Ionization acids and bases

The activities of many enzymes vary with pH in the same way that simple acids and bases ionize. This is not surprising, since, as we saw in Chapter 1, the active sites generally contain important acidic or basic groups (Table 5.1). It is to be expected that if only one protonic form of the acid or base is catalyti-cally active, the catalysis will somehow depend on the concentration of the active form. In this chapter we shall see that kcM, KM, and kcJKM are affected in different ways by the ionizations of the enzyme and enzyme-substrate complex. 

Strong acids and bases ionize completely in solution, while weak acids and bases partially ionize. The partial ionization of weak acids and bases creates solutions in which an equilibrium is established. 

Arrhenius s definition of acids and bases is the definition that most people know. Acids can be recognized because their chemical formulas have an H at the beginning, like HBr and HN03. Bases are easy to recognize because their chemical formulas end with OH, like NaOH or KOH. There are a few strong acids and bases that you should be familiar with. These strong acids and bases ionize completely in solution and dissociate into as many hydro-nium ions and hydroxide ions as are available. 

Weak acids and bases ionize only slightly in aqueous solution. Because their solutions conduct electricity poorly, they are called weak electrolytes. Compounds whose solutions do not conduct electricity at all are called non-electrolytes. An outline of the electrolytic properties of compounds is presented in Table 9.2. 

Relationship between the acid and base ionization constants of a conjugate acid-base pair. 

In Section 16.2 we discussed the effect of a common ion on acid and base ionizations. Here we will examine the relationship between the common ion effect and solubility. 

EHEKS In solution, strong acids and bases ionize completely, but weak acids and bases ionize only partially. 

Strong acids and bases ionize completely in aqueous solutions. Weak acids and bases ionize only partially in aqueous solutions. An acid-base reaction is shown below. A titration was done by adding a base to a known concentration and fixed volume of an acid. The reaction follows ... 

Acids and bases neutralize each other, forming water H aq) + H20 1). Strong acids and bases ionize fully when dissolved in water, which means they are also strong electrolytes. 

The reactions between salts and water can be studied in terms of acid and base ionizations of the individual cations and anions making up the salt. (15.10)... 

In Section 12.1, we discussed the effect of a common ion on acid and base ionizations. Here we will examine the relationship between the common ion effect and solubility. As we have noted, the solubihty product is an equilibrium constant precipitation of an ionic compound from solution occurs whenever the ion product exceeds for that substance. In a saturated solution of AgCl, for example, the ion product [Ag ][Cr] is, of course, equal to K p. Furthermore, simple stoichiometry tells us that [Ag ] = [Cl ]. But this equality does not hold in all situations. 

Weak Acids and Bases Ionization of a Weak Acid... 

Acid and Base Ionization Constants Strong acids and strong bases are assumed to ionize completely. Most weak acids and bases ionize to a small extent. The concentrations of the acid, conjugate base, and ion at equilibrium can be calculated from... 

This relationship is general and shows that the product of acid- and base-ionization constants in aqueous solution for conjugate acid—base pairs equals the ion-product constant for water, K, . 

I Acid- and base-ionization constants are often iisted as I pKflS and pKbS pKb = -log Kb). 

Acids and Bases—ionization of a strong base and weak base (interactive). 

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