How to find Molar Mass?
Introduction to Molar Mass
What is Molar Mass?
Why is Molar Mass Important?
The Basic Formula for Molar Mass
The concept of moles
Before diving into the molar mass formula let us come back to the concept of moles. A mole of any substance contains the same number of entities (atoms, molecules, ions, etc.), about 6.022 × 10²³. This number is called Avogadro's number. So when we talk about a mole of water we are mentioning to 6.022 × 10²³ water molecules and it weighs 18.015 grams.
Formula for Molar Mass
Molar Mass = Sum of Atomic Masses of All Elements in the
Formula
Step-by-Step Guide to Finding Molar Mass
Now let us look at how to find molar mass for any substance
step by step. It is easier than you think!
Step 1: Identify the Chemical Formula
The first step is identifying the chemical formula of the
substance. For example, if you are trying to find the molar mass of water the
formula is H₂O. Make sure you have the correct formula for the compound you are
working with.
Step 2: Find the Atomic Weights
Each element has an atomic weight typically found on the
periodic table. For example:
- The atomic weight of Hydrogen (H) is about 1.008 g/mol.
- The atomic weight of Oxygen (O) is about 16.00 g/mol.
Step 3: Multiply and Add
Now multiply the atomic weight of each element by the number
of times that element appears in the formula. Then add them up. Let us go
through a couple of examples.
Example 1: Molar Mass of Water (H₂O)
Water’s formula is H₂O, meaning it contains 2 hydrogen atoms
and 1 oxygen atom.
- Atomic weight of Hydrogen = 1.008 g/mol
- Atomic weight of Oxygen = 16.00 g/mol
Now multiply and add:
Molar\ Mass = (2 \times 1.008) + (1 \times 16.00) = 2.016 +
16.00 = 18.016\ g/mol
So the molar mass of water is 18.016 g/mol.
Example 2: Molar Mass of Carbon Dioxide (CO₂)
The formula for carbon dioxide is CO₂, meaning it contains 1
carbon atom and 2 oxygen atoms.
- Atomic weight of Carbon = 12.011 g/mol
- Atomic weight of Oxygen = 16.00 g/mol
Now, multiply and add:
Molar\ Mass = (1 \times 12.011) + (2 \times 16.00) = 12.011
+ 32.00 = 44.011\ g/mol
So the molar mass of carbon dioxide is 44.011 g/mol.
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