Air is about 78% nitrogen gas (N2) by mass. The molar mass of nitrogen gas is 28.0 g/mol. A 100.0-g sample of air contains how many moles of nitrogen?
2.8
3.6
28
78

2.8 moles

Explanation:

Data obtained from the question include:

Percentage composition of N2 in air = 78%

Molar mass of N2 = 28g/mol

Mass of air = 100g

Number of mole of N2 =..?

Next, we shall determine the mass of N2 in air. This can be obtain as follow:

Mass composition of N2 in air = 78% of 100

= 78/100 x 100 = 78g

Therefore, the mass of the N2 in air is 78g

Finally, we shall determine the number of mole of N2 as follow:

Molar mass of N2 = 28g/mol

Mass of N2 = 78g

Number of mole of N2 =.?

Mole = mass /Molar mass

Number of mole of N2 = 78/28

Number of mole of N2 = 2.8 moles.

Therefore, 100g of air contains 2.8 moles of N2

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