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CHEMISTRY INVESTIGATORY

PROJECT

SESSION- 2015-16

TOPIC: - COLLIGATIVE PROPERTYMADE BY: - CHINMAYA JAGADEV

PATTANAYAKGUIDED BY: - MR. S.K.BAGH (PGT Chemistry)

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Certificate

This is to certify that Master Chinmaya Jagadev Pattanayak bearing Roll No. __________ of class-XII(science.) JAWAHAR NAVODAYA VIDYALAYA, Sarang, Dhenkanal (ODISHA) has successfully completed the project on the topic “COLLIGATIVE PROPERTY” under the guidance of Mr.S.K. Bagh (P.G.T.Chemistry). This project can be approved as a part of C.B.S.E in the session 2015-2016.

Signature of student:

Signature of Guide:- Signature of Principal:MR. S.K. BAGH MR. N.C. KAR

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ACKNOWLEDGEMENTI wish to express my deep sense of gratitude to them whose encouragement and cooperation has been a source of inspiration. It’s an honor to thank our principal Mr.N.C.Kar, Jawahar Navodaya Vidyalaya, Sarang, Dhenkanal for providing me the opportunity to make this project and learn through it. I would like to thank Mr.S.K. Bagh (PGT Chemistry) for providing us the right direction and for his cooperation and help in successful completion of our project.

I am indebted to both of them for their help.

.

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CONTENTS:-What is colligative property?Types of colligative propertyLowering Vapour Pressure (∆P) of solutions.

Boiling point elevation.Freezing point depressionOsmotic pressure of the solution.

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WHAT IS COLLIGATIVE PROPERTY? In chemistry, colligative properties are properties of solutions that depend upon the ratio of the number of solute particles to the number of solvent molecules in a solution, and not on the type of chemical species present. The number ratio can be related to the various units for concentration of solutions. The independence of the nature of solute particles is exact for ideal solutions, and approximate for dilute real solutions.

Here we consider only those properties which result because of the dissolution of nonvolatile solute in a volatile liquid solvent. They are independent of the nature of the solute because they are due essentially to the dilution of the solvent by the solute. The word colligative is derived from the Latin colligatus meaning bound together.

TYPES OF COLLIGATIVE PROPERTY:-1. Lowering Vapour pressure of solution: Roult’s law.

2. Elevation in boiling point (ΔTB ).3. Depression in freezing point (ΔTf ).4. Osmosis.

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1.Lowering Vapour Pressure (∆P) of solutions: Roult’s law:-

When a non-volatile solute is added to a solvent, the vapour pressure of the solution decreases.According to Roult’s Law, the vapour pressure of a solvent (P1) in a solution containing a non-volatile solute is given by

According to Raoult's Law,Vapour pressure of the pure solvent = P1°Vapour pressure of the solvent in solution = P1

    P1 = x1P1°

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  ΔP1 = P1° - P1

       = P1° - x1P1°                        = P1° (1 - x1)In a binary solution, 1 - x1 = x2

                        ΔP1 = P1° x2

                        ΔP1/P1° = (P1° - P1)/P1° = x2The lowering of vapour pressure relative to the vapour pressure of pure solvent is called relative lowering of vapour pressure.ΔP1/P1° → Relative lowering of Vapour pressureThus, the relative lowering in vapour pressure depends only on the concentration of solute particles and is independent of their identity.If the solution contains more than one non-volatile solute, then the relative lowering in vapour pressure of a solvent is equal to the sum of the mole fractions of all the non-volatile solutes.If n1 and n2 are respectively the number of moles of the solvent and solute in a binary solution, then the relative lowering in the vapour pressure of the solvent,(P1° - P1)/P1° = x1 + x2 + x3 + ... + xn

if n1 and n2 are the number of moles of the solvent and solute,

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(P1° - P1)/P1° = n2/(n1+n2)For dilute solutions n2 << n1

(P1° - P1)/P1° = n2/n1

n1 = W1/M1 , n2 = W2/M2

(P1° - P1)/P1° = (W2xM1)/(W1xM2)            W1 = Mass of solvent            W2 = Mass of solute            M1  = Molar mass of solvent            M2  = Molar mass of solute

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2. B oiling point elevation (ΔTB ):-The exact relation between the boiling point of the solution and the mole fraction of the solvent is rather complicated, but for dilute solutions the elevation of the boiling point is directly proportional to the molal concentration of the solute:

OR ΔTb = Kb.Cm Kb = Ebullioscopy constant, which is 0.512°C kg/mol for the boiling point of water. The vapour pressure of a liquid increases with an increase in temperature. When vapour pressure of the liquid becomes equal to the atmospheric pressure (or) external pressure, then liquid starts boiling. The temperature at

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which the vapour pressure of the liquid is equal to the external pressure is known as its boiling point.At any temperature, the vapour pressure of a solution containing a non-volatile solute is less than that of the pure solvent.The temperatures at which the vapour pressure of the solvent and the solution become equal to the atmospheric pressure are Tb0 and Tb.Tb-Tb0 =∆TbThus, it can be seen that the boiling point of a solution is greater than the boiling point of the pure solvent.The boiling point of a solvent changes as the concentration of the solute in the solution changes, but it does not depend on the identity of the solute particles.The elevation of the boiling point depends upon the concentration of the solute in the solution and is directly proportional to molality (m) of the solute in the solution.             ΔTb = Tb - Tb°                Tb > Tb°         ΔTb ∝ Concentration of solute        ΔTb ∝ m (Molarity)

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         ΔTb = Kb m

Kb = Boiling point elevation constant or molal elevation constant or ebullioscopic constant          

Molal elevation constant is defined as the elevation in the boiling point when 1mole of a solute is dissolved in 1kilogram of a solvent.If w2 grams of a solute with M2 molar mass is dissolved in w1gram of a solvent, then molality (m) of the solution is, m = (W2x1000)/(W1xM2)

ΔTb = Kb (W2x1000)/(W1xM2) 3. F reezing Point D epression (ΔTf ):-

The freezing point of a substance is defined as the temperature at which its solid phase is in dynamic equilibrium with its liquid phase. At the freezing point, the vapour pressure of the substance in its liquid phase is the same as the vapour pressure of the substance in its solid

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phase. When a non-volatile solute is added to a solvent, the freezing point of the solution gets lowered.According to Roult’s law, the vapour pressure of a solution containing a non-volatile solute is lower than that of the pure solvent. Thus freezing point of a solvent decreases when a non-volatile solute is added to it.

The depression in freezing point depends upon the concentration of the solution. For dilute solutions, depression in the freezing point is directly proportional to molality (m).

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Thus, ∆Tf =Kf mWhereKf =freezing point depression constant (or) molal depression constant (or) cryoscopic constant.Molal depression constant Kf can be defined as the depression in freezing point when 1mole of solute dissolved in 1kg of solvent. The unit for Kf is kelvin kilogram /mole.As Kf depends upon the nature of the solvent, its value is different for different solvents.The values of Kf can be calculated from this expression

Kf = (R x M1 x Tf2)/(1000 x ΔfusH)

    R = Gas constant   M1= Molar mass of the solvent   Tf  = Freezing point of the pure solventΔfusH = Enthalpy for the fusion of the solvent

If w2 grams of a solute with molar mass M2 is dissolved in w1 grams of a solvent, then molality m of the solution is given by W2 multiplied by 1,000 divided by w1 multiplied by M2

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Substituting this value of molality in the freezing point depression equation, we get depression in freezing point

Molarity , m = (W2 x 1000)/(W1xM2)

         ΔTf = Kf m         ΔTf = (Kf x W2 x 1000)/(W1xM2)             M2 = = (Kf x W2 x 1000)/(W1xΔTf)

Thus, the molar mass of a non-ionic solute can be calculated by using the depression in freezing point.

4. Osmosis:-Membranes which allows only solvent particles but not solute particles of solution is called semi-permeable membranes (or) SPM. These membranes can be of natural origin (or) synthetic origin.

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Vegetable membranes, membranes found under the shell of an egg are examples of natural membranes and cellophane is an example of synthetic membrane.Thus 'Osmosis' can be defined as the spontaneous flow of solvent through a semi-permeable membrane from a pure solvent to a solution or from a dilute solution to a concentrated solution.It is important to note that osmosis drives solvent molecules through a semi-permeable membrane from low solute concentrations to high solute concentrations. Osmosis ends when the solute concentration becomes equal on either side of the membrane and equilibrium is attained.The flow of solvent molecules from low concentration to high concentration can be stopped by applying some extra pressure on the high concentration side. The minimum

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pressure required to do so is known as the osmotic pressure of the solution.

Thus, osmotic pressure π of a solution is defined as the excess pressure that must be applied to a solution to prevent osmosis from taking place.Osmotic pressure does not depend on the identity of the solute, but on its concentration.Osmotic pressure for dilute solutions is proportional to molarity of the solution at a given temperature(T).                                  π ∝ C (at given T)π =  C R TR = Gas constantC = n2/Vπ =  n2RT / V

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If W2 grams of solute of molar mass M2 is present in the solution,

n2 = W2/M2

π =  W2RT / M2V

M2 = W2RT / πV

This is widely used to determine the molar masses of polymers and macromolecules, especially biomolecules, as they are generally unstable at higher temperatures and decompose before their boiling point is reached.If the solutions have the same concentrations (C1 = C2), then π1= π2.

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BIBLIOGRAPHY:-1. www.google.com2. www.slideshare.com3. www.icbse.com4. www.wikipedia.com5. www.yahoo.com