TYPES OF REACTIONTYPES OF REACTION(1)(1) Neutralisation or Acid-BaseNeutralisation or Acid-Base

(2)(2) PrecipitationPrecipitation

(3)(3) RedoxRedox

Suitable for Upper Secondary Students

Author: Toh Chui Hoon

NEUTRALISATIONNEUTRALISATION

• A reaction between an acid and a base.

• In this reaction, the acid donates a hydrogen ion (H+ or proton) to the base leading to formation of water.

• Examples of base: Oxides, Hydroxides and Carbonates

• Examples of acid: Hydrochloric acid, Sulphuric acid and Nitric acid

Examples of NeutralisationExamples of Neutralisation• Acid + Oxide

2HCl + CuO CuCl2 + H2O

• Acid + Hydroxide

H2SO4 + 2NaOH Na2SO4 + 2H2O

• Acid + Carbonate

2HNO3 + CaCO3 Ca(NO3)2 + H2O + CO2

Gives a H+ to O2- of CuO to form H2O

QUIZQUIZ• Which of the following basic ions can be

identified using products from acid-base reaction?

A: OH- B: O2- C: CO32- D: Cl-

ANSWER: Yes, it is C.

When acid is added to carbonates, bubbling or effervescence can be seen due to production of CO2 gas which will turn limewater, Ca(OH)2, cloudy. This is caused by production of CaCO3 as a result of acid-base reaction between aqueous CO2 and Ca(OH)2.

Ca(OH)2 + CO2 CaCO3 + H2O

Hint: There must visible change in the reaction.

PRECIPITATIONPRECIPITATION

• This reaction involves 2 water-soluble compounds leading to formation of a water-insoluble compound.

• Examples of water-soluble compounds: all Nitrates, most Sulphates except BaSO4 and PbSO4, most Chlorides except AgCl and PbCl2.

• Examples of water-insoluble compounds: Oxides, Hydroxides and Carbonates except those of Na+, K+ and NH4

+.

Coloured CompoundsColoured Compounds• Compounds containing transition metal ions are coloured.• Copper sulphate, CuSO4 is blue.• Iron(II) hydroxide, Fe(OH)2 is dirty-green.• Iron(III) hydroxide, Fe(OH)3 is reddish-brown.• Potassium dichromate(VI), K2Cr2O7 is orange.• Potassium manganate(VII), KMnO4 is violet.

Examples of PrecipitationExamples of Precipitation• HCl(aq) + AgNO3(aq) AgCl(s) + HNO3(aq)

• A white precipitate of silver chloride is seen.

• On further addition of aqueous NH3, silver chloride dissolved. After excess aq.

NH3 is added…

Examples of PrecipitationExamples of Precipitation

• KI(aq) + AgNO3(aq) AgI(s) + KNO3(aq)

• A yellow precipitate of silver iodide is seen.

Examples of PrecipitationExamples of Precipitation• Na2SO4(aq) + Ba(NO3)2(aq) BaSO4(s) + 2NaNO3(aq)

• A white precipitate of barium sulphate is seen.

Examples of PrecipitationExamples of Precipitation• H2SO4(aq) + Ba(NO3)2(aq) BaSO4(s) + HNO3(aq)

• A white precipitate of barium sulphate is seen.