Question

The density of a liquid is 1.2 g/mL. There are 35 drops in 2 mL. The number of molecules in one drop
(molar mass of liquid = 70 g/mol) is :
1.2
NA
(4) 1.2NA
35
1.2
35
(3512 NA​

Answer 1

Answer:

0.001 NA

Explanation:

2 ml = 35 drops

weight of 2 ml is 2.4 grams( by density )

2ml has 35 drops

so each drop's weight is 0.07g

then,. 70 g = NA molecules

0.07 g = ?

=> 0.001 NA

Answer 2

Answer : The number of molecules in one drop are, $9.8\times 10^{-4}N_A$

Explanation : Given,

Density of a liquid = 1.2 g/ml

First we have to calculate the volume of liquid in one drop.

As, 35 drops present in 2 ml volume of liquid

So, 1 drops present in $\frac{2}{35}ml$ volume of liquid

Now we have to calculate the mass of liquid.

$\text{Mass of liquid}=\text{Density of liquid}\times \text{volume of liquid}$

$\text{Mass of liquid}=1.2g/ml\times \frac{2}{35}ml=0.0686g$

Now we have to calculate the moles of liquid.

$\text{Moles of liquid}=\frac{\text{Mass of liquid}}{\text{Volume of liquid}}-\frac{0.0686g}{70g/mole}=9.8\times 10^{-4}mole$

Now we have to calculate the number of molecules in one drop.

As, 1 mole of liquid contains $N_A$

So, $9.8\times 10^{-4}mole$ mole of liquid contains $9.8\times 10^{-4}N_A$

Therefore, the number of molecules in one drop are, $9.8\times 10^{-4}N_A$