Question

How do you find molecular weight?

Answer 1

The calculator for molecular weight is based on the molecular formula of a compound it is not the simplest formula, which only includes the ratio f the types of atoms and not the number of each type of atom is multiplied by its atomic weight and then, added to the weights of the other atoms.

Complete step by step answer:
To understand this question we should first know about the molecular weight in brief.
Molecular weight – the sum of atomic masses of all atoms in a molecule is known as molecular weight.
For more understanding of the question, let us calculate the molecular weight of some compounds.
For an instance, $N{{H}_{3}}$ is the molecular formula for ammonia, indicating that this molecule has $4$ atoms, $1$ atom of nitrogen $\left( N \right)$ and $3$ atoms of hydrogen $\left( H \right)$. Now we have to find the atomic weight of $\left( N \right)$ and $\left( H \right)$ using a periodic table of elements, which is $14$ and $1$ respectively. Now in order to determine molecular weight of ammonia we have to apply the contribution from each atom that is
$N{{H}_{3}}=14\left( 1 \right)+1\left( 3 \right)$
$\Rightarrow 14+3$
$\Rightarrow 17$ grams/mole
Similarly, to find out the molecular weight of water $\left( {{H}_{2}}O \right)$. This molecule has $3$ atoms in which $2$ atoms of Hydrogen $\left( H \right)$ and one atom of oxygen $\left( O \right)$. Now we have to find the atomic weight of hydrogen as well as oxygen from the periodic table of elements, which is $1$ and 16 respectively.
Now we have to add the contribution from each atom that is
${{H}_{2}}O=1\left( 2 \right)+16\left( 1 \right)$
$=18$ grams/mole

Note: As molecular weight is calculated in practice by summing the atomic weights of the atoms making up the substances molecular formula. So, we have to write the correct atomic weight from the periodic table. The units of molecular weight is the ratio of the mass of a molecule to the unified atomic mass unit, which is also known as Dalton.