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Chapter 2. Environmental Measurements
2.1 (a) During drinking water treatment, 17 lb. of chlorine (Cl) are added daily to disinfect 5
million gallons of water. What is the aqueous concentration of chlorine in mg/L? (b) The
chlorine demand is the concentration of chlorine used during disinfection. The chlorine residual
is the concentration of chlorine that remains after treatment so the water maintains its
disinfecting power in the distribution system. If the residual concentration is 0.20 mg/L, what is
the chlorine demand in mg/L?
Solution:
a) 17 lb. chlorine added to 5 million gallons of water. Chlorine dosage in mg/L:
b) Chlorine demand:
6
17 / 454 1000 1 0.41 /
5 10 / 1 1 3.78
lb day g mg gal mg L
gal day lb g L
×× × =
×
0.41 / 0.20 / 0.21 /mg L mg L mg L−=
2.2 A water sample contains 10 mg NO3-/L. What is the concentration in (a) ppmm, (b) moles/L,
(c) mg NO3--N/L, and (d) ppbm?
Solution:
10 g NO3-/L in various units.
a) 1 L water = 1 kg water (in water, mg/L = ppm)
b) 62 grams NO3- = 1 mole NO3-
c) 62 grams NO3- = 1 mole NO3-; 14 grams N = 1 mole N; 1 mole NO3- = 1 mole N
d) 1 L water = 1 kg water; 1 kg = 106 mg; 1 billion = 103 million
3
10 / 10
1/
mg L ppm as NO
kg L
−
=
4
3
10 1 1 1.6 10 /
1, 000 62
mg g mole moles NO L
L mg g
−−
× ×=×
33
3
33
10 1 1 14 2.3 NO - N/L
62 1 1
mg NO mole NO mole N g N mg
L g NO mole NO mole N
×××=
3
10 / 1000
10, 000
1/ 1
mg L million
ppb as NO
kg L billion
−
×=
2.3 A liquid sample has a concentration of iron (Fe) of 5.6 mg/L. The density of the liquid is
2,000 g/L. What is the Fe concentration in ppmm?
Solution:
2.4 Coliform bacteria (for example, E. coli) are excreted in large numbers in human and animal
feces. Water that meets a standard of less than one coliform per 100 mL is considered safe for
human consumption. Is a 1 L water sample that contains 9 coliforms safe for human
consumption?
Solution:
Standard requires < 1 coliform/100 mL, or 10 coliform/1 L
9.0 mg N/L and nitrite (NO2-) at 0.5 mg N/L. Convert these concentrations to mg NH3/L and mg
NO2-/L.
Solution:
2.6 Nitrate concentrations exceeding 44.3 mg NO3-/L are a concern in drinking water due to the
infant disease, methemoglobinemia. Nitrate concentrations near three rural wells were reported
as 0.01 mg NO3- N/L, 1.3 mg NO3- N/L, and 20.0 mg NO3- N/L. Do any of these three wells
exceed the 44.3 ppmm level?
Solution:
2.7 Sulfate (SO42-) concentration is 10 mg SO42-/L and monohydrogen sulfide (HS-)
concentration is 2 mg HS-/L. What is the total inorganic sulfur concentration in mg S/L?
Solution:
Convert Sulfate (SO42-) to molarity and then use the molar concentration of sulfur to convert to
the concentration of sulfur. Add together the concentration of sulfur from both sulfate (SO42-)
and monohydrogen sulfide (HS-) to get the total inorganic sulfur concentration.
2.8 Suppose you must determine the amount of hydrogen halides (HCl, HBr and HF) in the flue
gas leaving a chemical reactor. The emission sampling train for hydrogen halide determination
calls for a total of 200 mL of 0.1 N H2SO4 as an absorbing solution. The absorbing solution will
be located on the impingers of the sampling train. (a) How many grams of H2SO4 should be
added to water to create 200 mL of a 0.1 N H2SO4 solution? (b) Calculate the molarity of the 0.1
N H2SO4 solution. (problem from EPA Air Pollution Training Institute,
http://www.epa.gov/apti/bces/)
Solution:
2.9 The concentration of cadmium (Cd) in a liquid is known to be 130 ppm at 20°C. Calculate
the total quantity of cadmium present in a one-gallon sample. The sample has a density of 62.4
lb/ft3. (problem from EPA Air Pollution Training Institute, http://www.epa.gov/apti/bces/)
Solution:
1 L water = 1 kg water (in water, mg/L = ppm). The density of water is 62.4 lb/ft3
2.10 As a quality control check, a sample of acetone is taken from a process to determine the
concentration of suspended particulate matter. An 850-mL sample was placed in a beaker and
evaporated. The remaining suspended solids were determined to have a mass of 0.001 gm. The
specific gravity of acetone is 0.79 gm/cm3. (a) Determine the concentration of the sample as
mg/L. (b) Determine the concentration of the sample as ppm. (problem from EPA Air Pollution
Training Institute, http://www.epa.gov/apti/bces/)
a)
2.11 A paper mill produces paper from wood pulp. Pulp production (at the pulp plant) begins
with digesting the wood chips in a solution of sodium hydroxide and sodium sulfide. The sodium
hydroxide is diluted with water (shown in the reaction below) prior to being sent to the digester.
NaOH + H2O Na+ + OH- + H2O
If 4 kg of sodium hydroxide is added for each 1000 L of water, determine the following: (a) the
molarity of the resulting solution, (b) the normality of the resulting solution. (problem from EPA
Air Pollution Training Institute, http://www.epa.gov/apti/bces/)
2.12 In Florida, advanced wastewater treatment standards require that treated effluent have no
more than 5 ppm BOD5, 5 ppm TSS, 3 ppm total nitrogen (TN), and 1 ppm total phosphorus
(TP). a) What is the wastewater standard for TN and TP in mg/L? b) If all of the nitrogen is
transformed to nitrate during the advanced treatment, what is the effluent limit of nitrate in
mg/L? c) If your laboratory had obtained and processed 200-mL sample of treated wastewater
for the TSS test , how many mg of suspended solids were captured on the filter for this sample?
Solution:
2.13 Mirex (MW = 540) is a fully chlorinated organic pesticide that was manufactured to control
fire ants. Due to its structure, mirex is very unreactive; thus, it persists in the environment. Lake
Erie water samples have had mirex measured as high as 0.002 µg/L and lake trout samples with
0.002 µg/g. (a) In the water samples, what is the aqueous concentration of mirex in units of (i)
ppbm, (ii) pptm, (iii) µM? (b) In the fish samples, what is the concentration of mirex in (i) ppmm,
(ii) ppbm?
2.14 Total mercury concentrations in the San Francisco Bay Area are reported to be 1.25 ng/L in
water, 8 mg/L in rain, 2.1 mg/m3 in air, and 250 ng in one gram of dry sediment. (a) Report all
these concentrations in ppt. Assume the air temperature is 20oC.
1.25 𝑛𝑔
𝐿𝐻𝑔 × 1 𝑔
109𝑛𝑔 × 1.0 𝐿 H2O
1000 𝑔 H2O × 1 𝑔
1000 𝑚𝑔 = 1.25 ×10−12𝑔
𝑔 × 1012 𝑝𝑝𝑡
𝑚𝑎𝑠𝑠 𝑓𝑟𝑎𝑐𝑡𝑖𝑜𝑛 = 𝟏.𝟐𝟓 𝒑𝒑𝒕 𝑯𝒈
8𝑚𝑔
𝐿𝐻𝑔 = 8 𝑝𝑝𝑚 𝐻𝑔 × 106𝑝𝑝𝑡
1 𝑝𝑝𝑚 = 𝟖.𝟎×𝟏𝟎𝟔 𝒑𝒑𝒕 𝑯𝒈
Solving for ppmv in equation 2.9:
2.15 Leachate is produced when precipitation infiltrates a sanitary landfill , contacts the waste
material, and appears at the bottom of the stored waste. Assume 6 kg of benzene (molecular
formula of C6H6) were placed in the landfill and it is all dissolved in the 100,000 gallons of
leachate produced during one year. What is the benzene concentration in the leachate during this
one year in (a) mg/L; (b) ppbm; and (c) moles/L?
Solution:
2.16 Chlorophenols impart unpleasant taste and odor to drinking water at concentrations as low
as 5 mg/m3. They are formed when the chlorine disinfection process is applied to phenol-
containing waters. What is the unpleasant taste and odor threshold in units of (a) mg/L, (b) µg/L,
(c) ppmm, (d) ppbm?
Solution:
2.17 The concentration of monochloroacetic acid in rain water collected in Zurich was 7.8
nanomoles/L. Given that the formula for monochloroacetic acid is CH2C1COOH, calculate the
concentration in µg/L.
Solution:
2.18 Assume that concentrations of Pb, Cu, and Mn in rainwater collected in Minneapolis were
found to be 9.5, 2.0, and 8.6 µg/L, respectively. Express these concentrations as nmole/L, given
that the atomic weights are 207, 63.5, and 55, respectively.
Solution:
