Mercury Problem Set

Rotary Furnace – New Idria Mine -

  1. Mercury Mines such as the New Idria mine in the South Bay extracted Cinnabar, HgS, from the hills and roasted it at 600C in furnaces like the one above in order to isolate pure liquid mercury. The chemical reaction that occurred in the furnaces is shown below.

HgS(s) + O2(g)+ heat → Hg (l) + SO2 (g)

a)What type of chemical reaction is this?

Although much of the mercury is produced in the liquid state, mercury has a relatively high vapor pressure, easily evaporating at these temperatures to the gaseous state.

b)How do you think they recovered the gaseous mercury?

c)Beyond the obvious concern about mercury poisoning due to mercury vapor inhalation or deposition in the surrounding environment, what concern does the production of SO2 raise?

a)Each flask used to store and transport the mined mercury held a maximum of 76 pounds of Hg (l). Assuming the reaction goes to completion, how many kg of pure cinnabar (HgS) would need to react in the furnace in order to produce enough mercury to fill a flask?

b)If 80.0 kg of ore are heated in a limited oxygen environment containing 15.0 kg of oxygen gas, how many kg of mercury can be produced?

  1. a) Write a balanced equation for the reaction between the sulfur dioxide product of the cinnabar roasting process given in question 1 and water vapor in the air.

b)Assuming the sulfur dioxide produced in the roasting process reacts to completion with water vapor in the air, how many moles of sulfurous acid (H2SO3) will be created as a result ofproducing enough mercury to fill the standard 76 lb flask?

c)If this sulfurous acid ends up dissolving in a nearby pond filled with 1.0 x107liters of neutral water, what will be the [H+] concentration (in mol/L) of that pond become? (Assume for now that the sulfurous acid creates one H+ ion for every one molecule of sulfurous acid dissolved.)

d)What other ways beyond molarity can we use to characterize the acidity of the pond?

  1. Concentration Exploration

Materials:

1 well plate

1 disposable pipette

Water

Food coloring “toxin”

a)Place nine drops of water in wells 1-8

b)Add one drop of food coloring into well 1. Use your pipette to pull up some of the solution and return the solution to the well to mix it thoroughly.

  1. The concentration of food coloring in well 1 is ______part in 10.
  1. What percentage of the solution in well 1 is food coloring? ______%

c)Take one drop of the solution from well 1 and add it to well 2. Mix.

  1. By how many times have you now diluted the original drop of food coloring? ______
  2. The concentration of food coloring in well 2 is one part in ______parts.
  3. What percentage of the solution in well 2 is food coloring? ______%.

d)Take one drop of the solution from well 2 and add it to well 3. Mix.

  1. By how many times have you now diluted the original drop of food coloring? ______
  2. The concentration of food coloring in well 3 is one part in ______parts.
  3. What percentage of the solution in well 3 is food coloring? ______%.

e)Keep diluting your solution until you have finished well 8.

  1. Which well corresponds to 1 part per million (1 ppm)? ______
  2. Which well corresponds to 1 part per billion (1ppb)? ______

f)In which well is the food coloring “contaminant” no longer visible? ______What concentration is this in ppm? ______

Are food coloring molecules present in this solution?

Assuming the food coloring represents a toxin, is the liquid in this well safe to drink?

g)In this example ppm represents parts per million in terms of volume. Sometimes ppm is used in terms of mass. What is the equivalent concentration in ppm and ppb of a 1 g/L aqueous solution of methyl mercury? What is the mass percent? (Remember that the density of water is 1 g/mL. You can assume that at this small concentration the density of the methyl mercury solution is also 1 g/mL.)

h)If you can’t see a toxin, how can you determine its concentration?

How many tuna sandwiches are too many?(Adapted from problem set designed by Adam Jew, Stanford University School of Earth Sciences)

  1. In February, Student Council announces the plans for our annual eat-athon fundraiser where students obtain pledges for each food item they can ingest in a given time frame. Instead of the traditional hot dog contest, this year they opt for tuna salad sandwiches. All money raised will go towards the purchase of a flat screen TV in the cafeteria just in time for March Madness. Ashley, David, and Olivia line up for the contest, eager to stuff themselves to the brim with tuna. David takes first place with 40 sandwiches consumed in 10 minutes. Ashley and Olivia come in far behind her with 10 and 5 sandwiches respectively. Bravo David, he has raised enough money to buy a flat screen T.V. for the cafeteria. Several days later, however, he becomes severely ill, with headaches, delusions and muscle spasms.

Let’s say that David weighs 170 lbs and that each tuna sandwich in the contest had 2.0 oz of chunk light fish. Chunk light fish has been shown to contain 20.g of methylmercury/kg.

a)How many micrograms (µg) of methylmercury did David ingest during the contest?

b)Based on his weight, how many micrograms of methylmercury is the maximum he should eat on one day? (The US EPA has a recommended maximum intake of Hg of 0.1micrograms per kg body weight per day. (0.1µg/kg/day)).

c)How many sandwiches of chunk light tuna are safe for him to eat in one day?

Graphical Analysis(Adapted from problem set designed by Adam Jew, Stanford University School of Earth Sciences)

  1. Experimental techniques can be usedto determine the concentration of mercury present in a water sample.

A scientist runs tests on a series of five standard (known) water samples containing mercury and three drinking water samples. The tests yield a peak area whose value depends on the concentration of mercury present.

a)How can the data below be used to identify the concentration of mercury in thedrinking water samples?

Table 1: Standards

Hg Concentration (ng/L) / Peak Area determined from EXAFS
1.00 / 110.67
10.0 / 2338.36
25.0 / 6310.63
50.0 / 12729.33
100.0 / 26005.79

Table 2:Drinking Water samples

Sample / Dilution (1:x) / Peak Area / Hg Concentration of diluted sample (ng/L) / Hg Concentration of original water sample (ng/L)
A / 10 / 3500.06
B / 500 / 13693.58
C / 1000 / 230.93

Dilution (1:x) means that 1 part of the original water was diluted to final volume of x parts. For example, if the dilution is labeled 10, it could mean that 1 ml of sample water was diluted to a total of 10 mL or that 10 mL was diluted to a total volume of 100 mL, etc.

b)Dilution Practice: If the concentration of the diluted sample A were found to be 3 ng/L, what would the concentration of the original drinking water be?

c)Use the data and a graphing program to determine the Hg concentration present in both diluted and the original water samples A, B, and C.

d)The drinking water standard established by the EPA is 1 ppb (µg/L). Do any samples exceed this limit?

  1. Comparison of Compact Fluorescent and Incandescent Lightbulbs Adapted from a problem set created by Casey McCullough Bellarmine College Preparatory


Incandescent / Battle of the Bulbs
An Analysis
By Casey McCullough
Bellarmine College Preparatory /
Fluorescent

Compact fluorescent bulbs have proven an incredibly easy (and therefore incredibly popular) means of reducing one’s impact on the environment. They provide the same light as a traditional incandescent bulb while using approximately 25 percent of the energy. This has obvious and significant benefits in terms of reductions of greenhouse gases and other harmful forms of air emissions.

However, unbeknownst to most Americans, CFLs contain mercury, a toxic heavy metal. Though it is a relatively small amount (4 mg per bulb)[1], the growing number of these bulbs makes their use a real concern. If not disposed of properly, that mercury can enter ground or surface water and eventually biologic systems. Has the widespread transition from one type of bulb to another, have we traded in one environmental problem to solve another?

The question becomes more complicated when you realize that one of the other leading ways that mercury enters the environment is through the combustion of coal. Since coal fuels more electricity generation than any other energy source (both in the U.S. and the world), this becomes an important issue. The greater efficiency of CFLs clearly results in reduced consumption of coal and a corresponding reduction in mercury emissions.

So, the question posed to you is this: if we were solely concerned with reducing mercury emissions (outlandish) AND we assumed that everyone simply throws away their CFLs rather than disposing of them appropriately (perhaps not so outlandish), which bulb results in a greater release of mercury to the environment?

Step One: Using the table to the right, calculate how many kilowatt-hours of electricity is consumed by each bulb over a period of 6000 hours of use, the average lifespan of a CFL bulb[2]. (A kilowatt-hour is a unit of energy which, as the name implies, comes from the product of kilowatts and hours, i.e. a 10 Watt bulb that is illuminated for 2 hours would use a total of 20 kilowatt-hours of energy.) /
Type of Bulb /
Incandescent /
Fluorescent
Power Used
(Watts) / 60 / 13
Light Output
(Lumens) / 800 / 800
Lifetime (Hours) / 750-1,000 / 6,000-15,000
Lifecycle Cost* / $40 / $10
Source: Energy Star:

Step Two: Use the attached documents from the Department of Energy ( and the EPA’s Toxic Releases Inventory (2007) to find the total amount of mercury released in 2007 as a result electrical utilities and the total electricity generated that same year. Calculate the total mercury emissions per kilowatt-hour for all electricity generation in the U.S.

Step Three: Use the results from Steps One and Two to calculate the total airborne emissions resulting from the use of CFLs and incandescent bulbs over a 6000 hour lifetime.

Step Four: Calculate and compare the total mercury released into the environment by each bulb, assuming that the CFL is discarded inappropriately. What do your results show you?

[1]4 mg figure from FACT SHEET: Mercury in Compact Fluorescent Lamps (

[2] 6000 hour figure is based on Energy Star minimum rating for CFLs. Though it’s irrelevant to this calculation, it’s worth noting that the average CFL is not only more efficient than the average incandescent, it’s also more durable. You’d need at least six incandescent bulbs to provide as many hours of service as one CFL. (