Identifying Anions and Cations

Group 2 ions (M²⁺)

Group 2 ions (M²⁺)

Calcium, magnesium, and strontium ions, tested with BaCl₂ and NaOH solutions

Ammonium ions (NH₄⁺)

Makes ammonia gas when heated with NaOH, turning red litmus paper blue

Halide ions (X-)

Form white, cream, or yellow precipitates with silver nitrate solution

Hydroxide ions (OH-)

Presence indicated by turning red litmus paper blue and/or alkaline pH on universal indicator paper

Carbonate ions (CO32-)

React with HCl acid to produce CO₂ gas, turning limewater milky

Sulfate ions (SO42-)

Identified by adding barium chloride after acidification, resulting in a white precipitate of BaSO₄

Solubility of M²⁺ hydroxides

Increases down group 2

Solubility of M²⁺ sulfates

Decreases down group 2

M²⁺ with ammonia solution

Reacts only with Mg²⁺

white ppt formed

NH₄⁺method

• 10 drops of ammonium chloride

• 10 drops of sodium hydroxide w/pipette

• Swirl and place in water bath, heating gently

• Tongs near mouth of test tube to test fumes

• litmus paper turns red to blue

X^- method

• Add sample to test tube w/pipette

• Small amount nitric acid + silver nitrate

• If present, either white, cream or yellow ppt going down group from Cl

X^- + ammonia

Cl: dissolves in dil. ammonia

Br: dissolves in conc. ammonia

I: doesn’t dissolve in dil. or conc.

CO₃^2- method

• 1cm³ dil. HCl acid

• 1cm³ sodium carbonate solution

• As soon as the sodium carbonate solution is added, attach bung w/delivery tube to deliver gas product into tube w/limewater (Ca(OH)₂)

• CO₃^2- will react with H⁺ ions from acid to produce CO₂ gas

• CO₂ gas turns limewater milky