Salts of Weak Bases and Strong Acids

We see that aqueous solutions of NaCl contain four ions, Na , Cl , H30 and OH .The cation of the salt, Na, is such a weak acid that it does not react appreciably with water. The anion of the salt, Cl , is such a weak base that it does not react appreciably with water. Solutions of salts of strong bases and strong acids are therefore neutral because neither ion of such a salt reacts to upset the H30 /0H balance in water. 

The saH of a stroiqi acid and a strong base is often referred to as a neutral salt. 

When salts derived from strong bases and weak adds are dissolved in water, the resulting solutions are always basic. This is because anions of weak acids react with water to form hydroxide ions. Consider a solution of sodium acetate, NaCH3COO, which is the salt of the strong base NaOH and the weak acid CH3COOH (acetic add). It is soluble and dissociates completely in water. 

Though the saH of a strong base and a weak acid is not strictly included in the definition 

Acetate ion is the conjugate base of a weak acid, CH3COOH. Thus, it reacts to some ex- of a basic saB (see Section 10-9), many tent with H3O+ to form CH3COOH. As H30 is removed from the solution, causing chemists refer to such a saB as a weak/y more H2O to ionize, an excess of OH builds up. So the solution becomes basic. The net basic salt. 

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Salts of strong bases and weak acids possess alkaline reactions in aqueous solution because of hydrolysis (Section 2.18). A solution containing one mole... 

The second case pertains to the hydrolysis of salts of strong bases and weak acids. This can be generally be shown as ... 

For example, suppose you are asked to determine if a solution of sodium carbonate, Na2C03, is acidic, basic, or neutral. Sodium carbonate is the salt of a strong base (NaOH) and a weak acid (HC03). Salts of strong bases and weak acids are basic salts. As a basic salt, we know the final answer must be basic (pH above 7). 

If a salt consists of the cation of a strong base and the anion of a weak acid, such as NaCHsCOO, only the anion reacts significantly with water. The reaction produces hydroxide ions. Therefore, the solution will have a pH that is greater than 7. Salts of strong bases and weak acids dissolve in water and form basic solutions. 

Alkalinity is a measure of the concentration of all electrolytes that give basic reaction when hydrolyzed in water, i.e., salts of strong bases and weak acids (hydrates, carbonates, bicarbonates, phosphates, silicates, borates, sulfites, etc.). Chlorides and sulfates do not contribute to alkalinity. The... 

Because soaps are salts of strong bases and weak acids, they should be weakly alkaline in aqueous solution. However, a soap with free alkali can cause damage to skin, silk, or wool. Therefore, a test for basicity of the soap is quite important. 

The correct answer is (E). NH4C1 is a salt formed from a weak base (NH3) and a strong acid (HC1). It will hydrolyze to form an acidic solution. The other two substances, NaF and K2C03, are salts of strong bases and weak acids. As a result, the conjugates, F and C03 , will hydrolyze to form basic solutions. 

We recognize that both NaCH3COO and NaCN are salts of strong bases and weak acids. The anions in such salts hydrolyze to give basic solutions. As we have done before, we first write the appropriate chemical equation and equihbrium constant expression. Then we complete the reaction summary, substimte the algebraic representations of equilibrium concentrations into the equilibrium constant expression, and solve for the unknown concentration(s). 

Write names and formulas for three salts of strong bases and weak acids other than those that appear in Section 18-8. 

Elevated pH values occur in waters whose chemistry is dominated by minerals, most of which, as noted above, are salts of strong bases and weak acids. Thus, in the absence of sources of acidity, mineral carbonate and silicate and alumino-silicate minerals tend to raise the pH to values of 9 to 10 or even higher. Such high pH s are found in arid soils and in some deep groundwaters that are not exposed to fresh recharge and so can be said to be rock dominated as opposed to water dominated. In such systems the minerals present can exist stably, without weathering. Water pH values above 10 are exceptional and may reflect contamination by strong bases, such as NaOH or Ca(OH)2. 

Not only in its manufacture but in its use does soap involve hydrolysis. Like other salts of strong bases and weak acids, sodium stearate and the other sodium soaps spontaneously hydrolyze somewhat in water, and upon this hydrolysis to some extent depends the detergent (cleansing) effect of soap. 

Figure 1.4, Hydrolysis of sodium acetate (salt of strong base and weak acid). Na and OIF do not have a tendency to combine because they are derived from strong alkali CHfCOO", however, has a tendency to combine with H of water because it is a base corrugate to a weak acid. This depletes H ions of water while OH remain unchanged. The solution becomes alkaline. (Hff shown as H for the sake of simplicity)...

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