The molecular weight of Nitric acid (HNO_{3}) is 63.012.

To calculate molecular weight of any compound, the first step is to know the constituent elements (atoms) and their number in that particular compound. Then calculate the total atomic weight of each element by multiplying its atomic weight by its number. The sum of total atomic weight of all constituent elements will be the molecular weight of the compound. Note that the value of atomic weight may differ from different sources. This is because some sources use conventional atomic weight while others use standard atomic weights. Another important point to consider is the isotopes of an element. Different isotopes of an element will have different atomic weights.

**CALCULATION PROCEDURE**

**Step 1: Find out the chemical formula and determine constituent atoms and their number in a Nitric acid molecule. **From the chemical formula, you will know different atoms and their number in a Nitric acid molecule. Chemical formula of Nitric acid is HNO

_{3}. From the chemical formula of Nitric acid, it is easy to find out that there are one Hydrogen (H) atom, one Nitrogen (N) atom and three Oxygen (O) atoms in a molecule of Potassium hydroxide.

**Step 2: Find out atomic weights of each atom (from periodic table). **Atomic weight of Hydrogen (H) : 1.008 (Ref: Pubchem-Hydrogen)

Atomic weight of Nitrogen (N): 14.007 (Ref: Pubchem-Nitrogen)

Atomic weight of Oxygen (O) : 15.999 (Ref: Pubchem-Oxygen)

**Step 3: Calculate the total weight of each atom present in Nitric acid by multiplying its atomic weight by its number. **

Number of Hydrogen atoms in Nitric acid: 1

Atomic weight of Hydrogen: 1.008

Total weight of Hydrogen atoms in Nitric acid: 1.008 x 1 = 1.008

Number of Nitrogen atoms in Nitric acid: 1

Atomic weight of Nitrogen: 14.007

Total weight of Nitrogen atoms in Nitric acid: 14.007 x 1 = 14.007

Number of Oxygen atoms in Nitric acid: 3

Atomic weight of Oxygen: 15.999

Total weight of oxygen atoms in Nitric acid: 15.999 x 3 = 47.997

**Step 4: Calculate the molecular weight of Nitric acid by adding up the total weight of all atoms. **

Molecular weight of Nitric acid (HNO_{3}):

1.008 (1.008 x 1 Hydrogen) + 14.007 (14.007 x 1 Nitrogen) + 47.997 (15.999 x 3 Oxygen)

So the molecular weight of Nitric Acid is 63.012.

Molecular weight of Nitric acid (KOH) | |||

Atoms (elements) in Nitric acid | Number of each atom in Nitric acid | Atomic weight of each atom | Total weight of each atom in Nitric acid |

H (Hydrogen) | 1 | 1.008 | 1.008 (1.008 x 1) |

N (Nitrogen) | 1 | 14.007 | 14.007 (14.007 x 1) |

O (Oxygen) | 1 | 47.997 | 15.999 (15.999 x 3) |

Molecular weight of Potassium hydroxide (KOH): | 56.1053 |