Question

The volume of a drop of water is 0.05ml and the density of the water is 1.0g/ml. How many water molecules is present in a drop of water?

Answer 1

no of molecules is 1.672x 10^21 ....

Answer 2

The volume of a drop of water is 0.05ml and the density of the water is $1.0\frac { g }{ ml }. 1.67\quad \times \quad { 10 }^{ 21 }$ molecules are present in a drop of water.

From the given,

Density of water = $1.0 \frac { g }{ ml }$

Volume of a drop of water = 0.05 ml

One mole of water contains $6.022\quad \times \quad { 10 }^{ 23 } mo{ l }^{ -1 }$

Molar mass of water = 18 g/mol

Let's calculate the number of molecules in the 0.05 ml of water drop.

$Number\quad of\quad molecules\quad =\quad \frac { 0.05\quad ml\quad \times \quad 1.00\quad .\frac { g }{ ml } }{ 18\quad \frac { g }{ mol } }\quad \times\quad 6.022\quad \times \quad { 10 }^{ 23 }\quad mo{ l }^{ -1 }$

$=\quad 1.67\quad \times \quad 1{ 0 }^{ 21 }\quad molecule$

Therefore,$\quad 1.67\quad \times \quad 1{ 0 }^{ 21 }\quad molecules\quad are\quad present\quad in\quad 0.05\quad ml\quad water\quad drop.$