Question

Acrylic acid, \(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{COOH}\), is a weak monoprotic acid. Write a balanced equation for the reaction that occurs when \(25.0 \mathrm{~mL}\) of \(0.200 \mathrm{M} \mathrm{KOH}\) is added to \(50.0 \mathrm{~mL}\) of \(0.200 \mathrm{M} \mathrm{C}_{2} \mathrm{H}_{3} \mathrm{COOH}\). Besides water, what species are present in the solution? Is this solution a buffer? Why or why not?

Short answer

The balanced chemical equation for the reaction between acrylic acid and potassium hydroxide is: \( \mathrm{C}_{2} \mathrm{H}_{3} \mathrm{COOH} + \mathrm{KOH} \rightarrow \mathrm{C}_{2} \mathrm{H}_{3} \mathrm{COOK} + \mathrm{H}_{2} \mathrm{O} \). After reaction, there are 0.005 moles of unreacted acrylic acid (\(C_2H_3COOH\)), 0.005 moles of its potassium salt (\(C_2H_3COOK\)), and potassium ions (\(K^+\)). The solution is a buffer, as it contains significant amounts of a weak acid and its conjugate base.

Step-by-step solution

Write the balanced chemical equation

The reaction between acrylic acid (weak monoprotic acid) and potassium hydroxide (strong base) can be written as: \[ \mathrm{C}_{2} \mathrm{H}_{3} \mathrm{COOH} + \mathrm{KOH} \rightarrow \mathrm{C}_{2} \mathrm{H}_{3} \mathrm{COOK} + \mathrm{H}_{2} \mathrm{O} \]

Determine the moles of each reactant

To find the moles of each reactant, multiply the concentration by the volume: - Moles of acrylic acid: \( moles = Molarity \times Volume = 0.200\: \cancel{mol \: L^{-1}} \times 50.0\: \cancel{mL} \times \frac{1\: L}{1000\: \cancel{mL}} = 0.010\: mol \) - Moles of potassium hydroxide: \( moles = Molarity \times Volume = 0.200\: \cancel{mol \: L^{-1}} \times 25.0\: \cancel{mL} \times \frac{1\: L}{1000\:\cancel{mL}} = 0.005\: mol \)

Calculate the moles of each species present in the solution after the reaction

Reaction between weak acid and strong base will go to completion. So, there will be no KOH left, and 0.005 moles of \(C_2H_3COOH\) react, leaving 0.005 moles unreacted. Therefore: - Moles of \(C_2H_3COOH\): \(0.010 - 0.005 = 0.005\: mol\) - Moles of \(C_2H_3COOK\): \(0.005\: mol\) - Moles of \(H_2O\): \(0.005\: mol\) (formed during the reaction)

Determine if the solution is a buffer

A buffer solution contains significant amounts of both a weak acid and its conjugate base. Here, we have \(0.005\: mol\) of unreacted acrylic acid and \(0.005\: mol\) of its conjugate base, the potassium salt of acrylic acid. So, the solution is a buffer. Species present besides water: Acrylic acid (\(C_2H_3COOH\)), its potassium salt (\(C_2H_3COOK\)), and potassium ions (as spectator ions - \(K^+\)). Thus, the solution is a buffer, and the species present in the solution besides water are acrylic acid (\(C_2H_3COOH\)), potassium salt of acrylic acid (\(C_2H_3COOK\)), and potassium ions (\(K^+\)).

Key concepts

Acrylic Acid

Acrylic Acid, with the chemical formula \( \mathrm{C}_{2} \mathrm{H}_{3} \mathrm{COOH} \), is a colorless liquid with an acrid smell. It belongs to a class of organic compounds known as carboxylic acids, which contain the \( \mathrm{COOH} \) functional group. This group is also responsible for the acidic nature of the compound. Acrylic acid is considered a weak acid, meaning it doesn’t completely dissociate into its ions in solution.
This ability to partially break apart in water allows it to participate in reversible chemical reactions. In its undissociated form, acrylic acid remains prevalent in the solution, hence the label "weak," in contrast to "strong acids" that fully dissociate. Additionally, acrylic acid is used in numerous industrial applications such as the manufacture of polymers, paint formulations, and even textiles.

• It is notable for being a monoprotic acid, which means it can donate one proton (\( \mathrm{H}^{+} \)) per molecule during a reaction.
• This single proton donation is crucial for balancing out chemical reactions, such as the interaction with bases.

Understanding acrylic acid's reaction dynamics is essential for exploring its buffering capacity and its role as a key component in certain chemical processes.

Weak Acids

In chemistry, weak acids are substances that partially ionize in solution. This partial ionization means they do not release all of their hydrogen ions (\( \mathrm{H}^{+} \)) when dissolved in water. Instead, an equilibrium is established between the undissociated and dissociated forms. The compounds remain in solution as a mix of ions and undissociated molecules.
Weak acids are characterized by their lower acid dissociation constant \( (K_a) \), which quantifies their ionization in water.

• A weak acid, like acrylic acid, is crucial in buffer solutions because it provides both the undissociated acid and its conjugate base.
• This balance allows the solution to resist changes in pH when small amounts of base or acid are added.

It's important to remember in calculations and reactions that weak acids do not completely dissociate, making them more stable and versatile in solution. They play a fundamental role in chemical buffers, which are essential in biological systems and various industrial applications. Thus, understanding weak acids helps explain their controlled reactivity and role in maintaining pH stability.

Chemical Reactions

Chemical reactions involve the rearrangement of atoms and the breaking and forming of bonds, transforming reactants into products. A key aspect of a chemical reaction is balancing the equation, which ensures that the same number of each kind of atom appears on both sides of the equation. This reflects the conservation of mass.
As seen with acrylic acid and potassium hydroxide, reactants undergo a chemical reaction to form products like the potassium salt of the acid and water.

• This particular reaction is an acid-base neutralization, combining a weak acid with a strong base.
• Neutralization reactions, like this, produce water and a salt.

It’s also seen that the reaction goes to completion, which means all available KOH reacts, leaving some unreacted acrylic acid and forming a salt, \( \mathrm{C}_{2} \mathrm{H}_{3} \mathrm{COOK} \). This salt formation is significant because it represents the conjugate base of the weak acid, crucial for buffer action.
By understanding chemical reactions, especially in the context of weak acid and base interactions, you can predict solution behavior and the formation of buffers and other products. This knowledge is essential in analyzing and optimizing chemical processes both in the lab and industry.