The Conjugate Acid-Base Pair

The Br0nsted-Lowry definition provides a new way to look at acid-base reactions because it focuses on the reactants and the products. For example, let s examine the reaction between hydrogen sulfide and ammonia  

In the forward reaction, H2S acts as an acid by donating an H to NH3, which acts as a base by accepting it. The reverse reaction involves another acid-base pair. The ammonium ion, NH4, acts as an acid by donating an H to the hydrogen 

A Br0nsted-Lowry acid-base reaction occurs when an acid and a base react to form their conjugate base and conjugate acid, respectively acid, -I- bas62 base, + acid  

The Conjugate Pairs in Some Acid-Base Reactions 

SAMPLE PROBLEM 18.4 Identifying Conjugate Acid-Base Pairs 

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For each of the following reactions, indicate the Brensted-Lowry adds and bases. What are the conjugate acid/base pairs ... 

Write the proton transfer equilibria for the following acids in aqueous solution and identify the conjugate acid-base pairs in each one (a) H2S04 (b) C6H5NH3+. anilinium ion ... 

Write the two proton transfer equilibria that show the amphiprotic character of (a) H2P04 (b) HC204, hydrogen oxalate ion. Identify the conjugate acid-base pairs in each equilibrium. 

C17-0020. Draw ball-and-stick models for the conjugate acid-base pair of each weak acid and weak base in Section Exercise. ... 

C17-0039. Write a paragraph describing the conjugate acid-base pair and explaining how each interacts with water. C17-0040. Update your list of memory bank equations. 

The pH is close to the p of the conjugate acid-base pair, so this is a reasonable result. 

The pH of the buffer solution, both before and after adding the solid NaOH, is close to the p of the conjugate acid-base pair. Moreover, the pH increases when NaOH is added. The solution becomes more basic as a consequence of the added hydroxide anions. 

Identify the conjugate acid-base pairs in each reaction. 

The conjugate acid-base pairs have the same subscript and are bracketed together. This reaction goes almost to completion because HCI is a good proton donor and hence a strong acid. 

Find the conjugate acid - base pairs for the following reactions. 

The simplest approach is to identify the conjugate acid-base pairs, the species whose formulas differ by just one proton. 

We ve seen in previous sections that the strength of an acid can be expressed by its Ka, and the strength of a base can be expressed by its Kb. For a conjugate acid-base pair, the two equilibrium constants are related in a simple way that makes it possible to calculate either one from the other. Let s consider the conjugate acid-base pair NH4+ and NH3, for example, where Ka refers to proton transfer from the acid... 

Write a balanced net ionic equation for the reaction of each of the following ions with water. In each case, identify the Bransted-Lowry acids and bases and the conjugate acid-base pairs. 

Use the conjugate acid-base pair HCN and CN- to derive the relationship between Ka and K. ... 

For each of the compounds in the center column of the Conjugate Acid-Base Pairs activity (eChapter 15.1), write the dissociation equations that convert it to its conjugate acid and its conjugate base. 

Aqueous equilibria play a crucial role in many biological and environmental processes. The pH of human blood, for example, is carefully controlled at a value of 7.4 by equilibria involving, primarily, the conjugate acid-base pair H2CO3 and HCO3-. The pH of many lakes and streams must remain near 5.5 for plant and aquatic life to flourish. 

The ionization of the acid HA in solvent S leads to a new acid HS+ and a base A. Equation (1.1) has a very wide scope and can be very well applied to neutral and positively and negatively charged acid systems. The acid-base pair that differs only by aproton is referred to as the conjugate acid-base pair. Thus, H20 is the conjugate base of the acid H30+. An obvious consequence of the concept is that the extent to which an acid ionizes depends on the basicity of the solvent in which the ionization takes place. This shows the difficulty in establishing an absolute acidity scale. Acidity scales are energy scales, and thus they are arbitrary with respect to both the reference point and the magnitude of units chosen. 

Ionization. Ionization refers to the dissociation of a neutral chemical into charged species. The most common form of neutral toxicant dissociation is acid-base equilibria. The hypothetical monoprotic acid, HA, will dissociate in water to form the conjugate acid-base pair (H+, A-) usually written as... 

In the earlier work (Forster, 1951 Weller, 1952) when the principal experimental information involved fluorescence intensities, the most useful algebraic expressions were those relating relative quantum yields of the conjugate acid base pair to the solution acidity. In favourable cases such expressions were used to obtain rate constants for the forward and reverse reactions, and hence equilibrium constants, though it was always necessary to make allowance... 

Hydrogen bromide is a gas at room temperature. It is soluble in water, forming hydrobromic acid. Identify the conjugate acid-base pairs. 

Hydrogen bromide provides the proton, so it is the Brpnsted-Lowry acid in the reaction. Water receives the proton, so it is the Brpnsted-Lowry base. The conjugate acid-base pairs are HBr/Br and H20/H30+. 

Ammonia is a pungent gas at room temperature. Its main use is in the production of fertilizers and explosives. It is very soluble in water. It forms a basic solution that is used in common products, such as glass cleaners. Identify the conjugate acid-base pairs in the reaction between aqueous ammonia and water. 

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