Base (Chemistry)
A base is a substance that accepts protons (H⁺ ions) from an acid or donates electron pairs, producing hydroxide ions (OH⁻) in aqueous solution, a bitter taste, slippery feel, and a pH above 7. Bases neutralise acids in reactions that form salt and water, making them essential in biological systems such as blood buffering, as well as in industrial processes like soap making. Common examples include sodium hydroxide (NaOH), ammonia (NH₃), and sodium bicarbonate (NaHCO₃).
Key Formula
B + H₂O → BH⁺ + OH⁻
LaTeX: \text{B} + \text{H}_2\text{O} \rightarrow \text{BH}^+ + \text{OH}^-
| Symbol | Meaning | Unit |
|---|---|---|
| B | Generic base molecule | none |
| H₂O | Water molecule | none |
| BH⁺ | Conjugate acid | none |
| OH⁻ | Hydroxide ion | none |
Worked Example
Problem
A 0.05 mol/L solution of sodium hydroxide (NaOH) fully dissociates. Find the [OH⁻] concentration and the pH at 25 °C.
Solution
Step 1: Write dissociation: NaOH → Na⁺ + OH⁻ Step 2: [OH⁻] = 0.05 mol/L (complete dissociation) Step 3: pOH = -log[OH⁻] = -log(0.05) = 1.30 Step 4: pH + pOH = 14, so pH = 14 - 1.30 = 12.70
Answer
[OH⁻] = 0.05 mol/L; pH = 12.70
Common Bases — Strength, Formula, and Uses
| Base Name | Formula | Strength | Common Use |
|---|---|---|---|
| Sodium hydroxide | NaOH | Strong | Soap making, drain cleaners |
| Potassium hydroxide | KOH | Strong | Biodiesel production, electrolytes |
| Calcium hydroxide | Ca(OH)₂ | Strong | Cement, water treatment |
| Ammonia | NH₃ | Weak | Fertilisers, household cleaners |
| Sodium bicarbonate | NaHCO₃ | Weak | Baking, antacids |
| Magnesium hydroxide | Mg(OH)₂ | Weak | Milk of magnesia, antacids |
Interactive Tools
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Related Terms
Acid (Chemistry)
An acid is a substance that donates protons (hydrogen ions, H⁺) to another substance or accepts electron pairs, resulting in a sour taste, ability to turn blue litmus red, and a pH below 7 in aqueous solution. Acids play a fundamental role in chemical reactions, biological processes, and industrial applications ranging from digestion to manufacturing. Common examples include hydrochloric acid (HCl), sulfuric acid (H₂SO₄), and acetic acid (CH₃COOH) found in vinegar.
pH Scale
The pH scale is a logarithmic measure of the hydrogen ion concentration [H⁺] in a solution, ranging from 0 to 14 at 25 °C, where values below 7 indicate acidic conditions, 7 is neutral, and above 7 is basic or alkaline. Introduced by Danish chemist Søren Peder Lauritz Sørensen in 1909, the scale compresses a trillion-fold range of H⁺ concentrations into a convenient 0–14 range. pH measurement is critical in agriculture, biology, medicine, food science, and environmental monitoring.
Brønsted-Lowry Theory
The Brønsted-Lowry theory, proposed independently by Johannes Nicolaus Brønsted and Thomas Martin Lowry in 1923, defines an acid as a proton (H⁺) donor and a base as a proton acceptor, expanding the earlier Arrhenius definition beyond aqueous solutions. This broader definition explains acid-base behaviour in non-aqueous solvents and introduces the concept of conjugate acid-base pairs, where the product of an acid after donating a proton is its conjugate base, and vice versa. The Brønsted-Lowry model is the most widely used framework for acid-base chemistry in biology, organic chemistry, and analytical chemistry.
From Latin "basis" meaning foundation or pedestal, rooted in Greek "basis" (stepping, base). In chemistry, the term was applied because bases were seen as the foundation upon which salts are built when they react with acids.