One of the tanks that a pediatric dentist uses to administer nitrous oxide is “empty”, meaning that the N2O inside is at the same temperature and pressure as the room. The ML-6 type cylinder has an internal volume of 165 liters. How many moles of nitrous oxide remain in the empty tank (Ideal gas constant = 0.082 L atm/K mol; assume the apparatus is at sea level; the ambient temperature is 22° C)?

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Correct Answer: **A.** *6.8 moles*

This question requires the use of the ideal gas law: PV = nRT. We are solving for number of moles (n). The temperature in the equation is in Kelvin, so a 22° C room would actually be 295 K approximately. The pressure (P) at sea level is 1 atmosphere. So, (1 atm X 165 L) / (0.082 L atm/K mol X 295 K) = 6.8 moles

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Photo attributed to Jurvetson.