Anion Testing Methods

Overview

This lecture explains how to test for the presence of anions—specifically carbonate, sulfate, and halide ions—in solutions using simple laboratory methods.

Tests for Carbonate Ions

• Add dilute hydrochloric acid to the test sample to check for carbonates.
• If carbonates are present, carbon dioxide gas is produced.
• Bubble any gas formed through lime water; if it turns cloudy, carbon dioxide is present, indicating carbonates.

Tests for Sulfate Ions

• First, add dilute hydrochloric acid to the sample to remove carbonate and sulfite impurities.
• Add barium chloride solution; barium ions react with sulfate ions to form barium sulfate.
• A white precipitate indicates the presence of sulfate ions.

Tests for Halide Ions

• Add dilute nitric acid to the sample to remove carbonate and sulfite impurities.
• Add silver nitrate solution; silver ions react with halide ions to form a precipitate.
• Precipitate color identifies the halide: white for chloride, cream for bromide, yellow for iodide.

Key Terms & Definitions

• Anion — A negatively charged ion.
• Carbonate Ion (CO₃²⁻) — An anion that produces carbon dioxide gas when reacted with acid.
• Lime Water — A solution of calcium hydroxide used to detect carbon dioxide.
• Precipitate — A solid formed from a reaction in solution.
• Halide Ions — Negatively charged ions of halogens (chloride Cl⁻, bromide Br⁻, iodide I⁻).

Action Items / Next Steps

• Review testing steps for each anion.
• Practice writing the chemical equations for each reaction.