Acetic acid dissociates/ionizes itself as follows:
CH3COOH(aq) ⇔ H+(aq) + CH3COO-(aq)
If you add sodium acetate, CH3COONa, to the solution:
a) a precipitate will be formed
b) more acetic acid will be ionized
c) the concentration of hydrogen ions will decrease
d) the solution will become more acidic
Le Chatelier's Principle. Which way will the reaction shift?
The correct answer is:
c) the concentration of hydrogen ions will decrease
Explanation:
Adding sodium acetate, CH3COONa, to the solution will result in the dissociation/ionization of CH3COONa into its respective ions:
CH3COONa(s) → Na+(aq) + CH3COO-(aq)
The presence of CH3COO- ions from CH3COONa will shift the equilibrium of the acetic acid dissociation reaction to the left side, according to Le Chatelier's principle. This means that more acetic acid molecules (CH3COOH) will be formed, but the concentration of hydrogen ions (H+) will decrease.
The presence of acetate ions increases the concentration of CH3COO- ions, which can combine with some of the hydrogen ions (H+) produced by the dissociation of acetic acid, leading to a decrease in the concentration of hydrogen ions. Thus, the solution becomes less acidic, not more acidic.
To determine the effect of adding sodium acetate (CH3COONa) to the solution of acetic acid (CH3COOH), we need to consider the chemistry behind the dissociation of acetic acid and the reaction between acetic acid and sodium acetate.
Acetic acid (CH3COOH) is a weak acid that partially ionizes in water. The equilibrium reaction is as follows:
CH3COOH(aq) ⇔ H+(aq) + CH3COO-(aq)
Now, let's analyze the possible effects of adding sodium acetate (CH3COONa):
a) A precipitate will be formed: This is unlikely to occur because sodium acetate is a salt that is highly soluble in water, and thus it does not usually form precipitates.
b) More acetic acid will be ionized: Adding sodium acetate will not directly affect the ionization of acetic acid. However, it can have an indirect effect on the equilibrium by shifting it to the left (Le Chatelier's principle) if sodium acetate reacts with the hydrogen ions (H+) or the acetate ions (CH3COO-) present in the solution.
c) The concentration of hydrogen ions will decrease: When sodium acetate is added to the solution, it dissociates into sodium ions (Na+) and acetate ions (CH3COO-). The acetate ions can react with the hydrogen ions, reducing the concentration of hydrogen ions in the solution. Therefore, the concentration of hydrogen ions will decrease.
d) The solution will become more acidic: The addition of sodium acetate, which is the conjugate base of acetic acid, can lead to a slight increase in the concentration of hydroxide ions (OH-) in the solution. However, the effect of this increase is usually negligible. Therefore, the solution will not become more acidic.
In conclusion, the correct answer is c) the concentration of hydrogen ions will decrease.