2j Preparing and analysing

Last lesson - Precipitation reactions

• Reactions that produce an INSOLUBLE SALT

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.

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

limewater “milky”)

Today’s lesson – Gas tests

You know all these already!

Gas tests?

AmmoniaCarbon dioxideChlorineHydrogenOxygenSulphur dioxide

Gas tests?

Ammonia – Turns damp red litmus paper blueCarbon dioxide – turns limewater “milky”Chlorine – bleaches damp litmus paper (white) Hydrogen – lighted splint – “popping sound”Oxygen – relights a glowing splintSulphur dioxide - pink acidified potassium

manganate solution turns colourless

Solubility of different salts

Which dissolve?Salt Soluble?

Sodium chloride

Sodium bromide

Sodium carbonate

Sodium sulphate

Potassium chloride

Potassium bromide

Etc.

When you have finished can you write down some general rules for which slats are soluble/insoluble

Solubility of salts• all common sodium, potassium and ammonium

salts are soluble• ⎯ all nitrates are soluble• ⎯ common chlorides are soluble, except silver

chloride• ⎯ common sulphates are soluble, except barium

and calcium sulphates• ⎯ common carbonates and hydroxides are

insoluble, except those of sodium, potassium and ammonium