GFG App
Open App
Browser
Continue

# Molar Mass

Molar Mass is defined as the mass in grams of one mole of the given compound. A mole is a unit to measure the quantity of any substance. Any substance or compound that contains the Na amount of entities, i.e., atoms, molecules, ions, is known as a mole, where Na is called the Avogadros Number and the value of Na is 6.023 × 1023

The molar mass is also known as the sum of the total mass (in grams) of all the atoms present in a molecule per mole of the substance. It is calculated by finding the sum of all the individual elements of the molecule and taking its unit gram. Molecular mass is measured in grams and sometimes in kilograms.

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. The unit of molar mass is grams/mol. 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. It is also represented using Avogadro’s Number, (represented as NA). The value of Avogadro’s Number (NA) is 6.023 × 1023

## 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. The following formula may be used to calculate molar mass is,

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

The number of atoms present in 12 grams of C-12 isotope is the number of particles present in 1 mole of the substance. One mole of any substance contains the same amount of units i.e. 6.023 × 1023 units. Therefore, for convenient 6.023 × 1023 is named Avogadro’s Number (NA).

## 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. In order to make the measurement of masses more useful and easier, quantities are to be represented on a macroscopic level. The bridge between the substance and the macroscopic level is molar mass. Molar mass is important in the mole concept. The formula of molar mass is grams per mole. The formula is written as:

Molar mass = mass/mole = g/mol

Units of Molar Mass: SI unit is kg/ mol or gm/mol.

Below are some of the important formulas regarding molar mass:

## How is Molar Mass Calculated?

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 Masses 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.

For example, the molar mass of Methane CH4 is calculated as,

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 Water

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 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 H2SO4

The chemical formula of Sodium Carbonate 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 the Percentage of Composition?

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,

## 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.

Example 4: Find the molar mass of Potassium Permanganate (KMnO4).

Solution:

The chemical formula of Potassium Permanganate is KMnO4. It contains 1 Potassium Atom, 1 Manganese Atom and 4 Oxygen Atoms. We know that the molecular weight of Potassium (K) is 39.098 g/mol, Manganese (Mn) is 54.937 g/mol and Oxygen (O) is 16 g/mol. Therefore, the molar mass of Potassium Permanganate is,

• K = 1 × 39.098 = 38.098 g/mol.
• Mn = 1 × 54.938 = 54.938 g/mol.
• O = 4 × 16 = 64 g/mol.

Molecular Weight of KMnO4 = 39.098 + 54.938 + 64

= 158.036 g/mol.

Therefore, the molar mass of KMnO4 is 158.036 g/mol.

Example 5: Find the molar mass of Magnesium Chloride(MgCl2).

Solution:

The chemical formula of Magnesium Chloride is MgCl2. It contains one Magnesium atom, one chlorine atom. We know that the molecular weight of Magnesium (Mg) is 24.305 g/mol, Chlorine (Cl) is 35.453 g/mol. Therefore, the molar mass of Magnesium Chloride is

• Mg = 1 × 24.305 = 24.305 g/mol
• Cl = 2 × 35.453= 70.906 g/mol

Molecular Weight of MgCl = 24.305 + 70.906
= 95.211 g/mol

Therefore, the molar mass of Magnesium Chloride is 95.211 g/mol.

## FAQs on Molar Mass

### Q1: 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.

### Q2: 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.

### Q3: Why Avogadro’s number is 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.