Molecular Weight Example

A Molecule It is a set of atoms joined by bonds. Molecular Weight, better named as Molecular mass, is the sum of all Atomic Masses of the atoms present in a molecule.

The data that must be known to calculate the molecular weight are only the Atomic Masses of the chemical elements. Generally, data are expressed in grams for each mole of substance (g / mol) in the International System of Measurement (SI).

Atomic Masses are universal data, provided by the International Union of Pure and Applied Chemistry (IUPAC). They can be easily obtained through the Periodic Table or Chemistry Books.

Molecular Weight serves to calculate amounts of chemicals that they love each other put to react with each other, to achieve that they interact stoichiometrically.

Examples of Molecular Weight

The Atomic Masses of the component atoms are listed first, expressed in "g / mol", the number of atoms of each element is counted, and at the end we proceed to the Total Sum.

1.- Molecular Weight of Water (H₂OR)

Count: 2 Hydrogen Atoms and 1 Oxygen Atom

Atomic Masses:

Hydrogen (H): 1 g / mol

Oxygen (O): 16 g / mol

Molecular weight = 2 * (1 g / mol) + (16 g / mol) = 18 g / mol

2.- Molecular Weight of Hydrochloric Acid (HCl)

Count: 1 Hydrogen Atom and 1 Chlorine Atom

Atomic Masses:

Hydrogen (H): 1 g / mol

Chlorine (Cl): 35.5 g / mol

Molecular weight = (1 g / mol) + (35.5 g / mol) = 36.5 g / mol

3.- Molecular Weight of Sulfuric Acid (H₂SW₄)

Count: 2 Hydrogen Atoms, 1 Sulfur Atom and 4 Oxygen Atoms

Atomic Masses:

Hydrogen (H): 1 g / mol

Sulfur (S): 32 g / mol

Oxygen (O): 16 g / mol

Molecular weight = 2 * (1 g / mol) + (32 g / mol) + 4 * (16 g / mol) = 98 g / mol

4.- Molecular Weight of Sodium Chloride (NaCl)

Count: 1 Sodium Atom and 1 Chlorine Atom

Atomic Masses:

Sodium (Na): 23 g / mol

Chlorine (Cl): 35.5 g / mol

Molecular weight = (23 g / mol) + (35.5 g / mol) = 58.5 g / mol

5.- Molecular Weight of Silver Nitrate (AgNO₃)

Count: 1 Silver Atom, 1 Nitrogen Atom and 3 Oxygen Atoms

Atomic Masses:

Silver (Ag): 107.87 g / mol

Nitrogen (N): 14 g / mol

Oxygen (O): 16 g / mol

Molecular weight = (107.87 g / mol) + (14 g / mol) + 3 * (16 g / mol) = 169.87 g / mol

6.- Molecular Weight of Potassium Permanganate (KMnO₄)

Count: 1 Potassium Atom, 1 Manganese Atom and 4 Oxygen Atoms

Atomic Masses:

Potassium (K): 39 g / mol

Manganese (Mn): 55 g / mol

Oxygen (O): 16 g / mol

Molecular weight = (39 g / mol) + (55 g / mol) + 4 * (16 g / mol) = 158 g / mol

7.- Molecular Weight of Sodium Hydroxide (NaOH)

Count: 1 Sodium Atom, 1 Oxygen Atom and 1 Hydrogen Atom

Atomic Masses:

Sodium (Na): 23 g / mol

Oxygen (O): 16 g / mol

Hydrogen (H): 1 g / mol

Molecular weight = (23 g / mol) + (16 g / mol) + (1 g / mol) = 40 g / mol

8.- Molecular Weight of Potassium Hydroxide (KOH)

Count: 1 Potassium Atom, 1 Oxygen Atom and 1 Hydrogen Atom

Atomic Masses:

Potassium (K): 39 g / mol

Oxygen (O): 16 g / mol

Hydrogen (H): 1 g / mol

Molecular weight = (39 g / mol) + (16 g / mol) + (1 g / mol) = 56 g / mol

9.- Molecular Weight of Methane (CH₄)

Count: 1 Carbon Atoms and 4 Hydrogen Atoms

Atomic Masses:

Carbon (C): 12 g / mol

Hydrogen (H): 1 g / mol

Molecular weight = (12 g / mol) + 4 * (1 g / mol) = 16 g / mol

10.- Molecular Weight of Ethane (C₂H₆)

Count: 2 Carbon Atoms and 6 Hydrogen Atoms

Atomic Masses:

Carbon (C): 12 g / mol

Hydrogen (H): 1 g / mol

Molecular weight = 2 * (12 g / mol) + 6 * (1 g / mol) = 30 g / mol

11.- Molecular Weight of Ammonia (NH₃)

Count: 1 Nitrogen Atom and 3 Hydrogen Atoms

Atomic Masses:

Nitrogen (N): 14 g / mol

Hydrogen (H): 1 g / mol

Molecular weight = (14 g / mol) + 3 * (1 g / mol) = 17 g / mol

12.- Molecular Weight of Hydrogen Peroxide (H₂OR₂)

Count: 2 Hydrogen Atoms and 2 Oxygen Atoms

Atomic Masses:

Hydrogen (H): 1 g / mol

Oxygen (O): 16 g / mol

Molecular weight = 2 * (1 g / mol) + 2 * (16 g / mol) = 34 g / mol