When cooking pasta, salt is often added to boiling water before the pasta. When

Question

When cooking pasta, salt is often added to boiling water before the pasta. When the salt is added, boiling ceases because the boiling point of the salt-water solution is higher than that of pure water, and boiling resumes when the temperature of the solution has been raised to the new boiling point. Assuming the salt completely dissociates after 1 teaspoon of sodium chloride has been added to 1.0 L of boiling water. The density of the sodium chloride and water at 100 oC are 2.156 g/cm3, and 0.9584 g/cm3, respectively, and 1 teaspoon = 4.9289 cm3. The boiling point of the water is ____ oC. (2 dec. places)

Explanation / Answer

density = mass / Voulme

d of NaCl = 2.156 gm/cm^3

2.156 = gm/cm^3

For 4.9289 cm^3 ; gms are ==>

gms = 2.165*4.9289 = 10.67 gms

moles of NaCl = 10.67 /.58.44 = 0.1825

Molality = moles of solute / weight of solvent in kg.

1 gm/cm^3 = 1 kg/L

0.9584 g/cm3 = 0.9584 Kg/L

mass = 0.9584*1 = 0.9584 Kg

Molality = 0.1825 / 0.9584 = 0.19 ; i= 2 fro NaCl

Boiling point elevation = 2*0.512 * 0.19 = 0.195

Boiling point of water is 100+0.019456 = 100.1945 C

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