Welcome back to Honors Chem with Fiveable! This is the last guide of this unit, you’re almost done with acid-base concepts! 👏

🍊 Acid-Base Theories and Applications

Understanding acid-base theories is essential for grasping the concept of how substances interact in various environments, from industrial processes to biological systems. Let's dive into the different acid-base theories and their applications!

📘 Arrhenius Theory

According to Svante Arrhenius, acids are substances that release hydrogen ions ($\text{H}^+$) when dissolved in water, while bases release hydroxide ions ($\text{OH}^−$).

Some example reactions include:

• Acidic: Hydrochloric acid (HCl) in water: $\text{HCl} = \text{H}^+ + \text{Cl}^−$
• Basic: Sodium hydroxide (NaOH) in water: $\text{NaOH} = \text{Na}^+ + \text{OH}^−$

Every theory has its limitations! This theory only applies to aqueous solutions and does not account for reactions where no ions are produced or where they occur without water.

Arrhenius Theory Practice Question

What ion is released by an Arrhenius base in an aqueous solution?

Answer: Hydroxide Ion (OH-)

📗 Brønsted-Lowry Theory

Johannes Brønsted and Thomas Lowry expanded the definition of acids and bases by stating acids are proton donors, whereas bases are proton acceptors.

Conjugate Acid-Base Pairs definition: Each reactant forms its conjugate product. Conjugate acids are where the proton (H+) ends up being accepted. The conjugate base is the substance which the donor proton is received from.

Identifying Conjugate Pairs

Take a look at the following reaction as an example, where acetic acid (CH₃COOH) reacts with water. In this reaction, acetic acid donates a proton (H⁺) to water, forming acetate ion (CH₃COO⁻) and hydronium ion (H₃O⁺).

When you have a chemical reaction involving an exchange of hydrogen ion, we can identify:

1. The acid, which donates the hydrogen ion
2. The base, which accepts the hydrogen ion
3. The conjugate acid
4. The conjugate base

How do you do that?! Well first, identify the two pairs of molecules. Our two pairs are:

Now, take a look at each pair and identify which one of the two molecules has an extra hydrogen. That molecule is the acid in the pair!

1. $\text{CH}_3\text{COOH}$ is the acid in the first pair.
2. $\text{H}_3\text{O}^+$ is the acid in the second pair.

If these two molecules are acids, then $\text{CH}_3\text{COO}^-$ and $\text{H}_2\text{O}$ must be bases. All that is left to do is identify which of the four molecules are conjugates. The conjugates are on the reverse side of the equation.

In this equation:

• $\text{CH}_3\text{COOH}$ is the acid.
• $\text{CH}_3\text{COO}^-$ is the conjugate base of acetic acid.
• $\text{H}_2\text{O}$ acts as a base accepting a proton, and…
• $\text{H}_3\text{O}^+$ is the conjugate acid of water.

Identifying Conjugate Pairs: Practice

Identify the conjugate base in the following reaction:

The conjugate base is OH− because it can accept a proton from the H2O.

📙 Lewis Theory

Gilbert N. Lewis proposed that acids are electron pair acceptors, while bases are electron pair donors. An example reaction is when boron trifluoride, a common Lewis acid, reacts with ammonia:

Coordination Compounds: The Lewis theory explains the formation of complex molecules where central metal ions bond with ligands acting as electron pair donors.

Lewis Theory Practice Question

Which part of a reaction acts as the Lewis base if it donates an electron pair?

Answer: The molecule or atom that donates an electron pair is the Lewis Base.

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🔍 Applying Acid-Base Theories

To understand neutralization reactions, consider an example where hydrochloric acid reacts with sodium hydroxide:

Here, we see a typical neutralization reaction forming salt (NaCl) and water. Additionally, understanding hydrolysis helps explain why some salts can dissolve in water to produce acidic or basic solutions due to their ability to react further with water molecules.

💼 Applications Across Fields

1. ⛽️ Industrial applications - Acid-base catalysis plays a significant role in chemical synthesis processes like producing esters or accelerating biodiesel production.
2. 🌧️ Environmental chemistry - Understanding the formation of acid rain involves recognizing sulfur dioxide and nitrogen oxides reacting with atmospheric moisture creating strong acids.
3. 🩸 Biological systems - Enzyme activity often hinges on pH levels which reflects their operating environment's acidity or basicity. Blood pH regulation relies on buffer systems maintaining a stable pH vital for physiological functions.
4. 🤓 Analytical Chemistry - Techniques like titration utilize these theories to determine concentrations of unknown acidic or basic solutions by measuring how much of a standard solution is required for neutralization.

Chemistry is everywhere!

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⭐️ Final Tips

1. Review each theory's definition – try making flashcards to memorize each one if needed, however, they do build off of each other.
2. Understand key terms like "proton donor" or "electron pair donor" as they apply across different contexts.
3. Practice writing balanced equations for reactions involving acids and bases according to each theory.
4. Always consider real-life applications; this will help solidify your understanding!

Don’t forget about the practice questions available as well. They will help you remember as you study. Happy learning! 🎉