Molecular Weight Formula


Molecular Weight Formula

The weight in atomic mass units of each of the atoms in a given formula is the molecular weight of a substance. An atomic mass unit is described as 1/12th the weight of the carbon-12 isotope. The old symbol was amu, while the most correct symbol is u (a lower-case letter u).

The molecular weight of a material is required to tell an individual how many grams there are in one mole of that substance.The mole is the typical method in chemistry for interacting as to how much of a substance is present.




Problem 1: What is the molecular weight of?


contains two atoms of iron and three atoms of oxygen

Mass of Fe = 55.847 amu,

Mass of O = 15.9994 amu

Molecular weight of  is

= 2 ×× 55.847 a\mu + 3 ×× 15.9994 amu

= 159.692 amu.


Problem 2: What is the molecular weight of ?


contains two atoms of potassium, one atom of sulphur and four atoms of oxygen

Molecular mass of K = 39.098 amu,

Molecular mass of s = 32.066 amu,

Molecular mass of o = 16.999 amu

Molecular weight of is

= 2 ×× 39.098 a\mu + 1 ×× 32.066 a\mu + 4 ×× 16.999 amu

= 174.298 amu

Practise This Question

On December 2006, a great earthquake occurred off the coast of Sumatra and triggered immense waves (Tsunami) that killed some 200,000 people. Satellites observing these waves from space measured 800 km from one wave crest to the next and a period between waves of 1 hr. what was the speed of the wave?