Question

Which of the following weigh the most?

• A. 0.5 mole of carbon
• B. 3.011×10²⁴ atoms of nitrogen
• C. 6.022×10²³ formula units of calcium carbonate

Answer 1

The correct option is C

6.022×10²³ formula units of calcium carbonate

Explanation for correct option:

Gram atomic mass of Calcium= 40 g mol^-1

Gram atomic mass of Carbon= 12 g mol^-1

Gram atomic mass of Oxygen= 16 g mol^-1

Gram formula mass of Calcium carbonate (CaCO₃)= 40 + 12+ 3(16)= 100 g mol^-1

According to the mole concept, 1 mole of a substance= Gram formula mass= 6.023 ×10²³ formula units

Therefore, 6.022×10²³ formula units of calcium carbonate weigh= 100 g

Explanation for incorrect options:

(a) 0.5 mole of Carbon (C)

1 mole of carbon weighs= 12 g

Gram atomic mass of Carbon= 12 g mol^-1

0.5 mole of Carbon= $0.5\times 12=6$ g

(b) 3.011×10²⁴ atoms of Nitrogen (N)

6.023 ×10²³ atoms of Nitrogen (N)= 14 g

1 atom of Nitrogen=$\frac{14}{6.023\times {10}^{23}}$

3.011×10²⁴ atoms of Nitrogen$\frac{14}{6.023\times {10}^{23}}\times 3.011\times {10}^{24}=70$ g

Therefore, option (c) is correct.