Question

In a mountainous location, the boiling point of pure water is found to be 95 oC. How many grams of sodium chloride must be added to 1 kg of water to bring the boiling point back to 100 oC?. Kb for water is 0.512 oC/m. Assume i = 2.

Answer 1

Answer:

285.6 g

Explanation:

The elevation of the boiling point of a solvent that has a solute nonvolatile dissolved is called ebullioscopy, and the change in the temperature may be calculated by the Raoult's law:

ΔT = Kb.W.i

Where ΔT is the temperature change, Kb is the ebullioscopy constant, W is the molality and i is the Van't Hoff factor, which determinates the particles that affect the proper.

The molality is:

W = m1/(M1xm2)

Where m1 is the solute mass (in g), M1 is the molar mass of the solute, and m2 is the mass of the solvent (in kg). Sodium chloride has molar mass equal to 58.5 g/mol (23 of Na and 35.5 of Cl), so:

(100 - 95) = 0.512xWx2

5 = 1.024W

W = 4.883 m

W = m1/(M1xm2)

4.883 = m1/(58.5x1)

m1 = 285.6 g