Question

Calculate the molecular masses of the following :
(a) Hydrogen, ${H_2}$
(b) Oxygen, ${O_2}$
(c) Chlorine, $C{l_2}$
(d) Ammonia, $N{H_3}$
(e) Carbon dioxide, $C{O_2}$
(Atomic masses : $C\, = \,12\,u$; $H\, = \,1u$ ; $O\, = \,16\,u$ ; $Cl\, = \,35.5\,u$; $N\, = \,14\,u$ )

Answer 1

Hint: Molecular mass of a compound is defined as the sum total of masses of elements present in that compound. It is calculated by multiplying the atomic mass of an element with the total no of atoms of that element in that compound

Complete step by step answer:
Molecular mass is often expressed in the unit $amu$
Hydrogen, ${H_2}$ is the first element in the periodic table having atomic number $1$. It is naturally present in the gaseous form with no odor and color. It is also believed to be the most abundant element present in the universe. Its atomic mass is $1\,u$
So the molecular mass of ${H_2}$ will be
=$2\, \times 1\, = \,2\,u$
Oxygen, ${O_2}$ is the first member of the group- $16$ elements in the periodic table. It is an essential element in most of the combustion reactions. It is also naturally present as colorless and odorless gas. Its atomic mass is $16\,u$.
 So the molecular mass of ${O_2}$ will be
=$16\, \times \,2\, = \,32\,u$
Chlorine, $C{l_2}$ is a member of the halogen family. It is pale yellow in gaseous form. Chlorine has various applications. It is widely used as a disinfectant. Its atomic mass is $35.5\,u$
So the molecular mass of $C{l_2}$ will be
=$35.5\, \times \,2\, = \,70\,u$
Ammonia, $N{H_3}$ is a colourless gas with a pungent smell. One molecule of ammonia has three hydrogen atoms and one nitrogen atom. It has a wide range of applications. It is commonly used as fertilizers in agriculture. Atomic mass of nitrogen is $14\,u$
So the molecular mass of $N{H_3}$ will be
=$(14 \times 1)\, + \,(1 \times 3)\, = \,17\,u$
One molecule of $C{O_2}$ has one atom of carbon and two atoms of oxygen. Atomic mass of carbon is $12\,u$.
So the molecular mass of $C{O_2}$ will be
=$(12 \times 1) + \,(16 \times 2)\, = \,44\,u$

Note:
Carbon dioxide, $C{O_2}$ is also a colourless and odourless gas, which results from the combustion of carbon. Carbon dioxide is also a greenhouse gas responsible for increasing the temperature of earth’s crust. It is soluble in water. It forms carbonic acid when mixed with water.