--%>
Assignment Help - homework help

Explain vapour pressure of liquid solutions.

Liquid solutions are obtained when the solvent is liquid. The solute can be a gas, liquid or a solid. In this section we will discuss the liquid solutions containing solid or liquid solutes. In such solutions the solute may or may not be volatile. We shall limit our discussion to the binary solution of the solid in liquid and liquid in liquid. Before we discuss the properties of these solution let us study about the vapour pressure of liquid.

When a liquid is taken in a beaker covered from above at certain temperature, a part of the liquid evaporates and its vapours fill the space available to them. The vapours formed will have an inclination to change back to its liquid state by the procedure of condensation. Gradually, equilibrium will be established between liquid and vapour phases. The pressure exerted by the vapours above the liquid surface in equilibrium with the liquid surface in equilibrium with the liquid at a given temperature is called vapour pressure of the liquid.

The vapour pressure of a liquid depends on Nature of liquid

Liquid which have weak intermolecular forces, are volatile and have greater vapour pressure. For instance, dimethyl ether has higher vapour pressure than ethyl alcohol.
    
Temperature 

Vapour pressure increases with the increase in temperature. This is due to the increase in temperature through which more molecules of the liquid can go into vapour phase.

The variation of vapour pressure of a liquid with temperature is given by the Claussius Clapeyron's equation.

2181_Liquid pressure.png   where, p1 and p2 are vapour pressures at temperature T1 and T2 respectively. Δvap.H is enthalpy of vaporization of liquid and R is universal gas constant.

Vapour pressure of the solution of solids in liquids

Let us consider the addition of a small amount of non-volatile solute such as glucose, sucrose, sodium chloride etc. to the liquid (solvent such as water) to form a solution. In such a case the vapour pressure of the solution is solely due to the solvent, as the solute is non-volatile. It is found that the vapour pressure of the solution is lower than that of the pure solvent.

Explanation: the lowering of vapour pressure can be explained on the basis of the surface area of the liquid from which evaporation occurs. In the case of the solution, a part of the liquid surface is occupied by solute particles, which are non-volatile. Therefore, evaporation of the liquid will take place from a lesser surface area. In other words, the particles (or molecules) of the liquid will now have a less tendency to escape into vapour state. This shall, therefore, result in lowering of vapour pressure.

   Related Questions in Chemistry

  • Q : Haloalkane how haloalkane can be

    how haloalkane can be prepared by refluxing alcohol with hydrohalic acids

    		•
  • Q : PH of an Alkyl Halide Briefly state the

    Briefly state the pH of an Alkyl Halide?

    		•
  • Q : Explain the molecular mass with respect

    During the formation of polymers, different macromolecules have different degree of polymerisation i.e. they have varied chain lengths. Thus, the molecular masses of the individual macromolecules in a particular sample of the polymer are different. Hence, an average value of the molecular mass is

    		•
  • Q : Equimolar solutions Select the right

    Select the right answer of the question. Equimolar solutions in the same solvent have : (a)Same boiling point but different freezing point (b) Same freezing point but different boiling poin (c)Same boiling and same freezing points (d) Different boiling and differe

    		•
  • Q : Avogadros hypothesis how avogadros

    how avogadros hypothesis used to deduce the atomicity of elementry gases ?

    		•
  • Q : Molarity what is the molarity of the

    what is the molarity of the solution prepared by dissolving 75.5 g of pure KOH in 540 ml of solution

    		•
  • Q : Problem on relative humidity Relative

    Relative humidity is the ratio of the partial pressure of water in air to the partial pressure of water in air saturated with water at the same temperature, stated as a percentage: Relative  =

    Q : Hydroxide is highly insoluble in

     : 1) Chromium(III) hydroxide is highly insoluble in distilled water but dissolves readily in either acidic or basic solution. Briefly explain why the compound can dissolve in acidic or in basic but not in neutral solution. Write appropriate equations to

    		•
  • Q : Problem based on normality Choose the

    Choose the right answer from following. NaClO solution reacts with H2SO3 as,. NaClO + H2SO3→NaCl+ H2SO4. A solution of NaClO utilized in the above reaction contained 15g of NaClO per litre. The

    		•
  • Q : Calculation of concentration of the

    Choose the right answer from following. 200ml of a solution contains 5.85 dissolved sodium chloride. The concentration of the solution will be(Na= 23: cl = 35.5 ) (a) 1 molar (b) 2 molar (c) 0.5 molar (d) 0.25 molar

    		•