Cell titration

A minor disadvantage of external generation of titrant is the dilution of the contents of the titration cell care is therefore necessary in suitably adjusting the rate of flow and the concentration of the generator solution. The procedure is, however, admirably suited for automatic control. 

Bromide. A 0.01 M solution of potassium bromide, prepared from the pure salt previously dried at 110°C, is suitable for practice in this determination. The experimental details are similar to those given above for chloride except that no methanol need be added. The titration cell may contain 10.00 mL of the... 

An electronic millivoltmeter or a pH meter can be used to measure the e.m.f. of the titration cell, but in the latter case, the instrument must be used in the millivolt mode, since pH has no significance in non-aqueous solutions. 

The simple electrical circuit shown in Fig. 16.15(h) is suitable for this procedure. The voltage applied to the titration cell is supplied by two 1.5 V dry cells and is controlled by the potential divider R (a 50-100 ohm variable resistance) it can be measured on the digital voltmeter V. The current flowing is read on the micro-ammeter M. 

Procedure. Place 25.0 mL of the thiosulphate solution in the titration cell. Set the applied voltage to zero with respect to the S.C.E. after connecting the rotating platinum micro-electrode to the polarising unit. Adjust the range of the micro-ammeter. Titrate with the standard 0.005 M iodine solution in the usual manner. 

Procedure. Pipette 25.0 mL of the thiosulphate solution into the titration cell e.g. a 150mL Pyrex beaker. Insert two similar platinum wire or foil electrodes into the cell and connect to the apparatus of Fig. 16.17. Apply 0.10 volt across the electrodes. Adjust the range of the micro-ammeter to obtain full-scale deflection for a current of 10-25 milliamperes. Stir the solution with a magnetic stirrer. Add the iodine solution from a 5 mL semimicro burette slowly in the usual manner and read the current (galvanometer deflection) after each addition of the titrant. When the current begins to increase, stop the addition then add the titrant by small increments of 0.05 or 0.10 mL. Plot the titration graph, evaluate the end point, and calculate the concentration of the thiosulphate solution. It will be found that the current is fairly constant until the end point is approached and increases rapidly beyond. 

A special titration cell is necessary which completely fills the cell compartment of the spectrophotometer. One shown in Fig. 17.24 can be made from 5 mm Perspex sheet, cemented together with special Perspex cement, and with dimensions suitable for the instrument to be used. Since Perspex is opaque to ultraviolet light, two openings are made in the cell to accommodate circular quartz windows 23 mm in diameter and 1.5 mm thick the windows are inserted in such a way that the beam of monochromatic light passes through their centres... 

Procedure. Place 80 mL of the arsenic/antimony solution in the titration cell of the spectrophotometer. Titrate with standard bromate/bromide solution at 326 nm taking an absorbance reading at least every 0.2 mL. From the curve obtained calculate the concentration of arsenic and antimony in the solution. 

Procedure. Charge the titration cell (Fig. 17.24) with 10.00 mL of the copper ion solution, 20 mL of the acetate buffer (pH = 2.2), and about 120mL of water. Position the cell in the spectrophotometer and set the wavelength scale at 745 nm. Adjust the slit width so that the reading on the absorbance scale is zero. Stir the solution and titrate with the standard EDTA record the absorbance every 0.50 mL until the value is about 0.20 and subsequently every 0.20 mL. Continue the titration until about 1.0 mL after the end point the latter occurs when the absorbance readings become fairly constant. Plot absorbance against mL of titrant added the intersection of the two straight lines (see Fig. 17.23 C) is the end point. 

Procedure. Transfer 10.00mL of the iron(III) solution to the titration cell (Fig. 17.24), add about 10mL of the buffer solution of pH = 4.0 and about 120mL of water the pH of the resulting solution should be 1.7-2.3. Insert the titration cell into the spectrophotometer immerse the stirrer and the tip of the 5mL microburette (graduated in 0.02 mL) in the solution. Switch on the... 

A variant of the Karl-Fischer water determination was described [40], By heating the drug substance, the contained water was transferred into a titration cell by a carrier gas. The automated system consisted of an oven sample processor and a coulometer. 

In the sodium borate solution containing bromide, when the pH 4 buffer is added before the potassium iodate solution, titrations give low total residual chlorine concentrations. This loss increases with the amount of stirring time between the addition of the reagents. Even for a stirring time of 10 seconds, there is a loss of about 17% of the total residual chlorine. If the solution were stirred for 30 min, 85% of the chlorine would have disappeared. The concentration of total residual chlorine determined by the reference methods does not change throughout the experiment. This implies that this loss of chlorine does not occur in the reaction vessel, but in the titration cell as a result of the analytical procedure. 

Fig. 1.97.1. Schema of the Coulometer MeBzelle DL 36 for measurement of residual moisture content (RM) after Karl Fischer. In the titration cell (1) iodine is electrolytically produced (3) from an iodine-containing analyt (2). Water in the titration cell reacts with the iodine. When the water is used up, a small excess of iodine is produced, which is detected by special electrodes, which leads to iodine production being stopped. The amount of water in the cell can be calculated from the reading of the coulometer, and the amount of electrical charge needed. The solids are introduced into the cell either by a lock, or the water is desorbed in an oven and carried by a gas stream into the cell. 10 pg in a sample can be detected with an accuracy of reading of 0.1 pg (KF Coulometer DL36, Mettler-Toledo AG, CH-8603 Schwerzenbach, Switzerland).

H+] is measured potentiometrically with a glass electrode. Briefly, the method involves the use of a glass electrode and a double-junction calomel reference electrode in the titration cell ... 

Figure 17.2 (a) and (b) illustrates the schematic diagram of amperometric titrations with the dropping mercury electrode having a titration-cell and an electric circuit respectively. 

The titration-cell Figure 17.2 (a) essentially comprises of apyrex 100-ml, four-necked, flat-bottomed flask. A semimicro burette (B) (graduated in 0.01 ml), a 2-way gas-inlet tube (A) to enable N2 to pass either through the solution or simply over its surface, a dropping mercury electrode (C) and an agar-potassium salt-bridge are duly fitted into the four necks with the help of air-tight rubber stoppers. 

The electrical circuit, Figure 17.2 (b), consists of two 1.5 V dry cells that provides a voltage applied to the above titration cell. It is duly controlled and monitored by the potential divider (R) and is conveniently measured with the help of a digital voltmeter (V). Finally, the current flowing through the circuit may be read out on the micro-ammeter (M) installed. 

A known volume of the solution under investigation is introduced in the titration cell,... 

Weigh accurately a sample of Ni-salt to yield a 0.001 M Ni-solution. To 25 ml of this solution placed in a titration cell add an equal volume (25.0 ml) of a supporting electrolyte and 2 ml of gelatin solution,... 

Figure 4.19 A constant current coulometry titration cell. The reagent is produced at the working electrode and reacts with the sample. The indicator electrodes detect the changing potential or conductivity of the solution and the amount of change that takes place is measured and related to the concentration of the reactant in the sample.

Figure 2. Flow cell (excluding pump and titration cell). Left Front view. Right Cross section along center line. I. Perspex cover. 2. Outlet tube (back to titration cell). 3. Flow channel. 4. Counter electrode (platinum). 5. Metal plate with cut edge exposed in the channel. 6. Seal of molded silicone rubber. 7. Piston for removal of air fix>m reference electrode compartment. 8. Reference electrode compartment. 9. Capillary holes connecting 8 to 3.10. Inlet tube (from titration cell). II. Reference electrode (Ag/AgCI, sat. KCI). (Reprinted from Ref. 3, with kind permission from Elsevier Science Ltd., Kidlington, Oxford, UK.)...

Procedure To the titration cell are added mercury (4-5 ml), a 6% (wt./vol.) NajPjOjo solution (10 ml) and a 3.0 M CHjCOONH. 5.5 M CHjCCXIH buffer solution (2 ml). The supporting mediiun is deaerated with an inert gas which is allowed to flow throughout the complete titration. The supporting medium is then reduced at —0.70 V to a background current of 100 fiA. The test solution is prereduced at —0.20 V to a background current of 100 /xA and subsequently reduced at —0.70 V to a background current of 100 /lA. 

Karl Fischer titration cell with pneumatic flapper door and stirrer... 

Elemental composition H 9.15%, N 42.41%, O 48.44%. Hydroxylamine may be measured by coulometric titration to a potentiometric end point using a coulometric titration cell. A standard solution of bromine may be used as oxidizer in the redox reaction. (Skoog, D. A., D. M. West, and F. J. HoUer. 1992. Fundamentals of Analytical Chemistry, 6th ed. pp. 467, Orlando Saunders College Publishing)... 

Controlled-current coulometry is also called coulometric titration. An apparatus for controlled-current coulometry is shown in Fig. 5.35 for the case of determination of an acid. It consists of a constant current source, a timer, an end-point detector (pH meter), and a titration cell, which contains a generating electrode, a counter electrode in a diaphragm, and two electrodes for pH detection. The timer... 

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