--%>

What is depression in freezing point?

Freezing point of a substance is the temperature at which solid and liquid phases of the substance coexist. It is defined as the temperature at which its solid and liquid phases have the same vapour pressure.

The freezing point of a pure liquid is preset. Now, if a non-volatile solute is dissolved in the pure liquid to constitute a solution, there occurs a lowering in the freezing point. The freezing point of solution refers to the temperature at which the vapour pressure of the solvent in two phases, i.e. liquid solution and solid solvent is the same. Since the vapour pressure of the solvent at a lower temperature.

Evidently the freezing point of the pure solvent is the temperature corresponding to the point B (T0 K) and that of the solution is the temperature corresponding to the point A'(T1 K). Clearly, (T0 - T1) or ΔTƒ is the freezing point depression. Since its magnitude is determined by that of lowering of vapour pressure, the freezing point depression depends upon the molal concentration of the solute and does not depend upon the nature of solid. It is, thus, a colligative property. The general relation between these two quantities for a solution of non-electrolyte is usually expressed in term of molality of the solution

ΔTƒ  Δp and Δp xB

ΔTƒ = kxB =415_freezing point.png 


For dilute solution, 272_freezing point1.png   and hence,1964_freezing point2.png.


ΔTƒ = k 1278_freezing point3.png  = k582_elevation in boiling point4.pngMA


If WA is the mass of solvent in kg, then   is equal to molality (m) of the solution

ΔTƒ = kMAm     (? kMA = Kƒ)

ΔTƒ =Kƒm, where Kƒ is called Freezing point depression constant or molal depression constant or cryoscopic constant.

As is clear from the above, depression in freezing point depends upon relative number of moles of solute and solvent but does not depend upon nature of solute, so it is a colligative property.

   Related Questions in Chemistry

  • Q : Explain Phase Rule The relation between

    The relation between the number of phases, components and the degrees of freedom is known as the phase rule. One constituent systems: the identification of an area on a P-versus-T with one phase of a component system illustrates the two degrees of freedom that

  • Q : Calculating Formulae Superphosphate has

    Superphosphate has the formula CaH4(PO4)2 H2O, what is the calculation to get the percentage of Phosphorus, I need to show the calculation. I know it is 30.9737622 u in weight and 2 atoms of the formula, but not sure how to work the calculation backwards.

  • Q : Meaning of molality of a solution The

    The molality of a solution will be: (i) Number of moles of solute per 1000 ml of solvent (ii) Number of moles of solute per 1000 gm of solvent (iii) Number of moles of solute per 1000 ml of solution (iv) Number of gram equivalents of solute per 1000 m

  • Q : Question relatede to calculate molarity

    Select the right answer of the question. What is molarity of a solution of HCl that contains 49% by weight of solute and whose specific gravity is 1.41 : (a) 15.25 (b) 16.75 (c) 18.92 (d) 20.08

  • Q : Vant Hoff factor The Van't Hoff factor

    The Van't Hoff factor of the compound K3Fe(CN)6 is: (a) 1  (b) 2  (c) 3  (d) 4  Answer: (d) K3[Fe(CN)6] → 3K+

  • Q : Ions in solution The accuracy of your

    The accuracy of your written English will be taken into account in marking. 1.    (a)   Identify the spectator ions in the following equation                    &nb

  • Q : Acid value definition The acid value

    The acid value definition is the number milligrams of KOH needed to neutralize the acid present in one gram oil and fats however why not employ NaOH for the neutralization?

  • Q : Eutectic Formation In some two

    In some two component, solid liquid systems, a eutectic mixture forms.Consider, now a two component system at some fixed pressure, where the temperature range treated is such as to include formation of one or more solid phases. A simple behavior is shown b

  • Q : Why medications include the hcl Why do

    Why do various medications include the hcl? Describe briefly?

  • Q : Calculate PH value for a acetic acid 1.

    1. A solution of 0.100 M acetic acid is prepared. a) What is its pH value? b) If 20% of the initial acetic acid is converted to the acetate form by titration with NaOH, what is the resultant pH?