Hydroxide concentration effect

Since addition of platinum, a good hydrogen evolution catalyst, does not alter the hydroxide concentration effect, the effect bears on oxygen, rather than hydrogen production. 

NOTE With these types of programs, free sodium hydroxide is not formed, even in the event of complete evaporation thus the damage caused by localized concentration effects (dissolution of iron forming the soluble, nonprotective, sodium ferroate [sodium hypoferrite] salt, together with hydrogen liberation, tube wastage, and ultimate failure) does not occur. 

In a first set of experiments, the impact of the sodium hydroxide concentration (0.1, 1.0, 2.0 M) and gas-flow direction (co-current, counter-flow) was analysed (50 ml h liquid flow, 65 pm film thickness) [5]. The higher the base concentration, the higher is the conversion of carbon dioxide. For aU concentrations, complete absorption is achieved, but at different carbon dioxide contents in the gas mixture. The higher the carbon dioxide content, the higher is the gas flow velocity and the larger must be the sodium hydroxide concentration for complete absorption. The gas flow direction had no significant effect on carbon dioxide absorption as the gas velocities were still low, so that no pronounced co- or counter-flow operation was realized. 

The effects of micelles of cetyltrimethylammonium bromide (CTABr), tetradecyl-trimethylammonium bromide (TTABr) and sodium dodecyl sulfate (SDS) on the rates of alkaline hydrolysis of securinine (223) were studied at a constant [HO ] (0.05 m). An increase in the total concentrations of CTABr, TTABr and SDS from 0.0 to 0.2 M causes a decrease in the observed pseudo-first-order rate constants (kobs) by factors of ca 2.5, 3, and 7, respectively. The observed data are explained in terms of pseudophase and pseudophase ion-exchange (PIE) models of micelles. Cationic micelles of CTABr speed attack of hydroxide ion upon coumarin (224) twofold owing to a concentration effect. ... 

In the former case the sodion is the precipitating ion, in the latter the chloride, it is evident however that the hydroxyl ion is more readily adsorded by the platinum than the chloride necessitating a greatly increased concentration of the sodium hydroxide to effect precipitation. 

Ammonia is alkaline in water because of this equilibrium, which produces hydroxide ions. The addition of an ammonium salt (NHj ions) will push the equilibrium back toward the left, i.e., lower hydroxide concentration, therefore lower pH. Increase of pH can be effected by addition of sodium or potassium hydroxide. This explains why some CdS depositions based on the Cd/NHs/thiourea formula include either an ammonium salt or an alkali metal hydroxide. 

Increase in pH (= increase in [OH ]) shifts the equilibrium to the left, resulting in a lower concentration of free Pb ions and thus a slower reaction to give PbSe. This means that, in contrast to the deposition from a selenourea bath described earlier, the rate is dependent on Pb concentration and possibly independent of hydroxide concentration at a constant free-Pb concentration. This would then suggest that the opposite mechanism, i.e., a complex decomposition, is effective for the selenosnlphate bath. It is stressed that these conclusions on selenide formation... 

Effect of Alkali Concentration. Figure 7A depicts that the variation of the conversion of glycol lignin with sodium hydroxide concentration reaches a plateau at about 60%. Also, the ether soluble material remains constant... 

These results can be rationalized by picturing the crystal violet carbonium ion as solubilized and oriented in the micelle, followed by attack by the aqueous hydroxide ion. The catalytic effect of the micellar solution has a twofold origin a concentration effect and an... 

The addition of hydroxide ions to substituted benzaldehydes (ArCHO + OH <=> ArCH(0H)0 ) is used to establish J-acidity scales in water-ethanol and water-DMSO mixtures containing sodium hydroxide as a base. The pK-values in such mixtures are linearly correlated with Hammett substituent constants. The independence of reaction constant p of solvent composition confirms that substituted benzaldehydes are suitable J- indicators for hydroxide solutions in water-ethanol and water-DMSO mixtures. Dependence of J- values on sodium hydroxide concentration is only slightly affected by ethanol up to 90 % and at a constant sodium hydroxide concentration shows only small increase between 90 and 98 % ethanol. J- increases more with increasing DMSO concentration, but the effect is much smaller than that of DMSO on H- values based on proton abstraction from aniline. 

Comparison of Aqueous and Water-Ethanol Solutions. The effect of the presence of ethanol in aqueous solutions of sodium hydroxide is usually small. This is shown by the similar shape of the dependence of J- on sodium hydroxide concentration (Figure 1) and by the small differences m J values obtained at the different constant ethanol concentrations up to 90 vol % (Table III). Even when the concentration of sodium hydroxide was kept constant (e.g., 0.1 M), the difference between J values in 90 vol % ethanol and 98 vol % ethanol was only 0.16 J- units (Figure 2). In this range of ethanol concentrations, it is necessary to consider the competitive influence of ethoxide ions, the addition of which would result in a decrease of the C6H5CO— absorbance indistinguishable from the decrease caused by hydroxide ion addition. In 90 vol % ethanol, the ratio of hydroxide and ethoxide concentrations is about 1 1, while in 98 vol % ethanol, it is possible to extrapolate (30) that about 90% of the base will be present as the ethoxide ion. 

For reactions which are first order in the dissolving reactant, the rate will be proportional to the solubility of that species, regardless of whether the reaction occurs in the bulk solution or in the film (Equations 5.4 and 5.7). Inorganic salts usually depress the solubility of organic solutes in water [5], which can lead to unusual effects. Fig. 5.6 shows howthe rate ofreaction of n-butyl formate with potassium hydroxide changes with hydroxide concentration [6]. There are three reasons for the decrease in the rate as the concentration of hydroxide is increased (i) salting out of the ester, (ii) a decrease in the diffusion coefficient of the n-butyl formate in water and (iii) a sharp decrease in the second-order rate constant presumably due to medium effects on lc2-... 

The solubility of TPP is much greater in benzene than in mineral oil, and It is therefore likely that its average location (10. 11)is nearer to the Interface and the copper does not have to be transported (e.g., as a complex) into the droplet Interior. Since the microdroplet has a net negative surface charge, it is expected that the local concentration of hydroxide Is lower, and that hydroxide cannot effectively penetrate very deeply into the surface region. This is consistent with the effect of hydroxide on an alkylation reaction, to be discussed below. This can account for its failure to Increase the rate of the base removal component, but Its role In promoting the dependence of k on copper ion remains unexplained. 

Figure 15 Effect of sodium hydroxide concentrations as a pretreatment for benzyla-tion on the thermoplasticity of Sugi surfaces. Note pretreatment time was 1 h. Benzyla-tion conditions were at 120°C for 1 h. Sugi Cryptomeria japonica D. Don). Angle of glossiness was 60°.

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