Question

Salt is often added to water to raise the temperature of the boiling point and to heat food more quickly. If you add 40.50 g of salt to 11.25 kg of water, what will be the change in the boiling point of your saltwater? The Kb of water is 0.51oC/m. (molar mass NaCl=58.44 g/mol).

Answer 1

To calculate the change in boiling point (
Δ
T
b
ΔT
b
​
) due to the addition of salt, you can use the formula:

Δ
T
b
=
i
⋅
K
b
⋅
m
ΔT
b
​
=i⋅K
b
​
⋅m

Where:

i
i is the van't Hoff factor (number of particles the solute dissociates into),
K
b
K
b
​
is the ebullioscopic constant (0.51 °C/m for water),
m
m is the molality of the solution.
First, find the molality (
m
m) of the solution using the formula:

m
=
moles of solute
mass of solvent (in kg)
m=
mass of solvent (in kg)
moles of solute
​


Find moles of NaCl:
40.50
 
g
58.44
 
g/mol
58.44g/mol
40.50g
​

Find molality:
moles of NaCl
11.25
 
kg
11.25kg
moles of NaCl
​

Next, determine the van't Hoff factor (
i
i). For NaCl, which fully dissociates in water,
i
=
2
i=2.

Now, substitute these values into the formula
Δ
T
b
=
i
⋅
K
b
⋅
m
ΔT
b
​
=i⋅K
b
​
⋅m to find the change in boiling point. Report the result.