Question

calculate the formula mass of each compound given below. keep at least one decimal place in atomic masses from the periodic table. a) hydrogen peroxide, H2O2. b) sulfuric acid, H2SO4.

Answer 1

Solution:

• Formula mass is the sum of the atomic masses of all the atoms in the compound's fromula.
• Formula mass is expressed in atomic mass units (a.m.u)

a) H₂O₂

Atoms	atomic masses (a.m.u)	no. of atoms	total massses = Atomic weight× no of atoms
H	1.008	2	1.008 × 2 = 2.016
O	15.999	2	15.999 × 2 = 31.998

*atomic weights have been directly taken from periodic table.

Now,

adding up all the masses, we get,

2.016 + 31.998 = 34.014 a.m.u

The formula mass of H2O2 is 34.014 which is written as 34.01 a.m.u

b) H₂SO₄

Atoms	no. of atoms	atomic weights*	total masses= Atomic weight× no of atoms
H	2	1.0079	1.008 × 2 = 2.016
S	1	32.065	32.065 × 1 = 32.065
O	4	15.999	15.999 × 4 = 63.996

*atomic weights have been directly taken from periodic table.

Now,

adding up all the masses, we get,

2.0158 + 32.065 + 63.996= 98.077 a.m.u

The fromula mass of H2SO4 is 98.077 which is written as 98.08 a.m.u.