Question

Calculate the total number of electrons in 36 mL of water.

• A. 10 $N_A$
• B. 5 $N_A$
• C. 15 $N_A$
• D. 20 $N_A$

Answer 1

The correct option is D 20 $N_A$

We know, density of water = 1 g/mL
So, mass of 18 mL of water = density $\times$ volume
mass = 1 $gm{l}^{-1}\times 36mL$ = 36 g
$\therefore$ Number of moles = $\frac{givenmass}{molarmass}=\frac{36}{18}=2mol$

Number of electrons in 1 molecule of $H_{2}O$ = $2\times 1+8$ = 10 electrons
1 molecule of $H_{2}O$ contains 10 electrons
1 mole of $H_{2}O$ contains 10 $N_A$ electrons
So, 2 moles of $H_{2}O$ contain 20 $N_A$ electrons.