Question

Calculate the molar mass of the following –
(A) ${{H}_{2}}O$
(B) $C{{O}_{2}}$
(C) $C{{H}_{4}}$

Answer 1

Hint: The molar mass can be calculated by adding the individual atomic masses of all the elements present in the compound. In case of multiple atoms of the same element in a compound, multiply the number of atoms with the atomic mass of the element and then add with the atomic masses of other elements.

Complete step by step solution:
- The molar mass of a given chemical compound or element can be given by dividing the mass of a given chemical compound or element divided by the amount of substance in moles.
- Molar mass of a chemical compound or element can also be defined as the weight of one mole of a chemical compound or element.
- We can also find the molar mass of a compound by using the atomic masses of all atoms in the molecule. We just have to add the standard atomic masses
-For a compound, we have to multiply the atomic mass of the element with the number of atoms of that element present in the compound. We have to follow the same procedure for each element. Then, adding these masses will provide us with the molar mass.
- For Part (A),
\[\begin{align}
  & \text{Molar mass of }{{H}_{2}}O\text{ = (2}\times \text{ atomic mass of }H)\text{ + atomic mass of }O \\
 & \\
\end{align}\] \[\text{Molar mass of }{{H}_{2}}0\text{ = (2}\times \text{1) g/mol + 16 g/mol}\]
\[\text{Molar mass of }{{H}_{2}}O\text{ = 18 g/mol}\]
- Similarly, for parts (B) and (C),
     \[\text{Molar mass of }C{{O}_{2}}=\text{ atomic mass of }C\text{ + (2}\times \text{atomic mass of }O\text{) = 12 g/mol + (2 }\times 16\text{ g/mol) = 44 g/mol}\]\[\text{Molar mass of }C{{H}_{4}}=\text{ atomic mass of }C\text{ + (4}\times \text{atomic mass of H) = 12 g/mol + (4 }\times 1\text{ g/mol) = 16 g/mol}\] \[\]

Additional Information:
- The molar mass can be calculated in many different ways depending upon the data given in the question. For example,
\[\text{molar mass = given mass of substance}\div \text{ number of moles of the substance }\]

Note: While calculating molar mass, be careful to multiply the number of atoms of the element with its atomic mass. Failure to do so will result in an incorrect answer.