Problem 102 - General Chemistry: Principles and Modern Applications

Question

To increase the ionization of formic acid, \(\mathrm{HCOOH}(\mathrm{aq})\) which of the following should be added to the solution? (a) \(\mathrm{NaCl} ;\) (b) \(\mathrm{NaHCOO} ;(\mathrm{c}) \mathrm{H}_{2} \mathrm{SO}_{4} ;\) (d) \(\mathrm{NaHCO}_{3}\)

Step-by-Step Solution

Answer

To increase the ionization of formic acid, sulphuric acid, H2SO4, should be added to the solution.

Step 1: Analyze NaCl

Sodium chloride, NaCl, is a salt which when added to the solution will increase the ionic strength of the solution. However, it will not contribute to the ionization of HCOOH, because NaCl won't interact with the acid or the base formed during the ionization.

Step 2: Analyze NaHCOO

Sodium formate, NaHCOO, is the salt result from the ionization of formic acid. If we add NaHCOO to the solution, it will provide more formate ions, HCOO-. This will push the equilibrium towards the left, reducing the ionization of formic acid due to Le Chatelier's principle.

Step 3: Analyze H2SO4

Sulphuric acid, H2SO4, it is a strong acid. If this is added to the solution, it can react with the formate ion, HCOO-, produced in the ionization of formic acid and convert it back to formic acid. Thus, addition of H2SO4 increases the ionization of formic acid, because the ion produced by ionization is consumed, removing it from the equilibrium and pushing the reaction towards right making more acid ionize.

Step 4: Analyze NaHCO3

Sodium bicarbonate, NaHCO3, is a weak base. If added to the solution, it reacts with the acid but as a weak base it can't shift the equilibrium as much as a strong acid like H2SO4.

Key Concepts

Formic Acid

Formic acid, represented by the chemical formula \(HCOOH\), is the simplest carboxylic acid. It is commonly found in various natural sources, such as the venom of ants. In chemical solutions, formic acid behaves as a weak acid. This means it doesn't completely dissociate in water; rather, it only partially ionizes. The ionization of formic acid in water results in hydrogenions \( (H^+) \) and formate ions \( (HCOO^-) \). When formic acid ionizes, the equilibrium can be affected by changes in the solution,such as the concentration of certain ions. Understanding what can increase the ionization of formic acid can help in manipulating equilibrium reactions involving weak acids.

• Weak Acid: Partially ionizes in water.
• Formate Ion: \( HCOO^- \), the result of ionized formic acid.

Le Chatelier's Principle

Le Chatelier's Principle is a fundamental concept in chemistry thatexplains how a system at equilibrium reacts to disturbances and stresses. According to this principle, if the conditions of a chemical equilibrium are changed (such as pressure, temperature, or concentrations), the equilibrium will shift to counteract the change and create a new equilibrium state. This principle is crucial in understanding reactions involving ionization, like with formic acid.
If in the exercise, we add sodium formate \((NaHCOO)\), the equilibrium will shift according to Le Chatelier's Principle. The addition of more formate ions means the system will attempt to reduce the disturbance by shifting the equilibrium towards forming more non-ionized formic acid, thus reducing ionization.

• Counteraction: Shifts in reaction to changes.
• Equilibrium Shift: System adjusts to restore balance.

Equilibrium in Chemistry

In chemistry, equilibrium refers to the state in which the forward and reverse reactions occur at the same rate, resulting in the concentrations of reactants and products remaining constant over time. Equilibrium doesn’t imply equal concentrations but indicates a balance in the reaction dynamics. When discussing the ionization of formic acid and any influences on it, equilibrium concepts are vital.
Adding a strong acid like sulfuric acid \((H_2SO_4)\) to a solution containing formic acid influences the equilibrium. The strong acid consumes products (like formate ions), thereby shifting the equilibrium to favor more ionization of formic acid to restore balance. This results in more hydrogen ions being released into the solution, increasing the ionization.

• State of Balance: Forward and reverse reactions occur at the same rate.
• Influences: Changes can shift equilibrium and affect concentrations.