Question

Calculate the approximate number of molecules in a drop of water with a mass of 0.10 g. A. 3 x 1021 molecules B. 4 x 1023 molecules C. 6 x 1021 molecules D. 2 x 1023 molecules

Answer 1

ms/Mwt = 0.10÷18 = 0.005 mol

No of molecules =

0.005 ×6.02×10^23= 3×10^21

Ur answer is A

Answer 2

Answer: The correct answer is Option A.

Explanation:

To calculate the number of moles, we use the equation:  

$\text{Number of moles}=\frac{\text{Given mass}}{\text{Molar mass}}$     ....(1)

For water droplet:

Given mass = 0.10 g

Molar mass of water = 18 g/mol

Putting values in above equation, we get:

$\text{Moles of water droplet}=\frac{0.10g}{18g/mol}\\\\\text{Moles of water droplet}=0.0055moles$

Now, according to Mole concept:  

1 mole of a compound contains $6.022\times 10^{23}$ number of molecules.

So, 0.0055 moles of water droplets will contain $0.0055\times 6.022\times 10^{23}=3.312\times 10^{21}\approx 3\times 10^{21}$ number of molecules.

Hence, the correct answer is Option A.