Question

Calculate the number of moles in 31.9g of hydrated Copper Sulphate(CuSO₄.5H₂O).

Answer 1

• The gram molecular mass is defined as the molecular mass of a mole of a substance expressed in grams.
• The relation between gram molecular mass, number of moles, and Avogadro's number is

The molar mass of a substance = 1 mole of that substance = 6.022×10²³ molecules.

• Number of moles of substance (n) = $\frac{\mathrm{Given}\mathrm{weight}\mathrm{of}\mathrm{substance}}{\mathrm{Molecular}\mathrm{weight}}$

The molecular weight of hydrated Copper Sulphate(CuSO₄.5H₂O) = Atomic weight of individual components of hydrated Copper Sulphate(CuSO₄.5H₂O).

i.e., The atomic weight of Copper =63.5g

The atomic weight of Sulphur(S) = 32 g

The atomic weight of Oxygen (O) = 16, since there are 4 oxygen atoms, Atomic weight = 16 × 4= 64g

The atomic weight of 5 water molecules (5H₂O)= 5(2+16)=90g [Atomic weight of 2Hydrogen atom + Atomic weight of 1 Oxygen Atom]

Therefore the relative molecular weight of hydrated Copper Sulphate(CuSO₄.5H₂O) = 63.5 + 32 + 64 + 90 = 249.5g

Given weight of hydrated Copper Sulphate(CuSO₄.5H₂O) =31.9g

Therefore Number of moles of hydrated Copper Sulphate(CuSO₄.5H₂O) = $\frac{31.9}{249.5}$ = 0.128 moles

Thus the number of moles present in 31.9g of hydrated Copper Sulphate(CuSO₄.5H₂O) is 0.128 moles.