Question

0.56 g of gas occupies \[{\rm{280c}}{{\rm{m}}^{\rm{3}}}\] at NTP. Then its molecular mass is:
A. 4.8
B. 44.8
C. 11.2
D. 22.4

Answer 1

Hint: The NTP denotes normal temperature and pressure. One mole of an ideal gas has a molar volume at NTP is 22.4 L. The temperature and pressure at NTP are 273 K and 1 atm respectively.

Complete Step by Step Solution:
Here in this question, we are given an amount of gas that occupies a certain amount of volume at NTP.
We have to find out the molecular mass of the gas.
We will have to convert \[{\rm{280c}}{{\rm{m}}^{\rm{3}}}\] into litres.
\[1c{m^3}\] is equal to 0.001 L.
So, \[{\rm{280c}}{{\rm{m}}^{\rm{3}}}\] is equal to 0.28 L.

We know that 1 mole of a gas at NTP occupies 22.4 L of volume.
We also know that one mole of a substance is its molecular mass.
0.28 L occupies 0.56 g of the ideal gas.
1 L will occupy \[\frac{{0.56g}}{{0.28L}}\] of the ideal gas.

So, 22.4 L will occupy \[\frac{{0.56g}}{{0.28L}}(22.4L)\] of the ideal gas.
Hence, 22.4 L will occupy 44.8 g of the ideal gas.
Therefore, the molecular mass of the ideal gas is 44.8g.
So, option B is correct.

Note: STP means standard temperature and pressure. At standard temperature and pressure, a substance carries a temperature of 273 K and the pressure is 1 atmosphere. This definition is given by The International Union of Pure and Applied Chemistry (IUPAC). The National Institute of Standards and Technology, however, specifies STP as 1 atm and \[20^\circ C\] (293.15 K, or \[68^\circ F\]).