At 9:30 one morning, a graduate student measures 350 grams of liquid benzene at 20C into

QUESTION:

At 9:30 one morning, a graduate student measures 350 grams of liquid benzene at 20C into a glass flask dirty enough that its contents cannot be seen, puts the open flask on a bunsen burner, turns the burner on, and goes for a coffee break. The conversation at the break is lively, and he doesnt get back until 10:10 a.m. He looks down into the flask, sees the liquid is boiling, turns the burner off, feels a little irritation in his eye and rubs the eye with his hand, picks up the flask, says Ouch (or something roughly equivalent), puts the flask down on his laboratory partners thermodynamics homework, and starts to prepare the next step of the experiment. (a) Suppose the heat input rate to the flask contents is 40.2 W. Calculate the time at which the benzene temperature reaches 40C. Neglect evaporation of benzene during the heating and take the heat capacity of liquid benzene to be constant at 1.77 J/(gC). (b) Calculate the quantity of benzene left in the flask at 10:10 a.m., assuming that once the benzene starts boiling, the rate of heat input to the flask (40.2 W) equals the rate of vaporization (g/s) times the heat of vaporization (J/g). (c) The graduate student was lucky. First, neither his faculty advisor nor the departmental safety officer came into the laboratory during this episode. More importantly, he was still alive and well at the end of the day. Identify as many of his safety violations as you can, explaining the danger and suggesting for each violation what he should have done instead.