Ions in Acids and Alkalis

This page explores the ionic nature of acids and alkalis, explaining how they produce hydrogen and hydroxide ions in aqueous solutions.

Ions are atoms or molecules that have gained or lost electrons, resulting in a net electrical charge. Positive ions (cations) form when atoms lose electrons, while negative ions (anions) form when atoms gain electrons.

Definition: Polyatomic ions are small groups of atoms held together by covalent bonds that can lose or gain electrons as a unit

The text explains how acids produce an excess of hydrogen ions (H+) when dissolved in water. For example, hydrochloric acid forms when hydrogen chloride gas dissolves in water and splits into H+ and Cl- ions.

Example: The reaction acid + alkali = salt + water is a fundamental neutralization process in chemistry

Alkalis, on the other hand, produce an excess of hydroxide ions (OH-) in water. For instance, solid sodium hydroxide dissociates into Na+ and OH- ions when dissolved.

Highlight: The concentration of hydrogen ions determines the acidity of a solution, while the concentration of hydroxide ions determines its alkalinity

The page concludes by explaining that neutral solutions, such as pure water, have a pH of 7 and contain low, equal concentrations of hydrogen and hydroxide ions.

Vocabulary: The term "aqueous" refers to solutions in which water is the solvent

Understanding the ionic behavior of acids and alkalis is crucial for predicting chemical reactions and interpreting pH changes in various solutions.

Acids, Alkalis, and Indicators

This page covers the practical aspects of working with acids and alkalis, including safety considerations and the use of indicators to measure pH.

International hazard symbols are used globally to identify potential dangers associated with chemicals. These symbols provide crucial information about the safe handling and storage of substances.

Highlight: Recognizing and understanding chemical hazard symbols is essential for laboratory safety

The page introduces various indicators used to determine the pH of solutions. Universal indicator, which produces a range of colors depending on pH, is particularly useful for obtaining approximate pH values.

Example: Litmus paper turns red in acidic solutions and blue in alkaline solutions

The text also discusses the pH scale in more detail, explaining that acids have a pH lower than 7, alkalis have a pH greater than 7, and neutral solutions have a pH of 7.

Vocabulary: Weakly alkaline pH values typically range from 7.1 to 10, while strongly acidic pH values are usually below 3

The page concludes with a brief mention of natural pH indicators, such as plant dyes from cherries and curry powder, which can change color based on the acidity or alkalinity of a solution.