3.0 DISCUSSION

In this experiment physical and transport properties are investigated in four sets which are

density and partial molar volumes, determination of molecular weight by viscosity

measurements, diffusion coefficient on silicahydrogel and determination of the concentration by

the help of rotation angle.

In the first set, partial molar volume of solution components are calculated by using

experimentally determined density values. Density is an intensive property which is weight of

unit volume of any substance. Pycnometer is used in the experiment for the calculation of the

density. Solution densities decreased due to the addition of alcohol since the density of alcohol is

lower than the water. In order to determine the partial molar volumes of alcohol and water 1/ρ

versus W2 graph is plotted. At the specific concentration which is given as 35 %, the tangent to

the curve gives the partial molar volume of the substances. According to the calculations and

Figure 1, partial molar volumes are obtained as 45.8574 mL/gmol for alcohol and 17.9118

mL/gmol for water.

There are some important points to be considered during this experiment. The air bubbles

in the pycnometer should be removed in order to get rid of weighting errors and overloading of

the pycnometer. The other important point is to weight the pycnometer as soon as possible after

filling them due to rapid evaporation of ethyl alcohol. For weighting a scale is used. There should

not be any air circulation around the scale and contact to the table of scale since these may result

as an error.

In the second set, molecular weight of Sodium Alginate is determined by viscosity

measurement. Oswalt viscometer and viscotester are used to determine the viscosity of the

Sodium Alginate and PVA (without Oswalt viscometer). In order to determine the molecular

weight of a substance, a viscosity versus concentration graph is used. By extrapolating the curve

to zero the viscosity value is found.

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In this experiment several reasons cause some errors. These reasons are; the capillary of

Ostwald Viscometer has been broken several times and it has been repaired. So, it can’t work

regularly. Also, if we slant the Oswald Viscometer the time will be increase. Hence, we can’t

calculate the viscosity correctly. Our viscotester is old, so we can’t measure correctly.

In the third set, diffusion coefficient of silicahydrogel which means the ratio of flux to

concentration gradient was obtained by the mass transfer between water and silicahydrogel. This

coefficient is calculated by using the amount of H+ diffused into the water. As the time increased,

pH of the solution decreased due to the increase in the diffused H+ amount until system reaches to

the equilibrium.

A stirrer was used in order to obtain homogeneous solution and increase diffusion rate.

Since the stirrer may cut the silicahydrogel into pieces, the mixer should not touch the

silicahydrogel. If it touches, silicahydrogel and water are mixed without diffusion. Electrode,

which measures the pH value, should not contact with mixer for protection.

The experimental value of diffusion coefficient is lower than the theoretical experimental

one. Because there may be already diffused H+ ions that exist in the water. pH-meter is not

sensitive.Therefore, we can’t measure pH value exactly.

In the fourth and last set of the experiment, we measure the rotation angle(optical

rotation) to calculate concentration of saccharose solution. This measurement is made by disk

polarimeter which looks like refractometer. By using the disk polarimeter, specific gravity,

purity, concentration, and contents of active materials can be determined. If the rotation is

clockwise the rotation angle is said to be positive, when the rotation it is counterclockwise the

angle is negative. By the given data we plot the calibration curve and by its slope we calculate the

specific optical rotation of saccharose. Then the average concentration of sample solution is

calculated as 0.9718 gr/100mL by the help of this.

There is some error in this experiment, because sensitive eyes are required for this

experiment.

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Viscosity changes with temperature and sometimes also with pressure.

Specific volume is the number of cubic feet occupied by one pound of the

substance.Density is the weight per unit volume of the substance. Therefore,

specific volume is the reciprocal of the density.

Because, specific volume is smaller than the density.So, calculation with specific

volume is easier than the density.

Volumetric flowrate will decrease when the viscometer is slanted. Hence, the time

will increase and the experiment error will increase

If temperature increases, viscosity decreases or vice versa.

The nature of the material to be tested(if it is of high or low viscosity whether it is

elastic or not;the temperature of viscosity,accuracy and precision required are

important criteria for selecting viscometer.

Capillary(f.e. Ostwaldviscometer),rotational(concentric cylinder viscometer),

moving body(falling ball viscometer)

When the void area increases, the mass transfer area increases. Then the diffusion

increases, so the effectice diffusion coefficient increases.

When we stir the solution, we create turbulence. By the turbulence the mass

transfer is increased.

Concentration, the length of containing vessel, temperature and wave length of

radiation effects the rotation angle.

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