Question

The density of a liquid is 1.2 g/mL. That are 35 drops in 2 mL. The number of molecules in 1 drop is (molecular weight of liquid = 70):

• A. $\frac{1.2}{35}{N}_A$
• B. ${\left(\frac{1}{35}{N}_A\right)}^2$
• C. $\frac{1.2}{(35{)}^2}{N}_A$
• D. $1.2N_A$

Answer 1

Answer: (C)

$\frac{1.2}{(35{)}^2}{N}_A$

Volume of one drop $=\frac{2}{35}mL$

Moles in one drop $=\frac{2\times 1.2}{35\times 70}=\frac{1.2}{(35{)}^2}mol$

Number of molecules in one drop $=\frac{1.2}{(35{)}^2}\times N_A$