Question

Which of the following samples contains the smallest number of atoms ?

• A. 1 g of $CO_2(g)$
• B. 1 g of $C_8H_{18}$
• C. l g of $C_2H_6(g)$
• D. 1 g of LiF(s)

Answer 1

Answer: (A)

1 g of $CO_2(g)$

Answer 2

(A) Molar mass of $CO_{2}=44\,g\,mol^{-1}$ $44\,g\,CO_{2} \equiv 3 \times 6.02\times 10^{23}$ atoms $1\,g$ of $CO_{2}$ $=\frac{2\times6.02\times10^{23}}{4}$ atoms $=0.068\times6.02\times10^{23}$ atoms (B) Molar mass of $C_{8}H_{18}=114\,g\,mol^{-1}$ $1\,g$ of $C_{8}H_{18}=\frac{26\times6.02\times10^{23}}{144}$ atoms $=0.18\times6.02\times10^{23}$ atoms (C) Molar mass of $C_{2}H_{6}=30\,g\,mol^{-1}$ $1\,g$ of $C_{2}H_{6}=\frac{8\times6.02\times10^{23}}{30}$ atoms $=0.27\times6.02\times10^{23}$ atoms (D) Molar mass of LiF $=7\times19=26$ $1 g$ of LiF $=\frac{2\times6.02\times10^{23}}{26}$ atoms $=0.077 \times 6.02\times10^{23}$ atoms Clearly $(A)$ has minimum number of atoms