Molecular mass of substance (elements or compound) is the relative mass of its molecule Compared with that of an atom Of carbon-12 isotope taken as 12.
In other word molecular mass of substance represent the number of times the molecule of that substance is heavier than 1/12 of the mass of an atom of C-12 isotope.
Calculations of Molecular Mass
- The molecular mass is equal to the sum of atomic masses of all atom present in one molecule of the substance.
- A molecule is made up of two or more atom of the same or different elements and each has definite atomic mass , therefore molecular mass of a molecule of substance can be calculated by adding atomic mass Of all the atom present in one molecule of the substance.
1) A molecule of hydrogen has the formula H2 , it contains two atom of hydrogen. Atomic mass of hydrogen 1.0u
So, 2, hydrogen = (2×1. 0)
2) A molecule of oxygen has the formula O2 , it contains two atom of oxygen. Atomic mass of oxygen 16u.
So, 2 ,Oxygen = (2×16)
3) A molecule of ozone has the formula O3 , it contains three atom of oxygen. Atomic mass of oxygen 16u.
So, 3 Oxygen = ( 3×16)
4) A molecule of carbon dioxide has the formula CO2 , it contains two atom of oxygen and one carbon atom. Hence the Atomic mass of carbon- 12u and oxygen- 16u.
So, One carbon + two oxygen = ?
(1×12) + (2×16)
12 + 32 = 44u.
1) What is molecular mass?
Answer: The molecular mass is equal to the sum of atomic masses of all atom present in one molecule of the given substance.
2) Calculate the molecular mass of ZnO?
Answer: molecular mass of ZnO is following.
A molecule of Zinc oxide has the formula ZnO , it contains one atom of Zinc and one atom of oxygen. Atomic mass of Zinc 65u.and Atomic mass of oxygen 16u.
One atom of Zinc (1×65) = 65
One atom of oxygen (1×16) =16
ZnO ( 65+16) = 81 u.
4) Calculate the molecular mass of C12H22O11?
Answer: A molecule of sugar has the formula C12H22O11 , it contains 12-atom of carbon22- atom of hydrogen, and 11- atom of oxygen. Atomic mass of carbon 12u, hydrogen 1u, and Atomic mass of oxygen 16u.
12-atom of carbon C- (12×12) = 144
22-atom of hydrogen H- (22×1) = 22
11-atom of oxygen O- (11×16) =176
C12H22O11: (144+22+176) =342 u.