Fundamental Principles of Acids and Bases

Properties of Acids and Bases

Characteristics of Acids

• Acids are proton donors.
• Historically believed to contain hydrogen and oxygen, they are currently defined by the hydrogen ion (H+) as the initial particle.
• They dissociate in H₂O and act as conductors.
• When reacting with a base, an acid loses its properties.
• They cause color changes in indicators.
• When reacted with a metal, they release free hydrogen (H₂).

Characteristics of Bases

• Bases have a soapy texture.
• Previously believed to be defined by the hydroxide (OH-) group, a base is now defined as a substance that accepts hydrogen ions.
• They are electrolytes and therefore conduct electricity.
• When reacted with an acid, they lose their properties and change the color of certain dyes.

Acid-Base Strength and Classification

Acid Rules

A) Ternary Acids (HXO): These follow the ternary rule where oxygen content affects strength (O < 2).

B) Binary Acids: Of the binary acids, only three are strong: Chlorine (HCl), Bromine (HBr), and Iodine (HI).

Base Rules

A) Hydroxides: Sodium (Na), Potassium (K), and Calcium (Ca) hydroxides are strong bases.

B) Conjugate Bases: In these systems, the forces are contrary to the strength of the acid from which they originated.

Ionic Equilibrium of Water

The dissociation of water is represented as: H₂O ⇌ H⁺ + OH^-.

The equilibrium constant is K_w = 1.0 × 10^-14. Therefore, K_w = [H⁺] · [OH^-] = 1.0 × 10^-14.

In pure water, the concentrations of H⁺ and OH^- are the same. When you add an acid or base, the concentration is altered, but the ion product remains the same because it is a constant.

Methods for Determining pH

The method for determining pH is simple: acid-base indicators are substances that represent one color in an acidic environment and another in a basic environment.

For example, an indicator might switch colors between pH 8 and pH 10. There are universal indicators with a range from 1 to 12, showing a specific color for each pH level. Another way to determine pH is by knowing the formula of the acid or base; using the concept of pH, one can calculate the concentration of H⁺ in different systems.

Buffer Solutions and pH Stability

A buffer solution (or regulator) is one that resists changes in pH even when adding measured quantities of an acid or base.

Buffer solutions are generally composed of:

• A weak acid and its salt (e.g., CH₃COOH and CH₃COONa).
• A weak base and its salt (e.g., NH₃ and NH₄Cl).

Neutralization and Titration Techniques

Neutralization can be achieved in a laboratory setting through titration, which is a controlled neutralization process. This allows you to determine the unknown concentration of an acid or base.

The procedure involves gradually adding a solution of known concentration to one of unknown concentration. This is performed by adding a solution from a burette into a vessel containing a fixed volume of a solution of unknown concentration to which an acid-base indicator has been added. Then, a drop of the solution is released from the burette until a color change occurs. This indicates that the equivalence point has been reached, meaning the solution has been neutralized.