If you want to lower water's freezing point 18 degrees C by adding NaCl, what must the molality of the salt solution be? (K(f) for water ris 1.86 degree C/m)

4.84 m

Explanation:

To solve this problem we need Frezing point depression.

Formula is: ΔT = Kf . m . i

ΔT = 18°C

This is data. ΔT is the difference, Freezing T° of pure solute - Freezing T° of solution.

Kf = 1.86 °C/m

m = molality. Our unknown.

i = Ions dissolved in solution, also called Van't Hoff factor.

NaCl → Na⁻  +  Cl⁻

Sodium chloride can produce 2 moles of ions.

We replace data: 18°C = 1.86 °C/m  .  m   .  2

18°C / (1.86 °C/m) . 2 = m

molality = 4.84

answer: c. the experiment shows that the red substance experienced a chemical change.

explanation: chemical change is the change in which chemical composition of the substance changes. physical change is the change in which there is no change in chemical composition.

chemical changes are accompanied by following changes:

a) precipitate formation

b) energy is released or absorbed

c) formation of bubbles

d) change in color

as it is given that the red color has disappeared and there is production of gas, it means the red substance has undergone a chemical change.

e

let that person have a turn to speak : )