1. Environmental Engineering: Fundamentals, Sustainability, Design
Second Edition
James R. Mihelcic • Julie Beth Zimmerman
Chapter 2
Environmental Measurements

2. Mass concentration units
Concentration...it's a matter of taste.
Why study concentration?
Why does concentration matter?
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3. Mass concentration units
Concentration...it's a matter of taste.
Why does concentration matter?
Concentration is the driving force for:
Diffusion: a higher concentration gradient means more rapid diffusive mass transport.
Chemical reactions: in some cases, a higher concentration results in a higher reaction rate.
Biotic effects: for nutrients that might stimulate nuisance plant growth in lakes, a higher concentration means a faster growth rate; for toxic chemicals, a higher concentration means more severe effects.
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4. Table_2-1

5. Solid/Mass concentration units Mass/mass and Mass/volume units
Table_2-2

6. Visualizing "parts per"
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7. Visualizing "parts per"
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8. Chemical Structure of PCB
Fig_2-1

9. Gas concentration units Volume/volume and mole/mole units
It's in the air
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10. Table_2-2

11. Gas concentration units Volume/volume and mole/mole units
Under the Clean Air Act , the U.S. EPA has set National Ambient Air Quality Standards. For example, the standard for a solid such as lead is expressed on a mass per volume basis, e.g µg of Pb in 1 m3 of air (15 µg/m3) and a gas such as NO2 is expressed on a volume per volume basis or 53 m3 of NO2 in 1 billion cubic meters of air.
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12. Gas concentration units Volume/volume and mole/mole units
Why are there two different modes of expression: mass per volume and volume per volume?
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13. If the contaminant is solid
the volume of solid contaminant does not change and thus concentration decreases as the air parcel rises.
Table_2-2

14. If the contaminant is a gas
the contaminant concentration remains the same at any altitude
Table_2-2

15. Table_2-2

16. Volume ratio = Mole ratio (Mole fraction)
Using a volume ratio and the ideal gas law allows for quick conversions between units of volume and moles.
Volume ratio = Mole ratio (Mole fraction)
ppmv = Volume ratio × 106 = Mole ratio × 106
Table_2-2

17. Partial pressure units
Atmospheric pressure is the force per unit area exerted on the Earth's surface by the weight of the atmosphere above it. A column of air of one square centimeter (cm2) extending from the Earth's surface to the top of the atmosphere has a mass of ~1 kilogram and, by definition, exerts a pressure of 1 atm.
On average, a column of air one square centimetre [cm2] (0.16 sq in) in cross-section, measured from sea level to the top of the atmosphere, has a mass of about 1.03 kilograms (2.3 lb) and weight of about 10.1 newtons (2.3 lbf). That force (across one square centimeter) is a pressure of 10.1 N/cm2 or 101,000 (1.01×105 N/m2 ). A column 1 square inch (6.5 cm2) in cross-section would have a weight of about 14.7 lb (6.7 kg) or about 65.4 N. 1 atm = ×105 Pa. (1 Pa = 1 N/cm2 )
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18. Partial pressure units
The pressure of each part of a gas that it exerts on its surrounding is called the partial pressure of that gas.
Dalton's law of partial pressure:
Ptotal = ∑ Pi
Pi = volume fraction × Ptotal
Dalton's Law of Partial Pressures Explained
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19. Partial pressure units
N2 moles = 2 M x 5L = 10 moles
O2 moles = 1.5 M x 5L = 7.5 moles
CO2 moles = 30 – 10 – 7.5 = 12.5 moles
CO2 partial pressure = 1.5 atm x (12.5/30) = atm
Dalton's Law of Partial Pressures Example
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20. Partial pressure units
ppmv = Pi /Ptotal × 106
= Volume ratio × 106
= Mole ratio × 106
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21. Mass (g) = number of moles x molar mass (g/mole)
What Exactly is a Mole?
One mole of a substance = 6.022x1023 atoms or molecules of that material.
Mass (g) = number of moles x molar mass (g/mole)
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22. Derivation of (2.19) & (2.20)
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23. Liquid concentration units
Mole/volume units
Molarity (M), or moles per liter, is another way to express concentration, mostly for liquid. This approach is most often used to report concentrations of chemicals dissolved in water and is particularly useful in making calculations relating to chemical reactions where the stoichiometry is expressed in molar units.
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24. Mole/volume units
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25. Liquid concentration units
Mole/volume units
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26. Mole/volume units
Addition of 40 grams of Ca2+ or 100 grams of CaCO3 to one liter of water would yield a 1 molar (1 M) solution.
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27. Solubility
Most gases are only slightly soluble in water. In dilute aqueous (or water) solutions, the concentration of a substance in the gas phase is linearly related to the concentration of that substance in the aqueous phase.
Hi = Henry’s law constant – the slope of the above linear relationship
Solubility

28. Solubility Pi = partial pressure of the substance i in the gas
Ci = molar fraction of the substance i in the aqueous solution
Hi = Henry’s law constant
Solubility

29. Solubility
Solubility

30. Limitations of Normality units
Equivalent weight
The concept of molarity alone is insufficient to describe all phenomena in hydrochemistry because charge balance calculations require equivalent concentrations.
number of moles of protons that it can donate
number of moles of H+ that would react with that base
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31. Law of Electroneutrality
Normality:
Equivalent weight: ×
Law of Electroneutrality

32. Normality vs. Molarity
equivalents (eq) vs. moles
Normality, or equivalent concentration (eqv/L) differs from its cousin molarity in that it refers to equivalents (eq) instead of moles. Equivalents are something like reactive units, i.e. the number of valences taking place in a reaction.
number of moles of protons that it can donate
The same solution can have different normalities for different types of reaction - for example 1M sulfuric acid solution is 2N for acid/base reactions, but it is 1N in the reaction of barium sulfate precipitation. To calculate normality of the solution you have to know its exact molarity as well as stoichiometry of the reaction substance will be used in.
Despite the fact that normality depends on the reaction, some reagents are sold in normal concentrations. It may happen when the reagent is used solely for one specific reaction, or when the reagent always - for all practical purposes - behave as if it had the same normality. Good example of such reagent is hydrochloric acid, which is 1N regardless of whether it is used for neutralization or chlorides precipitation.
number of moles of H+ that would react with that base
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33. Normality vs. Molarity The equivalent of a substance is the
number of moles multiplied by its valence z:
moles: n number of entities (molecules, ions, electrons)
equivalents: neq = z · n number of reactive units
eqvi = zi Mi
number of moles of protons that it can donate
number of moles of H+ that would react with that base
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34. The conversion table between
Normality vs. Molarity
The conversion table between
meq/L (= 10-3 eq/L) and mM (= 10-3 mol/L)
On an equivalent basis, a 1 M solution of sulfuric acid is twice as strong as a 1 M solution of HCl.
number of moles of H+ that would react with that base
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35. Other types of units Equivalents
number of moles of protons that it can donate
number of moles of H+ that would react with that base
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36. Other types of units Equivalent weight
The equivalent weight of a substance is defined as its molecular weight divided by the number of equivalents contributed per mole. For CaCO3
Thus the gram equivalent weight (gew) of CaCO3 is 50, i.e. there are 50g of CaCO3 per equivalent.
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37. Solids and Turbidity
Reporting particle concentrations In air and water
Total dissolved solids
Suspended solids
Volatile suspended solids
Solids and Turbidity

38. Solids and Turbidity
Solids and Turbidity

39. Solids and Turbidity
Solids and Turbidity

40. Fig_2-2

41. Particle concentrations
The total solids content (TS, mg/l) of a water sample may be divided into dissolved (e.g. salts) and suspended (e.g. particulates) fractions. Each of these may be further divided into inorganic and organic (volatile) fractions.
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42. total dissolved solids total suspended solids
(saltiness)
(as turbidity)
total solids
total dissolved solids
total suspended solids
(organic matter)
(organic matter)
volatile suspended solids
(inorganic matter)
fixed suspend solids
Fig_2-3

43. Total suspended solids (TSS, mg/L) represents the concentration, after drying, of the particles retained on a filter. The filter is then ignited and the material remaining (ash) is termed fixed suspend solids (FSS, mg/L) and that lost volatile suspended solids (VSS, mg/L). FSS and VSS represent the inorganic and organic fractions, respectively. Total dissolved solids (TDS, mg/L) are those which pass through a filter and are quantified by drying the sample.
Several of these fractions have significance in environmental engineering applications:
TDS (saltiness) is important with respect to drinking water and irrigation;
TSS (as turbidity) is used as a standard for safe drinking water consumption; and
VSS (organic matter) provides a measure of a water to consume oxygen.
Fig_2-3

44. Table_2-3

45. Table_2-4

46. Table_2-5

47. Table_2-6

48. Table_2-7

49. Table_2-8