Strong bases Hydroxide ions

Strong bases are those compounds that totally dissociate in water, yielding some cation and the hydroxide ion. It is the hydroxide ion that we normally refer to as the base, because it is what accepts the proton. Calculating the hydroxide ion concentration is really stredghtforward. Suppose that you have a 1.5 M (1.5 mol/L) NaOH solution. The sodium hydroxide, a salt, completely dissociates (breaks apart) into ions  

If you start with 1.5 mol/L NaOH, then you have the same concentration of ions  

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M(aq)+ -I- OH(aq) . Howcvcr, wheu there is a strong covalent bond between M and the oxygen, then the substance can act as an acid that is, MOH + nH20 = MO(aq) -I- H30(aq). Amphotcric hydroxides will act as a base in the presence of a strong acid and as an acid in the presence of a strong base. Hydroxide ions can also form bridges between metal ions. See Water pK Bases... 

Since the added solid NaOH will completely dissociate, the major species in solution before any reaction occurs are HC2H3O2, Na, C2H302, OH , and H2O. Note that the solution contains a relatively large amount of the very strong base hydroxide ion, which has a great affinity for protons. The best source of protons is the acetic acid, and the reaction that will occur is... 

Bromomethyl-5-nitrofuran offers an incoming nucleophile a choice of reaction sites product formation seems to be determined mainly by the nature of the nucleophile but is also strongly dependent upon the solvent and other conditions. The hard base hydroxide ion removes a methylenic proton from the active methylene group and the new nucleophile displaces bromide from another molecule to produce, eventually, the bis(5-nitro-2-furyl)ethene (Scheme 35, A).191... 

Likewise the very strong, hard base, hydroxide ion, can displace the weaker soft base, sulfite ion, from the soft acid, melhylmercury cation ... 

Ford and co-workers have also recently developed a homogeneous catalyst system for the water-gas shift reaction (95). Their system consists of ruthenium carbonyl, Ru3(CO)12, in an ethoxyethanol solvent containing KOH and H20 under a CD atmosphere. Experiments have been conducted from 100-120°C. The identity of the H2 and CD2 products has been confirmed, and catalysis by both metal complex and base has been verified since the total amount of H2 and COz produced exceeds the initial amounts of both ruthenium carbonyl and KOH. The authors point out that catalysis by base in this system depends on the instability of KHC03 in ethoxyethanol solution under the reaction conditions (95). Normally the hydroxide is consumed stoichiometrically to produce carbonate, and this represents a major reason why a water-gas shift catalyst system has not been developed previously under basic conditions. As has been noted above, coordinated carbonyl does not have to be greatly activated in order for it to undergo attack by the strongly nucleophilic hydroxide ion. Because of the instability of KHC03... 

This equilibrium hes far to the left because the base, CH3NH2, is weak and the conjugate base, OH ion, is strong. The hydroxide ion has a much greater attraction for a hydrogen ion than a molecule of methyl amine has. 

Claisen-Schmidt condensation. Condensation of an aromatic aldehyde with an aliphatic aldehyde or ketone in the presence of a relatively strong base (hydroxide or alkoxide ion) to form an a,(3-unsaturated aldehyde or ketone. 

Calcium (Ca, at. mass 40.08) occurs in compounds in the II oxidation state. The hydroxide, Ca(OH)2 (solubility 1.3 g/1.), is a strong base. Calcium ions form sparingly soluble compounds with oxalate and carbonate, and also form weak complexes with EDTA and tartrate. 

Some substances can act as a Bronsted-Lowry acid in one reaction and a Bronsted-Lowry base in another. Consider the following net ionic equations for the reaction of dihydrogen phosphate ion with either the acid hydrochloric acid or the strong base hydroxide. 

When strong acids and strong bases (hydroxides) are mixed, the fundamental chemical change that always occurs is that ions react with OH ions to form water. 

Hydrolysis of esters in aqueous base is often called saponification, a reference to the use of this reaction in the manufacture of soaps (Section 26.2A) through hydrolysis of triglyceride ester groups. Although the carbonyl carbon of an ester is not strongly electrophilic, hydroxide ion is a good nucleophile and adds to the carbonyl carbon to form a tetrahedral carbonyl addition intermediate, which in turn collapses to give a carboxylic acid and an alkoxide ion. The carboxylic acid reacts with the alkoxide ion or other base present to form a carboxylate anion. Thus, each mole of ester hydrolyzed requires one mole of base. 

The mechanisms of these ring openings are straightforward extensions of reactions you already know. In base, the strongly nucleophilic hydroxide ion attacks the oxirane and displaces the oxygen atom from one carbon in an Sn2... 

Hydroxide ion lies below phenol m Table 1 7 hydrogen carbonate ion lies above phe nol The practical consequence of the reactions shown is that NaOH is a strong enough base to convert phenol to phenoxide ion but NaHCOs is not... 

Although nucleophilic aromatic substitution by the elimination-addition mecha nism IS most commonly seen with very strong amide bases it also occurs with bases such as hydroxide ion at high temperatures A labeling study revealed that hydroly SIS of chlorobenzene proceeds by way of a benzyne intermediate... 

Strong and Weak Bases Just as the acidity of an aqueous solution is a measure of the concentration of the hydronium ion, H3O+, the basicity of an aqueous solution is a measure of the concentration of the hydroxide ion, OH . The most common example of a strong base is an alkali metal hydroxide, such as sodium hydroxide, which completely dissociates to produce the hydroxide ion. 

Absorption Spectra, of Aqueous Ions. The absorption spectra of Pu(III) [22541-70 ] Pu(IV) [22541 4-2] Pu(V) [22541-69-1] and Pu(VI) [22541-41-9] in mineral acids, ie, HCIO and HNO, have been measured (78—81). The Pu(VII) [39611-88-61] spectmm, which can be measured only in strong alkaU hydroxide solution, also has been reported (82). As for rare-earth ion spectra, the spectra of plutonium ions exhibit sharp lines, but have larger extinction coefficients than those of most lanthanide ions (see Lanthanides). The visible spectra in dilute acid solution are shown in Figure 4 and the spectmm of Pu(VII) in base is shown in Figure 5. The spectra of ions of plutonium have been interpreted in relation to all of the ions of the bf elements (83). 

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