Identification of Gases, Cations, and Anions in Analytical Chemistry

Vocabulary practice flashcards covering qualitative analysis tests, characteristic precipitates, colour changes, and key chemical compounds for gas, cation, and anion identification.

Alkaline pyrogallol solution

A colourless solution used in gas identification that absorbs oxygen gas ($\text{O}_2$) and turns brown.

Cobalt chloride paper

A test paper that turns from blue to pink in the presence of water vapour ($\text{H}_2\text{O}$).

Mixed acid anhydride

A term designating nitrogen dioxide ($\text{NO}_2$) because it dissolves in cold water to produce a mixture of nitrous acid ($\text{HNO}_2$) and nitric acid ($\text{HNO}_3$).

Nessler's reagent

An alkaline solution of potassium mercuric iodide ($\text{K}_2\text{HgI}_4$) that turns pale brown or gives a reddish brown precipitate upon reacting with ammonia.

Iodide of Millon's base

The reddish brown precipitate ($\text{H}_2\text{NHgOHgI}$) formed when excess ammonia gas is passed into Nessler's reagent.

Diamine silver chloride

The soluble complex salt ($\text{[Ag(NH}_3)_2\text{]Cl}$) formed when the curdy white precipitate of silver chloride ($\text{AgCl}$) dissolves in excess ammonium hydroxide.

Tetrammine copper (II) sulphate

The complex salt forming a deep blue or inky blue solution ($\text{[Cu(NH}_3)_4\text{]SO}_4$) when copper (II) hydroxide dissolves in excess ammonia or ammonium hydroxide solution.

Litharge

The buff yellow residue of lead [II] oxide / lead monoxide ($\text{PbO}$) formed on strong heating of lead nitrate or lead carbonate, which fuses with glass.

Chromium sulphate

The compound ($\text{Cr}_2(\text{SO}_4)_3$) formed that is responsible for turning acidified potassium dichromate solution from orange to clear green in the presence of sulphur dioxide.

Starch iodide paper

A test paper containing potassium iodide and starch that turns blue black in the presence of chlorine gas ($\text{Cl}_2$) due to liberated iodine ($\text{I}_2$).

Brown ring test

A confirmatory test for the nitrate ion ($\text{NO}_3^{1-}$) in which a brown ring forms at the junction when salt solution is mixed with acidified ferrous sulphate and concentrated sulphuric acid.

Barium sulphate

A white precipitate ($\text{BaSO}_4$) formed during the sulphate ion test that is insoluble in dilute hydrochloric acid ($\text{HCl}$) and dilute nitric acid ($\text{HNO}_3$).

Lead acetate paper

A moist test paper or solution that turns silvery black or black upon exposure to hydrogen sulphide ($\text{H}_2\text{S}$) due to the formation of lead sulphide ($\text{PbS}$).

Iron (II) hydroxide

A dirty green precipitate ($\text{Fe(OH)}_2$) formed by the reaction of iron (II) ions ($\text{Fe}^{2+}$) with sodium hydroxide or ammonium hydroxide, insoluble in excess alkali.

Iron (III) hydroxide

A reddish brown precipitate ($\text{Fe(OH)}_3$) formed by the reaction of iron (III) ions ($\text{Fe}^{3+}$) with sodium hydroxide or ammonium hydroxide, insoluble in excess alkali.

Gelatinous white precipitate

The characteristic physical form of zinc hydroxide ($\text{Zn(OH)}_2$) precipitate, which is soluble in both excess sodium hydroxide and excess ammonium hydroxide.

Chalky white precipitate

The characteristic physical form of lead hydroxide ($\text{Pb(OH)}_2$) precipitate, which is soluble in excess sodium hydroxide but insoluble in excess ammonium hydroxide.

Decrepitation

The crackling sound produced by certain crystalline salts, such as lead nitrate ($\text{Pb(NO}_3)_2$), when subjected to strong heating.

Flame test

An analytical method in which a substance on a cleaned platinum wire is heated in a non-luminous burner flame to identify metallic cations by characteristic colours.

Sodium zincate

The soluble sodium salt ($\text{Na}_2\text{ZnO}_2$) formed when zinc metal or its amphoteric oxide ($\text{ZnO}$) reacts with concentrated sodium hydroxide solution.