Question

The density of water and ethanol at room temperature is $1.0\, g/mL$ and $0.789\, g/mL$ respectively. What volume of ethanol contains the same number of molecules as are present in $100\, mL$ of water?

• A. 307.8 mL
• B. 168.7 mL
• C. 323.9 mL
• D. 253.3 mL

Answer 1

Answer: (C)

An equal number of moles contain equal number of molecules.
$\frac{\text { wt. of } C _{2} H _{5} OH }{\text { mol. wt. of } C _{2} H _{5} OH }=\frac{\text { wt. of } H _{2} O }{\text { mol. wt. of } H _{2} O }$
$\frac{0.789 \times \text { volume of } C _{2} H _{5} OH }{46}=\frac{1.0 \times 100}{18}$
Volume of $C _{2} H _{5} OH =\frac{100}{18} \times \frac{46}{0.789}$
$=323.9\, mL$.