# Write an expression for the acid ionization constant for hcho2

Rearranging our equation and writing it in standard quadratic form, we have Solution of this equation by use of the standard quadratic formula, gives Of the two solutions, only the one that gives a positive value for x is chemically reasonable.

## If the acid is weak write an expression for the acid ionization constant ka

This observation is general: It is always easier to remove the first proton from a polyprotic acid than the second. To the number of significant figures we are using, the subtraction yields 0. Thus, From our result we can calculate the percent of molecules ionized: b Proceeding similarly for the 0. The numbers on the constants refer to the particular proton of the acid that is ionizing. From Table Thus, we will assume that x is negligible compared to 0. A more complete list is given in Appendix D. We first imagine that the solution consists of 0. This trend is intuitively reasonable; on the basis of electrostatic attractions, we would expect a positively charged proton to be lost more readily from the neutral H2SO3 molecule than from the negatively charged HSO3— ion.

These acids are known as polyprotic acids. Some metal hydroxides are not as strong simply because they are not as soluble.

## Rank the acids in order of decreasing acid strength.

As long as successive Ka values differ by a factor of or more, it is possible to obtain a satisfactory estimate of the pH of polyprotic acid solutions by considering only Ka1. As expected, the pH of a solution of a weak acid is higher than that of a solution of a strong acid of the same molarity. Proceeding as in Sample Exercises Notice also that the value of Ka1 for sulfuric acid is listed simply as "large. The pH of the 0. Finally, we can compare the pH value of this weak acid to a solution of a strong acid of the same concentration. Consequently, the pH can be determined by considering only Ka1, thereby treating the acid as if it were a monoprotic acid. By comparison, the pH of a 0.

Let's calculate the pH of a 0. The pH of the 0. Consequently, the pH can be determined by considering only Ka1, thereby treating the acid as if it were a monoprotic acid. Refer to Table The concentration of acetic acid before any of it ionizes is 0.

In doing these calculations, it is important to realize that proton-transfer reactions are generally very rapid.

### If the acid is weak write an expression for the acid ionization constant ka

Calculating Ka from pH In order to calculate either the Ka value for a weak acid or the pH of its solutions, we will use many of the skills for solving equilibrium problems that we developed in Section As shown in Figure By comparison, the pH of a 0. You should always check the validity of any simplifying assumptions after you have finished solving a problem. The Table below is a listing of base ionization constants for several weak bases. This approach is both inexpensive and effective. This fact is further demonstrated in Sample Exercise Thus, we can write the following: [ As a result, we anticipate that the equilibrium will lie far to the left, and that x will be very small compared to the initial concentration of acetic acid. The rate of reaction with the metal is much faster for the solution of a strong acid. A strong base is a base, which ionizes completely in an aqueous solution. An equilibrium expression can be written for the reactions of weak bases with water. Let's calculate the pH of a 0. Ammonia absorbs the heat and then releases it into space as the gas circulates through the coils. This result is in accord with what we see in Figure

Thus, Solving for x, we have The small value of x indicates that our simplifying assumption was justified.

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