Balancing under basic conditions

Here s a summary of the method for balancing a redox reaction equation for a reaction under acidic conditions (excess H+) (see the next section for details on balancing a reaction under basic conditions) ... 

Balancing Redox Reactions under Basic Conditions... 

Yes, balancing redox equations can involve quite a lot of bookkeeping. Not much can be done to remedy that unfortunate fact. But here s the good news The process for balancing redox equations under basic conditions is 90 percent identical to the one used for balancing under acidic conditions in the preceding section. In other words, master one, and you ve mastered both. 

Under basic conditions, balance as you do with acidic conditions but then neutralize any H+ by adding OH. ... 

Follow the nine steps for balancing a redox reaction equation under basic conditions ... 

Michael acceptors which carry a good leaving group at the a-carbon atom or whose electron-withdrawing group itself can serve as the leaving group may be cyclopropanated by active methylene compounds under basic conditions via a prototropic shift subsequent to the Michael addition as outlined in equation 139. Thus, the basicity of the carbanions involved must be balanced to allow the requisite prototropic shift otherwise, the reaction will be very slow or will not work. 

When diols and dihalides are allowed to react under basic conditions, products resulting from multiple displacements are possible. Thus, 18-crown-6 can be formed as shown above as well as 36-crown-12. The latter is less likely than the former owing to its large size. Typically, linear oligomerization would predominate during the synthesis. Addition of template ions has often proved to be useful in altering the balance of product between cyclic and linear materials. 

The interpretation of these two schematic views confronts some difficulties. Option (1) requires the extrusion of a hydrogen from a methylene hardly active in acidic medium (acetic acid). Under basic conditions, it would be necessary first to convert the sulfide to a sulfoxide such as V to achieve sufficient activation of this methylene. This oxidation may be accomplished by LTA as indicated previously. Nevertheless, the ensuing cyclobutane fragmentation in VI— the actual oxidative step—by concurrent attack of acetate and departure of Pb(II) diacetate (X = PbOAc2 in Scheme 27.1) has no precedent in LTA-amine chemistry, although it is electronically balanced. Besides, the final product of this sequence would be sulfoxide VII. Having no reductive work-up procedure, this sulfoxide should survive until the isolation step. Since this is not the experimental fact, option (1) must then be discarded. 

Dissolution and redeposition phenomena are currently used to reach this goal. The dissolution of convex asperities is balanced by deposition on concave regions. The net result is an increase in the neck size between the elementary particles and the smoothing of asperities. The smallest pores disappear first. Several parameters may be used to increase the dissolution phenomenon. At room temperature amorphous silica is insoluble (5 ppm) in alcohol, but its solubility is around 70 ppm in water [13]. Under basic conditions the solubility of silica increases. The temperature is a parameter that can be used to increase silica solubility, and these experiments are advantageously performed under pressure in an autoclave. However, the temperature must be low enough (<180°C) to avoid silica-quartz transformation. 

Lee et al. used the Langmuir film balance technique to determine the hydrolytic kinetics of stereo-complex monolayers formed from PLLA/PDLA mixtures spread at the air-water interface. The hydrolysis of the mixture monolayers under basic conditions is slower than that of individual PLLA or PDLA monolayers, depending on the composition or the degree of com-plexation. In the presence of proteinase K, the hydrolysis rate of mixture monolayers with >50 mol% PLLA is much slower than that of the singlecomponent PLLA monolayer. The monolayers formed from mixtures with <50 mol% l-PLA do not show any degradation. It is concluded that the slower hydrolysis of mixture monolayers is mainly due to the strong interaction between PLLA and PDLA chains, which prevents the penetration of water or enzyme into the bulk. In an in vivo study on the biocompatibility of PLLA and stereo-complexed nanofibres by subcutaneous implantation in rats, Ishii et al. also observed that stereo-complexed nanofibres exhibit slower degradation than PLLA. ... 

In solving this problem the major effort was to balance a redox equation for a reaction under basic conditions. This allowed us to find the molar relationship between dithionite and chromate ions. The remainder of the problem was a stoichiometry calculation for a reaction in solution, much like Example 4-10 (page 127). A quick check of the final result involves (1) ensuring that the redox equation is balanced, and (2) noting that the number of moles of Cr04 is about 1.5 (i.e., 100 X 0.0148), that the number of moles of 8204 is about 2.25 (i.e., 1.5 X 3/2), and that the mass of Na2S204 is somewhat more than 350 (i.e., 2.25 X 175). 

You have seen many balanced chemical equations and net ionic equations that represent redox reactions. There are specific techniques for balancing these equations. These techniques are especially useful for reactions that take place under acidic or basic conditions, such as the acidic conditions used in coating a master CD with silver. 

Redox reactions do not always take place under neutral conditions. Balancing half-reactions is more complicated for reactions that take place in acidic or basic solutions. When an acid or base is present, or OH ions must also be considered. However, the overall approach is similar. This approach involves writing the correct formulas for the reactants and products, balancing the atoms, and adding the appropriate number of electrons to one side of the half-reaction to balance the charges. 

The half-reaction method of balancing equations can be more complicated for reactions that take place under acidic or basic conditions. The overall approach, however, is the same. You need to balance the two half-reactions, find the LCM of the numbers of electrons, and then multiply by coefficients to equate the number of electrons lost and gained. Finally, add the halfreactions and simplify to give a balanced net ionic equation for the reaction. The ten steps listed above show this process in more detail. 

However, in our opinion, Holm s basic balance equation is incorrect. Heat losses are equated to the difference between the reaction heat and the enthalpy of the combustion products cp(Tc — T0) when the equation is written in this way it is incorrect to take Tc from someone else s experiments which were performed under different conditions. Even if Tc in fact changes little from one case to another, the small difference Q — cp(Tc —T0) is completely determined by the losses and depends on the conditions of the experiment. 

Layered tin sulfide mesostructures were synthesized using a cationic surfactant as template, and tin chloride and sodium sulfide as sources of tin and sulfide [36], The structure was composed of Sn2S64 dimers charge-balanced by dodecylammonium cations. A mesostructured tin sulfide mesh phase was synthesized by reacting SnCl4, (NH4)2S and hexadecylamine (HDA) under aqueous basic conditions at 150°C [37], The structure was found to be... 

Considering the models in Table I, it follows that the response of model III-T will be more close to reality due to (i) the correct way the transfer phenomena in and between phases is set up, and (ii) radial gradients are taken into account. Therefore, the responses of the different models will be compared to that one. It is obvious that the different models can be derived from model III-T under certain assumptions. If the mass and heat transfer interfacial resistances are negligible, model I-T will be obtained and its response will be correct under these conditions. If the radial heat transfer is lumped into the fluid phase, model II-T will be obtained. This introduces an error in the set up of the heat balances, and the deviations of type II models responses will become larger when the radial heat flux across the solid phase becomes more important. On the other hand, the one-dimensional models are obtained from the integration on a cross section of the respective two-dimensional versions. In order to adequately compare the different models, the transfer parameters of the simplified models must be calculated from the basic transfer... 

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