[COLIGATIVE PROPERTIES] [III Group]

A. TITLE

: Coligative PropertiesB. DATE

: April, 2sc 2013C. PURPOSE

: To learn about the effect kind of solution toward the boiling point

D. BASIC THEORY:

Colligative properties are properties of solutions that depend on the ratio of the number of solute particles to the number of solvent molecules in a solution. They are independent of the nature of the solute particles.

Colligative properties include: (1) relative lowering of vapor pressure; (2) elevation of boiling point; (3) depression of freezing point and (4) osmotic pressure. Measurements of these properties for a dilute aqueous solution of a non-ionized solute such as urea or glucose can lead to accurate determinations of relative molecular masses. Alternatively, measurements for ionized solutes can lead to an estimation of the percentage of ionization taking place.

Vapor pressureThe relationship between the vapor pressure and concentration is given by Raoult's law, which states that:

The vapor pressure of an ideal solution is dependent on the vapor pressure of each chemical component and the mole fraction of the component present in the solution.Colligative properties are mostly studied for dilute solutions.

When a nonvolatile solute is added to a liquid to form a solution, the vapor pressure above that solution decreases. To understand why that might occur, let's analyze the vaporization process of the pure solvent then do the same for a solution. Liquid molecules at the surface of a liquid can escape to the gas phase when they have a sufficient amount of energy to break free of the liquid's intermolecular forces. That vaporization process is reversible. Gaseous molecules coming into contact with the surface of a liquid can be trapped by intermolecular forces in the liquid. Eventually the rate of escape will equal the rate of capture to establish a constant, equilibrium vapor pressure above the pure liquid.

If we add a nonvolatile solute to that liquid, the amount of surface area available for the escaping solvent molecules is reduced because some of that area is occupied by solute particles. Therefore, the solvent molecules will have a lower probability to escape the solution than the pure solvent. That fact is reflected in the lower vapor pressure for a solution relative to the pure solvent. That statement is only true if the solvent is nonvolatile. If the solute has its own vapor pressure, then the vapor pressure of the solution may be greater than the vapor pressure of the solvent.

Note that we did not need to identify the nature of the solvent or the solute (except for its lack of volatility) to derive that the vapor pressure should be lower for a solution relative to the pure solvent. That is what makes vapor pressure lowering a colligative property--it only depends on the number of dissolved solute particles. Summarizes our discussion so far. On the surface of the pure solvent (shown on the left) there are more solvent molecules at the surface than in the right-hand solution flask. Therefore, it is more likely that solvent molecules escape into the gas phase on the left than on the right. Therefore, the solution should have a lower vapor pressure than the pure solvent.

Figure 1: The Vapor Pressure of a Solution is Lower than that of the Pure Solvent

Boiling point and freezing pointBoth the boiling point elevation and the freezing point depression are proportional to the lowering of vapor pressure in a dilute solution

Boiling point elevation

One consequence of Raoult's law is that the boiling point of a solution made of a liquid solvent with a nonvolatile solute is greater than the boiling point of the pure solvent. The boiling point of a liquid or is defined as the temperature at which the vapor pressure of that liquid equals the atmospheric pressure. For a solution, the vapor pressure of the solvent is lower at any given temperature. Therefore, a higher temperature is required to boil the solution than the pure solvent. is a phase diagram for both a pure solvent and a solution of that solvent and a nonvolatile solute that explains that point graphically.

Figure 2: Phase Diagram for a Solvent and its Solution with a Nonvolatile SoluteBoiling Pointtotal = Boiling Pointsolvent + TbTb = b * Kb * i,

Where : (Kb = ebullioscopic constant, which is 0.512C kg/mol for the boiling point of water; b = molality; i = Van 't Hoff factor)

Boiling point is achieved in the establishment of equilibrium between liquid and gas phase. At the boiling point, the number of gas molecules condensing to liquid equals the number of liquid molecules evaporating to gas. Adding any solute effectively dilutes the concentration of the liquid molecules, slowing the liquid to gas portion of this equilibrium. To compensate for this and re-attain the equilibrium, boiling point is achieved at higher temperature. Any description of a colligative property which includes steric occlusion, or blocking of the surface to reduce the vapor pressure has no basis in reality, despite the fact that this explanation is frequently taught. This is also why vapor pressure and boiling point are independent of a liquid's accessible surface area. Alternatively, measurements for ionized solutes can lead to an estimation of the percentage of ionization taking place.

Freezing point depression (cryoscopy)

As you may have noticed when we looked at the , the freezing point is depressed due to the vapor pressure lowering phenomenon. The points out that fact:

Figure 3: Phase Diagram for a Solution and the Pure Solvent Indicating the Freezing Point Depression

Where: (Kf = cryoscopic constant, which is -1.86C kg/mol for the freezing point of water; b = molality; i = Van 't Hoff factor)

Note that the sign of the change in freezing point is negative because the freezing point of the solution is less than that of the pure solvent. Just as we did for boiling point elevation, we use molality to measure the concentration of the solute because it is temperature independent. Do not forget about the van't Hoff factor, i, in your freezing point calculations.

One way to rationalize the freezing point depression phenomenon without talking about Raoult's law is to consider the freezing process. In order for a liquid to freeze it must achieve a very ordered state that results in the formation of a crystal. If there are impurities in the liquid, i.e. solutes, the liquid is inherently less ordered. Therefore, a solution is more difficult to freeze than the pure solvent so a lower temperature is required to freeze the liquid.

Freezing point, or the equilibrium between a liquid and solid phase is generally lowered in the presence of a solute compared to the solid phase, hence, fewer molecules participate in the equilibrium. Again, re-establishment of equilibrium is achieved at a lower temperature at which the rate of freezing becomes equal to the rate of liquefying.

The freezing point of a substance is defined as the temperature at which the vapor pressure of its liquid is equal to the vapor pressure of the corresponding solid. Since the addition of a non-volatile solute always lowers the vapor pressure of solvent, therefore, it will be in equilibrium with solid phase at a lower pressure and hence at a lower temperature. The difference between the freezing points of the pure solvent and the solution is called depression in freezing point or cryoscopy.

Osmotic pressure

Osmosis refers to the flow of solvent molecules past a semipermeable membrane that stops the flow of solute molecules only. When a solution and the pure solvent used in making that solution are placed on either side of a semipermeable membrane, it is found that more solvent molecules flow out of the pure solvent side of the membrane than solvent flows into the pure solvent from the solution side of the membrane. That flow of solvent from the pure solvent side makes the volume of the solution rise. When the height difference between the two sides becomes large enough, the net flow through the membrane ceases due to the extra pressure exerted by the excess height of the solution chamber. Converting that height of solvent into units of pressure (by using the ) gives a measure of the osmotic pressure exerted on the solution by the pure solvent. P stands for pressure, r is the density of the solution, and h is the height of the solution.

shows a typical setup for measuring the osmotic pressure of a solution.

Figure 4: Setup for Measuring the Osmotic Pressure of a Solution

Two laws governing the osmotic pressure of a dilute solution were discovered by the German botanist W. F. P. Pfeffer and the Dutch chemist J. H. vant Hoff:

1. The osmotic pressure of a dilute solution at constant temperature is directly proportional to its concentration.

2. The osmotic pressure of a solution is directly proportional to its absolute temperature.

These are analogous to Boyle's law and Charles's Law for gases. Similarly, the combined ideal gas law, PV = nRT, has an analog for ideal solutions:

Where: = osmotic pressure; V is the volume; n is the number of moles of solute; R = .08206 L atm mol-1 K-1, the molar gas constant; T is absolute temperature; i = Van 't Hoff factor.

This can be simplified to:

Where

: (M = Molarity).

E. DESIGN OF EXPERIMENT :

a) Tools and Materials :

Tools :

Beaker Glass

8 pieces

Thermometer

1 piece Clipper

1 piece Spatula

1 piece

Ohaus Balance

1 piece

Watch Glass

1 piece

Electrical stove

1 piece

Spiritus Burner

1 piece

Materials :

Sugar

Salt

Aquades

b) Experiment Step :

a. Increasing of Boiling Point from Elektrolit & non-Electrolit solution. 1. Prepared three beaker glass and fill each with 50 mL aquades 2. Add two of the beaker glass 3,42 gram of sugar and 0,58 gram of table salt 3. Heated three of the beaker glass until boiling and noted the temperature.b. The Increasing of Electrolit & Non-Electrolit Temperature. 1. Prepared beaker glass 100 mL 8 piece and give identity 1a,2a, 3a, 4a, 1b, 2b, 3b, 4b and fill the each with aquades 50 mL

2. Heated 8 of the beaker glass until boiling and noted the temperature3. Add sugar into the beaker glass 1a, 2a, 3a, 4a each 3,42 g ; 6,84 g ; 10,26 g ; 13,68 g. Shaked until sugar dissolved then heated until boiling and noted the temperature.4. Into the beaker glass 1b, 2b, 3b, 4b added each of table salt 0,58 g ; 1,17 g ; 1,75 g ; 2,35 g. Shaked until table salt dissolved then heated and noted the temperature.

5. Determine the molal in every solution, then prove the data make ghrapic between temperature toward sugar contents or table salt contents

c). Procedur :

1. Increasing Boiling Point from Electrolit & Non-Electrolit Solution

2. The Increasing of Electrolit & Non-Electrolit Temperature

F. EXPERIMENT RESULT :

NOPROCEDURRESULTHYPOTESISCONCLUSION

BEFOREAFTER

1.

Sugar : crystal rather brown

T1 = 280 C

Salt : colorless

T2 = 280 C

Aquades: colorless

T3 = 280C

Sugar : rather brown solution

Tb = 1010 C

Salt : colorless colorless Tb = 1040 C

Aquades: colorless solutionTb = 1000C

Salt has the highest temperatureThe NaCl or salt has higher temperature than sugar and aquades because NaCl solution is kind of electrolit solution.

NOPROCEDURRESULTHYPOTESISCONCLUSION

BEFOREAFTER

2.The color of aquades before addition sugar is colorless

The color of aquades before addition salt is colorless1. Sugar :a. rather turbid solution (+)

T1 = 100.5 0C

b. rather turbid solution (++)

T2 = 101 0C

c. rather turbid solution (+++)

T3 = 102 0C

d. rather turbid solution (++++)

T4 = 102 0C

2. Salt :a. colorless solutionT1 = 100 0C

b. colorless solution T2 =101 0C

c. colorless

solutionT3 = 101 0C

d. colorless

T4 = 102 0CThe boiling point of sugar 13.68 grams (the highest mass of sugar) has the highest temperature

The boiling point of salt 2.35 grams (the highest mass of salt) has the highest temperature

The higher mass, the higher boiling point.

G. DATA ANALYSIS :

In the first experiment, experiment about Increasing of Boiling Point Electrolyte and Non Electrolyte, we know that salt solution is electrolyte and sugar solution is non electrolyte. The boiling point of salt solution is higher than the boiling point of sugar solution , the boiling point of salt solution is 104, whereas the boiling point of aquades solution is 100 and the boiling point of of sugar solution is 101, in this experiment show that electrolyte solution has higher boiling point than non electrolyte boiling point because in electrolyte solution is occured in a perfect decomposition. And also , it is also influenced of Vant Hoff factor owned by electrolyte solution that total of particle in salt solution as many as twice from sugar solution. So, for boiling point of salt solution needs more heat energy to make it boiled than sugar solution and aquades.

In the second experiment, Increasing of Electrolyte and Non Electrolyte Temperature (in sugar solution), we make the differences in sugar mass. 3.42 grams the boiling point of it is 100.5C, 6.84 gams the boiling point of it is 101C, 10.26 grams the boiling point of it is 102C, and 13.68 grams the boiling point of it is 102C. the mass give effect to the boiling point of solution. This is happen because the higher the mass of substances, the molality will higher, so it make the boiling point is higher too.

In the next experiment (in salt solution) increasing the boiling point of salt solution. The variety of salt mass is 0.58 grams the boiling point of it is 100C, 1.17 grams the boiling point of it is 101C, 1.75 grams the boiling point of it is101C, and 2.35 grams the boiling point of it is 102C. Because higher the mass of substances, the molality will higher, so it make the boiling point is higher too.H. DISCUSSION :

In our experiment about Colligative Properties of Solution, In first experiment the boiling point of salt solution is higher than the boiling point of sugar solution , the boiling point of salt solution is 104 , the boiling point of aquades is 100 and the boiling point of of sugar solution is 101, it can happened because the salt solution is electrolyte. It is influenced of Vant Hoff factor owned by electrolyte solution that total of particle in salt solution as many as twice from sugar solution. So, for boiling point of salt solution needs more heat energy to make it boiled than sugar solution and aquades.

In the second experiment, we use sugar with mass 3.42 grams, 6.84 grams, 10.26 grams, and 13.68 grams. It will affect the boiling point of solution. This is happen because the greater the mass of substances, the higher the molality, so it make the boiling point is higher too. But the boiling point from experiment and from theory is little different, it is because the thermometer that we use is thermometer standard, that cant show value decimal.

In the next experiment (in salt solution) increasing the boiling point of salt solution. The variety of salt mass is 0.58 grams, 1.17 grams, 1.75 grams, and 2.35 grams. The higher the molality higher the boiling point of salt solution. For salt solution, amount of particle is twice from sugar solution, because Vant Hoff Factor of salt is 2, so although mass of salt that we use less than mass of sugar, the boiling point of salt is almost the same.

I. CONCLUSSION :Base on the experiment, we can conclude that : Colligative Properties of Solution is properties of solutions that depend upon the ratio of the number of solute particles to the number of solvent molecules in a solution.

The molality of solution will influence in boiling point. The greater the molality of solution, greater the boiling point. Electrolyte solution has the higher boiling point than non electrolyte. Because it is influenced by Vant Hoff Factor which isnt had by non electrolyte solution. J. ANSWER of QUESTION :QUESTION

1. Why the boiling point of sugar is higher than water?

2. Why colligative properties electrolyte solution is higher than nonelectrolyte solution?

ANSWER

1. The boiling point of sugar is higher than water because in the solution there are a lot of particles that hold out the aqueous to make the temperature vapor pressure equals the external atmospheric pressure (the meanimg of boiling point) and of course it needs more energy to evaporate the solution that hold out. Energy here is the heat.2. In colligative properties electrolyte solution is higher than non electrolyte solution because electrolyte solution has more particles than non electrolyte solution and of course it needs more energy to release from particles that hold out. Thats why the boiling point is higher.

BIBLIOGRAPY :

Hein, Morris and Susan Arena. 2007. Foundation of Collage Chemistry. Twelfth Edition. USA: John Wiley&Sons, Inc. Tim Kimia Dasar.2013.Petunjuk Praktikum Kima Lanjut.Unesa:Unipress.

Chang, Raymond.General Chemistry: The Essential Concept/Raymond Chang- 3rded.America:Von Hoffman Press, Inc.

Brady, James E. 1990. General Chemistry:Principle and Structure 5 thed. United State of America.

Svehla,G. 1979. Vogel:Longman Group Limited. London.

ATTACHEMENT

PictureExplanation

The result of the first experiment, after adding sugar, salt and aquades

The result of the second experiment after adding sugar, it showed that as much as the sugar that we add, it can make effect to the temperature and the color.

The result of the second experiment after adding salt, it showed that as much as the sugar that we add, it can make effect to the temperature.

Known :

mass C12H22O11 1 = 3.42 grams

mass C12H22O11 2 = 6.84 grams

mass C12H22O11 3 = 10.26 gramsmass C12H22O11 4 = 13.68 grams

mass NaCl 1 = 0.58 grams

mass NaCl 2 = 1.17 grams

mass NaCl 3 = 1.75 grams

mass NaCl 4 = 2.35 grams

i NaCl = 2

volume of Aqueous = 25 ml

Kb Aqueous = 0.520C/m

T0b = 1000C

calculation1. Boiling point of C12H22O11 3.42 grams

2. Boiling point of C12H22O11 6.84 grams

3. Boiling point of C12H22O11 10.26 grams

4. Boiling point of C12H22O11 13.68 grams

5. Boiling point of NaCl 0.58 grams

6. Boiling point of NaCl 1.17 grams

7. Boiling point of NaCl 1.75 grams

8. Boiling point of NaCl 2.35 grams

Mass of sugarTb experiment (C)Tb calculate (C)

3,42100,5100,104

6,48101100,208

10,26102100,312

13,68102100,416

Mass of Salt (gr)Tb experiment (C)

Tb calculate (C)

0,58100100,208

1,17101100,416

1,75101100,624

2,35102100,832

Boiling Pointtotal = Boiling Pointsolvent + Tb

Tb = b * Kb * i,

Freezing Pointsolution = Freezing Pointsolvent - Tf

Tf = b * Kf * i,

V = n .R. T. i

= M. R. T. i

50 ml of aquades + 3.42 grams of sugar

50 ml of aquades

50 ml of aquades + 0.58 grams of salt

Boiled

Noted the temperature

8 beaker glass 100 ml, consist of 50 ml of aquades

Boiled

1.a. added by 3.42 grams of sugar

1.b. added by 6.84 grams of sugar

1.c. added by 10.26 grams of sugar

1.d. added by 13.86 grams of sugar

2.a. added by 0.58 grams of salt

2.b. added by 1.17 grams of salt

2.c. added by 1.75 grams of salt

2.d. added by 2.35 grams of salt

Stirred until all matters are dissolved

Boiled

Noted the temperature

50 ml of aquades + 3.42 grams of sugar

50 ml of aquades

50 ml of aquades + 0.58 grams of salt

Boiled

Noted the temperature

1.a. added by 3.42 grams of sugar

1.b. added by 6.84 grams of sugar

1.c. added by 10.26 grams of sugar

1.d. added by 13.86 grams of sugar

2.a. added by 0.58 grams of salt

2.b. added by 1.17 grams of salt

2.c. added by 1.75 grams of salt

2.d. added by 2.35 grams of salt

8 beaker glass 100 ml, consist of 50 ml of aquades

Boiled

Stirred until all matters are dissolved

Boiled

Noted the temperature

EMBED Equation.3

[UNESA] | INTERNATIONAL CHEMISTRY EDUCATION 2012 14

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