(a) Define the term ‘molecular mass’.

(b) Determine the molecular mass of ZnSO4.


[Atomic mass of Zn = 65 u, S = 32 u, O = 16 u]


a) Molecular mass: The molecular mass of a substance is the sum of atomic masses of all the atoms in a molecule of the substance.


i. It is used for those substances whose constituent particles are molecules.


ii. The molecular mass remains the same even if millions of molecules are added.


iii. For example: The molecular mass of H2O = 2 × Atomic mass of hydrogen + Atomic mass of oxygen


= 2 + 16 = 18u


b) Molecular mass of ZnSO4:


Atomic mass of Zn + Atomic mass of S + 4× atomic mass of O


65 u + 32 u + 4× 16u


65 u + 32 u + 64 u


161 u


Thus, the molecular mass of ZnSO4 is 161u


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