Amateur Inorganic Qualitative Analysis / Properties of Ions

A wide variety of substances are present in amateur chemistry. Often, because of household (non lab-grade) sources, substances may be mixtures of unknown composition. It is good to have some idea on what reagents can be used to detect various cations or anions. One may also want to know what exclusive or interesting reactions happen with certain ions. This is detailed for each ion below.

Aluminium: Aluminium forms a gelatinous and partially transparent precipitate when neutralized with ammonia. This precipitate dissolves in excess sodium hydroxide to form a colorless solution.

Barium: Barium forms an insoluble sulfate, produced when a barium solution reacts with a sulfate solution. It also forms an insoluble carbonate. Its flame test is yellow-green.

Beryllium: Beryllium is extremely difficult to distinguish from aluminium. If berylliosis (an often debilitating and sometimes fatal lung disease) is produced by chronic inhalation of a certain dust, it very likely contains beryllium.

Bismuth(III): When zinc metal is placed in a bismuth(III) solution, a black precipitate of bismuth is formed. When a moderately concentrated clear solution is diluted, a white precipitate of bismuth(III) oxychloride forms, which turns yellowish as the solution is neutralized with sodium bicarbonate.

Bromide: A pale white precipitate is formed with silver (see silver for more information). Bromide reacts with hydrogen peroxide to form a light yellow bleach-smelling hypobromite solution. When acidified, this solution turns orange as elemental bromine dissolved in water is produced.

Cadmium: A cadmium solution forms a white precipitate when reacted with sodium hydroxide, which does not dissolve in excess of the reagent. When this white precipitate is heated, it turns brownish due to the formation of cadmium oxide. It likely forms a crumbly bluish-gray coating of cadmium on a piece of zinc.

Calcium: Calcium forms a slightly soluble sulfate, produced when a concentrated calcium solution reacts with a concentrated sulfate solution. It also forms an insoluble carbonate. Its flame test is red-orange (chloride or nitrate). Calcium chloride solution never evaporates in normal air.

Chloride: A white precipitate is formed with silver (see silver for more information). Lead forms a precipitate under certain circumstances (see lead for more information).

Chromate(VI): When hydrochloric acid and hydrogen peroxide is added, a dark blue chromium(VI) peroxo complex forms, which decomposes after a few seconds to either a purplish, greenish, or grayish chromium(III) solution, with evolution of oxygen gas. When ascorbic acid is added to the solution, it is reduced to a purplish chromium(III) complex. Lead forms a bright yellow precipitate with chromate solutions, which is more reddish after alkali is added.

Chromium(III): A huge number of colors are seen when it becomes neutralized or complexed. I do not know all of the possibilities.

Cobalt(II): A blue precipitate of cobalt(II) hydroxide is formed when it is neutralized by sodium hydroxide. This precipitate turns reddish upon long standing or heating. A moderately concentrated solution of cobalt(II) turns blue when heated but reverts back to burgundy when cooled. Cobalt(II) solutions are blue in a moderate concentration of chloride ions and blue-green in a high concentration of chloride ions. An acidic cobalt(II) solution reacts with magnesium metal to form magnetic black cobalt metal.

Copper(I): Most copper(I) compounds are insoluble in water, but soluble in ammonia. When reacted with alkalis, they acquire the yellow color of copper(I) oxide. The colorless ammine complexes turn blue on exposure to air. Copper(I) compounds have a blue flame color.

Copper(II): A bright blue ammine complex is formed when copper(II) compounds dissolve in aqueous ammonia. The copper(II) chloro complex reacts violently with aluminium metal, liberating hydrogen gas, copper metal, and aluminium hydroxide. The solution turns yellow-green when acidified and blue when neutralized. Most copper(II) compounds have a green or blue flame color.

Gallium: A warm gallium solution makes a piece of submerged zinc quite brittle due to internal alloying of the gallium metal.

Indium: Indium forms a gelatinous precipitate when reacted with ammonia. An indium solution forms a crumbly gray coating of indium metal on a submerged piece of zinc.

Iodide: A yellowish precipitate is formed with silver (see silver for more information). It reacts with small amounts of sodium hypochlorite to form a brown triiodide solution. With more it makes black glittering iodine crystals. With more bleach it makes colorless iodate, then periodate, which tends to precipitate in most solutions. Lead forms a bright yellow precipitate with iodide solutions.

Iron(II): Iron(II) solutions form a green-gray or white precipitate (depending on dissolved oxygen concentration) when neutralized with alkali or ammonia. This turns brown upon exposure to air. Iron metal, which turns brown when in solution for extended periods of time, is produced by the action of magnesium on solutions.

Iron(III): A blood red coloration is observed upon addition of acetic acid, while a yellow coloration is seen when hydrochloric acid is added. Copper or nickel metal reacts with the hydrochloric acid-iron(III) chloride complex, forming a green solution of copper(II) or nickel(II) mixed with iron(II).

Lead(II): Lead(II) at relatively high concentration forms a precipitate of lead(II) chloride with hydrochloric acid. This precipitate dissolves in excess HCl and in hot water (to a certain extent). This solution forms a bright yellow precipitate with any iodide or with a soluble chromate. The iodide precipitate also dissolves to a certain extent in boiling water, forming a colorless solution which reforms lead iodide when cooled in an ice bath. Lead(II) forms a pale white precipitate of lead bromide when treated with sodium bromide crystals, which soon transforms from an amorphous to a crystalline mass of crystals.

Lead(IV): Lead(IV) is not commonly found in solution, so it is ignored. Lead(IV) oxide may be detected by ascorbic acid. The brown coloration associated with this compound instantly disappears as it is reduced by the acid.

Lithium: It forms a slightly soluble carbonate when the hydroxide solution is exposed to air. Its flame test is pink-red.

Magnesium: Magnesium ions form an insoluble gelatinous carbonate and hydroxide when reacted with sodium carbonate and ammonia, respectively. Magnesium solutions are very slightly acidic. Magnesium chloride never evaporates in normal air.

Manganate(VII): This magenta solution is obvious even in extremely dilute solution. It supposedly reacts with filter paper to produce green manganate(VI) if there are no other oxidizing agents present. It instantly and complete decolorizes with ascorbic acid.

Manganese(II): It is light pink in highly concentrated solution. The precipitate of the hydroxide is light tan, quickly darkening to a dark brown coloration. The carbonate retains its lighter coloration, dissolving in hydrochloric acid to form carbon dioxide and a colorless or light pink solution. Bleach and alkali produce manganese dioxide with a manganese(II) solution.

Nickel(II): The green aqua complex turns yellowish when reacted with hydrochloric acid. It forms a greenish precipitate  of nickel(II) hydroxide with ammonia, which dissolves to form a blue solution upon addition of more ammonia.

Nitrate: When acidified with hydrochloric acid, copper dissolves, forming nitrogen dioxide fumes and a green solution. Gold also dissolves in this solution to some extent.

Nitrite: Forms brown fumes of nitric oxide and nitrogen dioxide when reacted with hydrochloric acid.

Phosphate: Silver forms a yellow precipitate with phosphate ions. Most transition metals form insoluble phosphates. Cobalt(II) ions form a violet precipitate with phosphate ions.

Potassium: Its flame test is light violet, easily blotted out by a little sodium impurity. It forms a relatively insoluble perchlorate and a quite insoluble periodate.

Silver(I): Silver cations can be detected by addition of sodium chloride. A rather dense and clumpy white precipitate looking similar to cottage cheese immediately falls out of solution. A more dilute solution may just form a cloudy suspension (very few other cations are likely to become cloudy with such a low concentration).  This precipitate will turn dark blue-gray in sunlight as elemental silver is produced. For a reassurance test, add ammonia. The precipitate should immediately dissolve, forming a silver ammine complex. Silver solutions form a light yellow precipitate with any iodide that does not dissolve in ammonia and does not darken on exposure to air. Silver forms a precipitate with bromide solutions that is slightly soluble in ammonia and slowly darkens on exposure to air.

Sodium: It has a yellowish flame test which is present in almost everything. One of the few insoluble sodium compounds is the bismuthate.

Strontium: Strontium forms an insoluble sulfate, produced when a strontium solution reacts with a sulfate solution. It also forms an insoluble carbonate. Its flame test is bright red (chloride or nitrate is best compound for such a test).

Sulfate: A precipitate is formed with soluble lead and barium salts. When heated strongly, most sulfates produce white fumes of sulfur trioxide as they decompose.

Tin(II): When zinc metal is placed in a moderately concentrated tin(II) solution, spongy tin will form as a layer over the zinc metal. Tin(II) forms a pale white precipitate when reacted with ammonia which turns blue-black when gently heated and burns when strongly heated in air. Addition of sodium or potassium iodide crystals to a concentrated tin(II) solution will turn them yellow. However, tin(II) iodide is quite soluble, so this will not work in most cases.

Tin(IV): When zinc metal is placed in a moderately concentrated tin(IV) solution, spongy tin will form as a layer over the zinc metal. Tin(IV) solution precipitates a bright white precipitate of tin dioxide when reacted with ammonia. This does not undergo any reaction when heated.

Titanium(IV): A bright orange solution is formed when hydrogen peroxide is added.

Zinc: A zinc solution forms a white precipitate when reacted with sodium hydroxide or ammonia. It dissolves in an excess of either solution. It forms a crumbly bluish-gray coating of zinc metal on a piece of submerged magnesium.