Question

What is the % M/M concentration of 5.00 mL of methanol in 25 g solution of methanol in water? The density of methanol is 0.791 g/mL. The density of water is 1.000 g/mL. What is the % V/V concentration for the solution? Please show work.

Answer 1

5% m/m (w/w) means 5g solute per 100 g solution.
mass = volume x density
mass = 5 mL x 0.791 g/mL = 3.96 g. Therefore, you have 3.96g/25 g soln. substitute into
(g solute/g soln)*100 = ?
(3.96/25)*100 = ?% m/m

We have 5 mL/(96.04g H2O+3.96g methanol)
Assuming the 96.04 g H2O (at density of 1.00 g/mL that is 96.04 mL H2O) will add to methanol to give the correct volume (it doesn't) the volume will be 96.04 + 5.00 mL or 101.04 mL.
(5.00 mL/101.04)*100 = ? v/v.