Qualitative Analysis: Identification of Ions and Gases

Vocabulary practice flashcards covering qualitative analysis tests for anions, aqueous cations, flame tests, and tests for identifying colourless and pungent gases.

Qualitative Analysis

The chemical process of identifying dissolved cations and anions in a solution by adding specific reagents and observing the resulting changes, as well as identifying gases.

Carbonate Ion ($\text{CO}_3^{2-}$) Test

Add dilute hydrochloric acid and bubble the gas given off into limewater. Effervescence occurs, and the liberated carbon dioxide gas ($\text{CO}_2$) forms a white precipitate of calcium carbonate with limewater.

Chloride Ion ($\text{Cl}^-$) Test

Add dilute nitric acid, followed by aqueous silver nitrate. A white precipitate of silver chloride is formed.

Bromide Ion ($\text{Br}^-$) Test

Add dilute nitric acid, followed by aqueous silver nitrate. A cream precipitate of silver bromide is formed.

Iodide Ion ($\text{I}^-$) Test

Add dilute nitric acid, followed by aqueous silver nitrate. A yellow precipitate of silver iodide is formed.

Nitrate Ion ($\text{NO}_3^-$) Test

Add aqueous sodium hydroxide and aluminium foil, then warm the mixture carefully. Effervescence is observed and ammonia gas ($\text{NH}_3$) is produced, turning moist red litmus paper blue.

Sulfate Ion ($\text{SO}_4^{2-}$) Test

Add dilute nitric acid, followed by aqueous barium nitrate. A white precipitate of barium sulfate is formed.

Sulfite Ion ($\text{SO}_3^{2-}$) Test

Add acidified aqueous potassium manganate(VII). The reagent changes colour from purple to colourless.

Aluminium Ion ($\text{Al}^{3+}$)

Forms a white precipitate with aqueous sodium hydroxide that dissolves in excess to form a colourless solution; forms a white precipitate with aqueous ammonia that is insoluble in excess.

Ammonium Ion ($\text{NH}_4^+$)

Produces no precipitate with aqueous sodium hydroxide, but gives off ammonia gas on heating that turns moist red litmus paper blue; shows no change when aqueous ammonia is added.

Calcium Ion ($\text{Ca}^{2+}$)

Forms a white precipitate with aqueous sodium hydroxide that is insoluble in excess; produces no precipitate or only a very slight white precipitate with aqueous ammonia.

Chromium(III) Ion ($\text{Cr}^{3+}$)

Forms a green precipitate with aqueous sodium hydroxide that dissolves in excess to give a green solution; forms a green precipitate with aqueous ammonia that is insoluble in excess.

Copper(II) Ion ($\text{Cu}^{2+}$)

Forms a light blue precipitate with aqueous sodium hydroxide that is insoluble in excess; forms a light blue precipitate with aqueous ammonia that dissolves in excess to yield a dark blue solution.

Iron(II) Ion ($\text{Fe}^{2+}$)

Forms a green precipitate with both aqueous sodium hydroxide and aqueous ammonia that is insoluble in excess and turns brown on standing.

Iron(III) Ion ($\text{Fe}^{3+}$)

Forms a red-brown precipitate with both aqueous sodium hydroxide and aqueous ammonia that is insoluble in excess.

Zinc Ion ($\text{Zn}^{2+}$)

Forms a white precipitate with both aqueous sodium hydroxide and aqueous ammonia that dissolves in excess of both reagents to form a colourless solution.

Blue Glass (Flame Test)

A piece of glass used to view flame tests by filtering out the yellow flame caused by sodium contamination, making it easier to observe the characteristic colours of other ions.

Lithium Ion ($\text{Li}^+$) Flame Colour

Red.

Sodium Ion ($\text{Na}^+$) Flame Colour

Yellow.

Potassium Ion ($\text{K}^+$) Flame Colour

Lilac.

Calcium Ion ($\text{Ca}^{2+}$) Flame Colour

Orange-red.

Barium Ion ($\text{Ba}^{2+}$) Flame Colour

Light green.

Copper Ion ($\text{Cu}^{2+}$) Flame Colour

Blue-green.

Hydrogen Gas ($\text{H}_2$) Test

A colourless, odourless gas tested by placing a lighted splint at the mouth of the test-tube; the flame is extinguished with a 'pop' sound.

Oxygen Gas ($\text{O}_2$) Test

A colourless, odourless gas tested by inserting a glowing splint into the test-tube; the glowing splint is rekindled (catches fire again).

Carbon Dioxide Gas ($\text{CO}_2$) Test

A colourless, odourless gas tested by bubbling it through limewater; a white precipitate is formed that dissolves upon further bubbling.

Chlorine Gas ($\text{Cl}_2$) Test

A yellow-green gas with a pungent smell tested by placing moist blue litmus paper at the mouth of the test-tube; the paper turns red and is then bleached.

Sulfur Dioxide Gas ($\text{SO}_2$) Test

A colourless gas with a pungent smell tested by placing filter paper soaked with acidified potassium manganate(VII) at the mouth of the test-tube; the purple acidified potassium manganate(VII) turns colourless.

Ammonia Gas ($\text{NH}_3$) Test

A colourless gas with a pungent smell tested by placing moist red litmus paper at the mouth of the test-tube; the moist red litmus paper turns blue.