Sabtu, 17 April 2010

Determination of Partial Molal Volume

CHAPTER I
INTRODUCTION

1.1 Background

Thermodynamics is a science-related operational microscopic properties which basically can be measured. The purpose of this study is to predict the types of chemical and physical processes that may be, and in what conditions and quantitatively calculate equilibrium properties during a process.

There are three main partial molal thermodynamic properties, namely:
Partial molal volume of the components in solution.
Partial molal enthalpy (also referred to as the differential heat of solution).
Partial molal free energy (called the chemical potential).

Molal volume of solution is defined as the volume expansion that occurs when one mole of component i added to the partial molal.Volume can also be defined as a contribution to the volume, of one component in a sample of the total volume. Partial molal volumes of a mixture varies depending on the composition, because each type of molecule to change its environment, if the composition changed from pure A to B pure. Nature partial molal most easily illustrated by the volume of contributions to the partial molal volumes of one component in the sample to volume total.

In this experiment, we will try to determine the partial molal volume of a solution, where we will find the relation between the partial molal volume with concentration.

1.2 Experiment Objectives
1.2.1 Experimental Purposes

The purpose of this experiment was to study and understand the method of determination of partial molal volume of solution.

1.2.2 Experiment objectives


The purpose of this experiment is to determine the partial molal volume of sodium chloride solution as a function of solution concentration using piknometer.


1.3 Principle Experiment

The principle of this experiment is the determination of partial molal volume of sodium chloride with different concentrations by measuring the density of the solution using piknometer.



CHAPTER II
LITERATURE REVIEW

In thermodynamics there are two types of variables, namely:
Extensive variables that depend on the amount of phase, eg, V, U, H, S, of A, G.
Intensive variables that do not depend on the number of phases, for example: P and T (Taba and Fauziah, 2006).

Molal volume of solution (V 1) is defined as the volume expansion that occurs when 1 mole of component i added to the solution. The total volume of solution containing 1000 g (55.51 mol) of water and solutes mmol given by the equation:

V = N 1 V 1 + N 2 V 2 = 55.51 V 1 + m V 2

Suppose V 1 ˚ is the molal volume of pure water (V 1 = 18.016 ˚ / 0.997044 = 18.069 cm 3 at 25 ˚ C), the molal volume of solute ( ) Is defined as follows:

V = N 1 V 1 ˚ + N 2 V 2 = 55.51 V 1 ˚ + m or

Where d = density of solution

d 0 = density of pure solvent

M 2 = molecular weight solutes

Thus obtained:
Where We = weight of empty piknometer

Wo = Weight piknometer containing pure water

We = Weight piknometer containing solution

(Taba and Fauziah, 2006).

Partial molal properties are most easily illustrated by the volume of contributions to the partial molal volume of one component in a sample of the total volume. Stating the total volume of mixture V, using the following:

V = n a. V a = n b. V b

The reasons underlying this simple result is as follows: imagine a very large sample from a mixture of specific composition. Then if a number n a substance A added for N a. V a. sample now occupies a larger volume, but the ratio remains the same components (Atkins, 1994).

Partial molar volume of a substance can be interpreted as a change in volume when 1 mol of the substance added to a mixture of a very large volume. The total volume of the mixture can be interpreted as the partial molar volume of component

There are three main partial molal thermodynamic properties, namely: (i) partial volume of component-kompenen in solution, (ii) the partial molal enthalpy, and (iii) the partial molal free enegi (Glance, 2009).

Partial volume (and the partial molal quantity generally) can be measured in several ways. One method is to measure the volume dependence on the composition and determining the slope of the dV / dn on the composition of the known (Atkins, 1994).

Molal molal volume and entropy is always positive, but the corresponding partial molal quantity need not be. For example, the partial molal volume limit of MgSO 4 (partial molal volume in the limit of zero concentration is -1.4 cm 3 / mol), which means the addition of 1 mol of MgSO 4 into the large volume of water that produces the decrease in volume of 1.4 cm 3. Depreciation occurs because the salt was decided that the open structure of water when hydrated ions so that the volume is slightly shrunk (Atkins, 1994).

Density of the substance is not a fixed quantity, but varies depending on the pressure and temperature when the measurement. For some substances (especially gases and liquids), the volume will be more easily measured than its mass, and if rapatannya known to the conversion factor between volume and mass can be obtained. By knowing the density and molar mass of a substance, we can easily calculate the molal volume, ie volume occupied by one mole of substance.

Vm = = Molar volume (cm 3 mol -1)(Oxtoby et al, 2001).

Behave in an ideal system with all the thermodynamic relations derived by this model. Because it's from ideal behavior, the thermodynamic relations derived can be described in two parts, namely:
Partial molal quantities, such as the partial molal volume, enthalpy, and so forth.
Activity and activity coefficient, the application of Debye-Huckel limiting law.

There are three main partial molal thermodynamic properties, namely:
Partial molal volume of the components in solution.
Partial molal enthalpy (also referred to as the differential heat of solution).
Partial molal free energy (called the chemical potential).

Partial molal volume of the components of a mixture changes depending on the composition, because each type of molecular environmental changes if the molecular composition changed from pure A to B pure. Molecular environmental changes and changes in the forces acting between molecules is what produces the variation of thermodynamic properties of the mixture if the composition changed. Partial molal volume of water and ethanol throughout full range of composition, at a temperature of 25 ˚ C. once we know the partial molal volume of water and ethanol or a mixture of these two particular composition, we can determine its properties (and Dogra Dogra, 1990).

The total volume of solution containing 1000 grams (55.51 moles) of water and m moles of solute is given by the equation

V = N 1 V 1 + N 2 V 2 = 55.51 V 1 + mV 2 (1)

Suppose V 1 o is a pure volumemolalair (V 1 o = 18.016 / 0.997044 = 18.069 cm 3 at 25 °), the molal volume of solution (ф) is defined as follows:

V = N 1 V 1 O + N 2 V 2 = 55.51 V 1 o + Mф (2)

or

ф = (3)

unknown

V = (4)

Where d: density of solution

d o: density of pure solvent

N 2: molecular weight solutes

Thus obtained:

ф = (5)

ф = (6)

Where W e: weight empty piknometer

W o: weight piknometer containing pure water

W: weight piknometer containing solution

(Taba and Fauziah, 2006).

Partial molal Quantities tell us how the properties of solutions change with concentration. We need to know the partial molal Quantities for all the extensive properties of a solution, including V, G, H, S, and A. For example, the partial molal volume is Important in Oceanography and aquaticenvironmental science, Which Is Why We Measure the partial molal volume of NaCl solutions in this lab. That is another example of partial molal volume is needed for careful Calculations in Biochemistry of the molecular weights of proteins and nucleic acids using ultracentrifugation (Atkins, 1994).

Number of partial molal us how the properties change with the concentration of the solution. We need to know the amount of partial molal for all extensive properties of solutions, including the V, G, H, S, and A. For example, the partial molal volume is important in oceanography and marine environmental science, which is why we measure the partial molal volume of NaCl solution at this laboratory. Another example is that the partial molal volume is needed in biochemistry for careful calculation of molecular weight of proteins and nucleic acids using ultracentrifugation (Atkins, 1994).

There are three main partial molal thermodynamic properties, namely

(A) The partial molal volume of the components in the solution

(B) partial molal enthalpy (also called heat differential)

(C) The partial molal free energy (chemical potential)

These qualities were obtained with the help of (a) graphical method, (b) using the relationship analitikyang shows the relationship J and n i, and (c) using a function called real molal scale which is determined as:

ф J i = (7)

where J i n is the molal price for pure components, and using interseft. One thing to remember is that the partial molal properties of a component in a solution, and molal properties for pure compounds is the same as if the solution is ideal (Dogra and Dogra, 1990).

Calculation of partial molal can transactions are carried out in several ways, namely:
Graph Method

In this method, the value of J plotted as a function of composition composition solution by keeping all other components and equipment, except one. If the plot is linear, the slope of the line will be a partial molal quantity of that component. It also shows that the partial molal properties of these components is also not dependent on the concentration. If the plot in this case is not linear, then:

J i = n → 0 (8)

(Dogra and Dogra, 1990)

Analytical Methods
If extensive price can be expressed as an algebraic function of these compositions, the partial molal properties can be computed in anallitik (Dogra and Dogra, 1990).

Sodium is a soft silver-white metal, which melted at a temperature of 97.5 ° C. Sodium rapidly oxidized in moist air, it must be kept entirely submerged in the solvent naphtha or xylene. This metal reacts violently with water, forming sodium hydroxide, and hydrogen:

2Na + 2H 2 O → 2Na + + 2OH - + H 2 ↑



CHAPTER III
EXPERIMENT METHOD

3.1 Materials


The materials used in them is 3 M NaCl, distilled water, paper labels, and the tissue roll.
Experiment Equipment

3.2 Tools

The tools used in this experiment is to squash them drinks 100 mL, 500 mL beaker, piknometer, analytical balance, pumpkin spray, pipette 50 mL volume, volume of 10 mL pipettes, pipettes volume 5 mL, bulb and pipette drops.

3.3 Experimental Procedure


3 M NaCl was diluted so that its concentration becomes and times the concentration originally by way memipet mother liquor (NaCl 3 M) were 25 mL for the concentration of 1.5 M and 12.5 mL for the concentration of 0.75 M. As for the concentration of 0.375 M NaCl 1.5 M was taken as much as 12.5 mL of 0.1875 M and for the concentration of 0.75 M NaCl was taken as much as 12.5 mL, then all the solution is diluted in a pumpkin drinks to mark the boundary with distilled water.
Empty Pikno clean, dry and weighed.
Piknometer filled with distilled water and then closed tightly and the outer layer was dried using a towel roll and then weighed.
Piknometer replaced with distilled water in 3 M NaCl, 1.5 M, 0.75 M, 0.375 M; and 0.1875 M. every turn of the solution, it must be rinsed piknometer repeatedly with a solution that will be used.
Recorded at room temperature.



CHAPTER IV
RESULTS AND DISCUSSION

4.3 Discussion

Through this experiment we can determine the molal volume of NaCl as a function of concentration by measuring the density of the solution. Solution density measurements carried out using piknometer.

In this experiment, NaCl was used as a material which will be determined the value of its partial molal volume in various concentrations. Dilution carried out to determine how the relationship with a large concentration of a solution of the partial molal volume. 3 M NaCl was used diluted into and from the original concentration. In addition to the concentration, density can also affect the partial molal volume. As for room temperature recording done in order to obtain the density of the solution.

Density measurements performed using piknometer. Measurement is done by weighing the empty and piknometer piknometer containing sample solution first. Piknometer empty weighing is done as a comparison. In order not to affect the results of measurements, piknometer used should be in a state of absolutely dry. Similarly, while changing the NaCl solution in different concentrations, piknometer should be cleaned and rinsed the inside with a solution that will be used. This needs to be done so that the solution to be measured density is not contaminated with other substances.

From this experiment, the obtained solution molal volume ( ) 3 M NaCl at 32.3953 , 1.5 M NaCl at 24.0522 , 0.75 M NaCl at 23.7124 , 0.375 M NaCl at 23.6374 , And NaCl at 23.5077 0.1875 .

Partial molal volume is the volume expansion that occurs when 1 mole of component I added to a solution. The result is negative, ie

The value of the partial molal volume showed a negative value, meaning the event of termination bonding solution, which occurred in this experiment is to break the bond between the ions Na + and Cl - ion. Where merupkan NaCl initially, then changed to the constituent ions, namely Na + and Cl -.




CHAPTER V
CONCLUSIONS AND RECOMMENDATIONS

5.1 Conclusion

From the experiments obtained slope value of 20.687 .

5.2 Suggestions

More assistants should oversee the workings praktikan and explain in more detail. Experiments carried out should also be used in various types of other substances in the determination of partial molal volume so that we can compare between the materials to each other value of the partial molal volume.



REFERENCES

Atkins, PW, 1994, Chemical Physics, grants, Jakarta.

Atkins, PW, Physical Chemistry, 7th Ed, Section 7.1, grants, Jakarta.

Dogra, SK, and Dogra, S., 1990, Physical and Chemical Problems, Penenrbit University of Indonesia, Jakarta.

Oxtoby, DW, Gillis, HP and Nachtriebe, NH, 2001, Principles of Modern Chemistry, grants, Jakarta.

Of view, Tuntung., Monday, 07 December 2009.

Taba, P., and Paulina, St., 2006, Practical Guide of Physical Chemistry, Physical Chemistry Laboratory Science, State UH, Makassar.

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