19. Convert 15 ppm of benzene to mg/m3 at 20 oC and 720 torr
Density of a gas is g/L = P(MW)/RT
(740 torr x 1 atm/760torr)(78.114g/mole)/ (.0821L atm/mole K)(293K) = 3.16g/L
1ppm =1 L Benzene/106 L of air = 1L ben/1000 m of air = 0.001 L ben/m3 = 0.00316 g/m3
x/3.16=15 = 47.4mg/m3 ???
To convert 15 ppm (parts per million) of benzene to mg/m3 (milligrams per cubic meter), you can use the following steps:
Step 1: Calculate the density of benzene at the given conditions.
The density of a gas can be calculated using the formula: density = (pressure × molecular weight) / (gas constant × temperature)
Given:
Pressure (P) = 720 torr
Molecular weight (MW) of benzene = 78.114 g/mol
Gas constant (R) = 0.0821 L·atm/mol·K
Temperature (T) = 20°C = 293 K
Using the formula:
Density = (720 torr × 78.114 g/mol) / (0.0821 L·atm/mol·K × 293 K)
Density ≈ 3.16 g/L
Step 2: Convert ppm to g/m3.
Since 1 ppm represents 1 part of benzene in 1 million parts of air, we can convert it to grams per cubic meter as follows:
1 ppm = 1 L benzene / 1,000,000 L air
1 ppm = 0.001 L benzene / 1 m3 air
1 ppm ≈ 0.00316 g/m3
Step 3: Calculate the mg/m3 of benzene.
To find the mg/m3 of benzene, we can use the equation:
x g/m3 / 3.16 g/m3 = 15 ppm
Solving for x:
x ≈ 15 ppm × 3.16 g/m3
x ≈ 47.4 mg/m3
Therefore, the conversion of 15 ppm of benzene to mg/m3 at 20°C and 720 torr is approximately 47.4 mg/m3.