Strong base, definition

Model 6 E2 Reactions—Strong Bases (definition of smaii vs. large)... 

Chromic hydroxide, Cr(OH)3, is a compound with low solubility in water. It is usually hydrated and does not have the definite composition represented by the formula. It is quite soluble either in strong acid or strong base. 

Discussion. The hydroxides of sodium, potassium, and barium are generally employed for the preparation of solutions of standard alkalis they are water-soluble strong bases. Solutions made from aqueous ammonia are undesirable, because they tend to lose ammonia, especially if the concentration exceeds 0.5M moreover, it is a weak base, and difficulties arise in titrations with weak acids (compare Section 10.15). Sodium hydroxide is most commonly used because of its cheapness. None of these solid hydroxides can be obtained pure, so that a standard solution cannot be prepared by dissolving a known weight in a definite volume of water. Both sodium hydroxide and potassium hydroxide are extremely hygroscopic a certain amount of alkali carbonate and water are always present. Exact results cannot be obtained in the presence of carbonate with some indicators, and it is therefore necessary to discuss methods for the preparation of carbonate-free alkali solutions. For many purposes sodium hydroxide (which contains 1-2 per cent of sodium carbonate) is sufficiently pure. 

In the above example, the anion (A) functions as a base when it combines with a hydrogen ion. (By definition, any substance that combines with hydrogen ions is a base. Like strong acids, strong bases ionize completely in a dilute aqueous solution.) Thus NaOH dissolves in water to form hydroxide ions, which in turn function as a base when they combine with hydrogen ions to form water, as shown by the general equations... 

It is possible to prepare concentrated suspensions of sodamide in liquid ammonia of up to 3 mol/liter, and subsequent introduction of acetylene gives a very concentrated solution of NaCeCH, which cannot be obtained by the procedure of exp. 2. The metallation of acetylene (pK - 25) by the strong base NaNH2 (pK NH3 - 34) is extremely fast. This reaction can be carried out in the presence of a small amount of triphenylmethane. As long as sodamide is still present, the red colour of Pl CNa is visible and the conversion is considered to be complete when this colour has definitely disappeared. Using this method, wastage of acetylene can be avoided... 

The hydride ion is a hydrogen atom with two electrons, which pair together as a lone pair. According to the Lewis definition, the hydride ion behaves as a base. In fact, the hydride ion is a very strong base. It will react with water, pulling a positive hydrogen ion off of the water to create H2 plus hydroxide ions, OH-, as follows ... 

The interaction of strong bases with polyhydroxy compounds, although extensively studied, has not yet been fully clarified. The available evidence indicates that the removal of a proton by a basic anion, to give an alcoholate (reaction 1), and the formation of an adduct (reaction 2) can both occur. In alcoholic media, reaction 1 has been definitely shown to occur. However, in aqueous media, differentiation between reactions 1 and 2 has not yet been possible. 

Let us compare anion radicals with dianions, which are definitely strong bases. For example, the cyclooctatetraene dianion (CgH ) accepts protons even from such solvents as dimethylsulfoxide and N, A -di methylformam ide. The latter are traditionally qualified as aprotic solvents. In these solvents, the cyclooctatetraene dianion undergoes protonation, resulting in the formation of cyclooctatrienes (Allendoerfer Riger 1965) see Scheme 1-19 ... 

Definition of Acids and Bases 222 Conjugate Acid-Base Pairs 222 Amphoteric Species 224 Strong Acids 225 Strong Bases 225 Weak Acids 226 Weak Bases 226 Polyprotic Acids 227 Acid and Base Strength Ka and Kb 228 Acid/Base Strength of Conjugate Acid-Base Pairs 230 Acid-Base Reactions 231... 

The 1,2- and 1,7-isomers are susceptible to degradation with strong base, which removes one boron atom from each of the cages. In the 1,2-isomers either the 3- or 6-boron atom is removed while for the 1,7-isomers either the 2- or 3-boron atom is removed. The boron atoms capable of extraction in each isomer are adjacent to both heteroatoms. These boron atoms are the most electron-deficient and the most susceptible to nucleophilic base attack. The 11-atom fragments are not normally isolated as the ollide ions themselves but in a protonated form (i.e., 1,2-B9C2H12-). The extra protons are easily removed with base prior to metal complexation. The ollide ions discussed in this section may well exist as open-face icosahedral fragments (Fig. 2). This point has not been definitely determined yet and an alternative... 

Accuracy compares measurements to a known standard. Quantitative measurements frequently have an international standard that is considered the truth. Qualitative measurements, however, require a strong operational definition of the standard based on customer expectations. 

The presence of a substituent in the 3-position of the NCA precludes equilibrium (6) and hence prevents the occurrence of reaction (18). It follows that, on the basis of the mechanisms described above, such NCA s should not polymerize unless a protic base (for example a primary or secondary amine) or other source of protons (for example, 3-methyl hydantoin) is present. If it could be established that polymerization does proceed with an aprotic base in aprotic media then some other mechanism of polymerization must be operative. This matter has been of central importance in discussions of various mechanisms of polymerization which have been advanced (Section 3). Experimentelly, it is not easy to obtain definitive evidence because of the high sensitivity of NCA s to protonic impurities (such as water and alcohols) in the presence of bases. It has been shown [18, 19, 38a] that proline NCA (X) and sarcosine NCA (I Ri = R2 = H, R3 = CH3) do not polymerize in the presence of tertiary bases under strictly aprotic conditions. With alkoxides, realization of such conditions is difficult, but it would appear that, at least with proline NCA, such strong bases can bring about ionization of the methine hydrogen and hence initiate polymerization as shown in (26). Evidence for this mechanism is provided by the observation that while sodium methoxide enriched... 

Titration curves for strong acids by strong bases and vice versa have four regions that can be calculated by using procedures of stoichiometry and definitions of solution concentration. 

---