Acid-Base Reactions: Titration, Neutralization, and Indicators

Acid-Base Reactions

Acid-base reactions are essential in chemistry, allowing us to determine the concentration of an acid or base solution through titration. This process involves using a solution of known concentration (a standard solution) and an acid-base indicator.

Neutralization

Neutralization is the combination of hydrogen ions (H⁺) and hydroxide ions (OH^-) to form water (H₂O) and a salt. These reactions are exothermic, meaning they release heat.

Acid + Base → Salt + Water

Titration of a Strong Acid with a Strong Base

When titrating a strong acid (e.g., hydrochloric acid, HCl) with a strong base (e.g., sodium hydroxide, NaOH), the reaction is a straightforward neutralization:

HCl + NaOH → NaCl + H₂O

Titration of a Weak Acid with a Weak Base

Titrating a weak acid with a weak base is more complex due to smaller pH jumps near the equivalence point, increasing the difficulty and potential for errors. The smaller the pH jump, the harder it is to accurately determine the equivalence point.

Indicators

Acid-base indicators are substances that change color depending on the pH of the solution. They are crucial for detecting the equivalence point in a titration. Indicators are typically weak organic acids or bases with distinct colors in their molecular and ionized forms. They can be classified as neutral, acid-sensitive, or base-sensitive.

Equivalence Point

The equivalence point is the pH at which the number of equivalents of acid equals the number of equivalents of base. At this point, moles of acid are equal to moles of base.

Normality in Acid-Base Reactions

Normality (N) is a concentration unit used in acid-base reactions, particularly when dealing with titrations and pH indicators. It can be expressed as:

• N = moles of H⁺ for an acid
• N = moles of OH^- for a base

Where N is the number of equivalents, and the number of protons (H⁺) ceded by an acid molecule or the number of hydroxides (OH^-) ceded by a base molecule.