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CHEMISTRY LEVEL 3


1. GAS LAWS
2. THE MOLE: Formulae and Chemical Equations
3. ORGANIC CHEMISTRY 1
4. NITROGEN AND ITS COMPOUNDS
5. SULPHUR AND ITS COMPOUNDS
6. CHLORINE AND ITS COMPOUNDS
7. A guide to chemical tests based on this module
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A guide to chemical tests based on this module


7.0 A guide to chemical tests based on this module


Gas or ions to test Preliminary tests and general properties Confirmatory test
CO2 Colourless, odourless, denser than air, slightly soluble in water, weakly acidic (turns blue litmus pink), extinguishes a glowing and burning wooden splint. Forms a white precipitate with calcium hydroxide solution, which dissolves on prolonged bubbling.
CO22- Effervesces with dilute acids; precipitates metal ions except of K+, Na+, NH4+; decompose on heating to form metal oxide and CO2; precipitated by ions of heavy metals Test for production of CO2, during heating or reaction with a dilute acid, as above.
HCO3- Produces effervescence with dilute acids; precipitates metal ions except K+, Na+, NH4+, Ca2+, and Mg2+; decompose on heating to produce CO2; unlike carbonate ions are not precipitated by ions of heavy metals (Cu2+, Zn2+; Fe2+; Pb2+ etc) Test for production, during heating or reaction with a dilute acid, of CO2 as above. No precipitate with ions of heavy metals.
H2 Colourless, neutral, odourless gas; insoluble in water; extinguishes a burning wooden splint with a pop sound Insert a burning wooden splint. Extinguishing of a burning splint with a pop sound
O2 Colourless, odourless, neutral gas which is insoluble (only slightly soluble) in water. It rekindles a glowing wooden splint. Insert a glowing wooden splint. Rekindling (relighting) of the splint confirms oxygen
H2O Colourless, neutral, and odourless as vapour or liquid; condenses readily on cool glass surfaces; turns anhydrous copper (II) sulphate blue or cobalt (II) chloride from blue to pink. Add 1 to 2 drops to anhydrous copper (II) sulphate. The salt should turn from white to blue.
NH3 Clourless, basic gas (turns red litmus blue) which is highly soluble in water; has a chocking pungent smell; forms white fumes with hydrogen chloride gas, and a blue precipitate with copper (II) ions, which dissolves in excess to form a deep blue solution. Turning of red litmus to blue (the only ordinary basic gas). Or Formation of white fumes with hydrogen chloride gas
N2O Neutral, colourless gas with a faint sweet (pleasant) smell; oxidizes metals. Like oxygen, it rekindles a glowing wooden splint. Insert a glowing wooden splint. Rekindling (relighting) of the splint confirms oxygen
NO Neutral, odourless, forms a red-brown gas when exposed to air; oxidizes metals Expose to the air. The colourless gas turns brown.
NO2 A red-brown acidic gas with a pungent chocking smell; highly soluble in water; extinguishes a burning and glowing wooden splint; produced when nitrates thermally decompose; oxidizes metals and other elements. Tested indirectly using the brown-ring test to check if it was released by a thermally decomposing nitrate. If so, it is NO2.
NO3- Soluble salts and, when heated, produces a gas that rekindles a glowing wooden splint, or red-brown gas or both. Add iron (II) sulphste solution, then concentrated sulphuric (VI) acid carefully down the wall of the test tube. A brown ring test at the boundary confirms presence of nitrate ions
SO2 Chocking, irritating and poisonous, acidic, and colourless gas, fairly soluble in water, extinguishes burning and glowing wooden splint; causes bleaching; is a reducer and therefore decolourizes manganate (VII) ions, bromine water and chlorine water, and other oxidizers. Bubble into water then test the resulting solution for sulphite ions, SO32-.
H2S Colourless, poisonous gas, with a rotten-egg smell, acidic (turns blue litmus red), slightly soluble in water, extinguishes burning and glowing wooden splint, a reducer and therefore forms a yellow residue when reacted with oxidizers e.g. SO2, Cl2, Br2, MnO4- etc, and decolourizes them. Blackening of lead acetate paper, or any source of lead (II) ions
SO42- Solids which are generally soluble, and thermally stable; however, on strong heating, produce colourless acidic gases with pungent chocking smell, and with bleaching effect; forms a white precipitate with barium ions; precipitate not soluble in dilute hydrochloric acid. Formation of a white precipitate with barium ions. The precipitate is insoluble in dilute hydrochloric acid.
SO32- Evolves a colourless, acidic gas with a pungent chocking smell when reacted with a dilute acid. The gas has a bleaching effect. Forms a white precipitate with barium ions, but the precipitate dissolves with effervescence in dilute hydrochloric acid. Formation of a white precipitate with barium ions. The precipitate dissolves in dilute hydrochloric acid, with effervescence.
Cl2 Yellow-green acidic gas with a chocking irritating smell, extinguishes burning and glowing wooden splints, causes bleaching. A yellow-green gas that turns blue litmus red then bleaches it.
HCl Colourless acidic gas with a pungent smell; highly soluble; extinguishes a burning and glowing wooden splint; forms white thick fumes with ammonia gas Formation of white fumes with ammonia gas.
Cl- Generally soluble in water; do not decompose on heating (no observable change); But when in solution, they can be precipitated with silver ions, and lead ions when cold. Formation of a white precipitate with silver nitrate solution