Molar Mass and Percent Composition: Molar mass is an important topic in chemistry that helps science enthusiasts understand how to measure the substance at the molecular level. The molar mass is also used to calculate the percent composition of an element. These two terms are explained here. Read the complete article for more information.
Molar Mass Definition
Molar mass is the mass of one mole of a given substance, typically expressed in grams per mole (g/mol). It is a fundamental concept in chemistry that helps relate the mass of a substance to the amount of particles it contains.
Unit of Molar Mass
The unit of molar mass is grams per mole (g/mol). This unit signifies the mass of one mole of a substance, which contains 6.022×1023 particles (Avogadro's number).
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Mole Definition
A mole is a unit of measurement for the amount of substance. One mole contains exactly 6.022×1023 particles, whether they are atoms, molecules, ions, or electrons. This number is known as Avogadro's number.
Formula for Molar Mass
The molar mass of a substance can be calculated using the formula:
Molar Mass=Mass of the substance (g)/Number of moles (mol)
Calculations of Molar Mass
To calculate the molar mass of a compound, sum the atomic masses of all the atoms present in the molecule. For example, for water (H₂O):
- Atomic mass of hydrogen (H) = 1 g/mol
- Atomic mass of oxygen (O) = 16 g/mol
- Molar mass of H₂O = 2×1 g/mol+16 g/mol=18 g/mol
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- Avogadro’s Number: Definition, Value, Meaning, Unit and Symbol
- Magnetic Field: Formula, Properties, and Applications
- Archimedes' Principle: Formula, Derivation, Applications and Examples
What is the Percentage Composition?
The percentage composition of a compound indicates the percentage by mass of each element in the compound. It can be calculated using the formula:
Percentage Composition=(Mass of the element in 1 mole of the compound/Molar mass of the compound)×100%
For example, in water (H₂O):
- Mass of hydrogen in 1 mole of H₂O = 2 g
- Mass of oxygen in 1 mole of H₂O = 16 g
- Molar mass of H₂O = 18 g/mol
Percentage composition of hydrogen:
(2/18)×100%=11.11%
Percentage composition of oxygen:
(16/18)×100%=88.89%
Difference Between Molar Mass and Percent Composition
To understand the key difference between molar mass and percentage composition read the table below:
| Aspect | Molar Mass | Percent Composition |
| Definition | The mass of one mole of a substance. | The percentage by mass of each element in a compound. |
| Unit | Grams per mole (g/mol). | Percentage (%). |
| Calculation Method | The sum of the atomic masses of all atoms in a molecule. | (Mass of the element in 1 mole of the compound/Molar mass of the compound)×100% |
| Purpose | To determine the mass of a substance for a given amount. | To identify the relative abundance of each element in a compound. |
| Relevance | Used in stoichiometric calculations in chemistry. | Used to determine the composition and purity of compounds. |
| Relationship | Directly related to the molecular formula of a substance. | Derived from the molar mass and individual atomic masses. |
Difference Between Molar Mass and Molecular Mass
To understand the key difference between molar mass and molecular mass read the table below:
| Molar Mass | Molecular Mass |
| ● The mass of one mole of a substance in grams per mole (g/mol). | ● The sum of the atomic masses of all atoms in a molecule, typically expressed in atomic mass units (amu). |
| ● It accounts for the number of particles in a substance. | ● It does not account for the number of particles. |
References and Further Reading
You can refer to the reference material in the links below for better preparation and understanding of scientific concepts.
- Books
NCERT Class 10 Science Textbook PDF
NCERT Class 12 Physics Textbook PDF
- Online Resources
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