# Chemistry - Combustion Method

This question is confusing me the way its presented and also is relating it to the combustion method that is used to analyze carbon and hydrogen. It can be used to give percent N.

It says a sample of a compound that weighs 8.75 mg gave 1.59 mL of N2 at 25 degrees Celsius and 749 mmhg. Find the percent of N in the compound?

How would I start this problem?

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1. Use PV = nRT to compute moles N2.
mols = grams/molar mass
Solve for grams N2 and convert to grams N.
Then (mass N/mass sample)*100 = percent.N
Remember that mass N and mass sample must be in the same units.

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2. I did what you said using the ideal gas law. I got 6.4 * 10-5 mol. I multiplied that by 28.02 to get the grams N2. Now to get the grams N, you just divide that number by 2 right?

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3. Yes, divide by 2.

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