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A gaseous sample of diatomic element X2 has a mass of 40 mg and occupies 4.8 mL at 1 atm pressure and 27 deg C. Using the ideal gas law (R = 0.08 atm*L / (mol*K)), find the atomic mass (in g/mol) of element X.

1. 50
2. 100
3. 75
4. 25

Correct answer: 100

Solution

Applying the ideal gas equation gives the number of moles of X2. Dividing the mass by moles gives the molar mass of X2. Since the molecule is diatomic (X2), the atomic mass of X is half the molar mass of X2.

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