The number of molecules in 18 mg of water in terms of Avogadro number N is

Question

The number of molecules in 18 mg of water in terms of Avogadro number N is (A)  10-3N  (B)  10-2N  (C)  10-1N  (D)  10 N

Tardigrade Admin · Accepted Answer

Given, weight of water =18 mg=18× 10-3g ∴ Number of moles =( textweight/ textmolar textmass) =(18× 10-3/18)=1× 10-3 and number of molecules = no. of moles × Avogadro number. = 1× 10-3× N =10-3N.

Q. The number of molecules in $18 m g$ of water in terms of Avogadro number $N$ is

$1 0^{- 3} N$

$1 0^{- 2} N$

$1 0^{- 1} N$

$10 N$

Given, weight of water $= 18 m g = 18 \times 1 0^{- 3} g$
$∴$ Number of moles $= \frac{weight}{molar mass}$
$= \frac{18 \times 1 0 ^{- 3}}{18} = 1 \times 1 0^{- 3}$
and number of molecules = no. of moles $\times$ Avogadro number.
$= 1 \times 1 0^{- 3} \times N$ $= 1 0^{- 3} N .$

Q. The number of molecules in 18mg of water in terms of Avogadro number N is

10−3N

10−2N

10−1N

10N