ppm——精选推荐

2
1 6.023
10
3.32 10
Thus the concentration = 8.2 x10‐8 M ( . .
)
Another common unit used with gases is g/m3
Example: Convert 320 g/m3 SO2 to ppb at 1 atm & 27 C
QUESTION • Convert a concentration of 32 ppb for any pollutant to its value on a) ppm scale (Answer = 0.032 ppm) b) molecules/cm3 scale (Answer = 7.9 x1011 molecules/cm3) c) molarity scale (Answer 1.3 x10‐9 M)
In general for water based solutions
mg/L = ppm g/L = ppb ng/L = ppt
Problem: Convert:
a) 0.04 g/L to ppm & ppb b) 3 ppb to g/L
APCH 211 TUT 7 (REVIEW TUT) 2011
units on top & bottom)
Using PV = nRT, moles of air = 40.7 mol Then molecules of air = 2.45 x1025 molecules (use Avogadro’s number) Note a billion is 109 So 2.45 x1016 molecule billion molecules of air
Converting Water Units
Unlike gases, the part per scale with water based solution refers to mass of solute to the mass of solution. Thus when looking at water, 1000mL or 1.0 L of natural water sample is very close to 1.0 kg, so if you have mg of solute per L, it is ~ to mg per kg, which works out to ppm.
Using Avogadro’s number can determine moles of air
1000, 000
1 6.023
10
1.66 10
Rearrange the ideal gas equation to solve for the volume
1.66 10
0.0821
298
1.0
Example: Assuming a temperature of 25 °C, and a pressure of 1 atm; Convert 2 ppm to molecules/cm3
Since molecules of air = 1000, 000, can convert this to a volume using PV = nRT
Problem: Convert: a) 0.04 mg/L to ppm & ppb 4.0 x 10‐5 ppm; 0.040 ppb a) 3 ppb to mg/L 3.0 mg/L
Since 2 ppm means there are 2 molecules of gas for every 1000, 000 molecules of air (volume calculated above), and simply convert 2 molecules to moles using Avogadro ’s number
APCH 211 TUT 7 (REVIEW TUT) 2011
Converting Gas Units
Central to conversion between different gas concentrations is PV = nRT
2ppm of a gas means:
there are 2 gas molecules for every 1 million molecules of air there are 2 moles of gas for every 1 million moles of gas 2 x 10‐6 atm partial pressure of gas for 1 atm total air pressure
Convert your grams to moles
320 10
1 64.1
4.99 10
APCH 211 TUT 7 (REVIEW TUT) 2011
Convert to molecules SO2 4.99 10
6.023 10 1
3.01 10
Then find molecules of air (recall ppm, ppb, or any parts per, is dimensionless, so need same
Convert from L to cm3: 4.06 x10‐14 cm3
Thus there are 2 molecules in 4.06 x10‐14 cm3
Or 4.92 x1013 molecules/cm3 (divide by 4.06 x10‐14 cm3)
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4.06 10
Follow up Convert 2 ppm to Molarity
Last ppb step
3.01 10 2.45 10
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QUESTION
Convert a concentration of 32 ppb for any pollutant to its value on
a) ppm scale, b) molecules/cm3 scale
c) molarity scale