topic12E

Topic 12E Chemical Reactions
Updated 2008-08-19 R
Please send comments to: J.Elfick@uq.edu.au
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Table of contents
12.11.3.0 Tests for an unknown substance, qualitative analysis
12.11.3.1 Borax bead tests to identify metals in metallic salts and minerals
12.11.3.2 Flame tests to identify metals and their compounds
12.11.3.2.1 Flame tests of some salts
12.11.3.2.2 Flame test sprays
12.11.3.3 Solubility tests, prepare a solution for group analysis
12.11.3.4 Test substances by action of heat in dry test-tube
12.11.3.5 Test substances by action with dilute hydrochloric acid and note gas produced
12.11.3.6 Test substances by action with hot concentrated sulfuric acid
12.11.3.7 Test substances by action of caustic soda solution, sodium hydroxide
12.11.3.8 Test substances by action of heat on charcoal with fusion mixture
12.11.3.9 Tests for aluminium compounds in solution
12.11.3.10 Confirmatory tests with original solution or solid

12.11.4.0 Group tests to identify cations, prepare a solution for group analysis
12.11.4.1 Group 1 tests for Ag⁺, Pb²⁺
12.11.4.2 Group 2 tests for Bi³⁺, Cd²⁺, Cu²⁺, Sn²⁺
12.11.4.3 Group 3 tests for Al³⁺, Cr³⁺, Fe²⁺, Fe³⁺
12.11.4.4 Group 4 tests for Co²⁺, Mn²⁺, Ni²⁺, Zn²⁺
12.11.4.5 Group 5 tests for Ba²⁺, Ca²⁺, Sr²⁺
12.11.4.6 Group 6 tests for K⁺, Mg²⁺, Na⁺, NH₄⁺

12.11.6.0 Group tests for metallic radicals
12.11.6.1 Chemistry of group separations.
12.11.6.2 Preliminary experiments before the separation of Group I metals, silver and lead.
12.11.6.3 Separation into groups.
12.11.7.1 Group I Insoluble chlorides, PbCl₂, AgCl [Hg₂Cl₂ omitted]
12.11.7.2 Group II Sulfides insoluble in dilute hydrochloric acid
12.11.7.2a Group IIa PbS, Bi₂S₃, CuS, CdS [HgS omitted]
12.11.7.2b Group IIb As₂S₃, Sb₂S₃, SnS, SnS₂
12.11.7.3 Group III Insoluble hydroxides, Fe(OH)₃, Cr(OH)₃, Al(OH)₃
12.11.7.4 Group IV Insoluble sulfides precipitated by hydrogen sulfide, ZnS, MnS, CoS, NiS
12.11.7.5 Group V Insoluble carbonates, CaCO₃, BaCO₃, SrCO₃
12.11.7.6 Group VI Magnesium, sodium and potassium, Mg, Na, K

12.11.3.10 Confirmatory tests with original solution or solid
Aluminium
Ammonium
Antimony
Arsenic
Barium
Bismuth
Cadmium
Calcium
Chromium
Cobalt
Copper
Iron
Lead
Magnesium
Manganese
Mercury
Nickel
Potassium
Silver
Sodium
Strontium
Tin
Zinc

12.11.3.0 Tests for an unknown substance, qualitative analysis
12.11.3.1 Borax bead test to identify metals in metallic salts and minerals
The test depend on the colours of metal oxides when heated. Coil the end of a platinum wire to prepare a loop big enough to curl around a match stick. Heat the loop in a Bunsen burner flame then dip the hot loop in borax powder, Na₂B₄O₇.10H₂O. Heat the attached borax in the hottest part of the flame so that it swells to lose water of crystallization then shrinks and fuses to form a transparent bead filling the loop of the platinum wire. Dip the bead in water then in a very small amount of the metal salt that sticks to the bead. Heat the bead and metal salt in either the outer oxidizing flame or inner reducing flame. of the bunsen burner. You can also use a white ceramic tile of saucer instead of platinum wire and microsmic salt [sodium ammonium hydrogen phosphate (Na(NH₄)HPO₄.4H₂O)] instead of borax. Also, you can use sodium carbonate, Na₂CO₃, for the bead test but the colours may be different. The colour of the bead depends on whether you use the outer colourless oxidizing flame or the inner blue reducing flame, the type of flame used, whether you examine the bead hot or cold and the degree of saturation if you are using solutions, the temperature of the bead when examined, and the concentration of the solution if a solution of salt is used instead of the solid salt. For most meals not listed below the flame is colourless.

Solid metal salt	Oxidizing flame	Oxidizing flame	Reducing flame	Reducing flame
-	Hot	Cold	Hot	Cold
Chromium	yellow to emerald-green	green	green	green
Cobalt	deep blue	blue	blue	blue
Copper	light blue-green	blue	-	red-brown
Gold	rose-violet	rose-violet	red	violet
Iron	brown when hot yellow when cold	yellow	green	green
Manganese	violet	amethyst	-	-
Nickel	violet to brown	red-brown	grey	grey
Tungsten	pale yellow	-	green	blue

12.11.3.2 Flame tests to identify metals and their compounds
Cations in an unknown solution can be identified by using flame tests. Add drops of concentrated hydrochloric acid to the solution. Dip a clean piece of platinum wire into it then hold it in a Bunsen burner flame. Dip platinum wire into concentrated hydrochloric acid then into powdered solid and heat in a non-luminous Bunsen burner flame. remember that each person observes colours differently. Check the flame test colours by doing the test for all the cations then compare with the following list of colours:
Ammonium compounds: green (faint colour).
Antimony: blue-green to light blue (faint colour)
Arsenic: light blue (moistened with hydrochloric acid)
Barium: pale green to yellow-green:
Bismuth: blue
Calcium: red
Calcium compounds: brick-red to yellow (masked by barium)
Copper: blue-green
Copper compounds: green (not halides) (CuBr₂blue-green)
Lead: light blue to blue
Lithium compounds: crimson (masked by barium or sodium)
Molybdenum: yellow-green:
Phosphates: blue-green (if when moistened with sulfuric acid).
Potassium: lilac but crimson through blue glass
Potassium compounds: pink-lilac to violet (not borates, phosphates, and silicates.) (masked by sodium or lithium).
Selenium: blue
Sodium: strong golden yellow but no colour viewed through blue glass
Sodium compounds: yellow (if the yellow flame persists and is not intensified by adding 1% NaCl to the dry compound.)
Strontium: crimson
Strontium compounds: scarlet (masked by barium)
Zinc: green-white

12.11.3.2.1 Flame tests of some salts
Soak paper in the following salts, leave to dry then ignite
Calcium chloride: orange
Copper (II) chloride: blue
Copper (II) sulfate: green
Lithium chloride: red
Potassium chloride: purple
Sodium borate, borax: green
Sodium carbonate: yellow
Sodium chloride: yellow
Strontium chloride: red

12.11.3.2.2 Flame test sprays
Use spray bottles, e.g. window cleaners or garden sprays, to spray saturated solutions of metal salts in ethanol onto roaring Bunsen burner flames in a darkened room. Th espray bottles should have a trigger mechanism and not a sscent bottle spray pump whicj may allow flash back. Be careful! Wear eye protection. The salts can include sodium chloride, potassium chloride, lithium chloride, copper sulfate.chlorides.

12.11.3.3 Solubility tests, prepare a solution for group analysis
See also 3.71.1: Solubility table and solubility rules
Dissolve 1 g of the substance in the first reagent below that can dissolve the substance
1. Water: Try to dissolve the salt in deionized water. If the salt does not dissolve, heat it in a test-tube to observe if the salt dissolves in hot water.
2. Dilute hydrochloric acid: If the salt does not dissolve in hot water, add dilute hydrochloric acid to observe if it dissolves.
3. Concentrated hydrochloric acid, 2.0 to 5.0 mL: When all substance is dissolved, dilute the solution to five times its bulk then leave to cool. If the dilution produces a precipitate because of hydrolysis of chlorides of bismuth, antimony or tin add some drops of concentrated hydrochloric acid.
4. Dilute nitric acid: It may dissolve compounds of lead, silver and mercury but avoid using nitric acid because may oxidize hydrogen sulfide.
5. Aqua regia: Heat with concentrated hydrochloric acid the add a few drops of concentrated nitric acid. Dilute as in 3. above.
6. Concentrated nitric acid: Warm with 2.0 to 5.0 ml. The solution must be evaporated to dryness and the residue dissolved in water or hydrochloric acid.
7. Insoluble residue: Filter it off, wash it, and fuse it in a crucible with four times its bulk of fusion mixture. Cool, boil with water, filter. Test filtrate for acid radicals. Dissolve precipitate of metal carbonates in hydrochloric acid, and analyse separately. If the solution so obtained gives no precipitate with that obtained by 1. to 6. above, analyse them together.

12.11.3.4 Test substance by action of heat in dry test-tube
1. Sublimation indicates the presence of ammonium halides, other halides, and some oxides.
2. Melting indicates the presence of sodium, potassium or ammonium nitrate, potassium chlorate, and other less common substances.
3. Decrepitation (crackling noise of some heated crystals) indicates the presence of sodium chloride lead nitrate and potassium chlorate.
4. Loss of water vapour indicates the presence of water of crystallization and some basic hydroxides, basic carbonates, and acid salts. Also, it may indicate that the substance has absorbed moisture from the atmosphere.
5. Loss of oxygen indicates oxides of silver, peroxides, sodium
or potassium nitrate, permanganates and chlorates.
6. Loss of carbon dioxide indicates carbonate or bicarbonate.
7. Loss of ammonia indicates an ammonium compound.
8. Loss of nitrogen dioxide (dinitrogen tetroxide, N₂O₄) indicates nitrates of heavy metals, e.g. copper, lead, zinc.
9. Loss of sulfur trioxide indicates some sulfates.
10 Loss of halogens indicates oxidation of a halide.

12.11.3.5 Test substances by action with dilute hydrochloric acid and note gas produced
1. Carbon dioxide produced indicates a carbonate or bicarbonate
2. Hydrogen produced indicates some free metals
3. Sulfur dioxide produced indicates sulfite or bisulfite
4. Sulfur dioxide and sulfur produced indicates thiosulfate
5. Hydrogen sulfide produced indicates sulfide
6. Nitrogen dioxide (N₂O₄) produced indicates nitrite
7. Chlorine produced indicates hypochlorite or oxidizing agent

12.11.3.6 Test substance by action with hot concentrated sulfuric acid
Gas evolved indication
1. Hydrogen chloride produced indicates chloride
2. Nitric acid produced indicates nitrate
3. Oxygen produced indicates peroxide, permanganate, chromate, dichromate
4. Chlorine peroxide (yellow-green gas, violent action) produced indicates chlorate
5. Sulfur dioxide produced indicates sulfite, thiosulfate or reducing agent
6. Hydrogen bromide, bromine and sulfur produced indicates bromide
7. Hydrogen iodide, iodine and hydrogen sulfide produced indicates iodide
8. Carbon monoxide and carbon dioxide produced indicates oxalate
9. Carbon monoxide only produced indicates formate
10. Acetic acid produced indicates acetate
If organic acid present, substance should be ignited, extracted with dilute hydrochloric acid and filtered before proceeding with main group separation.

12.11.3.7 Test substances by action of caustic soda solution, sodium hydroxide
Heat then if ammonia gas is produced indicates ammonium compound.

12.11.3.8 Test substances by action of heat on charcoal with fusion mixture
Appearance of the heated metal:
1. Aluminium produces a white residue. Add drops of cobalt nitrate solution and heat again to form a blue mass but this is also caused by fusible phosphates, arsenates, borates and silicates.
2. Arsenic produces fumes smelling of garlic and forms a white crust if seen at some distance from the flame.
3. Bismuth forms pink globules, becomes brittle and forms a yellow crust.
4. Cadmium forms a brown crust.
5. Copper forms red scales.
6. Lead forms grey-white soft globules and forms a red crust when hot and a yellow crust when cold.
7. Magnesium produces a white residue. Add drops of cobalt nitrate solution and heat again to form a green mass.
8. Silver has shining metal particles.
9. Tin forms hard white beads.
10. Zinc forms a yellow crust when hot and a white crust when cold. Zinc also produces a white residue. Add drops of cobalt nitrate solution and heat again to form a green mass.

12.11.3.9 Tests for aluminium compounds in solution
Put 2 drops of cobalt chloride solution (red) on apiece of filter paper. The drop 2 drops of aluminium sulfite solution of the filter paper. Hold the filter paper over a small flame, then ignite it over a saucer. A blue ash indicates aluminium compounds.

12.11.3.10 Confirmatory tests with original solution or solid
Aluminium
1. Heat solid on charcoal with fusion mixture, add a few drops of cobalt nitrate solution and heat again. A blue mass forms.
2. Organic reagent: “Aluminon”, 0.1% aqueous solution. To 5 mL of slightly acidic solution add ammonium acetate solution followed by reagent. A red colour or precipitate indicates presence of aluminium Use Group III precipitate dissolved in dilute HCl Iron also gives positive test so aluminium cannot be shown in its presence. Chromium gives a positive test but it may be removed by ammonia and ammonium.

Ammonium radical
NOTE. Nessler's reagent, solution, is not allowed in some school systems because it contains mercury.
Organic reagent: Nessler's solution, K₂HgI₄, in caustic soda solution. Add reagent to original solution. A brown colour or precipitate indicates the presence of ammonium ion. The test is very sensitive. The test solution must contain no NH₄⁺ added during analysis.

Antimony
1. Dilute with its own volume of water. Pass H₂S. An orange-red precipitate of antimony sulfide, Sb₂S₃, indicates the presence of antimony.
2Sb³⁺ + 3S^2- --> Sb₂S₃ (s)
2. Organic reagent: Gallocyanine, 0.05% in M HCl. To one drop of antimony solution on filter paper, add one drop of reagent. A colour change from wine-red to blue indicates the presence of antimony. Use Group IIb precipitate dissolved in concentrated HCl and diluted.

Arsenic
See 12.11.3.8: Test substances by action of heat on charcoal with fusion mixture

Barium
Confirm by flame test: Light green
Barium and strontium
Organic reagent: Rhodizonic acid (CO-CO.CONa)2, 0.1% aqueous solution. Put one drop of test liquid on filter paper then add one drop of reagent. A red-brown spot indicates the presence of Sr and Ba. When one drop of dilute Hcl is added, a barium spot is intensified and a Sr spot disappears. Use Group V precipitate after solution in dilute acetic acid. Prepare fresh solution of reagent if it has decolorized.

Bismuth
1. See 12.11.3.2: Flame tests
2. Organic reagent: Thiourea, H₂N.CS.NH₂, 10% aqueous solution. 10 mL Bi solution + 10 mL dilute HNO₃ + 1 mL reagent. A yellow colour indicates the presence of bismuth. Use Group IIa precipitate. Sb gives a weak reaction. Silver give a precipitate soluble in excess.

Cadmium
1. Ammonium hydroxide gives white precipitate easily soluble in excess.
2. Organic reagent: diphenyl carbazide, CO(NH.NH.C₆H₅)₂, in saturated alcoholic solution. Add few drops of reagent to Cd to give violet coloration. Use solution in dilute HNO₃ in Group separation. If Cu present as a blue solution, first saturate reagent with KCNS and add crystal KI, then Cu is reduced and does not interfere.

Calcium
Confirm by flame test: brick-red (green through blue glass)

Chromium
1. Fuse with sodium carbonate and a little potassium nitrate in a porcelain crucible. Dissolve in water, add acetic acid and lead acetate solution. A yellow precipitate forms. A filtrate may contain chromium and aluminium as sodium chromate and sodium aluminate. A yellow precipitate indicates the presence of chromium.
Pb²⁺ + CrO₄^2- --> PbCrO₄ (s) [yellow lead chromate]
2. Chromium (as chromate}
Organic reagent: Diphenyl carbazide, 0.2% solution in one part glacial acetic acid and nine parts methylated spirit. Make the chromate solution acidic with acetic acid or sulfuric acid. Add reagent. A deep violet-red colour indicates the presence of chromate. Use in Group III when in form of chromate.

Cobalt
Organic reagent: Alpha-nitroso-beta-naphthol. 1 g in 50 mL acetic acid. Dilute to 100 mL Add reagent to neutral or slightly acid solution. A brown colour indicates the presence of cobalt. Use in Group IV when in solution after treatment with KClO₃ and acid, or use the solution after Group III. Cu, Fe, Sn, Ag, Cr, Bi, all interfere with the test.

Copper
1. Ammonium hydroxide gives a pale blue precipitate that dissolves in excess to give a deep blue solution.
2. Organic reagent: Rubeanic acid, NH₂.CS.CS.NH₂, saturated 0.5% alcoholic solution. Use 10 mL of neutral Cu solution + 1 mL 5M CH₃COOH + drops of reagent. A green-black precipitate forms. Test with Group II precipitate. Ni and Co may interfere with the test. Dissolve CuS in dilute HNO₃ and neutralize with NaOH solution.

Iron
Organic reagent: “Cupferron”, 5% aqueous solution. Filter if reagent is turbid. Add reagent to strongly acidic HCl solution. A red-brown compound indicates the presence of iron. The reagents is unstable over long periods but decomposition may be delayed by a piece of solid ammonium carbonate added to the reagent.

Lead
Add potassium iodide solution to solutions of lead salts to form a yellow precipitate that is soluble in boiling water.
Organic reagent: Rhodizonic acid, sodium salt (CO-CO.C.ONa)₂, 0.1% aqueous solution. Add two drops of reagent to a sample of Group I precipitate still wet with acid. A violet colour indicates the presence of lead. Prepare a fresh solution of the reagent, if it has decolorized.

Magnesium
1. Heat on charcoal with sodium carbonate. Add a few drops of cobalt nitrate solution and heat again to produce a pink residue.
2. Organic reagent: The complex dye Titan yellow, as 0.1% aqueous solution. Add 2 mL 1% KOH to 2 drops of test solution. Boil to remove NH₄⁺ and add 2 drops of Titan yellow. A red colour or red precipitate indicates the presence of magnesium. Tests for Mg in a Group VI solution. Ammonium ions interfere with the test and must be removed.

Manganese
1. Fuse with sodium carbonate and some potassium nitrate in a crucible to form a blue-green mass.
2Mn(OH)₂ + 5O --> 2MnO₄^- + 2H⁺ + H₂O
[5O from oxidizing agents] [MnO₄^- = purple permanganate ion]
2. Organic reagent: Benzidine, 0.05% solution in 10% acetic acid. To one drop of solution on filter paper add one drop 0.05% NaOH then one drop of reagent. Use in Group IV when in solution in dilute acid. Dissolve Group IV precipitate in very dilute acid and use the solution, rejecting any undissolved solid.

Mercury
In this version of qualitative analysis, all reference to the use of mercury metals or mercury salts has been deleted because these chemicals are not allowed in school science experiments.

Nickel
Organic reagent: Dimethyl-glyoxime (CH₃C:NaOH)₂, 1% solution in methylated spirit. Slightly acid test solution warmed, reagent added followed by ammonium hydroxide until alkaline. A red precipitate indicates the presence of nickel. Bismuth interferes with the test.

Potassium
Reagent: Sodium perchlorate, 20% solution in equal parts of water and alcohol. Add reagent to equal bulk of test solution. A white precipitate of KClO₄ indicates the presence of potassium. Test in Group VI solution concentrated by evaporation and let cool. Do the test on a glass plate above a black background.

Silver
1. Add potassium chromate solution to neutral solution of a silver salt to form a brick-red precipitate.
2. Organic reagent: p-dimethylamino benzalrhodanine, 0.03% in acetone. It will detect AgCl in solution in water. A red colour indicates the presence of silver. Use a Group I precipitate.

Sodium
Organic reagent: Uranyl magnesium acetate. U0₂(CH₃COO)₂.Mg(CH₃COO)₂, Saturated aqueous solution. Add reagent to cold solution. A yellow precipitate indicates the presence of sodium. Test in Group VI solution concentrated by evaporation and let cool. Do the test on a glass plate above a black background.

Strontium
Confirm by flame test: Crimson
Sr²⁺ + SO₄^2- --> SrSO₄ (s)
Strontium and barium
Organic reagent: Rhodizonic acid (CO-CO.CONa)2, 0.1% aqueous solution. Put one drop of test liquid on filter paper then add one drop of reagent. A red-brown spot indicates the presence of Sr and Ba. When one drop of dilute Hcl is added, a barium spot is intensified and a Sr spot disappears. Use Group V precipitate after solution in dilute acetic acid. Prepare fresh solution of reagent if it has decolorized.

Tin
1. Use a borax bead containing some copper (II) sulfate. Add a sample of the original solid and heat again to produce a red bead.
2. Organic reagent: Cacotheline, C₂₁H₂₁O₇N₃, saturated solution in water. Tin must as Sn(II) in M HCl. Add drops of reagent. A violet colour indicates the presence of tin. Stability of reagent is about 14 days. Cu, Ni, Co, Cr and Fe interfere with the reaction. Do the test with Group IIb solution when as Sn(II).

Zinc
Filter and dissolve the precipitate in concentrated nitric acid. Add a little cobalt nitrate solution, evaporate to concentrate, and soak a filter paper in the mixture. Ignite the filter paper. A green ash (Rimann's green) indicates the presence of zinc. The green ash is a compound of zinc and cobalt oxides.
2ZnO₂^2- + 8H⁺ + 2S^2- --> 2ZnS (s) + 4H₂O

12.11.4.1 Group 1 tests for Ag⁺, Pb²⁺
1. First test: Add 2 drops of dilute hydrochloric acid to 5 drops of the original solution. A white precipitate identifies Ag⁺ or Pb²⁺. If no precipitate forms, go to (Group 2 test).
Pb²⁺ + 2Cl^- --> PbCl₂ (s)
Ag⁺ + Cl^- --> AgCl (s)

2. Second test: Add 2 to 5 drops of K₂CrO₄solution to 5 drops of the original solution. A red precipitate identifies Ag⁺. A yellow precipitate identifies Pb²⁺.
Pb²⁺ + CrO₄^{2- --->} PbCrO₄ (s)

12.11.4.2 Group 2 tests for Bi³⁺, Cd²⁺, Cu²⁺, Sn²⁺
1. First test: Add 10 drops of H₂S solution. A yellow precipitate identifies Cd²⁺. A brown-black precipitate identifies Cu²⁺or Bi³⁺or Sn²⁺. Then add 10 drops of NaOH solution and heat. A dissolving precipitate identifies Sn²⁺.
Cd²⁺+ S^2- --> PbS (s)2Bi³⁺ + 3S^2- --> Bi₂S₃ (s)
2. Second test: Add 10 drops of NH₃ solution to 5 drops of the original solution. A deep blue colour identifies Cu²⁺. A white precipitate that then dissolves identifies Cd²⁺. Add water to the original solution. A milky precipitate identifies Bi³⁺.
Cu²⁺ + 4NH₄OH --> [Cu(NH₃)₄]²⁺ + 4H₂O (deep blue solution)
Cd²⁺ + 4NH₄OH --> [Cd(NH₃)₄]²⁺ + 4H₂O
Bi³⁺ + 3OH^- --> Bi(OH)₃ (s)

12.11.4.3 Group 3 tests for Al³⁺, Cr³⁺, Fe²⁺, Fe³⁺
1. First test: Add 8 drops of NH₄Cl solution to 5 drops of the original solution. Test the solution with litmus paper. Add enough drops of dilute NH₃ solution to turn red litmus blue. A green precipitate identifies Fe²⁺or Cr³⁺. A red-brown precipitate identifies Fe³⁺. A white glassy precipitate identifies Al³⁺. If no precipitate forms, go to (Group 4 test).

2. Second test: Add to 5 drops of the original solution 6 drops of NaOH then 2 drops of NaHClO solution boil then add 2 drops of lead (II) ethanoate (lead (II) acetate solution)

3. Use lead acetate test paper. A yellow precipitate indicates Cr³⁺.
BE CAREFUL! WARNING! The following common test is too dangerous to be used in school science experiments:
Potassium hexacyanoferrate (III) (potassium ferricyanide) reacts with strong mineral acids to release TOXIC potassium cyanide.

4. Add to 5 drops of the original solution 5 drops of K₃Fe(CN)₆ solution. A deep blue precipitate identifies Fe²⁺. A green-brown precipitate identifies Fe³⁺.

12.11.4.4 Group 4 tests for Co²⁺, Mn²⁺, Ni²⁺, Zn²⁺
1. First test: Following Group 3 test, add to 5 drops of original solution 10 drops of H₂S solution. A black precipitate indicates Co²⁺or Ni²⁺. A dirty white precipitate indicates Zn²⁺.A pink precipitate indicates Mn²⁺.
Co²⁺ + S^2- --> CoS (s)
Ni²⁺ + S^2- --> NiS (s)
Zn²⁺ + S^2- --> ZnS (s)
Mn²⁺ + S^2- --> MnS(s)
2. Second test: Following Group 3 test, add to 5 drops of original solution 2 drops of sodium hydroxide solution and heat. A blue to pink precipitate indicates Co²⁺. Add to 5 drops of original solution 2 drops of butanedione (dimethylglyoxal). A bright red precipitate indicates Ni²⁺.
C. Third test: Following Group 3 test, add to 5 drops of original solution drops of dilute NH₃ solution until litmus paper test indicates it as basic. A white glassy precipitate that dissolves in excess NH₃solution indicates Zn²⁺.
D. Fourth test: Following Group 3 test, add to 5 drops of original solution 2 drops of NaOH solution then 2 drops of NaClO solution. A dirty white precipitate indicates Mn²⁺.

12.11.4.5 Group 5 tests for Ba²⁺, Ca²⁺, Sr²⁺
1. First test: Add 8 drops of NH₄Cl solution to 5 drops of original solution. Test with litmus paper. Add enough drops of dilute NH₃ solution to turn blue litmus red. Add 10 drops of H₂S solution - no precipitate forms. Add 8 drops of NH₄Cl solution to 5 drops of original solution. Add 2 drops of concentrated aqueous ammonia solution then 2 drops of ammonium carbonate solution. A white precipitate indicates Ba²⁺or Ca²⁺ or Sr²⁺.
2. Second test: Add to 5 drops of original solution 2 drops of saturated CaSO₄ solution. No precipitate indicates Ca²⁺. Immediate white precipitate indicates Ba²⁺. Slow precipitate on heating indicates Sr²⁺.

12.11.4.6 Group 6 tests for K⁺, Mg²⁺, Na⁺, NH₄⁺
1. There is no test for Group 6.
2. Verify K⁺ and Na⁺ with flame tests. To verify cations, add to 5 drops of original solution 3 drops of NaOH and boil. The sharp odour of NH₃identifies NH₄⁺. NH₃turns red litmus blue. Add 4 drops concentrated NH₄Cl solution to 5 drops of the original solution. Add enough aqueous ammonia solution to prepare the solution test alkaline. Add 4 drops of sodium phosphate (trisodium phosphate(V)-12-water) solution then stir. A white precipitate indicates Mg²⁺.
Mg²⁺ + HPO₄^2- + NH₄⁺ + OH^- --> MgNH₄PO₄ (s) (magnesium ammonium phosphate)

12.11.6.0 Tests for metallic radicals
See also 17.5.7.0: Explanation of group analysis
In this version of qualitative analysis, all reference to the use of mercury salts has been deleted because these salts are not allowed in school science experiments.

12.11.6.1 Chemistry of group separations.
This system of qualitative analysis is based on differences between the properties of 23 metallic radicals. The first separation into Groups is made by selecting a reagent which precipitates a few of the metals but leaves the remainder to be precipitated by a different reagent or reagents. A precipitate obtained in a given group may contain one or more of the metals of that group and it is then that use is made of specific differences of properties of the metals likely to be present. Before each Group separation show how each metal in the group behaves towards the reagents used.

12.11.6.2 Preliminary experiments before the separation of Group I metals, silver and lead.
1. Add dilute hydrochloric acid to solutions of silver nitrate and lead acetate. The white precipitates are the insoluble metal chlorides, AgCl and PbCl₂.
Ag⁺ + Cl^- --> AgCl(s)
Pb²⁺ + 2Cl^---> PbCl₂
2. Decant the liquid from each test-tube, then half fill with deionized water. Heat the solutions to boiling to show that lead chloride is soluble in boiling water, but silver chloride is not soluble. (If the solution is not boiled, some chromium may be present as a pale purple amine solution, Cr(NH₃)₆(OH)₃, that decomposes to chromium hydroxide on boiling. An amine is a coordination complex in which the molecules that donate a pair of electrons to a metal are ammonia molecules.) Add drops of potassium chromate to the clear lead chloride solution to form the yellow precipitate of lead chromate.
Pb²⁺ + CrO₄^2- --> PbCrO₄
c) Decant the liquid from the precipitate of silver chloride then add dilute ammonium hydroxide solution and shake the test-tube. Silver chloride dissolves because of the formation of a soluble silver amine complex ion.
AgCl + 2NH₄OH –> Ag(NH₃)₂Cl + 2H₂O
or AgCl + 2NH₄⁺ + 2OH^- --> Ag(NH₃)₂⁺ + Cl^- + 2H₂O

12.11.6.3 Separation into groups
1. Add dilute hydrochloric acid to the prepared solution then filter when cold. However, if effervescence of a gas occurs, pass the gas into limewater. Turbidity indicates the presence of a carbonate or bicarbonate.
2a. The precipitate may contain AgCl, PbCl₂ or Hg₂Cl₂ as a white precipitate.
See 12.11.7.1: Examine for Group I - Insoluble chlorides
2b. The filtrate should give no precipitate on adding one drop of HCl. Heat the filtrate then pass hydrogen sulfide until no further precipitate forms. Filter. Dilute some filtrate five times with water, then pass more hydrogen sulfide through the filtrate. If more precipitate appears, dilute the filtrate and continue passing more hydrogen sulfide through the filtrate until no more precipitate forms. Filter through the same filter paper. If no precipitate occurs on dilution, discard the diluted portion.
3a. The precipitate may contain HgS, PbS, Bi₂S₃, CuS, CdS, As₂S₃, Sb₂S₃, SnS, SnS₂.
See 12.11.7.2: Examine for Group II - Sulfides insoluble in dilute hydrochloric acid
3b. Put the filtrate into an evaporating dish and boil off the H₂S and allow solution to concentrate. Add dilute nitric acid and excess ammonium molybdate solution to a sample of the solution. Heat the solution but do not boil, then leave to stand. Discard any yellow precipitate that indicates phosphate. To the rest of the main solution add 2 mL of concentrated nitric acid and boil to oxidize iron (II) iron to iron (III) iron. Transfer to a boiling tube, add ammonium chloride solution and ammonium hydroxide solutions in excess. Boil and filter the solution.
4a. The precipitate may contain Fe(OH)₃, Al(OH)₃, Cr(OH)₃.
See 12.11.7.3: Examine by table for Group III - Insoluble hydroxides, Fe(OH)₃, Cr(OH)₃, Al(OH)₃
4b. The filtrate should contain excess ammonia. To test for ammonia, shake vigorously and smell. Pass hydrogen sulfide. Boil, filter. If the filtrate is brown, nickel is present in the solution. Boil the filtrate until no more ammonia is evolved. Filter. The filtrate should not now be brown.
5a. The precipitate may contain ZnS, MnS, NiS, CoS.
See 12.11.7.4: Group IV - Insoluble sulfides precipitated by hydrogen sulfide, ZnS, MnS, CoS, NiS
5b. To the filtrate add ammonium carbonate solution. Heat then filter.
6a. The precipitate may contain CaCO₃, BaCO₃, SrCO₃.
See 12.11.7.5: Group V - Insoluble carbonates, CaCO₃, BaCO₃, SrCO₃
6b. Examine the filtrate by table for Group VI.
See 12.11.7.6: Group VI - Magnesium, sodium and potassium, Mg, Na, K
If a test portion gives no precipitate on passing hydrogen sulfide, discard and treat remainder for later groups.

12.11.7.1 Group I Insoluble chlorides, PbCl₂, AgCl [Hg₂Cl₂ omitted]
1. Wash the precipitates twice with cold water and discard the washings. Make a hole in a filter paper with a pointed glass rod, and wash the precipitate through into a beaker. Boil with water and filter while hot.
2a. Residue: Wash the residue with hot water then pour warm ammonium hydroxide solution through the filter paper.
2b. Filtrate: The filtrate contains PbCl₂ although white crystals may separate on cooling. Add potassium chromate solution. A yellow precipitate of lead chromate indicates the presence of lead.
Pb²⁺ + 2Cl^- --> PbCl₂
Pb²⁺ + CrO₄^2- --> PbCrO₄ (s)
3a Residue: If the residue is black, it may be because of finely divided metallic mercury.
3b Filtrate: Acidify with nitric acid to form a white the precipitate of silver chloride that turns violet on exposure to light to indicate the presence of silver.
Ag⁺ + Cl^- --> AgCl (s)
Action of ammonia on silver chloride
AgCl + 2NH₄OH + Ag(NH₃)₂Cl + 2H₂O
[Ag(NH₃)₂Cl = soluble amine]
Precipitation of silver chloride by nitric acid.
Ag(NH₃)₂Cl + 2HNO₃ --> 2NH₄NO₃ + AgCl (s)
See 12.11.3.10 Confirmatory tests with original solution or solid, silver, lead

12.11.7.2 Group II Sulfides insoluble in dilute hydrochloric acid
Keep the precipitate covered by a watch glass over the funnel to minimize oxidation of copper sulfide to copper (II) sulfate, which would be washed out. Wash the precipitate well with hot water. Make a hole in the filter paper with a glass rod, and wash the precipitate through into evaporating dish. Add caustic soda solution and a drops of yellow ammonium sulfide. Heat briefly then filter.
Residue:
See 12.11.7.2a: Group IIa PbS, Bi₂S₃, CuS, CdS [HgS omitted]
Filtrate:
See12.11.7.2b: Group IIb As₂S₃, Sb₂S₃, SnS, SnS₂

12.11.7.2a Group IIa PbS, Bi₂S₃, CuS, CdS [HgS omitted]
1. Wash the precipitate with hot water. Make a hole in the filter paper and wash the precipitate into an evaporating basin. Add dilute nitric acid and boil. Sulfur will usually remain here. Transfer the whole to a boiling tube, add dilute sulfuric acid and alcohol to complete the precipitation of lead sulfate. Omit this step 1. if lead was not found present in Group I. Leave to stand then filter. --> 2a residue, 2b filtrate
2a. The residue may contain lead sulfate, and sulfur. Wash with hot water then wash into a boiling tube and boil with ammonium acetate solution. Filter --> 2a.1 residue, 2a.2 filtrate
2a.1 The residue may contain mercury sulfide. However, mercury salts are too dangerous for school science experiments.
2a.2 The filtrate contains lead. Add potassium chromate solution. A yellow precipitate of lead chromate, PbCrO₄, indicates the presence of lead.
Pb²⁺ + CrO₄^2- -->PbCrO₄ (s)
2b. The filtrate may contain bismuth, copper and cadmium nitrates. Add ammonia in excess. Warm and filter.
2b.1 The residue is white bismuth hydroxide. Wash the residue and dissolve it by pouring warm dilute HCl through the filter paper. Pour filtrate into beaker nearly full of water. Turbidity because of bismuth oxychloride, BiOCl, indicates the presence of bismuth.
Bi(OH)₃ + 3H⁺ –> Bi³⁺ + 3H₂O
Bi³⁺ + H₂O + Cl^- -->BiOCl (s) + 2H⁺
2b.2 Divide the filtrate into two parts.
2b.2.1 Part I. If the liquid is colourless, omit this step. Acidify with dilute acetic acid, add potassium ferrocyanide solution. A brown colour or a precipitate because of copper ferrocyanide indicates the presence of copper.
[Cu(NH₃)₄]²⁺ + 4H⁺ –> CU²⁺ + 4NH₄⁺
2Cu²⁺ + Fe(CN)₆^4- --> Cu₂Fe(CN)₆
copper + ferrocyanide ion --> copper ferrocyanide [brown precipitate]
2b.2.2 Part II. If coloured, the filtrate may also contain cadmium. The test for cadmium at this stage is too dangerous for school science experiments.
See 12.11.3.10 Confirmatory tests with original solution or solid, bismuth, cadmium, copper
Precipitation of sulfides
Pb²⁺ + S^2- --> PbS (s)
The red precipitate PbS is decomposed by more of the H₂S gas to black lead sulfide. [similarly Cu²⁺, Cd²⁺]
2Bi³⁺ + 3S^- --> Bi₂S₃ (s)
Action of dilute nitric acid.
SnS + 2H⁺ --> Sn²⁺ + H₂S (g)
CuS + 2H⁺ –> Cu²⁺ + H₂S (g) [Similarly CdS, PbS]
Bi₂S₃+ 6H⁺ --> 2Bi³⁺ + 3H₂S
Oxidation to sulfate
CuS + 8HNO₃ --> CuSO₄ + 8NO₂ + 4H₂O
Action of ammonia on bismuth, copper and cadmium nitrate solutions.
Bi³⁺ + 3OH^- --> Bi(OH)₃ (s)
Cu²⁺ + 4NH₄OH –> [Cu(NH₃)₄]²⁺ + 4H₂O [deep blue ion]
Cd²⁺ + 4NH₄OH –> [Cd(NH₃)₄]²⁺ + 4H₂O

12.11.7.2b Group IIb As₂S₃, Sb₂S₃, SnS, SnS₂
1. The filtrate may contain antimony, arsenic, stannous and stannic sulfides. Acidify with dilute hydrochloric acid the filtrate from Group II after treatment with caustic soda and ammonium sulfide. If Group IIb is present, it will precipitate now, and if absent only white sulfur is seen. If a precipitate appears, pass H₂S to complete the precipitation, heat, filter then discard the filtrate. Wash the precipitate with hot water, make a hole in the filter paper, and wash the precipitate through into an evaporating basin. Add a piece of solid ammonium carbonate, warm for a few minutes, then filter the solution.
2a. The residue may contain antimony and tin sulfides. Wash the residue. Make a hole in the filter paper and wash through with concentrated hydrochloric acid into an evaporating basin. Boil then divide the solution into two parts, Part 1 and Part 2. Leave to cool.
3a. Part 1. Dilute with its own volume of water. Pass H₂S. An orange-red precipitate of antimony sulfide, Sb₂S₃, indicates the presence of antimony.
2Sb³⁺ + 3S^2- --> Sb₂S₃ (s)
3b Part 2. Add zinc foil in an evaporating basin until effervescence stops. Any tin present will be as a grey precipitate around the rim of the evaporating basin.
Sn²⁺ + S^2- --> SnS (s)
Sn⁴⁺ + 2S^2- --> SnS₂(s)
2b. The filtrate may contain arsenic. Add dilute HCl carefully in a dish until effervescence stops. Pass H₂S and boil. A yellow precipitate of arsenic sulfide indicates the presence of arsenic.
2As⁺ + 3S^2- -->As₂S₃ (s)
See 12.11.3.10 Confirmatory tests with original solution or solid, antimony, arsenic, tin
4. Action of caustic soda and ammonium sulfide
The sulfur of the polysulfide, ammonium sulfide, oxidizes the lower sulfide and forms a thio salt.
As₂S₃ + 3S^2- + 2S --> 2AsS₄^3-[thio arsenate ion]
[2S from polysulfide]
The addition of acid precipitates the higher sulfide, arsenic sulfide, As₂S₅.
2AsS₄^3- + 6H⁺ --> As₂S₅ + 3H₂S (g)
Action of ammonium carbonate,
As₂S₅ + 5(NH₄)₂CO₃ + 3H₂O --> 2H₃AsO₄ + 5(NH₄)₂S + 5CO₂(g)
[H₃AsO₄ = arsenic acid]
With continued subsequent passage of H₂S
2H₃AsO₄ + 5H₂S --> As₂S₅ + 8H₂O
Action of concentrated hydrochloric acid on boiling with antimony and tin sulfides
Sb₂S₃ + 6H⁺ -->2Sb³⁺ + 3H₂S (g)

12.11.7.3 Group III Insoluble hydroxides, Fe(OH)₃, Cr(OH)₃, Al(OH)₃
1. The precipitate may contain iron (III) hydroxide, chromium (III) hydroxide and aluminium hydroxide. Wash well with hot water. Make a hole in the filter paper with a glass rod, and wash the precipitate through into a wide mouthed boiling tube. Add caustic soda solution and hydrogen peroxide solution, boil and filter.
2a. The residue is brown iron (III) hydroxide. Dissolve in dilute HCl, add potassium ferrocyanide solution. A blue the precipitate indicates the presence of iron. To the original solution add: 2.1 potassium ferricyanide solution. A blue precipitate indicates the presence of iron (II) iron, Fe (II). 2.2. Potassium thiocyanate (KCNS) solution. A red coloration indicates the presence of ferric iron, iron (III). Some manganese hydroxide may occur here but it will appear in Group IV.
Fe³⁺ + 3CNS^- --> Fe(CNS)₃ [iron (III) thiocyanate]
2b. The filtrate may contain chromium and aluminium as sodium chromate and sodium aluminate. A yellow colour indicates the presence of chromium. Divide into two parts.
3a Filtrate Part 1: If the solution is not yellow, omit this step Add acetic acid in excess, and then lead acetate solution. A yellow precipitate of lead chromate indicates the presence of chromium.
3b. Filtrate Part 2: Add litmus indicator solution. Add dilute HCl in excess, then NH₄OH just in excess, then shake and leave to stand. A blue lake of aluminium hydroxide, Al(OH)₃, and litmus indicates the presence of aluminium
AlO₂^- + 4H⁺ --> Al³⁺ + 2H₂O
Al³⁺ + 3OH^- --> Al(OH)₃ (s)
See 12.11.3.10 Confirmatory tests with original solution or solid, aluminium, chromium, iron
Precipitation of hydroxides
Fe³⁺ + 3OH^- --> Fe(OH)₃ (s)
Cr³⁺ + 3OH^- --> Cr(OH)₃ (s)
Al³⁺ + 3OH^- --> AI(OH)₃ (s)
Action of caustic soda and hydrogen peroxide. iron (III) hydroxide unchanged.
2Cr(OH)₃ + 3O + 4OH^- --> 2CrO₄^2- + 5H₂O
[3O from oxidizing agent] [chromate ion = CrO₄^2-]
Al(OH)₃ + OH^- -> AlO₂^- + 2H₂O
[AlO₂^- = meta-aluminate ion]

12.11.7.4 Group IV Insoluble sulfides precipitated by hydrogen sulfide, ZnS, MnS, CoS, NiS
1. The precipitate may contain zinc, manganese, cobalt and nickel sulfides and sulfur. If it is not black, cobalt and nickel are both absent. Wash the precipitate. Dilute the dilute hydrochloric acid with five times its own volume of water and pour this through the filter paper.
2. The residue may contain cobalt or nickel as sulfides. Transfer the residue to an evaporating basin, add concentrated hydrochloric acid and a crystal of potassium chlorate. Heat until all substances are dissolved then heat to evaporate until nearly dry.
3a. The nickel solution is yellow-green with a yellow crystal deposit. Add an alkaline solution of dimethyl glyoxime. A red colour or a red precipitate indicates the presence of nickel.
3b. A cobalt solution is pink and deposits blue crystals.
For confirmation apply the borax bead test.
Blue bead: cobalt.
Brown bead: nickel.
1a. The filtrate may contain zinc and manganese chlorides. Boil the filtrate in an evaporating basin dish to remove hydrogen sulfide. If the liquid is still turbid, finely divided sulfur is suspended in it. Add potassium chlorate, boil until clear then leave to cool. Add excess sodium hydroxide solution then filter.
4a. The residue is manganese hydroxide that turns brown on filter paper. Wash into a boiling tube, allow to settle, pour off the water. Add concentrated nitric acid and lead dioxide then boil. Dilute and allow to settle. A crimson colour because of permanganic acid indicates the presence of manganese.
4b. The filtrate contains zinc as sodium zincate. Pass hydrogen sulfide. A white precipitate, often discoloured, of zinc sulfide indicates the presence of zinc.
See 12.11.3.10 Confirmatory tests with original solution or solid, cobalt, manganese, nickel, zinc
Precipitation of sulfides.
Zn²⁺ + S^2- --> ZnS (s)
Mn²⁺ + S^2- --> MnS (s)
Co²⁺ + S^2- -->CoS (s)
Ni²⁺ + S^2- --> NiS (s)
If ammonium sulfide is used, some sulfur may also occur because ammonium sulfide also contains also polysulfides of the type NH₄HS_x. A typical reaction:
Zn²⁺ + S₂^2- --> ZnS (s) + S (s)
Action of very dilute hydrochloric acid. Cobalt and nickel sulfides are unchanged.
ZnS + 2H⁺ --> Zn²⁺ + H₂S (g)
MnS + 2H⁺ --> Mn²⁺ + H₂S (g)
Action of excess sodium hydroxide solution on zinc and manganese chlorides.
Zn²⁺ + 2OH^- --> Zn(OH)₂ (s)
Zn(OH)₂ + 2OH^- --> ZnO₂^2- + 2H₂O
[ZnO₂^2- = soluble zincate ion]
Mn²⁺ + 2OH^- --> Mn(OH)₂ (s)
On exposure to air the manganese hydroxide turns into brown manganese hydroxide.
4Mn(OH)₂ + O₂ --> 4MnO.OH + 2H₂O
[MnO.OH = hydrated manganese sesquioxide]

12.11.7.5 Group V Insoluble carbonates, CaCO₃, BaCO₃, SrCO₃
1. The precipitate may contain calcium, strontium and barium carbonates. Wash well with hot water. Pour through the filter paper some warm dilute acetic acid. To a small portion of the filtrate add potassium chromate solution and boil. If there is a the precipitate add potassium chromate solution to the whole and boil. If there is no the precipitate discard sample and treat whole as filtrate. Filter.
2a. The residue is pale yellow barium chromate that indicates the presence of barium, See 12.11.3.2: Confirm by flame test.
2b. The filtrate may contain calcium and strontium as acetates. Divide into two parts.
3a. Part I. Add calcium sulfate solution and boil. A faint white precipitate of strontium sulfate indicates the presence of strontium.
3b. Part II.
3b.1. If strontium is absent, add excess ammonium hydroxide and ammonium oxalate solution. A white precipitate of calcium oxalate indicates the presence of calcium.
3b.2. If strontium is present, add dilute sulfuric acid, boil, filter, and reject the precipitate of strontium sulfate. Add excess ammonium hydroxide and ammonium oxalate solution to the filtrate. A white precipitate of calcium oxalate, CaC₂O₄, indicates the presence of calcium.
Ca²⁺ + C₂O₄^2- --> CaC₂O_4
(s)calcium oxalate [C₂O₄^2-= oxalate ion]
See 12.11.3.10: Confirmatory tests with original solution or solid, barium, calcium, strontium
Precipitation of carbonates
Ba²⁺ + CO₃^2- --> BaCO₃ (s)
Sr²⁺ + CO₃^2- --> SrCO₃ (s)
Ca²⁺ + CO₃^2- --> CaCO₃ (s)
Action of dilute acetic acid
BaCO₃ + 2H⁺ --> Ba²⁺ + H₂O + CO₂ (g)
SrCO₃ + 2H⁺ --> Sr²⁺ + H₂O + CO₂ (g)
CaCO₃ + 2H⁺ --> Ca²⁺ + H₂O + CO₂ (g)
Action of potassium chromate
Ba²⁺ + CrO₄^2- --> BaCrO (s) barium chromate.
Calcium and strontium chromates are soluble in acetic acid, so do not precipitate.

12.11.7.6 Group VI Magnesium, sodium and potassium, Mg, Na, K
1. If calcium was found in Group V, add to the filtrate ammonium oxalate solution and boil. Filter, and reject the precipitate of calcium oxalate. If calcium was absent from Group V, omit this step. Divide the filtrate into two parts.
2a. Part I Add ammonia and sodium phosphate solution. Shake well and leave to stand. A white crystalline precipitate of magnesium ammonium phosphate indicates the presence of magnesium.
Mg²⁺ + HPO₄^2- + NH₄⁺ + OH^- --> MgNH₄PO₄ (s) + H₂0
[MgNH₄PO_{4 =} magnesium ammonium phosphate]
2b. Part II Evaporate to dryness in an evaporating basin or platinum foil). Heat until no more fumes from dissociating ammonium compounds are seen. Examine residue by flame test. A persistent gold yellow flame indicates the presence of sodium. A lilac flame indicates the presence of potassium. If sodium is present, examine the flame through blue glass for potassium.
See 12.11.3.10: Confirmatory tests with original solution or solid, magnesium, potassium, sodium