Question

A drop of ethanol has a mass of `2.3xx10^(-3)` `"g"`. How many molecules of ethanol are in the drop?

Answer 1

The drop of ethanol contains `3.0xx10^19` molecules of ethanol.

Explanation:

The molar mass of ethanol is `"46.069 g/mol"`.
https://pubchem.ncbi.nlm.nih.gov/compound/ethanol

You will first need to determine the moles of ethanol present in the drop by dividing its mass by the molar mass of ethanol. Then calculate the number of molecules of ethanol by multiplying the moles ethanol times `6.022xx10^23"molecules/mol"`.

Determine Moles

`2.3xx10^(-3)color(red)cancel(color(black)("g C"_2"H"_5"OH"))xx(1"mol C"_2"H"_5"OH")/(46.069color(red)cancel(color(black)("g C"_2"H"_5"OH")))="0.000050 mol C"_2"H"_5"OH"=5.0xx10^(-5) "mol CH"_5"OH"`

Calculate Molecules

`5.0xx10^(-5)color(red)cancel(color(black)("mol C"_2"H"_5"OH"))xx(6.022xx10^23"molecules C"_2"H"_5"OH")/(1color(red)cancel(color(black)("mol C"_2"H"_5"OH")))=3.0xx10^19"molecules C"_2"H"_5"OH"`