Question

If density of methanol is 0.793kg/L , what is its volume needed for making 2.5L of its 0.25M solution?

Answer 1

`"25.2 mL"`

Explanation:

`"Molarity" = "Moles of solute"/"Volume of solution (in litres)"`

For given solution

`"0.25 M" = "n"/"2.5 L"`

`"n = 0.625 moles"`

`"0.625 moles"` of methanol is needed.

Molar mass of methanol `("CH"_3"OH") = "32 g/mol"`

• Mass of methanol needed `= 0.625 cancel"mol" × "32 g"/cancel"mol" = "20 g"`

Density of methanol `= "0.793 kg/L" = "793 g/L"`

`"Volume" = "Mass"/"Density"`

• Volume of methanol needed `= "20 g"/"793 g/L" = "0.0252 L" = "25.2 mL"`

Answer 2

Well, first off we calculate the required molar quantity of methanol....

Explanation:

And since `"concentration"="moles of solute"/"volume of solution"`...if we gots a `2.5*L` volume of its `0.25*mol*L^-1` solution.....then we got a molar quantity of....

`0.25*mol*L^-1xx2.5*L=0.625*mol` with respect to `"methanol"`.

And thus a mass of `0.625*molxx32.04*g*mol^-1=20.0*g` with respect to methanol.

And so we need a volume of `(20.0*g)/(793*g*L^-1)=0.0253*L-=25.25*mL`...

It is not very realistic to measure out such volumes of methanol....if you rigorously dry ethanol or methanol (and this is not so straightforward), when you expose the dry solvent to the air you can literally see the volume increase as the alcohol sucks up atmospheric moisture. The lower alcohols are very hydrophilic.