Question

Complete combustion of 3 g ethane gives $x\times {10}^{22}$ molecules of water. The value of x is
(Round off to the nearest integer)
[Use : $N_A=6\times {10}^{23}$

Answer 1

moles of ethane =$\frac{3g}{30g/mol}=0.1mol$
$C_2{H}_6+3.5O_2\to 2C{O}_2+3H_{2}O$
1 mol of ethane gives 3 mol of water
0.1 mol ethane gives 0.3 mol of water
Number of molecules in 0.3 mol water
$=0.3\times 6\times {10}^{23}=18\times {10}^{22}molecules$
value of x is 18