Chemical reactions Study Guide

Neutralisation is a fundamental chemical reaction where an acid reacts with an alkali (a soluble base) or an insoluble base to form a salt and water. This reaction essentially cancels out the acidic and alkaline properties of the reactants. Acids release hydrogen ions (H+) in solution, while alkalis release hydroxide ions (OH-). When these two ions meet, they combine to form water (H2O), which is neutral. The remaining ions from the acid and the base then combine to form a salt. For example, when hydrochloric acid (HCl) reacts with sodium hydroxide (NaOH), the H+ from the acid combines with the OH- from the alkali to form H2O, and the remaining Na+ and Cl- ions combine to form sodium chloride (NaCl), which is a salt. This can be represented by the word equation: Acid + Alkali/Base → Salt + Water. It's an important concept in chemistry with many applications, from treating indigestion with antacids to controlling pH in industrial processes. The pH of the final solution after complete neutralisation should be close to 7, indicating a neutral solution. If the reactants are not mixed in the correct stoichiometric ratio, the resulting solution may still be acidic or alkaline.

Ionic equations are a way to represent chemical reactions by focusing only on the species that actively participate in the reaction. These are often used for reactions occurring in solution, particularly precipitation reactions, acid-base neutralisation, and redox reactions. To construct a balanced ionic equation, you start with a full balanced chemical equation. The next step is to identify all aqueous ionic compounds and dissociate them into their constituent ions. Solid, liquid, and gaseous substances, along with covalent compounds, are not dissociated. For example, NaCl(aq) dissociates into Na+(aq) and Cl-(aq), but H2O(l) and AgCl(s) do not dissociate. Once all dissociable aqueous compounds are written as ions, you identify and cancel out any spectator ions. Spectator ions are those that appear on both sides of the equation in exactly the same state and form; they do not undergo any chemical change. The remaining ions and neutral species form the net ionic equation. This final equation must be balanced in terms of both atoms (and therefore charge carriers) and overall charge. Balancing the charge means the sum of the charges on the reactants' side must equal the sum of the charges on the products' side.