# Chem geniuses, i need some help

Discussion in 'Pre-Medical - MD' started by WorkOnIt, Nov 15, 2002.

1. ### WorkOnIt Junior Member

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! I need some help from my fellow chem geniuses. This is the prob. that has me stuck:

The effusion rate of an unknown gas is measured and found to be 31.50 mL/min. Under identical expermential conditions, the effusion rate of O2(oxygen) is found to 30.50 mL/min. If the choices are CH4, CO, NO, CO2, and NO2, what is the indentity of the unknown gas?

My book says the answer is NO. but i dont see how the answer is obtain. what steps and equation are used???

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3. ### BrainDrain Member

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just plug into formula:

Effusion Rate O2/Effusion Rate X=square root(Mol.W X/MW O2)

squared(30.5/31.5)=Mol.W X/32

Mol.W X=30

which is the Mol. Wt. of NO

Hope you can understand this

4. ### WorkOnIt Junior Member

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thanks for reply. it took me a min., but i got it. but just to be sure , this is how u would do it, right:

squared(30.5/31.5)=Mol.W X/32

976= 31 Mol. W X

976/31.5=30.9 but i guess u can take NO since its the nearest 30. if thats how u do it, sorry but i'm just a bit of a perfectonist

5. ### BrainDrain Member

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The answer is EXACTLY 30.

squared(30.5/31.5)=Mol.W X/32

squared(0.968)=Mol.W X/32

0.9375 X 32=Mol.W

Mol. W=30.00

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