Molar Mass: Formula, Molar Mass Unit & Percentage

Molar mass, in chemistry, is defined as the mass of a sample divided by the amount of substance in the sample, measured in moles.

• The term mole refers to the atomic mass of a molecule measured in grams. Atomic mass is the mass of a single atom and molecular mass is the mass of a group of atoms.
• The mole concept summarizes the mass of a single atom or molecule into a unit. ‘U’ refers to the mass of a large group of comparable molecules in grams.
• The number of units in a mole is the amount of a substance that is exactly 6.02214076 × 10²³ (a fundamental constant known as Avogadro's number or Avogadro's constant)" Elemental Units" of this substance.
• For individual elements or individual atoms, the molar mass is simply the mass of the element expressed in atomic mass units.
• The atomic mass and the molar mass of a single atom are exactly the same.
• Since the molar mass and the atomic mass are identical for individual atoms, the molar mass can be used to measure the identity of a particle

Read Also: Atoms & Molecules

Key Terms: Molar Mass, Relative Molecular Mass, Molecular Weight, Avogadro Constant, Percentage Of Composition

Read Also: Atomic And Molecular Masses

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What is Mole?

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A mole can be defined in chemistry as: 

•  The word "mole" was introduced around 1896 by the German chemist Wilhelm Ostwald, The term derived from the Latin word moles, meaning "heap" or "heap". 
•  The number of moles of a molecule cannot always be equal to the number of moles of its constituents. 
•  For example, one mole of water contains Na the number of molecules of H₂O. However, each water molecule contains 2 hydrogen atoms and one oxygen atom. Therefore, one mole of H₂O contains 2 moles of hydrogen and one mole of oxygen.

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What is Molar Mass?

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The "mass per mole" can be used to describe the molar mass. In other words, the molar mass is the sum of the masses of all the atoms of a substance, expressed in moles. It is expressed in the unit grams per mole.

• Elements and molecules are represented by their molar mass. For individual elements or atoms, the molar mass is simply the mass of the element, expressed in atomic mass units.
• For example, the atomic mass of helium is 4. Since it has only one atom and is monatomic in nature, helium has a molar mass of 4.
• The molar concept facilitates the macroscopic representation of quantitative information about the processes occurring in a chemical equation.
• In the chemical reaction 2H₂O = O₂ + 2H₂, two moles of water are broken down into two moles of molecular hydrogen and one mole of molecular oxygen.
• The mole can be used to determine the simplest formula of a compound and the amounts required for chemical reactions. 
• The related concept of molarity is useful when dealing with reactions that occur in solutions.
• The number of moles of a solute in a liter of solution is called its molarity (M).

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Molar Mass Formula 

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To make measurements of mass useful we must express chemical quantities at the macroscopic level. 

The bridge between the particulate and the macroscopic levels is molar mass, the mass in grams of one mole of a substance. the units of molar mass follow its definition; grams per mole. Mathematically, the defining equation of molar mass is:

The definition of atomic mass, the mole, and molar mass are all directly or indirectly related to carbon-12. Thus,

• The mass of one atom of carbon-12 atomic mass of carbon-12 is exactly 12 atomic mass units.
• The molar mass or molecular weight which is the sum of the total mass in grams of all the atoms that make up a mole of a molecule. 

Units of Molar Mass

The unit of molar is as follows:

And The S.I. Unit For Mole Is Kg·mol^-1.

There Are Some Formulas For Understanding Mole Concept :

•  Mass Of 1 Mole Of Atoms = Ar In Grams
•  Number Of Moles Of Atoms = Mass Of The Element In Grams/ Relative Atomic Mass, Ar
•  Mass Of 1 Mole Of Molecules = Mr In Grams
•  Number Of Moles Of Molecules =. Mass Of The Substance In Grams/ Relative Molecular Mass (Mr)
•  Mass Of Substance Containing 1 Mole Of Particles - Molar Mass 
•  Percentage Yield: Actual Mass Of Product Obtained /Theoretical Mass Of Product Obtainable

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Percentage Of Composition

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The relative amounts of each element in a compound are shown by the percentage composition. Divide the mass of the entity present in the substance by the substance's total mass to determine the percentage of composition.

%C_E = \(\frac{g^E}{g^T}\) x 100

In this case, 

• %C_e denotes the compositional percentage of element E. 
• G_e denotes the total amount of element E in the compound. 
• G_t denotes the total amount of all the elements present in the compound.

To show the ratio in percentage terms, it is multiplied by 100.

Read Also: Measurement Of Mass And Weight

Calculation Of Molar Mass 

The molar mass of a compound is calculated by adding the quality atomic masses (in g/mol) of the constituent atoms. Suppose the mass of gold is 196.96 amu or 196.96 g/mol. In 196.96 grams of gold, there’s one mole or 6.022 x 10²³ gold atoms.

Read Also: Difference Between Element And Compound

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Things To Remember 

• Molar mass is the mass of a given substance divided by the quantity of the particular substance.
• Molar Mass Formula is given as Molar Mass = Mass Of Given Substance / Amount Of Substance.
• The S.I. Unit For Molar Mass is Kg/Mol.
• The number .6.02214076 × 10²³ mol^-1 is popularly known as the avogadro constant.
• The atomic mass of an element is the mass of one atom of the element expressed in atomic mass units (amu).

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