Which of the following statements about boiling points are false:
A. the boiling point of 0.1 m KF(aq) is lower than the boiling point of 0.1 m ethanol(aq)
B. the boiling point of a 0.5 m aqueous solution of NaOH is the same as the boiling point of a 0.5 m aqueous solution of NaCL
C. the boiling point of 1 m aqueous NaNO3 is lower than the boiling point of 1 m aqueous Ca(N03)2
D. the boiling point of a solution made by dissolving 20 g of C2H6O2 in 0.50 kg of water is lower than the boiling point of a solution of 20 g of NaCL in 0.50 kg of water
E. the boiling point of 2 m Nal in water is 101 degrees celcius
You can use delta T = i*kb*m for each of these. For example, for A.
i = 2
Kb = 0.51
m = 0.1 all for KI.
for ethanol,
i = 1
Kb = 0.51
m = 0.1
therefore, A is false.
Introduction
To determine which of the statements about boiling points are false, we need to consider the concept of boiling point elevation. Boiling point elevation occurs when a non-volatile solute (a solute with negligible vapor pressure) is added to a solvent, and it results in an increase in the boiling point of the solution compared to the pure solvent.
The boiling point elevation can be calculated using the equation:
ΔTb = Kbm
Where:
ΔTb = Boiling point elevation
Kb = Molal boiling point elevation constant (a characteristic property of the solvent)
m = Molality of the solute (moles of solute per kg of solvent)
Using this information, we can analyze each statement:
A. The boiling point elevation depends on the molal concentration of the solute rather than the identity of the solute. Therefore, the statement is false. We cannot determine if the boiling point of 0.1 m KF(aq) is lower or higher than the boiling point of 0.1 m ethanol(aq) without more information.
B. This statement is true. Assuming both NaOH and NaCl are completely ionized in aqueous solution, the boiling point elevation depends only on the molality of the solute. Since both solutions have the same molality (0.5 m), the boiling points will be the same.
C. This statement is true. Again, assuming complete ionization, the boiling point elevation depends only on the molality of the solute. Since both solutions have the same molality (1 m), the boiling points will be the same.
D. This statement is true. The boiling point elevation depends on the molal concentration of the solute. In this case, the solution with 20 g of C2H6O2 (ethylene glycol) has a greater molal concentration compared to the solution with 20 g of NaCl. Therefore, the boiling point of the C2H6O2 solution will be higher.
E. This statement is false. The boiling point elevation depends on the molal concentration of the solute, and the colligative properties like boiling point elevation are proportional to the number of particles in solution (van't Hoff factor). However, the statement does not provide information about the molal concentration or the van't Hoff factor. Without this information, we cannot determine the boiling point of the solution.
In summary, the false statement is E.