Question

1. consider the following equilibrium: hno2(aq) + h2o(l) ⇌ h3o+(aq) + no2-(aq)

in which direction will the equilibrium shift if
a. naoh is added? why?
b. nano2 is added? why?
c. hcl is added? why?
d. the solution is made more dilute? why?

Explanation:

Step1: Analyze effect of adding NaOH

NaOH is a strong - base. It will react with \(H_3O^+\) in the solution. The reaction is \(OH^-(aq)+H_3O^+(aq)
ightleftharpoons2H_2O(l)\). When \(H_3O^+\) is consumed, according to Le - Chatelier's principle, the equilibrium \(HNO_2(aq)+H_2O(l)
ightleftharpoons H_3O^+(aq)+NO_2^-(aq)\) will shift to the right to replenish the \(H_3O^+\) that has been removed.

Step2: Analyze effect of adding \(NaNO_2\)

\(NaNO_2\) dissociates in water as \(NaNO_2(s)
ightarrow Na^+(aq)+NO_2^-(aq)\). This increases the concentration of \(NO_2^-\) in the solution. According to Le - Chatelier's principle, the equilibrium will shift to the left to reduce the excess \(NO_2^-\) concentration.

Step3: Analyze effect of adding HCl

HCl is a strong acid. It dissociates as \(HCl(aq)
ightarrow H^+(aq)+Cl^-(aq)\), and \(H^+\) will combine with water to form \(H_3O^+\). So the concentration of \(H_3O^+\) in the solution increases. According to Le - Chatelier's principle, the equilibrium will shift to the left to reduce the excess \(H_3O^+\) concentration.

Step4: Analyze effect of dilution

When the solution is made more dilute, according to Le - Chatelier's principle, the equilibrium will shift in the direction that produces more moles of particles. In this case, the right - hand side has 2 moles of ions (\(H_3O^+\) and \(NO_2^-\)) while the left - hand side has 1 mole of solute (\(HNO_2\)). So the equilibrium will shift to the right.

Answer:

A. The equilibrium will shift to the right because \(NaOH\) reacts with \(H_3O^+\), decreasing its concentration and the system tries to replenish it.
B. The equilibrium will shift to the left because the addition of \(NaNO_2\) increases the concentration of \(NO_2^-\) and the system tries to reduce it.
C. The equilibrium will shift to the left because \(HCl\) increases the concentration of \(H_3O^+\) and the system tries to reduce it.
D. The equilibrium will shift to the right because dilution favors the side with more moles of particles.