What mass of water (in grams) is needed to dissolve 28.7 g of ammonium nitrate NH4NO3 in order to prepare a 0.452 m (molal) solution?

Answer 1

Molal is the number of moles per kg of solvent (not solution).

or molal = moles/(kg of water)

thus mass needed (in kg) =
(moles NH4NO3)/0.452

calculate (moles NH4NO3) from the data in the question then use the expression above to find the kg of water needed. Hence convert kg to g as asked for in the question.

Answer 2

793.4 g