Comparing the Strengths of Acids

Acids ionize and produce hydrogen ions in aqueous solution. The strength of an acid depends on how completely it ionizes. Strong acids undergo essentially complete ionization, whereas weak acids are only partly ionized at equilibrium. Like other reversible reactions, the ionization of a weak acid can be represented by an equilibrium constant expression. The value of this expression, called the acid ionization constant, K, is a measure of the strength of a weak acid. 

Can you compare the strengths of several acids by measuring the pH of their solutions and calculating 

1 OOM hydrogen peroxide (H2O2) 0.1 OOM permanganic acid (HMn04) 24-well microplate thin-stern pipettes (12) pH papers (various pH ranges) distilled water 

Always wear safety goggles, gloves, and a lab apron. 

Explain the difference between the terms weak acid and dilute acid. 

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Since two product molecules are produced from two reactant molecules, the ionization ratio of the acid is expressed as the product of the product concentrations divided by the product of the reactant concentrations). This numerical ratio can be used to compare the strengths of acids. It is very important to realize just how simple this notion is. The equilibrium constant (in this case the ionization constant of an acid) is merely a ratio of the molecules which have donated a proton to water to those which have not. 

We can compare the strengths of acids in terms of percent ionization only if concentrations of the acids are the same. 

Example 15.12 compares the strengths of acids based on their molecular structures. 

It is evident that p/Ca values provide a very convenient way of comparing the strengths of acids (or of bases). The stronger an acid is, the lower its pAa (the stronger a base is, the higher its pAa). The pH at which an acid or base is half ionized is equal to its p a- When the pH is one unit below the pAa, an acid is 9% ionized, and a base is 91% ionized (see Section 17.0). 

One method of comparing the strengths of acids and bases is by means of the equilibrium constant ... 

This method of comparing the strengths of acids according to the extent of reaction with the solvent cannot be used for all solvents. If the solvent is inert, e.g., a hydrocarbon, other methods must be adopted. Some of them will be discussed later. 

It is possible to compare the strengths of weak acids by the values of their acid dissociation constants Ka. Figure 3.1 shows the titration curves for acids (HA or BH+) of different Ka values. The ordinate shows poH, which is defined by paH = -loga(SI I)). paH corresponds to the pH in aqueous solutions (see Section 3.2). The poH of non-aqueous solutions can be measured with a glass pH electrode or some other pH sensors (see Sections 3.2.1 and 6.2). For the mixture of a weak acid A and its conjugate base B, poH can be expressed by the Henderson-Hassel-balch equation ... 

Strong and Weak Acids. In order to compare the strength of adds it is necessary to have solutions of the same concentration. Prepare 50 cc. each of 0.1 A hydrochloric and acetic acids by diluting 5 cc. of 1 A add with 45 cc. water. Carefully compare the conductivity of these 0.1 A acids, using electrodes B. Carefully compare the intensity of the sour or add taste, but do not swallow any of the acid. Rinse out the mouth with water. Quite a bit of experimenting is necessary to find just the amount of acid... 

Compare the strength of arsenic and arsenious acids. Of what general rule is this comparison an example ... 

The strength of acids can be measured and compared by the value of their protolysis equilibrium constant. For the protolysis of acetic acid this equilibrium constant can be expressed as... 

However, it should be emphasized that the measurement and quantification of the acid/base strength of zeolites is complex and that it is difficult to directly compare the aciti base strength of a solid with that of a liquid. This results from the feet that the stabilization of carbocations and carbanions in a microporous solid differs from that in strongly polar acid and base solutions. For zeolites, it can be stated that the concentiatlbn of aluminum in the lattice is directly proportional to the concentration of acid sites and the polarity of the lattice and to a first approximation indirectly proportional to the strength of acid sites [40]. For a given chemical composition of the zeolite, the polarity of the lattice increases with decreasing framework density [41],... 

Though the means of comparing the strengths of Lewis acids is not entirely satisfactory, SO3 is clearly one of the strongest. 

The pKj and plCj, values provide a convenient means of comparing the strengths of weak acids and bases. The lower the pK, the stronger the acid the lower the pK, the stronger is the base. The pK values of a series of drugs are given in Talsle 3.6. plC and pX, values of conjugate acid-base pairs are linked... 

Compare the strength of a weak acid with the strength of its conjugate base and the strength of a weak base with the strength of its conjugate acid. 

Although the Brpnsted-Lowry model helps explain acid strength, the model does not provide a quantitative way to express the strength of an acid or to compare the strengths of various acids. The equilibrium constant expression provides the quantitative measure of acid strength. 

The twenty amino acids combine to form proteins in living systems. Research the structures and values for five amino acids. Compare the strengths of these acids with the weak acids in Table 19-2. 

Compare the strengths of several common acids and bases. 

The strength of an acid depends on a number of factors, such as the properties of the solvent, the temperature, and, of course, the molecular structure of the acid. When we compare the strengths of two acids, we can eliminate some variables by considering their properties in the same solvent and at the same temperature and concentration. Then we can focus on the structure of the acids. 

Compare the strengths of the following pairs of acids (a) H2SO4 and H2Se04, (b) H3PO4 and H3ASO4. 

They are characterized by the levelling of basic properties of the strongest bases, since they are transformed into an equivalent quantity of the solvent base. There are no limitations to the strength of acids, which makes it possible to compare the relative acidic properties of all the acids which are stable in these melts at a definite temperature. 

I Compare the strength of a weak acid with the strength of its conjugate base. 

How would you compare the strengths of two weak acids experimentally By looking up information in a table or a handbook ... 

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