JEE Main · 2021 · 18 Mar 2021 · Shift 1 · Some Basic Concepts of Chemistry

Complete combustion of 3 g of ethane gives

x \times 1 0^{22}

molecules of water. The value of

x

is
____ . (Round off to the nearest integer).
[Use :

N_{A} = 6.023 \times 1 0^{23}

; Atomic masses in u : C:12.0,O:16.0; H:1.0]

Answer: 18

Solution

Complete combustion follows

C_{2} H_{6} + \frac{7}{2} O_{2} \to 2 C O_{2} + 3 H_{2} O

. Ethane has a molar mass of

30 g mo l^{- 1}

, so

3

g is

0.1

mol, and each mole of ethane yields three moles of water, giving

0.3

mol of water. The number of molecules is

0.3 \times 6.023 \times 1 0^{23} = 1.807 \times 1 0^{23}

, that is

18.07 \times 1 0^{22}

, so

x = 18

JEE Main · 2021 · 18 Mar 2021 · Shift 1 · Integer answer