Question

The molecular mass of air, at standard pressure and temperature, is approximately 28.97 g/mol. Calculate the mass of 3.33 moles of air. Next, cancel like terms and units. Which of the following shows the correct terms and units canceled?

Answer 1

Answer: 99.5 g


1) Data:


molar mass, MM = 28.97 g/mol

number of moles = 3.33 moles

2) Formula: 

mass in grams = number of moles × molecular mass

3) Calculations:

mass in grams = 3.33 mol × 29.87 g/mol = 99.5 g

Note that the unit mol cancel because it is in the numerator of the first factor and in the denominator of the second factor.

Answer 2

The molecular mass of air, at standard pressure and temperature, is approximately 28.97 g/mol. Calculate the mass of 3.33 moles of air.

Finally, solve (remember significant figures):

A:  

99.5

⇒ 96.5