Question

9.
Density of a gas at 300 K and 210 torr is 0.434 gL-1. What is its molar mass?
(1) 14.78 g/mole
(2) 73.43 g/mole
(3) 38.68 g/mole
(4) 43.28 g/mole in this qn pls explain which should be used as value of R and should we convert torr to atm? and why not change to atm..quick and fast.. the first,correct answer with pakka explanation will be marked as brainliest and i would follow them..​

Answer 1

Given:-

→ Temperature = 300 K

→ Pressure = 210 torr

→ Density of the gas = 0.434 g L⁻¹

To find:-

→ Molar mass of the gas.

Solution:-

Since, the pressure is given in 'torr' and volume is in 'Litres' , thus value of Gas Constant [R] will be :-

62.36 L torr K⁻¹ mol⁻¹

_______________________________

Now, we know that :-

P = dRT/M

Where :-

• P is the pressure.

• d is density of the gas.

• R is Gas Constant.

• T is temeperature.

• M is molar mass of the gas.

Substituting values, we get :-

=> 210 = 0.434×62.36×300/M

=> 210 = 8119.272/M

=> M = 8119.272/210

=> M = 38.66 ≈ 38.68 g/mole

Thus, molar mass of the gas is 38.68g/mol [Option.3].

Some Extra Information:-

We have studied that the number of moles (n) of the substance is related to the molar mass (M) as :-

n = m/M. [where , m = mass in grams]

Substituting this value in the Ideal gas equation :-

=> PV = nRT

=> PV = m/M RT

=> P = mRT/MV

=> P = dRT/M [Since, d = m/V]