What is the freezing point of a 10% (by mass) solution of CH3OH in water?

Answer 1

10% w/w means 10g solute/100 g solution. That is 10g CH3OH/(90g H2O + 10g CH3OH).
Convert 10 g CH3OH to mols. That's mols = grams/molar mass = ?

Change to m. m = mols/kg solvent. You have mols and kg solvent is 0.025 g.

Then delta T = Kf*molality
You have Kf (1.86), m from above, solve for delta T.

Subtract delta T from the normal freezing point (0C) to find the the new freezing point.