Benzene is a known human carcinogen. The boiling point of benzene is 80. degreeC

Question

Benzene is a known human carcinogen. The boiling point of benzene is 80. degreeC (reference 1). Research online to find the short term exposure limit (STEL) for benzene. What does the STEL mean? A friend is planning to do an experiment with liquid benzene at 21 degreeC on the open bench top in a small (18 m^3) poorly ventilated room (i.e. consider the room to be a closed system for this question). Convert the STEL to vapour pressure for this room. Disclaimer: You should never work with a human carcinogen outside a fumehood under any circumstances! Calculate the theoretical vapour pressure of benzene inside the room at 21 degreeC. Use your data to explain to your friend why he can or cannot do the experiment. Fully explain why the following equation (derived from the ideal gas law) cannot be used to calculate the vapour pressure/temperature data at another temperature/pressure. P_1 / T_1 = P_2 / T_2

Explanation / Answer

a) 5 ppm for 15 minutes. This means that once this time is passed, you cannot keep continuing woirking with it, cause it's nocive.

b) with the 5 ppm, means that the concentration is 5 mg/L so, all we have to do is convert it to moles/L with the molecular weight which is 78.12 g/mol so:

M = 5 mg/L * 1g/1000 mg * 1 mol / 78.12 g = 6.4x10-5 moles/L

PV = nRT

P = nRT/V ----> P = MRT

P = 6.4x10-5 * 0.0821 * (273+21) = 1.5449x10-3 atm

c) PV = nRT

P = nRT/V

P = 1 * 0.082 * 294 / 18000

P = 1.34x10-3 atm

This pressure is lower than the pressure of benzene. Because of this, your friend cannot do the experiment here, because the pressure of the benzene will overlap the room and it will pass the stel for benzene, therefore, you cannot work here.

I have a doubt in part d, so I will answer til here. But Hope this helps and feel free to tell me something in a comment if you think that there's something else you need.

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