Molecular Mass: An Introduction
Molecular mass is the mass of a given molecule. It is measured in Daltons. Molecular mass is most commonly used when referring to the mass of a single or specific well-defined molecule and less commonly than molecular weight when referring to a weighted average of a sample. The molecular mass of small to medium size molecules measured by mass spectrometry and it can be used to determine the composition of elements in the molecule or compound.
What is Molecular Mass?
Molecular mass is also called molecular weight. Molecular mass is the mass or weight of a molecule. Different molecules of the same compound may have different molecular masses because an element has different types of isotopes which are present in the compound. The related quantity of relative molecular mass is the ratio of the mass of a molecule to the united atomic mass. The molecular mass and relative molecular mass are distinct but related to molar mass. The molar mass is defined as the mass of a given substance divided by the number of moles of a substance. The unit of molar mass is g/mol.
How to Find Molecular Mass?
To find the molecular mass, find the atomic masses of each element by using a periodic table. Multiply the number of atoms with an element's atomic mass and add the masses of all elements in the molecule.
Formula of Molecular Mass/Molecular Mass Equation
The formula of molecular mass or molar mass is:
\[\text{molarmass} = \dfrac{{\text{mass}}}{{\text{number of moles}}}\]
How to Calculate Molecular Mass?
The total mass of a compound is called molecular mass or molecular weight. It is equal to the sum of the individual atomic masses of each element.
Molecular Mass Examples
There are some examples of molecular mass.
H2O: The atomic mass of hydrogen in the periodic table is 1u and the atomic mass of the oxygen atom is 18u. So, we can calculate the molecular mass of water molecules as follows:
\[{H_2}O = 2 \times 1 + 16 = 18u\]
Hence, the molecular mass of water molecules is 18u.
NH3: The atomic mass of Hydrogen in the periodic table is 1u and the atomic mass of nitrogen is 14u. So, we can calculate the molecular mass of ammonia molecule as follows:
\[N{H_3} = 3 \times 1 + 14 = 17u\]
Hence, the molecular mass of ammonia gas is 17u.
CaCO3: The atomic mass of calcium is 40u, the atomic mass of carbon is 12u, and the atomic mass of oxygen is 16u in the periodic table. So, we can calculate the molecular mass of calcium carbonate as follows:
\[CaC{O_3} = 40 + 12 + 3 \times 16 = 100u\]
Hence, the molecular mass of calcium carbonate is 100u.
CaCl2: The atomic mass of calcium is 40u and the atomic of chlorine is 35.45u in the periodic table. So, we can calculate the molecular mass of calcium chloride as follows:
\[CaC{l_2} = 40 + 2 \times 35.45 = 110.9u\]
Hence, the molecular mass of calcium chloride is 110.9u.
Molecular Mass of Compounds
The molecular mass of a compound can be found by using the following steps:
Determine the molecular formula of the compound.
Use the periodic table to determine the atomic mass of each element present in the compound.
Multiply each element’s atomic mass with the number of atoms that element in the compound. This number is denoted by the subscript next to the element symbol in the molecular formula.
Add these values together for each different atom.
The total value will be the molecular mass of the compound.
Molecular Mass of Elements
The molecular mass of an element is the sum of the atomic mass of atoms present in that element. Find the atomic mass of each element by using the given mass in the periodic table.
Interesting Facts
Molecular mass is defined as the sum of atomic masses of elements present in a molecule whereas molar mass is the ratio of the mass of the compound and the number of molecules present in the compound.
As the molecular weight increases, mechanical properties generally increase.
Key Features of Molecular Mass
The molecular weight of a polymer is directly related to its properties (strength, processability, brittleness).
Hydrogen has the smallest molecular mass.
Molecular mass is useful in analysing the results of experiments.
Molecular mass can be calculated by knowing the molecular formula.
FAQs on Molecular Mass
1. What is the molecular mass equivalent to?
Molecular mass is a number equivalent to a molecule’s amount of nuclear
masses.
2. What are the characteristics of polymers?
A polymer is a large molecule made up of chains or rings of linked repeating subunits, which are called monomers. Because the molecules consist of many monomers, polymers tend to have high molecular masses, and polymers usually have high melting and boiling points.
3. What is a compound composed of identical molecules?
Any substance composed of identical molecules consisting of atoms of two or more chemical elements is called a chemical compound. All the matter in the universe is made up of atoms of more than 100 different chemical elements, which are found both in pure form and combined in chemical compounds.
4. What is an organic compound made of?
An organic compound is a member of a class of chemicals containing carbon atoms bound to one another and to other atoms by covalent bonds and found in the cells of living organisms. Generally, organic compounds contain carbon, hydrogen, and oxygen atoms.
