Question

difference between molecular mass formula ,unit mass, atomic mass and molar mass with 3 examples each

Answer 1

Let’s take oxygen, O2, for an example. Examples shall make it easier to understand.

We will use u, kg and g as the units of mass.
The full form of u is Unified atomic mass unit. Commonly people use amu (atomic mass unit) or Da (dalton) as well.
kg is kilogram and g is gram.

1 u = mass of one nucleon (proton/neutron; the constituents of the atomic nucleus).

1 u = 1.66 ×10^−27 kg.

Atomic Mass: An oxygen molecule is constituted of two oxygen atoms. O2 is basically ::O=O::
Atomic mass is the mass of one atom.
The mass of one oxygen atom is (15.9994 ± 0.0004) u or roughly 16 u.
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Molecular Mass: Mass of one molecule of oxygen i.e. of one ‘O2′ molecule (the whole ::O=O:: entity).
So the mass of one molecule of oxygen will be 2 x 16 u = 32 u.
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Molar mass: The mass of one mole of oxygen.
1 mole of oxygen = 6.022 × 10^23 number of oxygen molecules.

Let us try to calculate and see how it goes.

1 molecule of O2 weighs 32 u = 32 x 1.66 ×10^−27 kg
1 mole of oxygen = 6.022 × 10^23 number of oxygen molecules
So 1 mole of oxygen weighs 32 x 1.66 ×10^−27 x 6.022 × 10^23 kg = 0.031988864 kg = 31.988 g = approximately 32 g.
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Note: 1 mole of oxygen consists of a large number of molecules, hence we switched to a bigger unit (from u to g) for convenience.
I hope you get the differences now.