How many grams of salt (NaCl; molar mass = 58) will you need to add to 4 kg of ice water bath?

Making ice cream involves surrounding the ice cream canister with a bath of salted ice water. To get the mix to freeze at 6.00潞C, how many grams of salt (NaCl; molar mass = 58) will you need to add to 4 kg of ice water bath? (Kf of water = 1.86潞C/m)How many grams of salt (NaCl; molar mass = 58) will you need to add to 4 kg of ice water bath?
first it will freeze at -6C (do not forget the sign -)





the osmolarity of NaCl = delta T/Kf= 6/1.86=3.226





osmolarity = molarity * i


where i=2 for a biatomic strong electrolyte





so molarity =3.226/2=1.613


mass by liter 1.613*58=93.55g/L





and for 4 liters you need 93.55*4=374.2g of NaC





remark :this is valid if the density of the salt solution is equal to 1 meaning that salt does not change the density