Question

The molecular mass of ${{(N{{H}_{2}})}_{2}}CO$ is:
(Given atomic mass of H=1, O=16, C=12, N=14)
(A) $90gm/mole$
(B) $80gm/mole$
(C) $60gm/mole$
(D) $62gm/mole$

Answer 1

Hint: Molecular mass is the mass of a given molecule. It is interesting to note that different molecules of the same compound can have different molar mass, because the molecules contain different isotopes of an element.

Complete step by step solution:
Molecular mass is the total mass of a compound, it is easy to find the molecular mass of a substance. The steps require to find the molecular mass of a substance is mentioned below:
Step1- write down the given molecular formula of the molecule.
Step2- with the help of the periodic table, determine the atomic mass of each element present in the molecule.
Step3- The subscript next to the symbol of each element in the molecular formula tells us about the number of atoms of each element in the molecule. If there is no subscript next to the symbol of an element in the molecular formula it means that there is only one atom of that element present in the molecule. Multiply the atomic mass of each element with the number of atoms of that element in the molecule.
Step4- Add all the values together for different atoms present in the molecule.
Given - ${{(N{{H}_{2}})}_{2}}CO$
Atomic mass of H= 1
Atomic mass of N= 14
Atomic mass of C= 12
Atomic mass of O= 16
Molecular mass of $N{{H}_{2}}$= $14+(2X1)=16$
Molecular mass of ${{(N{{H}_{2}})}_{2}}$= $16X2=32$
Molecular mass of CO= $12+16=28$
Hence the molecular mass of ${{(N{{H}_{2}})}_{2}}CO$= $32+28=60$$gm/mole$

Hence the correct option is (C).

Note: The atomic mass of an element is expressed in unified atomic mass also known as Dalton. And the molecular mass of an element is expressed in kilogram per mole or gram per mole.