2j preparing and analysing. last lesson tests for cations li +, na +, k +, ca 2+ using flame tests...

2j Preparing and analysing

Last lesson tests for cations

• Li+, Na+, K+, Ca2+ using flame tests• NH4+ using NaOH(aq)

• Cu2+, Fe2+ and Fe3+ using NaOH(aq)

Flame tests

Ion Colour of flameLi+ ScarletNa+ YellowK+ LilacCa2+ Brick red

Testing for NH4+ (“ammonium ion”)

• Add NaOH (aq)

• Warm gently• Test gas given off with damp red litmus• Ammonia gas is given off which turns the

damp red litmus BLUE.

Testing for Cu2+, Fe2+ and Fe3+ using NaOH(aq)

Testing for Cu2+, Fe2+ and Fe3+ using NaOH(aq)

Metal ion

Result of adding NaOH (aq)

Cu2+ Pale blue precipitate of Cu(OH)2

Fe2+ Dirty green precipitate of Fe(OH)2

Fe3+ Rusty brown precipitate of Fe(OH)3

Common hydroxides (EXCEPT Na, K and NH4) are INSOLUBLE so form precipitates

Today’s lesson

• chloride, bromide and iodide, using dilute nitric acid and silver nitrate solution

• sulphate, using dilute hydrochloric acid and barium chloride solution

• sulphite, using dilute hydrochloric acid and identifying the sulphur dioxide evolved

• carbonate, using dilute hydrochloric acid and identifying the carbon dioxide evolved

Precipitation reactions

• Reactions that produce an INSOLUBLE SALT

Testing for Cl-, Br- and I- ions

Testing for Cl-, Br- and I- ions

• Add SMALL amounts of silver nitrate solution to salts containing halogen ions that have been dissolved in dilute nitric acid.

Type of ion (dissolved in HNO3(aq))

Result of adding dilute silver nitrate

Cl-

Br-

I-

Testing for Cl-, Br- and I- ions

• Add SMALL amounts of silver nitrate solution to salts containing halogen ions that have been dissolved in dilute nitric acid.

Type of ion (dissolved in HNO3(aq))

Result of adding dilute silver nitrate

Cl- White precipitate of silver chloride

Br- Cream precipitate of silver bromide

I- Pale yellow precipitate of silver iodide

Testing for sulphate ions SO42-

(aq)

• Add SMALL amounts of barium chloride solution to salts containing sulphate ions that have been dissolved in dilute hydrochloric acid.

Testing for sulphate ions SO42-

(aq)

• Add SMALL amounts of barium chloride solution to salts containing sulphate ions that have been dissolved in dilute hydrochloric acid.

• If sulphate ions are present, a white precipitate of barium sulphate is formed.

Testing for sulphite ions SO32-

(aq)

• Add dilute hydrochloric acid.• Test the gas given off for sulphur dioxide by

passing through pink acidified potassium manganate solution which turns colourless.

Testing for carbonate ions CO32-

(aq)

• You know this one!

A recap!

Acid + base salt + waterAcid + metal salt + hydrogenAcid + carbonate salt + water + carbon dioxide

The salt made by sulphuric acid is a metal sulphateThe salt made by hydrochloric acid is a metal chlorideThe salt made by nitric acid is a metal nitrate

Testing for carbonate ions CO32-

(aq)

• You know this one!• Add dilute hydrochloric acid• Test the gas given off for carbon dioxide (turns

limewater “milky”)