dioxide and water vapor miss. Based on this information, we can say that this ghg would add more to the greenhouse effect than methane currently does.

6. If the concentration of methane in the troposphere increased by 50%, what might happen to the concentration of OH in the troposphere?

OH also works to scrub the atmosphere of methane, so the more methane there is, the less OH there is. A 1% increase in methane = a 0.32% decrease in OH, so a 50% increase in methane would mean a 16% decrease in OH. (0.32 × 50 = 16)

Our answer only takes into account a few of the thousands of reactions that take place in the atmosphere at any given time. For this level, this simple answer is fine.

7. What is the relationship between formaldehyde and methane?

The series of reactions that removes methane from the troposphere results in the formation of formaldehyde.
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