# One method is with an effective solvent such anhydrous acetic acid

One method is with an effective solvent such anhydrous acetic acid

Because acetic acid is a stronger acid than water, it must also be a weaker base, with a lesser tendency to accept a proton than $$H_2O$$. Measurements of the Spanking Sites dating sites conductivity of 0.1 M solutions of both HI and $$HNO_3$$ in acetic acid show that HI is completely dissociated, but $$HNO_3$$ is only partially dissociated and behaves like a weak acid in this solvent. This result clearly tells us that HI is a stronger acid than $$HNO_3$$. The relative order of acid strengths and approximate $$K_a$$ and $$pK_a$$ values for the strong acids at the top of Table $$\PageIndex$$ were determined using measurements like this and different nonaqueous solvents.

From inside the aqueous possibilities, $$H_3O^+$$ ‘s the strongest acidic and you may $$OH^?$$ ‘s the strongest ft which can exists for the harmony with $$H_2O$$.

The leveling effect applies to solutions of strong bases as well: In aqueous solution, any base stronger than OH? is leveled to the strength of OH? because OH? is the strongest base that can exist in equilibrium with water. Salts such as $$K_2O$$, $$NaOCH_3$$ (sodium methoxide), and $$NaNH_2$$ (sodamide, or sodium amide), whose anions are the conjugate bases of species that would lie below water in Table $$\PageIndex$$, are all strong bases that react essentially completely (and often violently) with water, accepting a proton to give a solution of $$OH^?$$ and the corresponding cation:

## Polyprotic Acids and you will Angles

Because you read, polyprotic acids like $$H_2SO_4$$, $$H_3PO_4$$, and you may $$H_2CO_3$$ contain more than simply you to definitely ionizable proton, additionally the protons are destroyed when you look at the a stepwise fashion. New totally protonated types is almost always the most powerful acid because is easier to get rid of a beneficial proton out-of a basic molecule than off an excellent negatively energized ion. For this reason acidic stamina decreases towards the loss of subsequent protons, and you may, correspondingly, the fresh new $$pK_a$$ grows. Consider $$H_2SO_4$$, such:

The hydrogen sulfate ion ($$HSO_4^?$$) is both the conjugate base of $$H_2SO_4$$ and the conjugate acid of $$SO_4^$$. Just like water, HSO4? can therefore act as either an acid or a base, depending on whether the other reactant is a stronger acid or a stronger base. Conversely, the sulfate ion ($$SO_4^$$) is a polyprotic base that is capable of accepting two protons in a stepwise manner:

## In contrast, in the second reaction, appreciable quantities of both $$HSO_4^?$$ and $$SO_4^$$ are present at equilibrium

Like any other conjugate acidbase pair, the strengths of the conjugate acids and bases are related by $$pK_a$$ + $$pK_b$$ = pKw. Consider, for example, the $$HSO_4^?/ SO_4^$$ conjugate acidbase pair. From Table $$\PageIndex$$, we see that the $$pK_a$$ of $$HSO_4^?$$ is 1.99. Hence the $$pK_b$$ of $$SO_4^$$ is ? 1.99 = . Thus sulfate is a rather weak base, whereas $$OH^?$$ is a strong base, so the equilibrium shown in Equation $$\ref$$ lies to the left. The $$HSO_4^?$$ ion is also a very weak base ($$pK_a$$ of $$H_2SO_4$$ = 2.0, $$pK_b$$ of $$HSO_4^? = 14 ? (?2.0) = 16$$), which is consistent with what we expect for the conjugate base of a strong acid.

• $$NH^+_+PO^_ \rightleftharpoons NH_+HPO^_$$
• $$CH_3CH_2CO_2H_+CN^?_ \rightleftharpoons CH_3CH_2CO^?_+HCN_$$

Identify the conjugate acidbase pairs in each reaction. Then refer to Tables $$\PageIndex$$and$$\PageIndex$$ and Figure $$\PageIndex$$ to determine which is the stronger acid and base. Equilibrium always favors the formation of the weaker acidbase pair.

The conjugate acidbase pairs are $$NH_4^+/NH_3$$ and $$HPO_4^/PO_4^$$. According to Tables $$\PageIndex$$ and $$\PageIndex$$, $$NH_4^+$$ is a stronger acid ($$pK_a = 9.25$$) than $$HPO_4^$$ (pKa = ), and $$PO_4^$$ is a stronger base ($$pK_b = 1.68$$) than $$NH_3$$ ($$pK_b = 4.75$$). The equilibrium will therefore lie to the right, favoring the formation of the weaker acidbase pair: