Qulative Analysis

What is Qualitative analysis?

Process used to identify the cations and anions in an unknown substance

Basis of qualitative analysis

Differences in solubility, redox reactions, and precipitation of ions

Why do we observe appearance first?

To infer possible ions before performing tests

Colourless solid and solution

Transition metals likely absent

If the compound is a Black solid

Likely an oxide or sulfide

If it is a coloured solid or solution

Transition metal ion likely present

If there is an ammonia smell

Presence of ammonium ion (NH4+)

Why can colour be unreliable?

Some salts have misleading colours (e.g. anhydrous CuCl is brown, Fe(II) oxalate is yellow)

Crystalline and hydrated

Contains water of crystallization

Crystalline and wet (deliquescent)

Absorbs moisture from air and dissolves

Crystalline becoming powdery (efflorescent)

Loses water to the atmosphere

Liquid sample

Likely a soluble salt or organic substance

Black solid (ions present)

Cu²⁺, Co²⁺, Fe³⁺, Pb²⁺, Mn⁴⁺ (oxides/sulfides)

Blue solid (ions present)

Cu²⁺, Co²⁺ (anhydrous)

Green solid (ions present

Cu²⁺, Ni²⁺, Fe²⁺, Cr³⁺

Pink solid (ions present)

Co²⁺ (hydrated), Mn²⁺

Purple-black compound

KMnO₄

Red compound

Pb₃O₄

Reddish-brown solid

Fe³⁺, hot PbO

White solid (ions present)

Na⁺, K⁺, NH₄⁺, Ca²⁺, Zn²⁺, Al³⁺

Colourless solutions (ions present)

Na^⁺, K^⁺, Mg²⁺, NH⁴⁺, Ca²⁺, Ba²⁺, Zn²⁺, Pb²⁺, Sn²⁺

Orange Solution

Cr₂O₇²⁻ of NH₄⁺ or K⁺, HgO