Finding molar mass using mass percentages?

Question

Yep, I'm asking another molar mass with mass percentage question hehe. These just always get me...

Air is a mixture of many gases. However, in calculating its "molar mass" we need to consider only three major components: nitrogen, oxygen, and argon. Given that one mole of air at sea level is made up of 78.08 percent nitrogen, 20.95 percent oxygen, and 0.97 percent argon, what is the molar mass of air?

Answer 1

The molar mass is the mass of one mole of a chemical element or chemical compound.

A mole is defined as Avogadro's number, approximately 6.022x1023, of particles of any kind of substance (atoms, ions, molecules, or formula units).

In chemistry, the unit is g/mol, although the International System unit is kg/mol - just be careful to put the units in the answer.

The molar mass of an element is the same as the atomic mass in the periodic table (in g/mol).

The molar mass of:

Nitrogen (N) = 14.0067 g/mol
Oxygen (O) = 15.9994 g/mol
Argon (Ar) = 39.9481 g/mol

Don;t just jump into the formula because Nitorogen in the air is actually N2 which has a molar mass of 28.0134 g/mol, and the Oxygen is O2, with a molar mass of 31.9989 g/mol. And of course Ar is just Ar as it is unreactive.

The question should actually have used the terms "molecular nitrogen", and "molecular oxygen" or dioxygen.

And to calculate the molar mass of a gas all you have to do is sum the relative proportions.

So the molar mass of air (here MM = molar mass) =

% of N * MM of N2 + % of O * MM of O2 + % Ar * MM of Ar =

0.7808*28.0134 + 0.2095*31.9989 + 0.0097*39.9481 =

28.96 g/mol

which corresponds to the accepted figure.

Answer 2

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RE:
Finding molar mass using mass percentages?
Yep, I'm asking another molar mass with mass percentage question hehe. These just always get me...

Air is a mixture of many gases. However, in calculating its "molar mass" we need to consider only three major components: nitrogen, oxygen, and argon. Given that one mole of air at...

Answer 3

if, per molecule, iron is 0.34% of myoglobin's mass (iron = 0.0034 times myoglobin), then the mass of myoglobin would equal the mass of iron divided by 0.0034. iron's molar mass is 55.85, so 55.85 divided by 0.0034 equals -- 16426g/mol? actually, that seems weird. are you sure it's 0.34%? it might be 34%; if so, the answer would be 164.26 gmol

Answer 4

0.7808 x 28 (for N2)
+
0.2095 x 32 (for O2)
+
0.0097 x 40 (for Ar)
= mass of one mole of air

Answer 5

(% of abundance of N2*molar mass+% of abd of O2*molar mass+%of abd of Ag*malar mass)/% of abd of all the given gases
78.08*28+20.95*32+.97*39.9/78.08+20.95+0.97
=28.95(ans)

Answer 6

weird-- I think I had this exact question on a chemistry test last year