Estimate the boiling point of a 0.6 molal solution of nacl in water. the boiling point elevation constant of water is 0.51 k/molal. give your answer in °c.

Respuesta :

To answer the question above, solve first for the boiling point elevation through the equation,

     ΔT = (Kb)(m)

where ΔT is the boiling point, Kb is constant for water, and m is the concentration. Substituting the known values,

     ΔT = (0.51 K/molal)(0.6 molal)
     ΔT = 0.306 K

The boiling point therefore of the solution is equal to 100.306°C. 

Answer: 100.306°C

Boiling point of 0.6 molar solution of NaCl in water is [tex]\boxed{-172.844^\circ\text{C}}[/tex].

Further Explanation:  

Colligative properties:

These properties are dependent only on concentration of solute particles, no matter what type of solute is used.

Following four are colligative properties:

  1. Relative lowering of vapor pressure.
  2. Elevation in boiling point.
  3. Depression in freezing point.
  4. Osmotic pressure.

Boiling point elevation is evaluated by following formula:

[tex]\Delta\text{T}_\text{b}=\text{k}_\text{b}\text{m}[/tex]                                   ...... (1)

Here,

[tex]\Delta\text{T}_\text{b}[/tex] is elevation in boiling point.

[tex]\Delta\text{k}_\text{b}[/tex] is molal boiling point constant.

m is molality of solution.

Substitute 0.6 m for m and 0.51 K/m for [tex]\Delta\text{k}_\text{b}[/tex] in equation (1).

[tex]\begin{aligned}\Delta\text{T}_\text{b}=&\text{(0.51 K/m)}(0.6\text{m})\\=&0.306\text{K}\end{aligned}[/tex]

Boiling point elevation is converted from Kelvin to degrees Celsius with help of following conversion factor:

[tex]0^\circ\text{C}=273.15\text{K}[/tex]

Therefore boiling point elevation is calculated as follows:

[tex]\begin{aligned}\Delta\text{T}_\text{b}&=\text{0.306 K}-\text{273.15 K}\\&=-272.844^\circ\text{C}\end{aligned}[/tex]

The formula to calculate the temperature change in the NaCl solution is as follows:

[tex]\Delta\text{T}_\text{b}=\text{Boiling point of NaCl}-\text{Boiling point of H}_{2}\text{O}[/tex]                  ...... (2)

Rearrange equation (2) to calculate boiling point of NaCl.

[tex]\text{Boiling point of NaCl}=\Delta\text{T}_\text{b}+\text{Boiling point of H}_{2}\text{O}[/tex]                   ....... (3)

Substitute [tex]100^\circ\text{C}[/tex] for boiling point of pure [tex]\text{H}_{2}\text{O}[/tex] and [tex]-272.844^\circ\text{C}[/tex] for [tex]\Delta\text{T}_\text{b}[/tex] in equation (3).

[tex]\begin{aligned}\text{Boiling point of NaCl}=&-272.844^\circ\text{C}+100^\circ\text{C}\\=&-172.844^\circ\text{C}\end{aligned}[/tex]

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Answer details:

Grade: Senior School

Chapter: Colligative properties

Subject: Chemistry

Keywords: colligative properties, boiling point, elevation in boiling point, boiling point of NaCl, NaCl, concentration, solute particles, relative lowering of vapor pressure, depression in freezing point, osmotic pressure, -172.844 degrees Celsius.