Less common ions, reactions

Words that can be used as topics in essays 5% rale buffer common ion effect equilibrium expression equivalence point Henderson-Hasselbalch equation heterogeneous equilibria homogeneous equilibria indicator ion product, P Ka Kb Kc Keq KP Ksp Kw law of mass action Le Chatelier s principle limiting reactant method of successive approximation net ionic equation percent dissociation pH P Ka P Kb pOH reaction quotient, Q reciprocal rule rule of multiple equilibria solubility spectator ions strong acid strong base van t Hoff equation weak acid weak base... 

In this section, you determined the solubility product constant, Kgp, based on solubility data. You obtained your own solubility data and used these data to calculate a value for Kgp. You determined the molar solubility of ionic solutions in pure water and in solutions of common ions, based on their Ksp values. In section 9.3, you will further explore the implications of Le Chatelier s principle. You will use a reaction quotient, Qsp, to predict whether a precipitate forms. As well, you will learn how selective precipitation can be used to identify ions in solution. 

Another crystallization technique is used when the isolation of a highly water-soluble compound in its salt form is required from aqueous reaction mixtures. This technique takes advantage of the common-ion effect and is based on the le Chatelier s principle, which states that, if, to a system in equilibrium, a stress is applied, the system will react so as to relieve the stress. Thus, in aqueous solutions, the solubility of the compound in salt form can be reduced by adding large amoimts of a common ion which is more soluble than the salt of the compoimd. 

Most probably, the real situation in these systems is one of compromise between the two possibilities discussed above, Le., the initiator is a mixture of perdhloric acid and acetyl perchlorate. It seems obvious to us that the mechanism of these polymerisations is psoidocationic and the minor effect of added perchlorate salts is simply due to homoconjugation of perchloric acid present at the beginning of the reaction or liberated in ontaneous transfer processes, and not to common-ion effects suppressing the concentration of free ionic chain carriers. 

This effect is a variation of Le Chatelier s principle, and is called the common ion (or mass-law) effect. The first step of the SN1 reaction is to produce the leaving group, and if there is already a large concentration of this present, the forward reaction is disfavoured as it would produce more of that species. 

C is correct. Reaction 2 will shift left via Le Chatelier s principle. The resulting increase in I03" will shift Reaction 1 to the left due to the common ion effect, creating precipitate in the already saturated solution. The H+ ion concentration in the formula for solubility is from hydrogen ions in solution before iodic acid is added. If a different acid were added (like HC1), the H+ ion concentration would move Reaction 2 to the right and thus Reaction 1 to the right. 

W e can add a couple of different things to the mixture that will affect it and demonstrate the common-ion effect. One of them would be sodium acetate, NaC.H.O.. Another would be hydrochloric acid. Think about this for a moment, keeping in mind Le Chatelier s principle. If sodium acetate is added to the mixture, it will dissociate into sodium ions and acetate ions. The increase in concentration ofthe acetate ions will drive the reaction to the left, which will further inhibit the dissociation of acetic acid. Adding hydrochloric acid will have the same effect because it will increase the concentration of protons, which will also drive the reaction to the left. Sodium acetate and hydrochloric acid have two features that allow them both to cause the common-ion effect to occur. First, they are both strong electrolytes, and second they each have an ion in common with the acetic acid equilibrium. These are the key ingredients that cause the common-ion effect. 

But think about the size of x. With no added I , we found x = 0.001 2s M. Now we anticipate that x will be smaller than 0.(X)1 2s M, because of Le Ch telier s principle. Addition of I" to Reaction 6-8 displaces the reaction in the reverse direction. In the presence of extra I", there will be less Pb. This application of Le Chitelier s principle is called the common ion effect. A salt is less soluble if one of its constituent ions is already present in the solution. 

The solubility of MgC03 can also be decreased by adding Na2C03, which increases the common ion [C03 ]. According to Le Chatelier s principle, the addition of the product C03 causes the equilibrium to shift in the direction of the reactants, which means it decreases the solubility of MgC03. In the reverse reaction, the conunon ion C03 combines with some of the Mg in solution to form solid MgC03, which reduces both the concentration of Mg " and the molar solubility S of MgC03. 

A.-T. Le, C.D. Lin, L.F. Errea, L. Mendez, A. Riera, B. Pons, Comparison of hyperspherical versus common-reaction-coordinate dose-coupling methods for ion-atom collisions at low energies, Phys. Rev. A 69 (2004) 062703. 

Most examples of quinone dehydrogenations adjacent to C- have been carried out on steroidal ketones and are essentially limited to readily enoli le species. Reactions on esters and amides (Table 8) are far less common and, because of their relatively low ease of enolization, require harsh conditions. Thus, unless stabilization of the intermediate carbonium ion is possible, - elevated temperatures and prolonged reaction times are required (Table 8), which increases the incidence of unwanted side reactions. Frequent by-products are those arising as a result of Diels-Alder reactions or Michael addition to the quinone." Allylic alcohols may be rapidly oxidized to aldehydes or ketones under these conditions " and require prior protection. 

Houcine, A., Mehdi, F., Yves Le, B., Rachid El, G. 2003. Synthesis of new bis-iminocoumarins by Schmidt reaction catalysed by ion-exchange resins. Synth. Common. 33 1821—1828. Irena, K. 2005. Synthetic and natural coumarins as cytotoxic agents. Curr. Med Chem. Anti-... 

Halide ions are poor nucleophiles and do not give an acyl addition product. Other weak nucleophiles give a low yield of an acyl addition product because the reaction is reversible. If this equilibrium can be controlled, there is a chance the product may be isolated or it may undergo another reaction. An equilibrium is effectively controlled by apphcation oiLe Chatelier s principle, which states that changes in concentration, temperature, volume, or partial pressure in a chemical system at equilibrium will shift the equilibrium to counteract that change. This principle is named after Henry Louis Le Chatelier (France/ Italy 1850-1936). In acyl addition reactions, changing the concentration and temperature is the most common action. 

The principle of Le Chatelier is the same for solution reactions as for the other cases we have studied, but two points should be noted (1) If one of the reacting substances is a pure solid (or, less commonly, a pure liquid that does not mix with the solution), its quantity does not matter, as long as some of it is present. (2) Increasing the volume by adding solvent shifts the equilibrium in the direction that produces a larger number of dissolved particles (molecules or ions). Thus, the equilibrium... 

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