5. The LC50 for fluorine is 0.29 mg/m3. What is this in ppm at 25 oC and 1 atm pressure? How does this compare to the PEL?
To convert the LC50 value from mg/m3 to ppm, you need to know the molecular weight of the substance. The molecular weight of fluorine (F2) is 38 g/mol.
1. Convert the LC50 value from mg/m3 to g/m3 by dividing it by 1000 since there are 1000 mg in 1 g:
LC50 (g/m3) = 0.29 mg/m3 / 1000 = 0.00029 g/m3
2. Convert g/m3 to moles per cubic meter:
Moles/m3 = (LC50 (g/m3)) / (Molecular weight)
= 0.00029 g/m3 / 38 g/mol = 7.63 x 10^-6 mol/m3
3. Now, convert moles per cubic meter to ppm. To do this, you need to know the ideal gas law:
PV = nRT
Where:
P = pressure (in atm)
V = volume (in m3) - in this case, we can assume it to be 1 m3
n = moles of gas
R = ideal gas constant (0.0821 L.atm/(mol.K))
T = temperature (in Kelvin)
Since we are given the pressure and temperature, we can rearrange the equation to solve for n:
n = PV / (RT)
4. Convert the given temperature from Celsius to Kelvin:
T (Kelvin) = 25 oC + 273.15 = 298.15 K
5. Calculate the moles of fluorine in 1 m3 of air:
n = (1 atm) x (7.63 x 10^-6 mol/m3) / [(0.0821 L.atm/mol.K) x (298.15 K)]
n ≈ 3.33 x 10^-8 mol
6. Finally, convert moles to ppm:
ppm = (moles / volume) x (10^6)
ppm = (3.33 x 10^-8 mol / 1 m3) x (10^6)
ppm ≈ 3.33 x 10^-2 ppm
So, the LC50 value for fluorine is approximately 0.029 ppm at 25 oC and 1 atm pressure.
Comparing with the PEL (Permissible Exposure Limit), if the PEL value for fluorine is lower than 0.029 ppm, then it suggests that the LC50 value is higher than the PEL, indicating that fluorine is more toxic than what is considered acceptable for occupational exposure. However, if the PEL value is higher than 0.029 ppm, then it implies that the LC50 value is lower than the PEL, suggesting that fluorine is considered less toxic and within acceptable limits for occupational exposure.