#### Question

# Effusion and Molar Mass?

Part A:

In an effusion experiment, it was determined that nitrogen gas, N2, effused at a rate 1.812 times faster than an unknown gas. What is the molar mass of the unknown gas?

the answer was m=91.98 g/mol

Part B:

Elemental analysis of the unknown gas from Part A revealed that it is 30.45% N and 69.55% O. What is the molecular formula for this gas? Express your answer as a chemical formula.

#### Answers

we use Grahame's law to workout the molar mass

( Rate x / Rate N2 ) ^2 = MM N2 / MM x

( 1 / 1.812) ^2 = 28 / MM x

MM x = 28 / 0.305

= 91.80 g / mole

mass of N in 1 mole of the gas = 30.45 5 of 91.80 = 28.0g or 2 moles of N

mass of O = 69.55 % of 91.8 = 63.8 g or 4 moles

molecular formula is N2O4 ..

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