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 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 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.
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