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?
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.
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?
Yes, divide by 2.
To find the percent of nitrogen (N) in the compound, you can use the ideal gas law and stoichiometry. Here's how you can start solving this problem:
1. Determine the moles of nitrogen gas (N2). To do this, you can use the ideal gas law equation: PV = nRT. Rearrange the equation to solve for n (moles of gas):
n = PV / RT
P = pressure (in atm, so convert mmHg to atm if necessary)
V = volume (in liters, so convert mL to L if necessary)
R = ideal gas constant (0.0821 L·atm/mol·K)
T = temperature in Kelvin (convert Celsius to Kelvin by adding 273)
Substitute the given values into the equation and calculate the moles of N2.
2. Determine the moles of nitrogen atoms (N). Since one molecule of N2 contains 2 nitrogen atoms, the moles of N2 you calculated in the previous step should be multiplied by 2 to get the moles of N.
3. Calculate the moles of the compound. Since you have the mass of the compound, you can use its molecular weight to convert the mass to moles. This can be done using the formula:
moles of compound = mass of compound / molecular weight
The molecular weight can be found by summing the atomic weights of the elements in the compound.
4. Finally, calculate the percent of nitrogen in the compound. Divide the moles of nitrogen by the moles of the compound and multiply by 100 to get the percentage.
Remember to double-check your units and conversions throughout the calculations to ensure they are consistent.