1129.9 grams of rock salt, NaCl needs to be added to a 3.78 kg of ice, to get the temperature to drop to -19C .
Freezing point depression refers to a property of solutions where addition of a solute lowers the normal freezing point of the solvent.
The Blagden's Law given as the equation above is used to determine the freezing point depression of ice:
where;
For NaCl, i = 2
Kf for water/ice = 1.86 °C kg/mol
molalityof NaCl = (mass/molar mass
l)/kg of ice
molar mass of NaCl = 58.5
mass of ice = 3.78 kg
Let molality of NaCl = m
ΔT = 19 °C
Substituting the values:
19 = 2 x 1.86 °C kg/mol x m
m = 5.11 mol/kg
mass of NaCl = 5.11 × 3.78 × 58.5
mass of NaCl = 1129.9 g
Therefore, the mass in grams of rock salt, NaCl that needs to be added to a 3.78 kg of ice, to get the temperature to drop to -19C is 1129.9 g
Learn more about freezing point depression at: https://brainly.com/question/26525184
