Question

2.8 L of an unknown gas (X2) under STP conditions weighs 5 g. Atomic mass of X is

Answer 1

Given:

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.

Answer 2

Answer:

20u

Explanation:

2.8 L → 2.8/22.4 mole = 0.124

molar mass of x2= 5/0.124 → 40g

∴ 1 mole = 40 g = Molar mass of X2

∴ Atomic mass of X = 20 u