. A 100 g of ammonium chloride solution is 30 % by mass with a density of 1.024 g/mL. Calculate molarity and molality of a solution.

Answer 1

molarity = M = mols/L
molality = m = moles/kg solvent.
M first. In steps:
density = 1.024 g/mL; therefore, 1000 mL has a mass of 1.024 x 1000 = 1024 g.
How much of that is NH4Cl? That's 1024 g x 0.30 = 307.2 g NH4Cl
How many moles is that? That's 307.2 g x 1 mol/53.5 g = 5.74 moles.
Therefore, M = mols/L = ?

molality = m = moles/kg solvent. In steps:
You have moles NH4Cl from above as 5.74 moles NH4Cl.
Total mass of solution from above is 1024 g.
Total mass of NH4Cl from above is 307.2 g
mass solution - mass solute = mass solvent = 1024 - 307.2 = ?. Convert to kg. m = mols/kg solvent = ?
Post your work if you get stuck.