Sodium hydroxide diffusion

Sodium hydroxide diffusion through a membrane toward a saiine solution (9 g/L) influence of the concentration... 

An unusual slurry process which works well with sodium hydroxide is based on diffusion of the aqueous reagent into pellets of acid polymer (28). The concentration of ions in the Hquid phase is preferably two to four times the stoichiometric level, and the temperature is maintained at 50—100°C. 

If the pump is a filter pump off a high-pressure water supply, its performance will be limited by the temperature of the water because the vapour pressure of water at 10°, 15°, 20° and 25° is 9.2, 12.8, 17.5 and 23.8 mm Hg respectively. The pressure can be measured with an ordinary manometer. For vacuums in the range lO" mm Hg to 10 mm Hg, rotary mechanical pumps (oil pumps) are used and the pressure can be measured with a Vacustat McLeod type gauge. If still higher vacuums are required, for example for high vacuum sublimations, a mercury diffusion pump is suitable. Such a pump can provide a vacuum up to 10" mm Hg. For better efficiencies, the pump can be backed up by a mechanical pump. In all cases, the mercury pump is connected to the distillation apparatus through several traps to remove mercury vapours. These traps may operate by chemical action, for example the use of sodium hydroxide pellets to react with acids, or by condensation, in which case empty tubes cooled in solid carbon dioxide-ethanol or liquid nitrogen (contained in wide-mouthed Dewar flasks) are used. 

Huizenga, J. R., Grieger, P. F. Wall, F. T. (1950b). Electrolytic properties of aqueous solutions of polyacrylic add and sodium hydroxide. II. Diffusion experiments using radioactive sodium. Journal of the American Chemical Society, 72, 4228-32. 

The diaphragm cell consists of multiple electrolytic cells having the anode plates and cathodes mounted vertically and parallel to each other. The cathodes, often flat hollow perforated steel structures that are covered with asbestos fibers, serve as the diaphragm that prevents the mixing of hydrogen and chlorine and back diffusion of hydroxide (OH) ions from the cathode to the anode. Brine fed into the cell is decomposed to approximately half of its original concentration to produce chlorine gas at the anode and hydrogen and sodium hydroxide at the cathode. 

Mishra and Gode developed a direct current polarographic method for the quantitative determination of niclosamide in tablets using individually three different buffer systems, namely Mcllraine s buffers (pH 2.20 8.00), borate buffers (pH 7.80—10.00), and Britton Robinson s buffers (pH 2.00—12.00) as well as 0.2 M sodium hydroxide. The drug was extracted from the sample with methanol, appropriate buffer was added to an aliquot and the solution then polarographed at the dropping-mercury electrode versus saturated calomel electrode at 25°C [36], The resultant two-step reduction waves observed were irreversible and diffusion-controlled. For the quantitative determination, the method of standard addition was used. Niclosamide can be determined up to a level of 5—10 pg/mL. 

Photolysis at 254 nm of phenylbutazone (220) in aqueous solution raised to pH 8 to 9 with sodium hydroxide gave a mixture of ring-opened products. Reisch etal. identified samples of aniline, the malonamides (221) and (222) and the 2-oxohexanamide (225). When the solution was basified with diethylamine, the amino diamide (223) was produced in addition to (222) and (225). In methanol solution the malonamides (221) and (224) were obtained [132]. In an older study by Pawelczyk and Wachowiak, a 20% solution (pH 10.5) of phenylbutazone sodium was kept in a clear glass bottle in diffused daylight for 2 years. 

The diaphragm prevents the diffusion of sodium hydroxide toward the anode. This wall allows for the slow passage of solution and the free passage of sodium ions. It is made of asbestos fibers supported on an iron screen. The anode solution level is maintained higher than in the cathode compartment to retard back migration. If sodium hydroxide built up near the... 

Water generated at the anode diffuses through the diaphragm and goes to the cathode, reacting with sodium to form sodium hydroxide. 

The separation of anions X can be used as another example. If the mobile phase contains diluted sodium hydroxide, a membrane allowing the diffusion of cations is used. The passage of hydronium ions towards the electrolyte will neutralise OH-ions. At the anode, Na+ ions will migrate and react with OH- ions. 

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