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Molar Mass

Last Updated : 18 Apr, 2024
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Molar Mass is defined as the mass in grams of one mole of the given compound. It is also called Molecular Weight.

Let’s learn about molar mass in more detail.

What is Molar Mass?

Molar mass is the mass of one mole of the compound in grams. It is also defined as “mass per mole”. Molar mass is the sum of the mass of atoms in 1 mole of a substance.

Mole is the unit used as a standard value in chemistry, and the standard value of 1 mole of any substance (atoms, molecules, etc.) is 6.023 × 1023 units.

Molar Mass Unit

The standard unit of molar mass is grams per mole. The molar mass unit is represented as grams/mol. The SI unit of molar mass is kg mol-1.

Mole Definition

Mole, also written as mol, is the fundamental unit used to measure the amount of substance. A mole is defined as the amount of substance containing the same number of different entities (such as atoms, ions, molecules, and compounds) as the number of atoms in a sample of pure 12C weighing precisely 12 g.

Even a gram of any pure element contains a high amount of atoms. One mole is also defined as the amount of a substance that contains as many entities as there are atoms in exactly 12 g of the 12C isotope. 

Molar Mass Formula

We can calculate the mass of atoms, molecules, etc. However, it becomes difficult to calculate the mass of each particle present in the substance.

The following formula is used to calculate molar mass :

Molar Mass of Substance = (Mass of Substance in grams)/(Number of Moles of Substance) = g/mol

Below are some of the important formulas regarding molar mass:

Formulas Related to Molar Mass

Number of Moles of Atom (Mass of Element in Gram)/(Relative Atomic Mass)
Number of Moles of Molecules (Mass of Substance in Gram)/(Relative Molecular Mass)
Percentage Yield (Actual mass of Product)/(Theoretical Mass of Product)
Percentage of Composition (Mass of Entity present in Substance)/(Total Mass of Substance)
Mole fraction formula (Number of Moles of Component in Mixture)/(Total Number of Moles in Component)

Learn More :

How To Calculate Molar Mass

The French physicist Jean Baptiste introduced “Avogadro’s number”. Avogadro’s number is present in 1 mole of a substance. The substance can be atoms, molecules, etc.

1 mol = 6.023 × 1023 units

Molar Mass of Compounds

The molar mass of the compound is the total molar mass of all the atoms present in the compound. It is calculated by taking the individual molar mass of each atom of the compound and adding all of them. 

Molar Mass of CH4

It is clear from the chemical formula of methane that it has 1 carbon atom and 4 hydrogen atoms.

Thus, the molar mass of Methane is calculated as,

Mass of 4 hydrogen atoms = 4 × Mass of 1 Hydrogen atom = 4 × 1 = 4 amu

Mass of 1 carbon atom = 1 × Mass of 1 Carbon atom = 1 × 12 = 12 amu

Molar mass of Methane = 4 + 12 = 16 amu

Now, let’s take a look at some more examples to understand to find the molar mass of molecules,

Molar Mass of H2O

The molar mass of water is the total sum of atomic masses of the atoms, and water (H2O) contains 2 atoms of hydrogen and 1 atom of oxygen. The atomic mass of hydrogen is 1 amu and the atomic mass of oxygen is approximately 16 amu. Therefore, the molar mass of water becomes 18 g/mol.

Molar mass of H2O

Molar Mass of CO2

The molar mass of CO2 is the total sum of atomic masses of the atoms, and CO2 contains 2 atoms of oxygen and 1 atom of carbon. The atomic mass of carbon is 12 amu and the atomic mass of oxygen is approximately 16 amu. Therefore, the molar mass of CO2 becomes 44 g/mol.

Molar Mass of CO2

Molar mass of H2SO4

The chemical formula of Sulfuric Acid is H2SO4. It contains two hydrogen atoms, one sulfur atom and four oxygen atoms. We know that the molecular weight of Hydrogen (H) is 1.0078 g/mol, Sulfur (S) is 32.065 g/mol, and Oxygen (O) is 16 g/mol. Therefore, the molar mass of sodium carbonate is,

  • H = 2 × 1.0078 = 2.0156 g/mol.
  • S = 1 × 32.065 = 32.065 g/mol.
  • O = 4 × 16 = 64 g/mol.

By adding all we get = 2.0156 + 32.065 + 64 = 98.081 g/mol. Therefore, the molar mass of H2SO4 is 98.081 g/mol.

Molar mass of NaOH

The chemical formula of Sodium Hydroxide is NaOH. It has one hydrogen atom, one oxygen atom, and one Sodium atom. We know that the molecular weight of Hydrogen (H) is 1 g/mol, Oxygen (O) is 16 g/mol and Sodium (Na) is 23 g/mol.

Therefore, the molar mass of sodium hydroxide is,

  • Na = 1 × 23 = 23 g/mol
  • O = 1 × 16 = 16 g/mol
  • H = 1 × 1 = 1 g/mol

By adding all we get = 23 + 16 + 1 = 40 g/mol. Therefore, the molar mass of NaOH is 40 g/mol.

Molar mass of NaCl

The chemical formula of Sodium Chloride is NaCl. It has one Sodium atom and one Chlorine atom. We know that the molecular weight of Sodium (Na) is 23 g/mol and Chlorine (Cl) is 35.5 g/mol.

Therefore, the molar mass of sodium chloride is,

  • Na = 1 × 23 = 23 g/mol
  • Cl = 1 × 35.5 = 35.5 g/mol

By adding all we get = 23 + 35.5 = 58.5 g/mol. Therefore, the molar mass of NaCl is 58.5 g/mol.

Molar mass of Urea

The chemical formula of Urea is NH2CONH2. It has two Nitrogen atoms, four Hydrogen atoms, one Carbon atom, and one Nitrogen atom. We know that the molecular weight of Nitrogen (N) is 14 g/mol, Hydrogen (H) is 1 g/mol, Carbon (C) is 12 g/mol, and Oxygen (O) is 16 g/mol.

Therefore, the molar mass of Urea is,

  • N = 2 × 14 = 28 g/mol
  • H = 4 × 1 = 4 g/mol
  • C = 1 × 12 = 12 g/mol
  • O = 1 × 16 = 16 g/mol

By adding all we get = 28 + 4 + 12 + 16 = 60 g/mol. Therefore, the molar mass of Urea is 60 g/mol.

What is Percentage of Composition?

Percentage of Composition refers to the proportion or distribution of different components within a mixture or a compound. It is used to express the relative amount or concentration of each component as a percentage of the total.

The percentage of composition of any compound is calculated by following the steps given below,

Step 1: Find the molar mass of the substance (atom) for which we have to find the percentage composition.

Step 2: Find the molar mass of the given substance.

Step 3: Calculate the percentage of the composition by using the formula,

Percentage = (Mass of Substance / Mass of Compound) × 100

Example: Find the mass percentage of hydrogen in a water molecule.

Solution:

Chemical Formula of Water = H2O

Thus, water has 2 hydrogen atoms and 1 oxygen atom

Mass of 2 hydrogen atoms in 1 mole of water = 2 × Mass of Hydrogen atom = 2 × 1 = 2 g

Mass of 1 mole of water molecule = 2 × Mass of Hydrogen atom + 1 × Mass of Oxygen atom

                                                       = 2 × 1 + 1 × 16 = 18 g

Mass Percentage of Hydrogen in Water = 2 / 18 × 100 = 11.11 %

Molar Mass of Various Compounds

The molar mass of some compounds is discussed in the following table,

Compounds

Chemical Formula

Molar Mass

Urea CH4N2O 60.06 g/mol
Sulphur S 32.065 g/mol
Oxygen O 15.99 g/mol
Oxalic Acid C2H2O4 90.03 g/mol
Aluminium Al 26.981 g/mol
Carbon C 12.011 g/mol
Hydrogen H 1.007 g/mol
Sodium Na 22.989 g/mol
Calcium Ca 40.078 g/mol
Copper Cu 63.546 g/mol
Iron Fe 55.845 g/mol
Helium He 4.002 g/mol
Iodine I 126.904 g/mol
Oxygen Gas (O2) O2 15.999 g/mol
Chlorine Cl 35.453 g/mol
Hydrogen Gas (H2) H2 2.016 g/mol
Phosphorus P 30.973 g/mol
Benzene C6H6 78.11 g/mol
Methane CH4 16.04 g/mol
Sodium Carbonate Na2CO3 105.988 g/mol
Acetic Acid CH3COOH 60.052 g/mol
Calcium Carbonate CaCO3 100.086 g/mol
Ethanol C2H5OH 46.07 g/mol
Sucrose C12H22O11 342.3 g/mol

Related :

Solved Examples on Molar Mass

Example 1: Find the molar mass of Sodium Carbonate(Na2CO3).

Solution: 

The chemical formula of Sodium Carbonate is Na2CO3. It contains two sodium atoms, one carbon atom and three oxygen atoms. We know that the molecular weight of Sodium (Na) is 22.98g/mol, Carbon (C) is 12.011 g/mol and Oxygen (O) is 16 g/mol. Therefore, the molar mass of sodium carbonate is

  • Na = 2 × 22.98 = 45.96 g/mol
  • C = 1 × 12.011 = 12.011 g/mol
  • O = 3 × 16 = 48 g/mol

Molecular Weight of Na2CO3 = 45.96 + 12.011 + 48 
                                              = 105.971 amu

Therefore, the molar mass of Na2CO3 is 105.971 g/mol.

Example 2: Find the molar mass of hydrochloric Acid (HCl).

Solution:

The chemical formula of Hydrochloric acid is HCl. It contains one Hydrogen atom, one chlorine atom. We know that the molecular weight of Hydrogen (H) is 1.0078g/mol, Chlorine (Cl) is 35.453 g/mol. Therefore, the molar mass of hydrochloric acid is

  • H = 1 × 1.0078 = 1.0078 g/mol
  • Cl = 1 × 35.453 = 35.453g/mol

Molecular Weight of HCl = 1.0078 + 35.543 
                                        = 36.460 g/mol

Therefore, the molar mass of HCl is 36.460 g/mol.

Example 3: Find the molar mass of Glucose (C6H11O6).

Solution:

The chemical formula of Glucose is C6H11O6. It contains six carbon atoms, eleven hydrogen atoms and six oxygen atoms. We know that the molecular weight of Carbon (C) is 12.011 g/mol, Hydrogen (H) is 1.0078 g/mol and Oxygen (O) is 16 g/mol. Therefore, the molar mass of glucose is,

  • C = 6 × 12.011 = 72.066 g/mol.
  • H = 12 × 1.0078 = 12.094 g/mol.
  • O = 6 × 16 = 96 g/mol.

Molecular Weight of C6H11O6 = 72.066 + 12.094 + 96
                                               = 180.16 g/mol. 

Therefore, the molar mass of Glucose is 180.16 g/mol.

FAQs on Molar Mass

What is Molar Mass?

The molar mass of the compound is defined as the mass of one mole of a compound measured in grams. It is calculated in g/mol. 

Are Molar Mass and Molecular Mass the same?

No, molar mass and molecular mass are not the same. Molar mass is the mass of one mole of the substance, which is measured in grams and molecular mass is the mass of one molecule and is measured in AMU.

Why is Avogadro’s Number called a Mole?

The mole (mol) is a unit that is equal to Avogadro’s number. The word ‘mole’ has come from the word molecule. 1 mole of any substance is equal to 6.023 × 1023 units, which is the Avogadro’s number. For example, 1 mole of water molecule contains 6.023 × 1023 molecules.

What is Avogadro’s Law?

Avogadro’s law or the theory of Avogadro is an experimental law which is related to the volume of gas w.r.t the amount of gas. Avogadro’s law states “equal quantities of all gases have same number of molecules at the same temperature and pressure”.

What is One Mole Equal To?

One mole is the collection of 6.0221367 × 1023 units of a substance. Here, the substance is atoms, molecules, or ions.

What is Molar Mass of Fluorine?

The molar mass of fluorine (F₂), which is the diatomic form of the element, is approximately 38.00 grams per mole (g/mol).

What is Molar Mass of Benzene?

Molar mass of Benzene is approximately 72.06 grams per mole (g/mol)



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