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what is elevation of boiling point and depression of freezing point

what is elevation of boiling point and depression of freezing point


 

Grade:Upto college level

2 Answers

Akshay Meena
askIITians Faculty 34 Points
10 years ago

Boiling-point elevation describes the phenomenon that the boiling point of a liquid (a solvent) will be higher when another compound is added, meaning that a solution has a higher boiling point than a pure solvent.This happens whenever a non-volatile solute, such as a salt, is added to a pure solvent, such as water.

In sum, The boiling-point elevation means that when a solute is dissolved in a solvent, the boiling point of the resulting solution is higher than that of the pure solvent. 

ΔTb = Tb (solution) - Tb (pure solvent) = Kb * bB * i

[Where : Kb =   RTb2M/ΔHv, where R is the gas constant, and Tb is the boiling temperature of the pure solvent [in K], M is the molar mass of the solvent, and ΔHv is the heat of vaporization per mole of the solvent]

 

Freezing-point depression describes the process in which adding a solute to a solvent decreases the freezing point of the solvent. 

ΔTF = TF (solution) - TF (pure solvent) = KF * b * i 

[Where : KF = The cryoscopic constant, which is dependent on the properties of the solvent, not the solute. Note: When conducting experiments, a higher KF value makes it easier to observe larger drops in the freezing point. For water, KF = 1.853 C°·kg/mol.

 

Thanks & Regards
Akshay Meena, 
askIITians Faculty
M.Tech, IIT Kharagpur


Akshay Meena
askIITians Faculty 34 Points
10 years ago

Boiling-point elevation describes the phenomenon that the boiling point of a liquid (a solvent) will be higher when another compound is added, meaning that a solution has a higher boiling point than a pure solvent.This happens whenever a non-volatile solute, such as a salt, is added to a pure solvent, such as water.

In sum, The boiling-point elevation means that when a solute is dissolved in a solvent, the boiling point of the resulting solution is higher than that of the pure solvent. 

ΔTb = Tb (solution) - Tb (pure solvent) = Kb * bB * i

[Where : Kb =   RTb2M/ΔHv, where R is the gas constant, and Tb is the boiling temperature of the pure solvent [in K], M is the molar mass of the solvent, and ΔHv is the heat of vaporization per mole of the solvent]

 

Freezing-point depression describes the process in which adding a solute to a solvent decreases the freezing point of the solvent.

ΔTF = TF (solution) - TF (pure solvent) = KF * b * i 

[Where : KF = The cryoscopic constant, which is dependent on the properties of the solvent, not the solute. Note: When conducting experiments, a higher KF value makes it easier to observe larger drops in the freezing point. For water, KF = 1.853 C°·kg/mol.

 

Thanks & Regards
Akshay Meena, 
askIITians Faculty
M.Tech, IIT Kharagpur

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