Consider a 0.85 M solution of each of the following salts in distilled water. Wi

Question

Consider a 0.85 M solution of each of the following salts in distilled water. Will the solution be acidic, neutral, or basic? You may need to reference a table of Ka and Kb tables values. CH3CH2NH3OI, NH4NO2, NH4CH3COO, (CH3CH2)2NH2ClO4

Explanation / Answer

The solution will be neutral unless hydrolysis occurs. Hydrolysis will occur if the cation of the salt forms a weak base when it reacts with water. Hydrolysis also occurs if the anion of the salt forms a weak acid. Following are some examples. Example 1 - CaCl2 Ca2+ + 2H2O ----> Ca(OH)2 + 2H+ If this reaction occurred, the solution would be acid due to H+. But, this reaction will not occur because Ca(OH)2 is a strong base and it will ionize to produce mostly Ca2+ and H2O. Cl- + H2O ----> HCl + OH- If this reaction occurred, the solution would be basic due to the OH-, but it doesn't occur because HCl is a strong acid. It ionizes to produce Cl- and H2O. Neither ion hydrolyzes, so the solution remains neutral. Example 2 - NaC2H3O2 Na+ + H2O ----> NaOH + H+ This reaction won't occur because NaOH is a strong base. It immediately ionizes to form Na+ and water. C2H3O2- + H2O ----> HC2H3O2 + OH- This reaction will occur because HC2H3O2 is a weak acid. It doesn't ionize much, so will remain in the molecular form. When it forms, OH- is produced which makes the solution basic. Therefore, NaC2H3O2 in water is basic. Example 3 - NH4NO3 NH4+ + H2O ----> NH3 + H3O+ This reaction occurs to produce the weak base NH3. The H3O+ ions produced cause the solution to be acidic. NO3- + H2O ----> HNO3 + OH- This reaction will not occur because HNO3 is a strong acid, which immediately ionizes to form NO3- and H2O. OH- does not form, so NO3- leaves the solution neutral. Overall, the solution will be acidic when NH4NO3 is added to water because the NH4+ ion hydrolyzes to produce H3O+ In summary, hydrolysis occurs when a weak base or weak acid is a product, and the pH is affected. If a strong base or strong acid is a product, hydrolysis does not occur and the solution remains neutral. The weak bases are NH3 and the amines like CH3NH2. Weak acids include acetic (HC2H3O2), carbonic (H2CO3), phosphoric acid (H3PO4), hydrosulfuric acid (H2S). Some ions also act as weak acids, like dihydrophosphate (H2PO41-), monohydrogenphosphate (HPO42-), and bicarbonate (HCO31-). The strong bases include Groups IA and IIA hydroxides. Strong acids include HCl, HNO3, H2SO4, HCl04, HClO3, HI, and HBr. The anions of these acids do not hydrolyze (do not affect the pH).

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