Question

53. 2.8 L of an unknown gas (X2) under STP conditions
weighs 5 g. Atomic mass of X is
(1) 8 u
(2) 10 u
(3) 15 u
(4) 20 u​

Answer 1

Answer:

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4.)20

The volume of X2 at STP = 2.8 L

The mass of gas X = 5 gm

To Find:

The atomic mass of X.

Calculation:

22.4 L of gas at STP = 1 mole

⇒ 2.8 L of gas at STP = (1 / 22.4) × 2.8 mole

⇒ 2.8 L of gas at STP = 0.125 moles

- Molar mass of X2 = Mass / No of moles

⇒ Molar mass of X2 = 5 / 0.125

⇒ Molar mass of X2 = 40 gm

⇒ Molar mass of X = 20 gm

- Molar mass is the atomic mass of a substance depicted in grams.

- Hence, the atomic mass of the given gas X is 20 amu.