Question

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

M methanol = mols methanol/L solution.

mols methanol = grams/molar mass = ?
L solution = volume methanol + acetonitrile.

Convert g methanol to mL methanol using density. Add to volume of acetonitile (mL + mL) and convert to L. Plug L into the mols/L above and solve for M methanol.