A cylinder of compressed gas rolls off a boat and falls to the bottom of a lake.

Question

A cylinder of compressed gas rolls off a boat and falls to the bottom of a lake. Eventually it rusts and the gas bubbles to the surface. A chemist collects a sample of the gas with the idea of trying to identify the gas. The wet gas collected occupies a volume of 287 mL at a pressure of 787 torr and temperature of 28.0oC. The vapor pressure of water at 28.0oC is 0.0372 atm.

1. Calculate the volume (L) that the gas occupies after it is dried (the water vapor removed) and stored at STP.

The mass of the dry gas is 463 mg. A fragment of the tank indicates that the gas is a monoatomic element.

2. Write out the full name of the gas.

Explanation / Answer

0.0372 atm @ 760 Torr / atm = 28 Torr water vapor

P1V1T2 = P2V2T1
(793 - 28)(275 ml)(273K) = (760 Torr)(V2)(301K)

1. Calculate the volume (L) that the gas occupies after it is dried and stored at STP.
your answer is
V2 = 251 ml

======================================...

find moles, using the molar volume of gases at STP
0.251 litres @ 1 mole / 22.4 litres = 0.0112 mmolaes

find molar mass
0.939 grams / 0.0112 moles = 83.8 g/mol

2. Write out the full name of the gas.
Krypton

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