Calculation of the Number of Moles of KCl:
To determine the number of grams of KCl required to lower the freezing point of water, we first need to calculate the number of moles of KCl required. We can use the formula:

ΔT = K_f * m * i

Where:
ΔT = change in freezing point (-8.0°C)
K_f = freezing point depression constant for water (1.86°C/m)
m = molality of the solution (moles of solute per kilogram of solvent)
i = van't Hoff factor (the number of ions produced by the solute in the solution)

In this case, we are assuming KCl completely dissociates into K+ and Cl- ions in water, so the van't Hoff factor (i) is 2.

Calculation of the Molality:
The molality (m) is defined as the number of moles of solute per kilogram of solvent. In this case, the solvent is water, and we have 1 kilogram (1000 grams) of water. To calculate the molality, we need to convert the grams of KCl to moles.

The molar mass of KCl is 74.55 g/mol.

Number of moles = mass of KCl / molar mass of KCl
Number of moles = 1000 g / 74.55 g/mol

Calculation of the Freezing Point Depression:
Now, we can substitute the values into the freezing point depression equation:

ΔT = K_f * m * i
-8.0°C = 1.86°C/m * (1000 g / 74.55 g/mol) * 2

Simplifying the equation:
-8.0°C = 3.96 * (1000 g / 74.55 g/mol)

Calculation of the Mass of KCl:
To find the mass of KCl required, we rearrange the equation:

Mass of KCl = (ΔT / (K_f * m * i)) * molar mass of KCl

Substituting the values:
Mass of KCl = (-8.0°C / (1.86°C/m * (1000 g / 74.55 g/mol) * 2)) * 74.55 g/mol

Simplifying the equation:
Mass of KCl = (-8.0°C / (1.86°C/m * 13.42 mol/kg)) * 74.55 g/mol

Mass of KCl = -8.0°C / 24.72 mol/kg * 74.55 g/mol

Mass of KCl = -0.324 kg * 74.55 g/mol

Mass of KCl = -24.15 g

Conclusion:
The negative mass of KCl indicates that no KCl needs to be added to lower the freezing point of water to -8.0°C. This suggests that the freezing point of pure water is already below -8.0°C, and no KCl is required to further depress it.