Question

If 1 ml of water has 20 drops and A is Avogadro’s number then number of molecules in the drop of water are.....

Answer 1

Answer: $1.62594\times 10^{21}$number of molecules in one drop of water.

Solution:

1 mL of water contains:

Density of water = 1 g/mL

Mass of water = $(density)\times (volume)=1g/mL\times 1mL=(1) g$

Number of moles in 1 mL= $\frac{\text{number of moles}}{\text{molecuar mass of water}}=\frac{1 g}{18g/mol}=0.0555 mol$

According to question in 1 mL there are 20 drops, then number of mole in one drop will be:

$\frac{1}{20}\times 0.0555=0.0027 \text{moles of water}$

Number of molecules in the drop of water:

$1 mol=\text{Avogadro number}=N_A= 6.022\times 10^{23} \text{per mole}$

Then in 0.0027 moles of water :

$=0.0027\times 6.022\times 10^{23}= 1.62594\times 10^{21}\text{water molecules}$

$1.62594\times 10^{21}$number of molecules in one drop of water.