Qualitative Analysis: Flame Tests, Precipitation Reactions, Anion & Gas Tests

These flashcards cover flame tests, precipitation reactions with sodium hydroxide, tests for ammonium, carbonate, halide and sulfate ions, standard laboratory gas tests, and safety considerations.

What colour is produced by Li⁺ in a flame test?

Red

What flame colour identifies Na⁺ ions?

Yellow

Which flame colour indicates K⁺ ions?

Lilac

What colour appears in a flame test for Cu²⁺?

Blue-green

What is observed when sodium hydroxide is added to a Ca²⁺ solution?

A white precipitate forms and is insoluble in excess NaOH.

Describe the result of adding NaOH to a Cu²⁺ solution.

A light-blue precipitate forms that is insoluble in excess NaOH.

What initial precipitate forms with Fe²⁺ and NaOH, and how does it change on standing?

A green precipitate forms; it turns brown at the surface on standing.

What precipitate is produced when Fe³⁺ reacts with NaOH?

A red-brown precipitate that is insoluble in excess NaOH.

How does Zn²⁺ behave with NaOH?

A white precipitate forms that dissolves in excess NaOH to give a colourless solution.

How can you distinguish Ca²⁺ from Zn²⁺ using sodium hydroxide?

Both give white precipitates, but only the Zn²⁺ precipitate dissolves in excess NaOH.

Which simple test differentiates Fe²⁺ from Fe³⁺ ions?

Add NaOH: Fe²⁺ gives a green precipitate; Fe³⁺ gives a red-brown precipitate.

Describe the laboratory test for NH₄⁺ ions.

Add dilute NaOH and warm; damp red litmus paper at the tube mouth turns blue if ammonia is released.

What procedure confirms the presence of carbonate ions in a solid?

Add dilute HCl and pass the evolved gas through limewater; limewater turning milky indicates CO₂ from a carbonate.

Which two reagents are added to detect halide ions (Cl⁻, Br⁻, I⁻) in solution?

Dilute nitric acid followed by silver nitrate solution.

What colour precipitate indicates chloride ions with AgNO₃?

White precipitate

What colour precipitate indicates bromide ions with AgNO₃?

Cream precipitate

What colour precipitate indicates iodide ions with AgNO₃?

Yellow precipitate

Which reagents are used to test for sulfate ions (SO₄²⁻)?

Dilute HCl or dilute HNO₃ followed by barium chloride or barium nitrate solution.

What observation confirms sulfate ions during the Ba²⁺ test?

Formation of a white precipitate of barium sulfate.

How is hydrogen gas identified?

It ‘pops’ with a lighted splint.

How is oxygen gas identified?

It relights a glowing splint.

What is the positive test for carbon dioxide gas?

It turns limewater milky.

How do you test for chlorine gas?

It bleaches damp litmus or universal indicator paper.

What result indicates the presence of ammonia gas?

It turns damp red litmus paper blue.

Why should experiments that generate Cl₂, SO₂ or NH₃ be carried out in a well-ventilated lab?

Even small amounts of these gases can cause respiratory distress.

What happens to the green Fe(OH)₂ precipitate if left exposed to air?

It oxidises and turns brown due to formation of Fe(OH)₃.