Question

Two gases A and B [molecular weight of A=20 and molecular weight of B=30] are mixed in the ratio a:b and the average molecular mass of the gas mixture is 24. What will be the average molar mass of the gas mixture, if gases A and B are mixed in the ratio b:a?​

Answer 1

molecular mass of gas mixture is 30

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Answer 2

Answer:

If the gases A and B are mixed in the ratio b:a, the molar mass of gas mixture = 30

Explanation:

Given,

• Two gases A and B
• Molecular weight of A = 20
• Molecular weight of B = 30
• The average molecular mass of gas mixture = 24

To find:

The ratio of a:b if A and B gases are mixed.

Solution:

$\frac{a}{a+b} (20) + \frac{b}{a+b} (30) = 24$  ..............................(1)

20a + 30b  = 24(a+b)

20a + 30b = 24a + 24b

30b - 24b = 24a - 20a

6b = 4a

$\frac{a}{b} = \frac{6}{4}$

$\frac{a}{b} = \frac{3}{2}$    they are mixed in b/a order.

Therefore,

b = 3  and a = 2

$Average molar mass = \frac{2}{3+2}(20) + \frac{3}{2+3}(30)$

$Average molar mass = \frac{2}{5}(20) + \frac{3}{5}(30)$

Average molar mass = 12 + 18

Average molar mass = 30

If the gases A and B are mixed in the ratio b:a, the molar mass of gas mixture = 30

Answer = 30

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