If a liter of solution is needed, how many grams of ethanol, C2H6O will be added when a scientist creates a 0.25 molal solution?

11.52g of ethanol

Explanation:

Molality is an unit of concentration defined as ratio between moles of solute (In this case, ethanol) and kg of solvent.

As solvent is water, 1 liter of water weights 1kg.

That means to create a 0.25molal solution it is necessary to have 0.25 moles of ethanol.

Molar weight of ethanol (C₂H₆O) is:

C: 12.01g/mol * 2 = 24.02g/mol

H: 1.01g/mol * 6 = 6.06g/mol

O: 16g/mol * 1 = 16g/mol

24.02g/mol + 6.06g/mol + 16g/mol = 46.08g/mol

As you need 0.25 moles, there is necessary to weight:

0.25 moles * (46.08g/mol) = 11.52g of ethanol