Conjugate acid-base pairs table

TABLE P a 10.3 Conjugate Acid-Base Pairs Arranged by Strength Acid name Acid formula Base formula Base name PKb... 

A practical problem in solution preparation usually requires a different strategy than our standard seven-step procedure. The technician must first identify a suitable conjugate acid-base pair and decide what reagents to use. Then the concentrations must be calculated, using pH and total concentration. Finally, the technician must determine the amounts of starting materials. The technician needs a buffer at pH = 9.00. Of the buffer systems listed in Table 18-1. the combination of NH3 and NH4 has the proper pH range for the required buffer solution. 

C18-0053. From Table 18-1. select the best conjugate acid-base pairs for buffer solutions at pH 3.50 and 12.60. If you were going to add HCl solution as part of the buffer preparation, what other substance should you use in each case ... 

Table 5.1 gives commonly used examples of conjugate acid-base pair combinations and the pH range for which each is useful. This range corresponds to the pH range defined by the buffer region in the titration curve for each, and the middle of the range corresponds to the midpoint of each titration. 

For example, to prepare a pH = 9 buffer solution, one would prepare a solution of ammonium chloride (refer to Table 5.1), and then add a solution of sodium hydroxide while stirring and monitoring the pH with a pH meter. The preparation is complete when the pH reaches 9. The required conjugate acid-base pair would be NH3 - NHj. Recipes for standard buffer solutions can be useful. Table 5.2 gives specific directions for preparing some popular buffer solutions. 

The definition of pH is pH = —log[H+] (which will be modified to include activity later). Ka is the equilibrium constant for the dissociation of an acid HA + H20 H30+ + A-. Kb is the base hydrolysis constant for the reaction B + H20 BH+ + OH. When either Ka or Kb is large, the acid or base is said to be strong otherwise, the acid or base is weak. Common strong acids and bases are listed in Table 6-2, which you should memorize. The most common weak acids are carboxylic acids (RC02H), and the most common weak bases are amines (R3N ). Carboxylate anions (RC02) are weak bases, and ammonium ions (R3NH+) are weak acids. Metal cations also are weak acids. For a conjugate acid-base pair in water, Ka- Kb = Kw. For polyprotic acids, we denote the successive acid dissociation constants as Kal, K, K, , or just Aj, K2, A"3, . For polybasic species, we denote successive hydrolysis constants Kbi, Kb2, A"h3, . For a diprotic system, the relations between successive acid and base equilibrium constants are Afa Kb2 — Kw and K.a Kbl = A w. For a triprotic system the relations are A al KM = ATW, K.d2 Kb2 = ATW, and Ka2 Kb, = Kw. 

Another feature of the Henderson-Hasselbalch equation is that, for every power-of-10 change in the ratio [A ]/[HA], the pH changes by one unit (Table 9-1). As the base (A ) increases, the pH goes up. As the acid (HA) increases, the pH goes down. For any conjugate acid-base pair, you can say, for example, that, if pH = pKA — 1, there must be 10 times as much HA as A. Ten-elevenths is in the form HA and one-eleventh is in the form A. ... 

TABLE 10.3 Conjugate Acid-Base Pairs Arranged by Strength... 

TABLE 15.1 Relative Strengths of Conjugate Acid -Base Pairs ... 

Table 10-2 displays relative acid and base strengths of a number of conjugate acid-base pairs. 

The bulk of this Appendix is on acidity because many more functional groups are acidic than are basic. Basically (oooh, sony), only one functional group is basic amines. There is variation among aliphatic, aromatic, and heteroaromatic amines these are covered thoroughly in text sections 19-5 and 19-6. One point in the text. Just before Table 19-3, deserves emphasis for any conjugate acid-base pair ... 

Table 15.2 lists some important conjugate acid-base pairs, in order of their relative strengths. Conjugate acid-base pairs have the following properties ... 

Table 9-2 lists values of K, pK , K, and p/C for some conjugate acid base pairs at 25 °C. 

If they are equal, the ratio is 1, and the log of 1=0. Therefore, under those circumstances, pH = pK. Table 9-1 informs us that the conjugate acid-base pair, H2PO4 - HP04 ", is characterized by a pK of 6.80. The desired buffer will be prepared by dissolving equal molar quantities of KH2PO4 and K2HPO4 in water. 

Table 2. Examples of conjugate acid-base pairs.

As the strength of an acid increases (Kg gets larger), the strength of its conjugate base must decrease (Ky gets smaller) so that the product X Ky remains 1.0 X 10 at 25 °C. TABLE 16.5 demonstrates this relationship. Remember, this important relationship applies only to conjugate acid—base pairs. 

The values of and for a number of common conjugate acid-base pairs are shown in Table 11.5. Because and values can range over many orders of magnitude, they are often expressed on a logarithmic scale similar to pH. We define pK and pK as follows ... 

The and pK values for a number of common conjugate acid-base pairs are also given in Table 11.5. 

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