Question

If the density of methanol is 0.793 kg L^-1, what is its volume needed for making 2.5 L of its 0.25 M solution?

Answer 1

Density of methanol = 0.793 kg L^-1

Molar mass of methanol (CH₃OH) = 12 + 4 + 16 = 32 u

Mass of methanol needed for making 1 L of its 1 M solution = 32 g

Mass of methanol needed for making 2.5 L of its 1 M solution = 32 x 2.5 g

Mass of methanol needed for making 2.5 L of its 25 M solution

= 32 x 2.5 x 2.5 g = 20 g = 0.02 kg

Density = Mass/Volume

or, Volume = Mass/Density = 0.02 kg/0.793 kg L^-1 = 0.025 L