Factors That Determine Acid Strength

We have already learned in Section 2.3 that a tremendous difference in acidity exists among compounds. HCl 0) is an extremely strong acid. Water (pK =15.7) is moderate in acidity, and CH4 (p/fa = 50) is an extremely weak acid. How are these differences explained There is one general rule. 

For now we will concentrate on how structural differences between molecules can profoundly affect acidity. In Chapter 6, we will learn how to relate the stability of a species to its relative potential energy. 

No matter which factor is discussed, the same procedure is always followed. To compare the acidity of any two acids  

The most important factor determining the acidity of H-A is the location of A in the periodic table. 

Examine acidity trends across a row of the periodic table by comparing CH4 and H2O, two compounds having H atoms bonded to a second-row element. We know from Table 2.1 that H2O has a much lower p a and therefore is much more acidic than CH4, but why is this the case  

---

Factors That Determine Acid Strength Example... 

A Summary of the Factors that Determine Acid Strength 71... 

The focus here is on two major factors that determine the strength of a Lewis acid where all Lewis acids have an atom that can accept one or more electron pairs. (1) In general, an atom that can accept only one electron pair (such as B) is more acidic than an atom that can accept more than one electron pair (such as Fe or Sn). (2) If two Lewis acids are in the same group of the periodic table (say,... 

Give two important factors that determine the strength of an acid. How does an increase in each factor affect the acid strength ... 

There are a few trends about acid strengths that you should be familiar with. If you consider the acid HA, the bond between H and A will have to be broken in order for the hydrogen ion to be donated. For binary acids (those containing only hydrogen and a nonmetallic element), there are two main factors that determine the ease of this process the polarity of the bond between H and A and the size of A. The factors can be summarized as follows ... 

There are a number of factors that determine whether a protonic acid can initiate polymerization of alkenes. Their acidity (pKa), and therefore the basicity of the resulting counteranion, determines the efficiency of initiation. Although reliable pKa values of acids stronger than sulfuric or hy-droiodic (pKa < -9) are difficult to obtain in aqueous solutions due to their nearly complete dissociation, the pKa values of acetic acid (4.75) and trichloroacetic acid (0.7) in water provide useful references. Conductometric and potentiometric estimates of the pK values of selected protonic acids in various organic solvents are summarized in Table 11 in descending acid strength. These values are not very precise, however, because the amount of moisture in each system was not monitored precisely. 

Thus, to explain the various acid strengths of the hydrogen halides, we must focus on the factors that determine AH0 and A5° for the acid dissociation reaction. 

Before we recognize factors that determine the relative strengths of acids and bases, it is important to have a clear understanding of acids and bases. 

The factors that determine the relative strengths of acids and bases ... 

The halogen oxoacids and oxoanions are produced by reaction of the halogens and their oxides with water. Most of the oxoacids are stable only in solution. Table 14.3 (next page) shows ball-and-stick models of the acids in which each atom has its lowest formal charge note that H is bonded to O. (We ll discuss factors that determine the relative strengths of the halogen oxoacids in Chapter 18.)... 

Thus there are two main factors that determine whether a molecule containing an X—H bond will behave as a Bronsted-Lowry acid the strength of the bond and the polarity of the bond. 

What are the factors that determine the acid-base properties of solid surfaces such as metal oxides On the basis of the discussion thus far it seems appropriate to relate the appearance of Lewis acidity and disappearance of Bronsted acidity to the increase in the degree of dehydroxylation. Indeed, the interconversion of Lewis and Bronsted acid sites has been demonstrated for some oxides, such as ZnO or supported Mo03 Cr203, or WO3, by IR studies of pyridine or ammonia adsorption [59]. But which factors determine the strength of acid sites ... 

---