Weak base reaction with acid

Another situation in which an inflection point may be missing or difficult to detect occurs when the analyte is a multiprotic weak acid or base whose successive dissociation constants are similar in magnitude. To see why this is true let s consider the titration of a diprotic weak acid, H2A, with NaOH. During the titration the following two reactions occur. 

A base is any material that produces hydroxide ions when it is dissolved in water. The words alkaline, basic, and caustic are often used synonymously. Common bases include sodium hydroxide (lye), potassium hydroxide (potash lye), and calcium hydroxide (slaked lime). The concepts of strong versus weak bases, and concentrated versus dilute bases are exactly analogous to those for acids. Strong bases such as sodium hydroxide dissociate completely while weak bases such as the amines dissociate only partially. As with acids, bases can be either inorganic or organic. Typical reactions of bases include neutralization of acids, reaction with metals, and reaction with salts ... 

Because carbonyl compounds are only weakly acidic, a strong base is needed for enolate ion formation. If an alkoxide such as sodium ethoxide is used as base, deprotonation takes place only to the extent of about 0. l% because acetone is a weaker acid than ethanol (pKa - 16). If, however, a more powerful base such as sodium hydride (NaH) or lithium diisopropylamide ILiNO -CjHy ] is used, a carbonyl compound can be completely converted into its enolate ion. Lithium diisopropylamide (LDA), which is easily prepared by reaction of the strong base butyllithium with diisopropylamine, is widely used in the laboratory as a base for preparing enolate ions from carbonyl compounds. 

When we write the net ionic equation for the neutralization of a weak acid or a weak base, we use the molecular form of the weak acid or base, because molecules are the dominant species in solution. For example, we write the net ionic equation for the reaction of the weak acid HCN with the strong base NaOH in water (Fig. J.3) as... 

We can ignore ions such as Sr2+, which come from strong acids or strong bases in this type of problem. Ions, such as C2H3O2", from a weak acid or a base, weak acid in this case, will undergo hydrolysis, a reaction with water. The acetate ion is the conjugate base of acetic acid (Ka = 1.74 x 10 5). Since acetate is a weak base, this will be a Kb problem, and OH will form. The equilibrium is ... 

A weak acid, HA, forms a conjugate base. A , that is relatively strong. The reaction of such an anion with water results in a solution that is basic. For example, consider acetic acid, CH3COOH(aq), a weak acid. The conjugate base of acetic acid, CH3COO (aq), is relatively strong, compared to water. It reacts with water to form a basic solution. 

Determine whether the cation is from a strong or weak base, and whether the anion is from a strong or weak acid. Ions derived from weak bases or weak acids react with water and affect the pH of the solution. If both ions react with water, compare the equilibrium constants K and Aib) to determine which reaction goes farthest to completion. 

Polynitroaliphatic alcohols are invaluable intermediates for the synthesis of energetic materials (see Section 1.11). The most important route to /i-nitroalcohols is via the Henry reaction where a mixture of the aldehyde and nitroalkane is treated with a catalytic amount of base, or the nitronate salt of the nitroalkane is used directly, in which case, on reaction completion, the reaction mixture is acidified with a weak acid. Reactions are reversible and in the presence of base the salt of the nitroalkane and the free aldehyde are reformed. This reverse reaction is known as demethylolation if formaldehyde is formed. 

The alkyl halide must be one that is reactive toward SN2 displacement. Alkyltriphenylphosphonium halides are only weakly acidic, and strong bases must be used for deprotonation. These include organolithium reagents, the sodium salt of dimethyl sulfoxide, amide ion, or substituted amide anions such as hexamethyldisilylamide (HMDS). The ylides are not normally isolated so the reaction is carried out either with the carbonyl compound present or it may be added immediately after ylide formation. Ylides with nonpolar substituents, for example, H, alkyl, or aryl, are quite reactive toward both ketones and aldehydes. Scheme 2.16 gives some examples of Wittig reactions. 

Methylammonium ion, being the conjugate acid of methylamine, is a weak acid (Reaction 6-28). Chloride is the conjugate base of HC1, a strong acid. In other words, Cl- has virtually no tendency to associate with H+, or else HC1 would not be a strong acid. Methylammonium chloride is acidic because methylammonium ion is an acid and Cl is not a base. 

This reaction occurs throughout the body and in certain circumstances is speeded up by the enzyme carbonic anhydrase. Carbonic acid is a weak acid and with bicarbonate, its conjugate base, forms the most important buffering system in the body. 

Acids and bases react according to the rules in Section 8.3, but their reactions are so common that further details need to be learned. The double substitution reaction of an acid with a base is called a neutralization reaction. The products are water and a salt. Strong acids react with water completely to form ions, and weak acids react with water only slightly, but both kinds of acids react with bases to form salts. Substances that react with water to form acids or bases are called anhydrides. Acids containing more than one ionizable hydrogen atom can be partially neutralized, forming acid salts. Carbonates and acid carbonates react similarly to bases (Section 8.4). 

Addition of thiamine. The conversion of pyruvate to acetyl CoA begins by reaction of pyruvate with thiamine pyrophosphate, a derivative of vitamin B, The hydrogen on the heterocyclic thiamine pyrophosphate is weakly acidic and can be removed by reaction with base to yield a nucleophilic ylide much like the phosphorus ylides u.sed in Wittig reactions /Section 19.12>. This nucleophilic yJide adds to the ketone carbonyl group of pyruvate to yield a tetrahedral intermediate. 

A weak acid shell resin based on poly(acrylic acid) c)iains grafted to a magnetic core, and containing about 50% y-Fe.>0g by weight, has been used in studies of the dealkalization of hard, alkaline waters [ 29 ]. The reaction removes divalent cations and bicarbonate from bore waters tbe resin is regenerated with mineral aeid. 

Stabilizers prevent acid-base reactions in the diesel fuel. Basic amines are usually used as stabilizers. They react with weakly acidic compounds with the formation of products that remain dissolved in the fuel and do not react further. 

Water, as we know, is a unique solvent. One of its special properties is its ability to act either as an acid and as a base. Water functions as a base in reactions with acids such as HCI and CH3COOH, and it functions as an acid in reactions with bases such as NH3. Water is a very weak electrolyte and therefore a poor conductor of electricity, but it does undergo ionization to a small extent ... 

ACID AMMONIUM FLUORIDE (1341-49-7) FiH H4N Reacts with water, forming a weak solution of hydrofluoric acid. Violent reaction with bases, releasing ammonia gas. Attacks glass, cement, and most metals in the presence of moisture. Upon contact with moisture and metal, this material may release flammable hydrogen gas which may collect in enclosed spaces. Do not use aluminum, nickel, or steel containers. When heated to decomposition, emits toxic and corrosive fumes of ammonia, hydrogen fluoride, and nitric oxides. 

ALUM (10043-01-3) Al2(SOj3 Noncombustible solid. Forms sulfuric acid with water. Aqueous solution has a violent reaction with bases, amines, amides, inorganic hydroxides, and many other materials. See also sulfuric acid. Dry material is weakly corrosive to carbon steel aqueous solution attacks aluminum and other metals, forming hydrogen gas. Hydrogen gas can accumulate to explosive concentrations within enclosed or confined spaces. 

COBALT CHLORIDE or COBALT(II) CHLORIDE (7646-79-9 7791-13-1, hexahydrate) C0CI2 Noncombustible solid. Incompatible with bases, alkali metals, ammonia vapors oxidizers, acetylene reaction may be violent. Contact with acids or acid fumes can produce highly toxic chloride fumes. Aqueous solution is a weak acid. Incompatible with metals can cause pitting attack and stress corrosion in... 

---