Question

Air contains 79% n2 and 21% o2 by volume. the percentage by mass of nitrogen gas in the air is

Answer 1

Hey dear,

● Answer -
w/w % of N2 = 0.8113 = 81.13 %

● Explanation -
As volume of O2/N2 in air is 79/21, same ratio will be applied to their mole percentage.
V1/V2 = 79/21
n1/n2 = 79/21

Also,
n1/n2 = (W1/M1)/(W2/M2)
79/21 = (W1/M1)/(W2/M2)
W1/W2 = 79/21 × M1/M2
W1/W2 = 79/21 × 32/28
W1/W2 = 4.3

Percentage by mass of oxygen -
W1/W % = W1/W1+W2

Percentage by mass of nitrogen -
W2/W % = W2 / (W1+W2)
W2/W % = W2 / (W2/4.3 + W2)
W2/W % = 1 / (1/4.3 + 1)
W2/W % = 0.8113 = 81.13 %

Hope this helped you...