Acids, Bases and Salts — Core Principles
Core Principles
Acids, bases, and salts are fundamental chemical classifications. Acids are substances that typically donate protons () or accept electron pairs, often characterized by a sour taste and a pH less than 7.
Bases are substances that accept protons or donate electron pairs, usually feeling slippery and having a pH greater than 7. Salts are ionic compounds formed from the neutralization reaction between an acid and a base, consisting of a cation from the base and an anion from the acid.
Key theories defining these include Arrhenius (based on and in water), Brønsted-Lowry (proton donors/acceptors), and Lewis (electron-pair acceptors/donors). The pH scale quantifies acidity/basicity, with .
The strength of an acid or base is determined by its extent of dissociation, quantified by or . Salts can undergo hydrolysis in water, leading to acidic, basic, or neutral solutions depending on the strengths of their parent acid and base.
Buffer solutions, composed of a weak acid/base and its conjugate, resist pH changes, playing vital roles in biological and chemical systems.
Often confused with
Side-by-side differences the NEET paper likes to test.
| Aspect | Acids, Bases and Salts | Acid-Base Theories |
|---|---|---|
| Definition of Acid | Arrhenius Theory: Produces $H^+$ (or $H_3O^+$) in water. | Brønsted-Lowry Theory: Proton ($H^+$) donor. |
| Definition of Base | Arrhenius Theory: Produces $OH^-$ in water. | Brønsted-Lowry Theory: Proton ($H^+$) acceptor. |
| Solvent Requirement | Arrhenius Theory: Restricted to aqueous solutions. | Brønsted-Lowry Theory: Not restricted to aqueous solutions. |
| Examples of Acids | $HCl$, $H_2SO_4$ | $HCl$, $H_2SO_4$, $NH_4^+$ |
| Examples of Bases | $NaOH$, $KOH$ | $NaOH$, $KOH$, $NH_3$, $CO_3^{2-}$ |
| Scope | Narrowest, only for substances producing $H^+$ or $OH^-$. | Broader, includes reactions without $OH^-$ formation, introduces conjugate pairs. |
The three major acid-base theories—Arrhenius, Brønsted-Lowry, and Lewis—represent an evolution in chemical understanding, each expanding the scope of what constitutes an acid or a base. Arrhenius is the most restrictive, focusing on and ions in water.
Brønsted-Lowry broadens this to proton transfer, introducing the concept of conjugate pairs and allowing for non-aqueous reactions. Lewis theory is the most encompassing, defining acids as electron-pair acceptors and bases as electron-pair donors, which explains a wider range of reactions, including those without proton transfer, like the formation of coordination compounds.
For NEET, understanding all three is crucial for classifying diverse chemical species.
Why it is tested: For NEET, understanding the distinctions between these acid-base theories is critical for correctly identifying acids and bases in various chemical contexts. Questions often test the ability to classify a given substance (e.g., $BF_3$, $NH_3$, $H_2O$) according to each theory, or to identify conjugate acid-base pairs. Numerical problems might involve $K_a$ and $K_b$ values, which are directly related to Brønsted-Lowry strengths. Conceptual clarity on these definitions is foundational for solving problems related to pH, salt hydrolysis, and buffer solutions.