How To Find The Number of Molecules of Gases N2, O2, CO2, and Ar Using Ideal Gas Law
October 9th, 2008
Chemistry Tutor Help - Chemistry Problem
A sample of air contains 74.25% nitrogen, 24.90% oxygen, 0.05% carbon dioxide, and 0.80% argon, by volume. How many molecules of each gas are present in 1.00 L of the sample at 25°C and 1.00 atm?
The composition of each gas in the volume of 1 L are obtain by multiply the percentage and the volume
Chemistry Tutor Help - Chemistry Problem Solving
This is a simple question, why because only need a simple formula that involved gases. Use the “ideal gas law” to solve this problem, from it you would find the moles and from the moles you can find the number of molecules in each gas.
Do you know that we only need 3 variable of the state of the gas to know the fourth variable, according of this problem we have had, temperature, pressure, and the volume thus we can calculate the moles.
Volume of each gas can be calculate by multiply the percentage with volume of the sample that is:
Volume gas = % x Volume of sample
from the formula above we get each gas volumes
N2 = 0.7425 L
O2 = 0.2490 L
CO2 = 5.10exp-4 L
Ar = 8.10exp-3 L
Next use the formula of ideal gas to find the mole of each gas p is the pressure in atm, V is the volume in liter, T is the temperature in Kelvin, and R is the gas constant 0.08206 and the ideal gas formula is:
PV = nRT solve for the “n”
n = PV/RT
We get:
moles of N2 = 0.030 mol
O2 = 0.010 mol
CO2 = 2.05.10exp-5 mol
Ar = 3.271.10exp-4 mol
The number of molecules in each gas are obtain by:
Number of molecules = N x mole
N is the avogadro number that is 6.022.10exp23
thus
N2 = 1.81.10exp23 molecules
O2 =6.022.10exp21molecules
CO2 =1.235.10exp19 molecules
Ar = 1.98.10exp20 molecules
Entry Filed under: Stoichiometry
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