Question

Calculate the number of molecules present in 1.8×10-2 g of H2O​

Answer 1

Answer:

Mass of H2o = 1.8×10^-2( given)

Atomic mass of H2o=18

No. of moles= given mass/ atomic mass

=1.8 ×10^-2/18

=10^-3 moles

no. of molecules present= no. of moles × 6.02×10^23

= 10^-3 × 6.02 × 10^23

no. of molecules= 6.02 × 10^20

Answer 2

Given :-

Mass of $H_2O = 1.8 \times 10^{-2}g$

To find :-

Number of molecules present.

Solution :-

We know,

The number of molecules present in 1 mole is equal to its molar mass.

Molar mass of $H_2O = 2\times 1 + 1 \times 16$

$18 u$

Now,

18 g of $H_2O contain \: 6.022 </p><p>\times 10^{23} molecules$

$1.8 \times 10^{-2 g} \: of H_2\: contain :-$

$\implies$ $\dfrac{6.022\times10^{23}}{18}\times 1.8\times 10^{-2}$

$\implies$ $\dfrac {6.022\times10^{23} } {18} \times \dfrac {18}{10^3}$

$\implies$ $6.022\times 10^{23} \times 10^-3$

$\implies$ $6.022 \times 10^{20} molecules$

hence, number of molecules will be $6.022 \times 10^{20} molecules$ in $1.8 \times 10^{-2}g$