The density of acetonitrile, CH3CN, is 0.786 g/mL, and the density of methanol, CH3OH, is 0.791 g/mL.

Question

A solution is made by dissolving 15.0 g of methanol in 250.0 mL of acetonitrile. Assuming that the
volumes of the solute and solvent are additive, what is the molarity of methanol in the solution?

Answer 1

mass = volume x density or
v = m/d
v methanol = 15.0 g/0.791 g/mL = 19.0 rounded.
v acetonitrile = 250 mL.
Total volume = 269 mL
moles CH3OH = grams/molar mass = 15.0/32 = 0.469 rounded
molarity = M = moles/L solution = 0.469/0.269 = ?
Check my arithmetic.