Chapter 12 Flashcards
(45 cards)
Ch. 12, Q1p1
What is a sulfhydryl group, and how does it
interact biochemically with heavy metals?
Sulfhydryl = -SH
Hg, Pb, Cd, Cr are all not very dangerous as free elements but become toxic when in their cation form. Biochemically this usually occurs by the strong affinity to the cation sulfur.
ch. 12 Q1p2
How
does the interaction of sulfhydryl and heavy metals affect processes in the body?
-SH, occur in enzymes that control the speed of critical metabolic reactions in the human body, readily attach themselves to ingested heavy metal cations or to
molecules that contain the metals.
Because the resultant metal–sulfur bonding affects the entire enzyme, it cannot act normally; as a result, human health is adversely affected, sometimes
fatally.
ch.12 Q2
What is meant by speciation? What is its
significance in environmental problems?
The toxicity for all four heavy metals depends very much on the chemical form of the element, i.e., upon its speciation. Substances that are almost totally insoluble pass through the human body without doing much
harm.
ch.12 Q3
What accounts for the recent decline in
emissions of mercury onto water and land?
This was accomplished as a “co-benefit” of the new reductions in sulfur dioxide and nitrogen oxide
emissions from the plants that would have been implemented by that date, it mainly involved capture of
oxidized mercury
ch.12 Q4
Is the liquid or the vapor of mercury more
toxic? Describe the mechanism by which mercury
vapor affects the human body.
Methylmercury is, in fact, the most hazardous form of
mercury, more dangerous even than the vapor form of the element.
ch12. Q5
What is an amalgam? Give two examples, and
explain how they are used.
An amalgam of sodium and mercury is used in some industrial chlor-alkali plants in the process that converts aqueous sodium chloride into the commercial products chlorine, Cl2, and sodium hydroxide, NaOH, (and gaseous hydrogen) by electrolysis.
ch12 Q6
Explain how the chlor-alkali process led to the
release of mercury to the environment.
The mercury is recovered after NaOH production, and is recycled back to the original cell. The recycling of mercury is not complete, however, and some finds its way into the air and into the water body from
which the plant’s cooling water is obtained and to which it is returned.
ch12. Q7
Name two uses for mercury in batteries.
- Hearing aids
Can’t find another but Matt said this would be on the test
ch12. Q8.
What are some important sources of airborne
mercury?
- Coal fired power plants
- Municipal and medical incinerators
- Forest fires
- *Not sure if these are the most important ones
ch12.Q9.p1
What three chemical forms of mercury are
emitted into the air from coal-fired power plants?
Hg^2+ (Coal) –> flame–>Hg^o(gas)—>Chlorine–>HgCl2(gas)
- Gaseous Elemental Mercury (GEM)
- Particulate Mercury (TPM)
- Reactive Gaseous Mercury (RGM)
*If this doesn’t make sense look at slide 21 in the power point
ch.12.q9p2
What is the chemical formula and approximate
atmospheric lifetime of each form of Hg emitted from coal fired power plants?
- Hg^o (GEM Lifetime) = Months to a year
- Hg^2+ (TMP Lifetime) = Few weeks
- HgCl2 (RGM Lifetime) = Days to a week
ch12.q9.p3
How can emissions of each form of Hg emitted from coal fired power plants be controlled?
- Hg^o (GEM) = To date it has proven to be virtually impossible to keep all or most elemental mercury vapor from being emitted from coal-fired power plants, since the gas Hg0 is inert
- Hg^2+ (TMP) = Particulate mercury can readily be captured by power plants
- HgCl2 (RGM) = Since the HgCl2 of RGM is water-soluble, it is efficiently removed from exhaust gases if they are scrubbed
ch12.q10
Write the formulas for the methylmercury
ion, for two of its common molecular forms, and
for dimethylmercury. What is the principal source
of exposure of humans to methylmercury?
Ion = CH3Hg+
Molecular = CH3HgOH , CH3HgCl
Dimethyl = CH3HgCH3
Source= Fish
ch12.q11
Explain why mercury vapor and methylmercury compounds are much more toxic than other forms of the element.
main toxicity of methylmercury occurs in the central nervous system. In the brain, methylmercury is converted to Hg2+, which probably is responsible for
the brain damage. Mercury vapor is also oxidized to this ion once it has entered the cell. Thus the usual barriers in the cell to Hg2+ are circumvented
by Hg0 and CH3HgX, which, by their electric neutrality can penetrate the cell’s defenses, and then be converted to the highly toxic +2 ionic form.
ch12.q12
Discuss the sources and relative importance
of different dietary sources of mercury.
- Most of the mercury present in humans is in the form of methylmercury. Almost all methylmercury originates from the fish in our food supply: mercury in fish is usually at least 80% methylmercury.
- Mercury is leached from rocks and soil into water systems by natural processes, some of which are accelerated by human activities. Flooding of vegetated areas can release mercury into water.
ch12.q13
What is meant by Minamata disease? Explain
its symptoms and how it first arose.
Minamata, Japan (village), a chemical plant employing Hg2+ as a catalyst in production of polyvinyl chloride discharged mercury containing residues into Minamata Bay. Hg2+ then formed from the inorganic mercury through biomethylation by microbes in the bay’s sediments then bioaccumulated to concentrations @ 100 ppm in the fish (main food for residents)
Symptoms:
- numbness in arms and legs,
- blurring and even loss of vision,
- loss of hearing
- muscle coordination, and
- lethargy and irritability.
ch12.q14
Explain how lead in ammunition can be a
danger to wildlife.
Condors in California suffer from lead poisoning, sometimes fatally, when they eat deer that have been shot and then abandoned by hunters; the lead bullets
explode into many fragments on impact and contaminate the meat. Humans too may be at risk when they eat game meat that is shot with lead
ammunition.
ch12.q15
What are the two common ionic forms of
lead?
Lead (II) - inorganic salts. Lead sulfides and oxides poorly soluble, acetates and chlorates most common soluble form
Lead (IV) - organometallic compounds e.g., tetraethyl-lead, lead oxides (PbO2, Pb2O3 and Pb3O4)
“As expected from its s2p2 valence-shell electron configuration, the common ions of lead are the !2 (loss of both p electrons) and !4 (loss of all s and p electrons).”
ch12.q16
Explain how lead can dissolve—e.g., in
canned fruit juice—even though it is insoluble in
mineral acids.
some lead in the solder that was used commonly in the past to seal tin cans will dissolve in the dilute acid of fruit juices and other acidic foods if air is present—i.e., once the can has been opened—since lead is oxidized by oxygen in acidic environments:
2 Pb(s) + O2 + 4 H+ –> 2 Pb2+(aq) + 2 H2O
ch12.q17.p1
Explain why lead contamination of
drinking water by lead pipes is less common
in hard-water areas than in soft-water areas.
What can result in the release of lead from
old water pipes into the drinking water they
carry?
The contamination of water by lead is less of a problem in areas of calcareous water, since an insoluble layer containing compounds such as PbCO3 forms on the surface of the lead by reaction of the metal with dissolved oxygen and the carbonate ion, CO3^2-, in the water. This layer prevents the metal underneath from dissolving in the water
that passes over it.
ch12.q17.p2
What can result in the release of lead from
old water pipes into the drinking water they
carry?
- Lead in water is more fully absorbed by the body than is lead in food.
- *Not sure if this is asking for health Effects?
Lead used in the solder in the joints of domestic copper water pipes, and lead used in previous
decades and centuries to construct the pipes themselves, can dissolve in drinking water during its transport to the point of consumption, particularly
if the water is quite acidic or if it is particularly soft.
ch12.q18
Why were lead compounds used in paints?
Why were mercury compounds used in paints?
- lead =Pigments in paint
- mercury = Fungicides, anti-mildew paint
ch12.q19
Explain why heavy metal compounds such as
PbS and PbCO3 are much more soluble in acidic
water.
Most lead occurs as insoluble PbS and PbCO3
PbS(s) -> Pb2+ + S2- Ksp = 8.4 x 10-28
PbCO3(s) -> Pb2+ + CO32- Ksp = 8.4 x 10-13
In acidic waters
PbS(s) + H+ -> Pb2+ + H2S(aq)
Rxns of the anions increase solubility
S2- + H2O -> HS- + OH-
CO32- + H2O -> HCO3- + OH-
*Page 579 in the text book explains it really well
ch12.q20
In what forms does lead exist in the lead
storage battery?
elemental lead is stable as an electrode in the lead storage battery, (page 573)
