Understanding Acids, Bases, and pH in GCSE Chemistry

Introduction to Acids and Bases

In GCSE Chemistry, understanding acids and bases is crucial for grasping chemical reactions and pH. This topic covers the fundamental concepts of acidity, basicity, and the pH scale, as well as their practical applications.

Acids and Their Properties

Acids are substances that release hydrogen ions (H+) when dissolved in water. They have a sour taste and can react with metals to produce hydrogen gas. Common examples of acids include hydrochloric acid (HCl), sulfuric acid (H2SO4), and acetic acid (CH3COOH).

Bases and Their Properties

Bases are substances that release hydroxide ions (OH-) when dissolved in water. They have a bitter taste and a soapy feel. Common examples of bases include sodium hydroxide (NaOH), ammonia solution (NH3), and calcium hydroxide (Ca(OH)2).

The pH Scale

The pH scale is a logarithmic measure of the hydrogen ion concentration in a solution. It ranges from 0 to 14, with 7 being neutral. Solutions with a pH less than 7 are acidic, while those with a pH greater than 7 are basic (alkaline).

Worked Example: Calculating pH

Problem: Calculate the pH of a 0.001 M hydrochloric acid solution.

Solution:

• HCl is a strong acid, so it completely dissociates in water: HCl → H+ + Cl-
• The concentration of H+ is equal to the concentration of HCl: [H+] = 0.001 M
• pH = -log[H+] = -log(0.001) = 3

Neutralization Reactions

Neutralization is the reaction between an acid and a base, resulting in the formation of a salt and water. During this process, hydrogen ions from the acid combine with hydroxide ions from the base to form water molecules.

For example, when hydrochloric acid (HCl) reacts with sodium hydroxide (NaOH), the products are sodium chloride (NaCl) and water (H2O):

HCl + NaOH → NaCl + H2O

Preparation of Salts

Salts can be prepared by various methods, including the reaction of an acid with a metal, a metal oxide, a metal hydroxide, or a metal carbonate. These reactions involve the neutralization of the acid by the base, resulting in the formation of a salt and water (or carbon dioxide, in the case of metal carbonates).

Worked Example: Salt Preparation

Problem: Write a balanced equation for the reaction between hydrochloric acid and sodium hydroxide to produce sodium chloride and water.

Solution:

HCl + NaOH → NaCl + H2O

This article has provided an overview of acids, bases, and pH in GCSE Chemistry. For more detailed information and practice questions, refer to BBC Bitesize and your exam board's specification.