Question

Justify that 180 g of glucose and 342 g of sucrose have the same number of molecules but
different number of atoms present in them.

Answer 1

Given:

180g C6H12O6(Glucose) and 342g C12H22O11(Sucrose)

(C = 12u, H = 1u, O = 16u)

To Prove:

They have same number of molecules but different number of atoms.

Proof:

No. of moles of Glucose = Given weight of glucose / Molecular weight of glucose

= 180/(6*12+12*1+6*16)

= 180/180

= 1 mole of Glucose

= 6.022*10²³ molecules of Glucose       ....(Avogadro's Number)

Similarly,

No. of moles of Sucrose = Given weight of sucrose / Molecular weight of sucrose

= 342/(12*12+22*1+11*16)

= 342/342

= 1 mole of Sucrose

= 6.022*10²³ molecules of Sucrose

Therefore, no. of molecules of Glucose = no. of molecules of Sucrose

1 molecule of Glucose contains 6+12+6 = 24 atoms.

∴ 6.022*10²³ molecules of Glucose contain 24*6.022*10²³ atoms.

1 molecule of Sucrose contains 12+22+11 = 45 atoms.

∴ 6.022*10²³ molecules of Sucrose contain 45*6.022*10²³ atoms.

Thus, 180 g of Glucose and 342 g of Sucrose have the same number of molecules but  different number of atoms present in them.