Molecular Mass



  • Periodic Table, Periodic Properties and Variations of Properties
  • Chemical Bonding
    • Chemical Bond
    • Types of Chemical Bond
    • Electrovalent (or Ionic) Bond
    • Formation of an Electrovalent (or Ionic) Bond
    • The Covalent Bond
    • Types of Covalent Bond
    • Formation of Covalent Bond
    • Properties and Comparison of Electrovalent and Covalent Compounds
    • Effect of Electricity on Electrovalent and Covalent Compounds
    • Coordinate Bond
    • Formation of Coordinate Bond
  • Study of Acids, Bases and Salts
  • Analytical Chemistry
    • Analytical Chemistry
    • Colours of the Salts and Their Solutions
    • Action of Sodium Hydroxide Solution on Certain Metallic Salt Solutions
    • Action of Ammonium Hydroxide on Certain Salt Solutions
    • Action of Alkalis on Certain Metals
    • Action of Alkalis on Metal Oxides
  • Mole Concept and Stoichiometry
    • The Gas Laws
    • Fundamental Laws of Gases
    • Pressure and Volume Relationship or Bolye's Law
    • Temperature - Volume Relationship or Charles's Law
    • Gay Lussac’s Law of Combining Volumes
    • Avogadro’s Law
    • Gas Equation
    • Standard Temperature Pressure (S.T.P.)
    • Absolute Zero
    • Atomic Mass
    • Molecular Mass
    • Mole Concept
    • Relationship Between Vapour Density and Relative Molecular Mass
    • Percentage Composition, Empirical and Molecular Formula
    • Empirical Formula of a Compound
    • Determination of Empirical Formula
    • Determination of Molecular Formula
    • Chemical Equation
    • Balancing Chemical Equation
    • Numerical Problems of Chemical Equation
  • Electrolysis
    • Electrolysis
    • Electrolytes
    • Nonelectrolyte
    • Electrochemical Cells
    • Electrodes
    • Oxidation, Reduction and Redox Reactions
    • Arrhenius Theory of Electrolytic Dissociation
    • Electrochemical Series
    • Preferential Or Selective Discharge of Ions at Electrodes
    • Examples of Electrolysis
    • Electrolysis of Molten Lead Bromid
    • Electrolysis of Acidified Water Using Platinum Electrodes
    • Electrolysis of Copper Sulphate Solution Using Platinum Anode and Copper Or Platinum Cathode
    • Electrolysis of Aqueous Copper Sulphate - Using Copper Electrodes
    • Applications of Electrolysis
  • Metallurgy
  • Study of Compounds
  • Hydrogen Chloride
    • Hydrogen Chloride
    • General Preparation of Hydrogen Chloride Gas
    • Laboratory Preparation of Hydrogen Chloride Gas
    • Physical Properties of Hydrogen Chloride Gas
    • Chemical Properties of Hydrogen Chloride Gas
    • Hydrochloric Acid
    • Laboratory Method of Preparation of Hydrochloric Acid
    • Properties of Hydrochloric Acid
    • Uses of Hydrochloric Acid
    • Tests for Hydrogen Chloride and Hydrochloric Acid
  • Ammonia
    • Ammonia
    • General Methods of Preparation of Ammonia Gas
    • Laboratory Preparation of Ammonia Gas
    • Preparation of Aqueous Ammonia
    • Manufacture of Ammonia (Haber's Process)
    • Physical Properties of Ammonia
    • Chemical Properties of Ammonia
    • Tests for Ammonia Gas and Ammonium Ion
    • Uses of Ammonia
  • Nitric Acid
    • Nitric Acid
    • Laboratory Preparation of Nitric Acid
    • Manufacture of Nitric Acid
    • Physical Properties of Nitric Acid
    • Chemical Properties of Nitric Acid
    • Uses of Nitric Acid
    • Tests for Nitric Acid and Nitrates
    • Effects of Heat on Nitrates
  • Sulphuric Acid
    • Sulphuric Acid
    • Preparation of Sulphuric Acid
    • Manufacture of Sulphuric Acid (Constant Process)
    • Physical Properties of Sulphuric Acid
    • Chemical Properties of Sulphuric Acid
    • Uses of Sulphuric Acid
    • Tests for Sulphuric Acid and Sulphates
  • Organic Chemistry
    • Carbon: a Versatile Element
    • Classification of Compounds of Carbon
    • Organic Compounds
    • Special Features of Carbon
    • Organic Compounds in Daily Life
    • Hydrocarbons
    • Classification of Organic Compounds Based on the Pattern of Carbon Chain
    • Classification of Organic Compound Based on the Kind of Atoms
    • Homologous Series of Carbon Compound
    • Nomenclature of Organic Compounds (IUPAC)
    • IUPAC Nomenclature of Hydrocarbons
    • IUPAC Nomenclature of other classes
    • Alkyl Group
    • Functional Groups in Carbon Compounds
    • Isomers
    • Hydrocarbons: Alkanes
    • Methane
    • Laboratory Preparation of Methane
    • Ethane
    • Laboratory Preparation of Ethane
    • Hydrocarbons: Alkenes
    • Ethene (Ethylene)
    • Preparation of Ethene (Ethylene)
    • Hydrocarbons: Alkynes
    • Ethyne
    • Laboratory Preparation of Ethyne
    • Alcohol
    • Ethanol
    • Laboratory Preparation of Ethanol
    • Carboxylic Acids
    • Ethanoic Acid
  • Practical Work
    • Laboratory Preparation of Hydrogen
    • Laboratory Preparation of Oxygen
    • Laboratory Preparation of Carbon Dioxide
    • Laboratory Preparation of Chlorine
    • Laboratory Preparation of Hydrogen Chloride Gas
    • Laboratory Preparation of Sulphur Dioxide
    • Laboratory Preparation of Hydrogen Sulphide
    • Laboratory Preparation of Ammonia Gas
    • Laboratory Preparation of Water Vapour
    • Laboratory Preparation of Nitrogen Dioxide
    • Action of Heat on a Given Substance
    • Action of Dilute Sulphuric Acid on a Given Substance
    • Dry Test
    • Recognition of Substances by Colour
    • Recognition of Substances by Odour
    • Recognition of Substances by Physical State
    • Recognition of Substances by Action of Heat
    • Flame Test
    • Strength of Acidic or Basic Solutions
    • Indicators
    • Identification of Ions
    • Identification of Cations
    • Identification of Anions
    • Distinction Between Colourless Solutions of Dilute Acids and Alkalis
    • Distinguish Between Black Copper Oxide and Black Manganese Dioxide
  • Molecular mass
  • Characteristics of molecular mass
  • Gram molecular mass


This concept can be extended to calculate molecular masses. The molecular mass of a substance is the sum of the atomic masses of all the atoms in a molecule of the substance. It is, therefore, the relative mass of a molecule expressed in atomic mass units (u)

Example : 

(a) Calculate the relative molecular mass of water (H2O).
(b) Calculate the molecular mass of HNO3.


(a) Atomic mass of hydrogen = 1u, oxygen = 16 u
So the molecular mass of water, which
contains two atoms of hydrogen and one
atom of oxygen is = 2 × 1+ 1×16
= 18 u
(b) The molecular mass of HNO3 = the
atomic mass of H + the atomic mass of
N+ 3 × the atomic mass of O
= 1 + 14 + 48 = 63 u

Formula unit mass of a substance

The formula unit mass of a substance is the sum of the atomic masses of all atoms in a formula unit of a compound. Formula unit mass is calculated in the same manner as we calculate the molecular mass. The only difference is that we use the word formula unit for those substances whose constituent particles are ions. For example, as discussed above, sodium chloride has a formula unit NaCl. Its formula unit mass can be calculated as–

1 × 23 + 1 × 35.5 = 58.5 u 

Example: Calculate the formula unit
mass of CaCl2.
Atomic mass of Ca
+ (2 × atomic mass of Cl)
= 40 + 2 × 35.5 = 40 + 71 = 111 u

Molecular mass:

The molecular mass of a substance is the sum of the atomic masses of all the atoms in a single molecule of that substance.

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Molecular Mass and formula Unit mass [00:10:51]
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