You like boiled eggs for breakfast, but they take too long to cook, and you are always late to your early morning class. Lucky you! You have learned that adding table salt, NaCl (58.4 g/mol, 2.16 g/cm³), to water (K_b = 0.52^oC/m) increases the temperature at which it boils. You figure that you can cook eggs faster at a higher temperature in boiling salty water! What increase in the boiling point do you expect if you add 4 tablespoons (1 tbsp = 14.8 cm³) of salt to 16 oz of water (474 mL)?

Question

Quizplus · Accepted Answer

To solve for the increase in boiling point, we need to use the formula:
ΔTb = Kb * m * i
where:
ΔTb = increase in boiling point
Kb = molal boiling point elevation constant of water (0.512°C/m)
m = molality of the solution (mol solute/kg solvent)
i = van't Hoff factor (number of particles into which a compound dissociates in solution)

First, we need to calculate the molality of the solution:
16 oz of water = 474 mL of water
Assuming the density of water is 1 g/mL, the mass of 474 mL of water is 474 g (or 0.474 kg)
The molar mass of NaCl is 58.4 g/mol, so 4 tbsp of salt (59 g) is equivalent to 1 mol of NaCl.
Therefore, the molality of the solution is:
molality = mol solute/kg solvent = 1 mol/0.474 kg = 2.11 mol/kg

Next, we need to find the van't Hoff factor for NaCl. NaCl dissociates into two particles (Na+ and Cl-) in solution, so i = 2.

Now we can solve for ΔTb:
ΔTb = Kb * m * i = 0.512°C/m * 2.11 mol/kg * 2 = 2.16°C
Therefore, adding 4 tbsp of salt to 16 oz of water will increase the boiling point by 2.16°C, which will allow the eggs to cook faster. The closest answer choice is B) 4.8°C, which is not a correct answer.

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