Write the acid-base equilibrium that determines the pH of aqueous solutions of each of the follo

Write the acid-base equilibrium that determines the pH of...

Write the acid-base equilibrium that determines the $\mathrm{pH}$ of aqueous solutions of each of the following salts, and state whether the resulting solution is acidic, basic, or neither: (a) $\mathrm{NH}_4 \mathrm{I}$; (b) $\mathrm{NaClO}_4$; and (c) $\mathrm{NaCH}_3 \mathrm{CO}_2$.

Key Concepts

Acid-Base Equilibrium

Acid-base equilibrium involves the balance between the forward and reverse reactions in water when an acid or a base interacts with water. The equilibrium constant for these reactions helps predict the extent of proton transfer, which in turn allows one to determine the concentration of hydronium or hydroxide ions in solution and the corresponding pH.

Strength of Acids and Bases

The strength of an acid or a base, or its conjugate counterpart, determines its ability to donate or accept protons in water. Salts formed from strong acids and bases generally produce neutral solutions because neither ion significantly reacts with water. In contrast, salts derived from a weak acid or a weak base can lead to acidic or basic solutions due to the hydrolysis of the ions.

Salt Hydrolysis

Salt hydrolysis refers to the reaction of salt ions with water, where the ion derived from either a weak acid or a weak base reacts with water to produce either hydronium (H3O+) or hydroxide (OH?) ions. This reaction determines the pH of the solution by shifting the equilibrium towards either acidity or basicity, depending on which ion is reactive in water.

Conjugate Acid-Base Pairs

In aqueous solutions, salts dissociate into ions that are the conjugate acids or bases of their parent acids or bases. A conjugate acid is formed from a weak base and can donate a proton to water, while a conjugate base, formed from a weak acid, can accept a proton from water. Understanding these pairs is crucial, as the strength of the parent acid or base dictates the extent of the hydrolysis reaction and thus the resulting pH.

Transcript

00:04 In this question, we are asked to identify if a certain salt will act as an acidic, basic or neutral component when it is dissolved in water.

00:19 So we are asking to evaluate if the final solution is going to be acidic, basic, or neutral when the salt is dissolved in water.

00:27 So the first salt that we are asked to look into is ammonium phosphate.

00:33 So, ammonium, cations have a plus one charge and phosphate has a 3 minus charge.

00:43 And for that reason, we have to have three ammonium ions to neutralize the charge coming from the phosphate anion.

00:51 And this, when it's dissolved in water, it can separate into ammonium ions, three of them to be specific, and phosphate anions.

01:02 So both of these ions produced can react with water.

01:12 Ammonium will react with water to give rise to ammonia, nh3.

01:26 And then it will also produce hydronium ions.

01:33 From the proton that left ammonium ions, it can donate that to water and produce hydronium ions.

01:47 And then phosphate can also react with water and produce h .p .o .4 .2 minus along with hydroxyl groups.

02:20 So we see that we're producing both hydronium ions and hydroxyl ions.

02:25 So the next thing we have to find out is which we are producing more of in this solution.

02:34 Ion or hydroxyl ions.

02:36 And to answer that question, we have to look up the ca values.

02:40 We have to look up the ca value for ammonia...

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