Grade 10 Chemistry Knowledge area Chemical change Reactions

Grade 10 Chemistry Knowledge area: Chemical change

Reactions in aqueous solutions 3. 4 Other chemical reactions in aqueous solution 3. 4. 1 Ion exchange reactions A. Precipitation reactions Examples If the anion is: Chloride: Na. Cℓ(aq) + Ag. NO 3(aq) → Ag. Cℓ(s) + Na. NO 3 (aq) Bromide: Li. Br(aq) + Ag. NO 3 (aq) → Ag. Br(s) + Li. NO 3 (aq) Iodide: KI(aq) + Ag. NO 3 (aq) → Ag. I(s) + KNO 3 (aq) Sulphate: Zn. SO 4(aq) + Ba. Cℓ 2 (aq) → Ba. SO 4 (s) + Zn. Cℓ 2(aq)

Reactions in aqueous solutions B. Gas-forming reactions Examples Production of hydrogen: suur + metaal → sout + waterstof Production of carbon dioxide: acid + carbonate → salt + water + carbon dioxide

Reactions in aqueous solutions How does one test for the different gases? • Oxygen; • Hydrogen; • Carbon dioxide. C. Acid-base reactions (transfer of protons) Acids Properties of acids • Will not conduct a current in their natural form, but are conductors in aqueous solution because it ionises. • Taste acidic. • Influence the colour of indicators. • All have the same reaction with water: H+ + H 2 O → H 3 O+ Temperature rises if the acid is added to the water. • Contain hydrogen. • Neutralise a base.

Reactions in aqueous solutions Well-known acids and their uses Acid Formula Uses and examples Hydrochloric HCℓ Present in digestive juices in the stomach acid Swimming pool acid Soldering Nitric acid HNO 3 Production of fertilizers, explosives and colour dyes Sulfuric acid H 2 SO 4 Used in industry. Extraction of gold Effective dehydrating agent Phosphoric acid Used in some fizzy cool drinks to give a tang. Used by dentists in dental cement. H 3 PO 4

Reactions in aqueous solutions Acid Carbonic acid Formula H 2 CO 3 Uses and examples Fizzy cool drinks Ethanoic CH 3 COOH Vinegar and sour wine acid Oxalic acid (COOH) 2 Bleaches Parsley, rhubarb and tomatoes Bases Properties of bases • Taste bitter. • Feel soapy. • Influence the colour of indicators.

Reactions in aqueous solutions • Conduct a current in an aqueous solution because it dissociates. • Form hydroxide ions (OH-) in water. • Neutralise an acid. Well-known bases and their uses

Reactions in aqueous solutions Base Sodium carbonate/washing soda Formula Use and examples Na 2 CO 3 Production of glass Cleaning agents Sodium bicarbonate/baking soda Na. HCO 3 Rising agent in baked goods Sodium hydroxide/caustic soda Ammonia Na. OH Manufacturing of soap Drain cleaner Cleaning agents Making of fertilisers NH 3

Reactions in aqueous solutions Examples If an HCℓ solution reacts with a KOH solution, the following happens on a microscopic level: H+(aq) + Cℓ-(aq) + K+ (aq) + OH- (aq) → K+ (aq) + Cℓ(aq) + H 2 O(ℓ) The product is a neutral solution of a salt and water. The net reaction for a neutralisation reaction is: H+ (aq) + OH- (aq) → H 2 O(ℓ)

Reactions in aqueous solutions 3. 4. 2 Redox reactions occur in batteries, combustion of fuels and natural reactions like respiration. One substance donates electrons and undergoes oxidation – it becomes a positive ion. The other accepts electrons and undergoes reduction – it becomes a negative ion.