It's January in Nashville and your local weather station just informed you that the temperature outside is
15.4°F. You estimate the amount of ice on your driveway to be approximately 30 kg. What is the minimum amount
of sodium chloride in kilograms (kg) needed to lower the freezing point of the water so that the ice melts?

3.84 Kg of sodium chloride is needed to lower the freezing point of the water so that ice melts.

Explanation:

Data given:

mass of ice = 30 Kg

molar mass of NaCl = 58.5 grams/mole

ΔT(depression in freezing point) = 15.4 F  or - 9.22 degrees

Kf = 1.86 degree C/ mole

Molality = ?

mass of NaCl =?

i = 2 (because NaCl breaks into 2 ions)

ΔT = iKfm      equation 1

Depression in freezing point when ice melts, the temperature is 0 degrees so

the depression in temperature = 9.22 degrees

putting the values in the equation:

9.22 = 2 x 1.86 x x

mass = 3.84 kg of NaCl will be required to lower the freezing point of the water so that the ice melts.