Why formula mass and molecular mass separated differently while process of calculation is the same?
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Answer:
For covalent substances, the formula represents the numbers and types of atoms composing a single molecule of the substance; therefore, the formula mass may be correctly referred to as a molecular mass. Consider chloroform (CHCl3), a covalent compound once used as a surgical anesthetic and now primarily used in the production of tetrafluoroethylene, the building block for the “anti-stick” polymer, Teflon. The molecular formula of chloroform indicates that a single molecule contains one carbon atom, one hydrogen atom, and three chlorine atoms. The average molecular mass of a chloroform molecule is therefore equal to the sum of the average atomic masses of these atoms. Figure 3.1.1 outlines the calculations used to derive the molecular mass of chloroform, which is 119.37 amu.
Molecular mass is the sum of the atomic masses of the atoms in a molecule means it gives the mass of a molecule. Molecular mass is also known as molecular weight and it gives the mass of a molecule relative to that of a carbon twelve atoms which have a mass of twelve units.
The Formula mass of a substance is the sum of atomic masses of constituents atoms in an ionic compound or we can say that the sum of atomic masses of the ions present in the formula unit of an ionic compound.
Molecular mass and formula mass are somewhat the same terms but we use them differently because molecules are actually covalent compounds means they have only non-metals and an ionic compound cannot be a molecule therefore we just simply say formula mass when we are taking ionic compounds.