Question

the mass of one molecule of a substance is 11.79×10^-26kg.what is its molar mass?

Answer 1

We are given that the mass of one molecule of the substance is 11.79 X 10-26 Kg. So the mass of one molecule of the substance in grams will be 11.79 X 10-23 g. The molar mass of a molecule is the mass of 6.023 X 1023 molecules of that substance. Thus 

mass of 6.023 X 1023 molecules of the substance = 11.79 X 10-23 X 6.023 X 1023

= 71.011 g 

The molar mass of the substance is 71.011 g. This substance could be chlorine gas (Cl2) as the atomic mass of chlorine is 35.5 and there are two atoms of chlorine per molecule. So molar mass of chlorine molecule = 2 X 35.5 = 71 g 

Answer 2

Given,

The mass of one molecule of a substance = 11.79×10^-26kg

To find,

The molar mass of the substance.

Solution,

We can simply solve this numerical problem by using the following process:

As per the principles of stoichiometry;

1 mole of any substance contains Avogadro's number of molecules, that is, 6.022 x 10^23 molecules of that substance.

Now,

The mass of one molecule of a substance = 11.79×10^-26kg

The molar mass of the substance

= the total mass of Avogadro's number of molecules of that substance

= 11.79×10^-26kg x 6.022 x 10^23

= 11.79×10^-23 g x 6.022 x 10^23

= 70.99 grams = 71 grams approximately

Hence, the molar mass of the substance is approximately equal to 71 grams.