# Calculate the number of moles in this quantity: 250 mL ethyl alcohol, C2H5OH (0.789 g/mL)

## Question:

Calculate the number of moles in this quantity: 250 mL ethyl alcohol, {eq}C_2H_5OH {/eq} (0.789 g/mL)

## Converting volume to moles:

The first step in answering this question is to determine the mass of 250 mL ethyl alcohol. The second step is to convert the mass obtained into moles using the molar mass of ethyl alcohol.

Step 1: Use density to determine the mass of 250 mL ethyl alcohol.

Since density = 0.789 g/mL the mass of ethyl alcohol can be obtained as follows;

{eq}\rm mass = 0.789 \ g/mL \times250 \ mL {/eq}

{eq}\rm mass = 197.25 \ g {/eq}

Step 2: Use the molar mass of ethyl alcohol to determine the number of moles in 197.25 g.

Since molar mass of ethyl alcohol = 46.07 g/mol, the mole of ethyl alcohol can be obtained as follows;

{eq}\rm moles \ of \ ethyl \ alcohol=\frac{1 \ mol}{46.07 \ g}\times197.25 \ g {/eq}

{eq}\rm moles \ of \ ethyl \ alcohol=\textbf{4.28 moles} {/eq} 