CHAPTER 2 EXPERIMENTAL

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1 32 CHAPTER 2 EXPERIMENTAL 2.1 INTRODUCTION This chapter deals with the chemicals used and the various experimental techniques employed in the present investigation. The procedure of measuring densities () of the solutions using a single stem pycnometer, ultrasonic speed (u) by using a single-crystal variable-path multifrequency ultrasonic interferometer and viscosity () by using Ubbelohde type suspended level viscometer are explained in this chapter. The precautions to be followed in handling the equipments are also discussed. In addition to this, the procedure for calculating the uncertainties in the measurement of, u and for the solution are also given. 2.2 MATERIALS The chemicals used in the present investigation along with their abbreviated names, chemical formula, purity and grade and their make are listed in Table 2.1.

2 33 Table 2.1 Chemicals used for the study with abbreviated names, chemical formula, purity and their make Name Abbreviation Chemical Formula Purity Make Glycine Gly C 2 H 5 NO 2 99% Loba Chemie Pvt. Ltd., Mumbai L-Alanine Ala C 3 H 7 NO 2 99% Merck Specialities Pvt. Ltd., Mumbai L-Valine Val C 5 H 11 NO 2 99% Loba Chemie Pvt. Ltd., Mumbai L-Leucine Leu C 6 H 13 NO 2 99% Sisco Research Lab. Pvt. Ltd., Mumbai Sodium Fluoride - NaF 99% S.D fine Chem Ltd., Mumbai Potassium Fluoride - KF 99% Merck Ltd., Mumbai Sodium Carbonate - Na 2 CO % Sisco Research Lab. Pvt. Ltd., Mumbai Potassium Carbonate - K 2 CO % Sisco Research Lab. Pvt. Ltd., Mumbai Dimethylsulphoxide DMSO (CH 3 ) 2 SO 99.5% Merck Ltd., Mumbai

3 PREPARATION OF TERNARY SOLUTIONS All amino acids (glycine, L-alanine, L-valine and L-leucine), sodium fluoride, potassium fluoride, sodium carbonate, potassium carbonate and dimethylsulphoxide used in the study are of high purity grades as listed in the Table 2.1. All amino acids were used after they have been dried over P 2 O 5 in a desiccator for 72 h. Dimethylsulfoxide was stored over molecular sieves (Type 0.4nm Merck Ltd. Mumbai) to remove the water content. The solutions were prepared by mass and were stored in special airtight bottles to minimize absorption of atmospheric moisture and carbon dioxide. Double distilled deionised water with a conductivity of m was used to prepare aqueous salt solutions. All solutions were prepared afresh on molality basis. The mass measurements were made using a high precision AND electronic balance (Model HR 300, Japan) with a precision of ± 0.1 mg Precautions To prevent the formation of air bubbles all solutions were preheated to 5 0 C above the measuring temperature before taking reading (Ali et al 2006). 2.4 EXPERIMENTAL TECHNIQUES Density Measurements Description of pycnometer The densities of the solutions were measured using a single stem pycnometer (pyrex glass) of bulb capacity of dm 3 having a graduated stem with m 3 division. The capillary had a uniform bore and could be closed by a well-fitted glass cap as shown in Figure 2.1.

2 Calibration and calculation The marks on the stem of the pycnometer were calibrated by making use of

The change in volume of water was recorded at each mark on the pycnometer as a function of temperature

4 35 Figure 2.1 Pycnometer Calibration and calculation The marks on the stem of the pycnometer were calibrated by making use of known densities (Kell 1975) of triple distilled water at different temperatures. The change in volume of water was recorded at each mark on the pycnometer as a function of temperature in order to determine the total volume of pycnometer as well as volume between the two successive divisions of the graduated stem. From the known weight and density of water at different temperatures, the exact volume of the pycnometer at different marks on the stem of the pycnometer was calculated. Before using, the calibrated empty pycnometer was dried and then weighed. The sample solution was transferred into it with the help of jet. Care must be taken while filling the pycnometer that no air bubble was entrapped.

5 36 The excess solution sticking to the capillary was removed using the strips of Whatman filter paper. The weight of pycnometer containing the sample solution was again measured. The pycnometer with the sample solution was kept in a temperature controlled water bath (Euro Therm, Supplied by Mittal Enterprises, India) at the desired temperature, until no further change in the level of the solution in the capillary was observed. This level was noted and used in the calculation of densities as below: Weight of empty pycnometer = W 1 g Weight of pycnometer + Weight of sample = W 2 g Weight of sample = (W 2 W 1 ) g The exact volume, V of pycnometer for the particular mark on the stem is the ratio of the exact weight, (W 2 W 1 ) and density of water, 0 at the desired temperature, i.e. V W W (2.1) From the above equation, volume of the pycnometer for different marks on the stem of the pycnometer can be calculated. The values of volume at each mark of the stem of pycnometer as a function of temperature are plotted to calculate the density of the solution at a given temperature. 0.1 kg m 3. The reproducibility in the density measurements was within

6 Precautions i) The pycnometer is a highly delicate glassware, that it should be handled gently and carefully. ii) iii) iv) Direct handling of pycnometer with bare hand is prohibited. Tissue paper should be used to avoid the sticking of dust particles which would contribute to its weight later. Entrapment of air bubbles must be avoided carefully while filling the sample in the pycnometer. Excess liquid sticking to the walls of capillary should be removed using fine strips of Whatman filter paper. v) The pycnometer containing the test solution should be kept in thermostatic water bath atleast for 30 minutes to avoid thermal fluctuations Ultrasonic Speed Measurements Theory Longitudinal waves with frequencies above 20 KHz are termed as ultrasonic waves. The propagation of an ultrasonic wave in liquids and liquid mixtures is carried out by different methods (Mikhylov 1949, Kudryavtsev 1952, Parthasarthy 1935). An ultrasonic interferometer is a simple and direct device to determine the ultrasonic speed (u) in solutions with high degree of accuracy (Figure 2.2). The ultrasonic interferometer consists of a piezoelectric crystal slab (like quartz) with parallel faces developing charges of opposite polarity on their faces when it is strained. Such a crystal slab exhibits electrostriction when placed in a region of electric field.

7 38 Figure 2.2 Ultrasonic interferometer Description of interferometer The ultrasonic interferometer set up has basically a wheatstone s network. Two arms of the network are the load resistance of two identical pentode oscillators, the plate resistances of the pentodes forming the other two arms. The oscillators have been stabilized using a quartz crystal oscillator operating at a frequency of 2 MHz. A microammeter is connected between the junction of the load resistance and the load frequency choke. This acts as the detector. The output of one of the oscillators is fed to 2 MHz quartz crystal mounted to a cell. The cell can be filled up with any desired liquid in which the velocity of sound is to be determined. A reflector can be moved up or down using a screw head. The metal reflector can be kept as close to the crystal transducer as possible. A finite current may be allowed to pass through the microammeter. This is done by adjusting the adjust and gain knobs. The reflector, when moved, can go to such a height, a standing wave pattern

8 39 can be formed between the transducer crystal and the reflector. At this moment, the vibrating crystal will draw energy and thus load the oscillator to which it is connected. The loading causes a greater imbalance in the bridge leading to a decrease of current through the microammeter. The meter, thus, gives a minimum reading. As the reflector is moved further, the standing wave pattern could not be formed and the meter needle goes back to its original position. The distance d moved by the reflector to register the two consecutive minimum readings in the microammeter will corresponds to /2 of the ultrasonic wave in the liquid. Thus a measurement of d and a knowledge of the frequency f of the oscillator will enable one to determine the velocity u of propagation of the ultrasonic wave in the given liquid medium. A thermostatically regulated bath is connected to it to maintain the temperature of the liquid constant during the experiment Operation of interferometer ultrasonic speed: The following precautions were taken for the measurement of (i) Find the least count of the screw head attached to the reflector. (ii) The ultrasonic cell is filled 3/4 th of its capacity with the experimental liquid. Then fix the reflector unit on the top of the cell. Mount the cell in given sturdy metal base. Connect the output cable from the ultrasonic apparatus to the socket provided on the metal base. (iii) Switch on the ultrasonic apparatus. Keep the adjust and gain knobs in the minimum position. Just after a minute or so, the meter reading will register a maximum. Wait for some more time (i.e. about a minute or so). The meter will come back to zero reading on the dial.

9 40 (iv) Turn the gain knob to a maximum. The reading in the meter may be around 50 or 60 microampere. Now turn the adjust knob so that the meter reading is around 80 microampere. (v) Turn the screw gauge head such that the pitch scale reading is the least. In this position, the reflector is closest to the crystal the source of ultrasonic vibrations. Let the screw be turned and the reflector moved up. The meter reading in the ultrasonic interferometer will change. Note the head scale as well as the pitch scale reading (on the screw gauge) when the micro ammeter reading is the least Calculation of ultrasonic speed Measurements of ultrasonic speed with the help of ultrasonic interferometer are based on finding the wavelength in the medium. The plate current is extreme corresponding to the variation of the reflector distance by half wavelength or integral multiple of half wavelength. The ultrasonic speed is calculated by the relation: u f (2.2) The wavelength is calculated from the relation: d n 1 (2.3) 2 where d is the total distance moved by the micrometer screw for a maximum or minimum deflection; n is the number of maxima (or minima) ( 20) of anode current for a distance d.

10 41 The velocity is given by the relation: u 2fd n1. (2.4) Thus, the ultrasonic interferometer is a simple device by which the ultrasonic speed in liquid can be directly determined with a high degree of accuracy %. The reproducibility in the ultrasonic speed measurements was Precautions to be taken (i) Sudden rise or fall in temperature of the circulated liquid should be avoided to prevent thermal shock to the quartz crystal. (ii) The generator should always be switched on after filling the experimental liquid in the cell. (iii) Generator should be given a time of 15 minutes for warming up before the observation (Interferometer). (iv) The experimental liquid should be taken out of cell after use and the cell should be kept clean and dry. (v) Care must be taken to see that the reflector is not touching the bottom of the cell. Generally, the micrometer should be kept open at 25 mm after use. (vi) While cleaning the cell, care must be taken not to spoil the gold platting on the quartz crystal.

11 Technical Specifications 1) Model - M-84 2) High Frequency Generator Mains Voltage Measuring frequency Glow lamp Fuse Weight V, 50 Hz ,12 MHz (11 freq.) V, 0.3 amp ma kg approx. 3) Measuring Cell Max. displacement of the reflector- 20 mm Required quantity of liquid Least count of micrometer - 5 cc mm 4) Shielded Cable cm approximately. Length of connecting cable between the generator and the cell is Viscosity Measurements Description of viscometer The viscosities of pure liquids and their binary mixtures were measured by using Ubbelohde type suspended level viscometer (Stokes and Mills 1965). The viscometer consists of a suspended level arrangement formed by three parallel arms, i.e., receiving, measuring and auxiliary tubes (Figure 2.3).

12 43 AD X B Y C D Figure 2.3 Viscometer The measuring and receiving tubes were connected to each other through a bulb D, thus forming U shape of viscometer. Two bulbs, A and B one above the other were sealed to the measuring tube. The third arm, auxiliary tube was sealed to the measuring tube through a bulb C. The capillary of appropriate length and diameter lies in between bulbs, B and C.

13 44 for recording time. The two marks X and Y, marked near the bulbs A and B were used Special feature The viscometer was designed in such a way that i) the centers of gravity of the three bulbs A, B and C were aligned vertically so as to reduce the effect of gravity ii) the resulting flow time for triply distilled water was 204 s at K. As the flow time was greater than 100 s, the kinetic energy corrections were not necessary (Pal and Kumar 2004). Special feature of a suspended level viscometer was that the capillary effects of the two liquid surfaces were neutralized by each other so that the surface tension correction for the apparatus was negligible and the transport of momentum was carried out freely under the weight of the total volume of the test solution Working of the viscometer The sample solution was taken in the viscometer through the receiving tube. The volume of the solution in the viscometer should be adequate to avoid any air bubble being entrapped in the capillary tube while the fiducial bulb is filled. The viscometer containing the solution was clamped and immersed vertically in the thermostatic water bath and allowed to stand in it for about 30 minutes to minimize thermal fluctuation. The sample liquid was sucked into the bulb A above the fiducial bulb with the help of a rubber tube fitted to the measuring tube. Necessary care has been taken to allow the solution to stand for sometime in the limb to compensate the upward force on the solution. Then the solution was allowed to fall under its own weight by

14 45 removing the stopper of the tube. The flow time was measured by a digital stop watch (Racer, India) capable of registering time accurate to s. An average of four sets of flow times for each solution was taken for the purpose of calculation of the viscosity Calculation Poissuelle s law The viscosity of the test solution was obtained according to 4 r Pt (2.5) 8Vl where r = radius of the capillary P = pressure head t = time of fall V = volume taken l = length of capillary. The viscosity of the sample solution was obtained using the wellknown equation: t t (2.6) where 1 and 2 are the viscosities of the sample and water, t 1 and t 2 are their times of flow and 1 and 2 are their densities, respectively, at the corresponding temperature mpa s. The reproducibility in the viscosity measurements was within

15 Precautions i) The volume of solution in the viscometer should be adequate to avoid any air bubble being entrapped in the capillary tube while the fiducial bulb is filled. ii) The viscometer containing the test solution was kept in a thermostatic water bath for about 30 minutes to attain thermal equilibrium. 2.5 TEMPERATURE CONTROL All the measurements of density, viscosity and ultrasonic speed were made in an electronically controlled thermostatic water bath (Euro Therm, Mittal Enterprises, India) in order to maintain an uniform temperature. The bath consists of an immersion heater, a circulating pump and a check and contact digital thermal sensor with digital display with a relay to control the variations in temperature. The samples were allowed to stand for 30 minutes in thermostatic water bath to maintain thermal equilibrium with the bath liquid so that temperature becomes constant. The overall temperature of the test liquids during the measurements is maintained within an uncertainty of ± 0.01 K Specifications Name : Digital Ultra Cryostat Circulator, with Microprocessor based temperature controller Eurotherm make Temperature range : -5 ºC to 80 ºC Accuracy of control : 0.01 ºC ±1 digit

16 47 Mains power supply : 230 V ±2%; 50 Hz Single Phase AC Heater rating : Control 500 W ±2% Catalogue number : IRI PROCEDURE FOR MEASURING UNCERTAINTY The procedure for the measurement of uncertainty is carried out using the format given in JCGM 100:2008 as follows. The arithmetic mean or average observations is given by: q of the n experimental n 1 q q k (2.7) n k1 The variance 2 of the probability distribution of q, is given by n q 1/ n1 q q 2 2 s k j (2.8) 1 j The variance of the mean is given by s 2 2 q s q / n (2.9) k The standard uncertainty is estimated by taking square root of the equation (2.9) i.e. x s u (2.10) i X i The uncertainty values in density, ultrasonic speed and viscosity obtained by the above method are reported in the respective tables.

A Theoretical Study of Experimental Analysis Ultrasonic Interferometer

A Theoretical Study of Experimental Analysis Ultrasonic Interferometer R.Velavan, P.Myvizhi, Department of Physics, Bharath University, Chennai, India Department of Physics, Bharath Institute of Higher