Question

A .405 g sample of gas contains .0050 moles. What is the molar mass of this gas? Please round your answer to the tenths place.

I am confused by this.

Molar mass = mass of sample/moles of sample

The answer is either:

molar mass = .405g/.0050 = 81 g/mol

(I dividing mass by moles and am getting a whole number, and its asking me to round to the tenths place.

Could it be:
molar mass = .0050/.405 = 0.012?

Answer 1

Since
moles = grams/molar mass; then
molar mass = grams/moles
molar mass = 0.405 g/0.0050 moles = 81.00000. Rounding to the nearest tenth, I would put 81.0 g/mole as the answer.