School Science Lessons
2018-11-04
Please send comments to: J.Elfick@uq.edu.au

Chemistry Potassium
Table of contents
Potassium
Potassium properties: 7.2.2.35
Potassium compounds

Potassium, K
See: Potassium Elements, Compounds, (Commercial)
Potassium: 12.14.0
Potassium safety: 12.14.01
Potassium, K, Table of Elements
Potassium deficiency in soil: 1.12.0
Potassium deficiency symptoms: 1.2.4
Potassium, pieces (in liquid paraffin), toxicity: 3.6.12
Potassium safety: 12.14.01
Storing sodium and potassium: 3.4.13.9
Tests for potassium, sodium perchlorate: 12.11.3.25
Tests for potassium, tetraphenylborate: 12.11.3.1.1
Chemicals Not permitted in schools: 15.10.0 (See potassium and compounds) 12.11.3.1.1.

7.2.2.35 Potassium
Potassium experiments
Potassium, K (Dutch potasch, potasschen, potash) (Latin: kalium, K), metal, potassium rod stored in mineral oil, AAS solution
Toxic if ingested or contacts skin
Potassium is a soft and shiny white alkali metal, highest metal in the reactivity series so does not occur in the free state.
Potassium is about 2.5% of the earth's crust, is available as the metal in liquid paraffin and is used widely in chemistry.
Potassium is the " K" in the common fertilizer NPK, usually as K2O.
. Reacts with dilute HCl or H2SO4 to form H2 and metal ion, reacts with concentrated oxidizing acids, HNO3 or H2SO4 to produce high
oxidation number ions, and sulfur dioxide SO2 or nitrogen dioxide, NO2,
Potassium reacts with cold water and reacts with air to form peroxides.
Potassium has less concentration in extra cellular fluids than in intracellula fluids, where it is the primary cation.
Potassium ions are lost in sweat along with sodium ions.
Potassium metal is banned in many school systems.
Potassium reacts violently with water to form hydrogen gas that may ignite or explode.
Destroy potassium safely with 2-methylpropan-2-ol.
Potassium forms a crust of yellow oxide that may explode when cut.
For school science experiments use sodium or lithium instead of potassium.
Atomic number: 19, Relative atomic mass: 39.0983, r.d. 0.86, m.p. = 63.7oC, b.p. = 774oC.
Specific heat capacity: 753 J kg-1 K-1.

Potassium compounds
Illite, KAl4(Si, Al)8O20(OH)4, KAl4(Si, Al)8O18.2H2O, most common clay mineral Langbeinite, K2Mg2(SO4)3
Matches, safety matches, potassium chlorate
See diagram 3.1.2.6a: Matchbox
Plant nutrients from plant ash: 5.25
Poisons and First Aid (See potassium salts in table): 3.10.0
Potassium carbonate, K2CO3
Potash alum, aluminium potassium sulfate, KAl(SO4)2.12H2O
Potassium salts
Prepare chrome alum: 12.14.4
Prepare potash from ash: 5.40
Prepare potash alum from its constituent salts: 12.14.1
Prepare potash alum with aluminium foil: 12.14.2
Prepare potassium dichromate: 12.5.6
Prepare potassium permanganate: 12.8.3
Reactions of potassium salts with water: 14.2.1
Solubility in water of different salts: 3.9 (Table)
Sports drinks (electrolytes): 15.8.6
Superphosphate production: 12.14.5.

Potassium salts
Potassium acetate, CH3COOK, completely dissociated into ions, (E 261 acidity regulator, preservative, in sauces and pickles)
Potassium adipate, E357 (acidity regulator, buffer)
Potassium alginate, KC6H7O6, food stabilizer, thickener, emulsifier
Potassium aluminium silicate, E555: 35.15.0
Potassium aluminium sulfate, KAl(SO4)2.12(H2O), "alum"
Potassium amide, Highly toxic, Violent reaction with water, Not permitted in schools
Potassium antinomate, KSb(OH)6
Potassium ascorbate, KC6H7O6, E303, (antioxidant)
Potassium benzoate, C6H5COOK, preservative, E212
Potassium biphthalate
Potassium borohydride
Potassium bromate, KBrO4
Potassium bromide, KBr
Potassium carbonate, K2CO3
Potassium chlorate, KClO3
Potassium chloride, KCl
Potassium chromate, K2CrO4
Potassium chromium sulfate, KCr(SO4)2.12H2O
Potassium citrate, monobasic, potassium-2-hydroxypropane-1, 2, 3- tricarboxylate, E332 (food acid, acidity regulator, stabilizer)
Potassium cobaltcyanide, potassium hexacyanocobaltate
Potassium cyanate, Toxic if ingested but not as toxic an cyanides
Potassium cyanide, KCN, Extremely poisonous, Not permitted in schools
See diagram: Potassium cyanide
Potassium dichromate, K2Cr2O7
Glass cleaning with potassium dichromate solution
Potassium dihydrogen phosphate, KH2PO4, potassium dihydrogen orthophosphate (V) (in baking powder, buffering agents, nutrient
solutions)
Potassium dihydrogen phosphate, potassium phosphate monobasic, For 0.1 M solution, 13.6 g in 1 L water, Toxic if ingested
Potassium disulfite, potassium metabisulfite
Potassium ethanoate, CH3COOK, potassium acetate, white crystalline powder
Potassium ferricyanide, K3Fe(CN)6
Potassium ferrocyanide, K4Fe(CN)6.3H2O
Potassium fluoride, skin irritant, with acids forms Toxic HF fumes, Not permitted in schools
Potassium fluoride, Solution < 3%, Not hazardous
Potassium fumarate, E366 (food acid)
Potassium hexacyanocolbaltate, potassium cobaltcyanide, Toxic if ingested
Potassium hexacyanoferrate (III)
Potassium hexafluorophosphate
Potassium hydrogen carbonate, KHCO3
Potassium hydrogen ethanedioate, potassium hydrogen oxalate
Potassium hydrogen oxalate, Harmful, in alkali solutions
Potassium hydrogen phosphate, K2HPO4
Potassium phosphate dibasic, Toxic if ingested: 5.4.3
Potassium hydrogen phthalate, Harmful, primary standard to prepare volumetric base solutions, alkali solutions
Potassium hydrogen sulfate, KHSO4, potassium bisulfate
Potassium hydrogen tartrate (KHC4H4O7)
Beeswing
Argol
Potassium hydroxide, KOH
Potassium iodate, KIO3
Potassium iodide, KI
Potassium lactate, E326 (humectant, bulking agent, acidity regulator)
Potassium magnesium sulfate, K2SO42MgSO4
Potassium malates E351 (acidity regulator)
Potassium metabisulfite (preservative, antioxidant): E224
Potassium monoxide, "potash", K2O, potassium monoxide equivalent in NPK fertilizer, but not K2O itself
Potassium niobate, KNbO3, perovskite ferroelectric crystal
Potassium nitrate, KNO3
Potassium nitrite, KNO2
Potassium oxalate, potassium ethanedioate, potassium ethanedioate-1-water, toxic fumes if heated
Potassium oxalate, Solution / mixture <5%, Not hazardous
Potassium perchlorate, KClO4
Potassium periodate, KIO4, ACS reagent
Potassium permanganate, KMnO4
Potassium peroxymonosulfate, swimming pool: 18.7.49
Potassium persulfate, K2S2O8
Potassium phosphate dibasic, Toxic if ingested: 5.4.3
Potassium phosphate dibasic, Harmful if ingested, skin irritant
Potassium phosphate, E340 (mineral salt, acidity regulator, stabilizer)
Potassium propionate, E283 (preservative)
Potassium pyrosulfate, potassium disulfate, K2S2O7, catalyst, the S2O72- ion looks like a dichromate ion
Potassium sodium tartrate, C4H4KNaO6
Rochelle salt, KNaC4H4O6.4H2O
Potassium sorbate, C6H7KO2, food preservative and additive E202, inhibits yeast and moulds, allergic reactions
Potassium sulfate, K2SO4
Potassium sulfide, K2S
Potassium superoxide, KO2, oxidizing agent, oxygen source
Potassium tartrate, argol, K2C4H4O6, E336 (acidity regulator, stabilizer)
Potassium tert-butoxide, potassium t-butoxide, K+(CH3)3CO, non-nucleophilic base
Potassium tetraborate, potassium tetraborate tetrahydrate, K2B4O74H2O, solvent of metallic oxides, lubricant
Potassium tetrachloropalladate, potassium tetrachloropalladium, Cl4KPd
Potassium thiocyanate, KSCN
Potassium triiodide, KI3, iodine water, Lugol's solution, (aqueous KI solution + dissolved I2, I2KI)

Potassium alum, KAl(SO4)2.12(H2O), "alum"
Alums
Potassium alum, aluminium potassium sulfate, potash alum, potassium aluminium sulfate, aluminium potash, potash alum, Harmful
Al2(SO4)3.K2(SO4).24H2O, K2SO4.Al2(SO4)3.24H2O
Artificial gemstones, potassium sulfate, aluminium sulfate: 12.10.2.6.1
Fireproof cloth: 3.5.11
Kalinite, Aluminium potassium sulfate
Potassium alum and clay suspensions: 7.6.2.2
Prepare invisible inks: 4.19
Prepare potash alum from its constituent salts: 12.14.1
Prepare potash alum with aluminium foil: 12.14.2
Prepare self-leavened flour, "self-raising flour": 19.1.8.1
Recycle aluminium drink-cans as potassium aluminium sulfate, alum: 12.7.3.1
Tests of river, lake or ocean (turbidity): 18.5.1

Potassium bromate, KBrO3
Potassium bromate, KBrO3, Toxic, skin irritant, powerful oxidizing agent, explosive mixture with combustibles
Potassium bromate, Solution < 0.1%, Not hazardous
Potassium bromate, flour treatment agent E924, effective after making dough
Potassium bromate with propanedioic acid, double autocatalytic reaction, oscillating reaction: 17.3.7
Prepare iodic acid, HIO3, and potassium iodate, KIO3: 12.19.6.3.

Potassium bromide, KBr
Potassium bromide, Toxic if ingested, colourless, white, cubic crystals or granules, r.d. 2.75, m.p. 730oC (photography, formerly a
sedative and was supposed to be put in tea of soldiers to control sexual urges), used to prepare bromine water.
For 0.1 M solution, 12 g in 1 L water.

Potassium carbonate, K2CO3
Potassium carbonate (anhydrous or hydrated), skin irritant, toxic if ingested
Lactic acid with potassium carbonate: 16.1.5.1.1.

Potassium carbonate, anhydrous, "potash" (pearl ash, industrial potassium carbonate), salt of tartar, white, odourless granules,
anhydrous potassium carbonate, r.d. 2.29, m.p. 891oC (anhydrous is hygroscopic, cakes in moist air), E501, strong alkaline solution.
For 0.1 M solution of potassium carbonate, use 13.8 g in water (soap making, glass making, sourdough).

Potassium chlorate, KClO3
Potassium chlorate, storage safety, KClO3, potassium chlorate (V), potassium perchlorate, spontaneous combustion, Oxidizing,
Not permitted in schools
Potassium chlorate, chlorate of potash
Potassium chlorate and potassium persulfate as oxidizing agents: 15.2.13
Potassium chlorate in pyrotechnic flash powders: 15.2.13.2
Chlorates, hazards (potassium chlorate and manganese dioxide): 3.7.2
Combustible solids, potassium chlorate: 3.5.10
Concentrated sulfuric acid with potassium chlorate, KClO3: 12.19.8.4
Decomposition of chlorates, potassium chlorate: 3.30.11
Gummi bears (gummi fruit) with potassium chlorate: 15.2.13.1
Heat potassium chlorate, manganese dioxide catalyst: 17.3.11
Sparklers (make sparklers): 15.2.13.3
Storing sodium chlorate and potassium chlorate: 3.4.13.10
Sugar with potassium chlorate, spontaneous combustion: 17.3.4

Potassium chlorate, KClO3, potassium perchlorate, Berthollet's salt (Claude Berthollet 1748-1822), colourless, white, odourless,
monoclinic crystals, r.d. 2.32, m.p. 368oC then decomposes, explodes in contact with sulfur compounds (in explosives, fireworks and
weed killers).
Do NOT use potassium chlorate to prepare oxygen with manganese dioxide catalyst.

Potassium chloride, KCl
E508 Potassium chloride
Ice melts, de-icers: 7.4.3.3
Muriate of potash, KCl: 6.17.2.1
Tests for electric polarity, potassium chloride with phenolphthalein: 3.4.5

Potassium chloride, KCl, sylvite (sylvine), mineral, muriate of potash fertilizer, white, odourless, cubic crystals or powder, slightly
hygroscopic, diet salt substitute, Toxic if ingested, extracted from waters of Dead Sea, sold as "lite salt".
Low cost: from supermarkets as "sodium free salt", from garden supply stores as potassium fertilizer.

Potassium chromate, K2CrO4
Coloured precipitates, double decomposition reactions: 12.2.1c

Potassium chromate, K2CrO4, Highly toxic if ingested, carcinogenic, sensitizes skin
Potassium chromate, Solution < 0.5% Not hazardous
Potassium chromate, K2CrO4, lemon yellow crystals, m.p. 975oC, alkaline aqueous solution.
Potassium chromate, as with other chromium (VI) salts, may be carcinogenic so handle it with care.
However, when used in dilute solution, near neutral pH, it is relatively safe.
When mixed with acid, chromate ions, CrO42-, first form dichromate ions, Cr2O72-, then chromic acid, H2CrO4.
Solutions containing chromic acid are powerfully oxidizing and highly corrosive.
Do NOT use the cleaning mixture called chromic acid, prepared by dissolving a metal chromate or dichromate in concentrated
sulfuric acid.
This cleaning mixture is NOT permitted in schools because it is dangerously corrosive to skin and eyes, and is probably no more
effective as a cleaning agent than strong detergent solutions or a suitable solvent.
The reactions of potassium chromate and dichromate with sulfur, carbon, magnesium, aluminium and phosphorus are dangerous and
are NOT permitted in schools.

Potassium chromium sulfate, KCr(SO4)2.12H2O
Potassium chromium sulfate, K2SO4.Cr2(SO4)3.24H2O, chrome alum, chromium alum, chromium potassium sulfate, alum and mordant,
chromic potassium sulfate, Toxic if ingested
Properties of chrome alum: 12.14.4.1.

Potassium dichromate, K2Cr2O7
Breath test for alcohol using potassium dichromate: 15.2.11
Coloured precipitates, double decomposition reaction: 12.2.1c
Diffusion in liquids: 10.1.3
Extract iodine from kelp: 10.13.2
Potassium dichromate as an oxidizing agent: 15.2.3
Potassium dichromate solution: 2.20.1
Prepare crystal clusters: 3.54.6 (See:2. )
Prepare ethanal with potassium dichromate: 16.3.2.7
Prepare potassium dichromate: 12.5.6
Reactions of dichromates, potassium dichromate: 12.5.3
Solubility and temperature, solubility of salts in water: 3.10
Solubility of potassium dichromate and temperature: 7.7.6.17.7.6.1

Potassium dichromate, K2Cr2O7, potassium bichromate (VI), Toxic, Corrosive, Oxidizing, Not permitted in schools
Potassium dichromate ACS reagent (Poison, OXD 1479), potassium dichromate (VI)
Potassium dichromate, orange-red crystals, Toxic, Corrosive, Oxidizing
Potassium dichromate, For 0.1 M solution, 29.4 g in 1 L water
Low cost: from pottery supply stores, may be called "potassium bichromate"
Potassium dichromate, K2Cr2O7, potassium bichromate, red prussiate of potash, ferro prussiate, bichrome, orange to red, odourless,
monoclinic crystals or granules, r.d. 2.69, m.p. 398oC, strong oxidizing agent, toxic and fire risk from oxidation.
It was formerly used mixed with sulfuric acid to clean laboratory glassware but nowadays this procedure NOT permitted in schools.
Oxidation reactions involve the reduction of solutions of chromate or dichromate ions that cause colour changes from yellow or
orange to pale green or colourless solutions.
The reactions with the formation of an insoluble metal chromate give brightly coloured precipitates.
Do NOT attempt to isolate these precipitates because they are carcinogenic.
Prepare these precipitates in the smallest quantities that allow them to be seen.
Do NOT use potassium dichromate solution to colour water for demonstrations.
Used in machines to breath test for alcohol.

Potassium hydrogen sulfate, KHSO4
Potassium hydrogen sulfate, potassium bisulfate, Toxic, corrosive to skin and eyes, SO2 formed when heated.

Glass cleaning with potassium dichromate solution
Glassware should be clean and dry before use.
When an experiment is completed, the students should discard leftover materials, and rinse all glassware in water.
Cleaning is best done immediately after use as this prevents the staining of work surfaces and the hardening of materials on the glass.
Strong cleaning solvents should be used by the teacher, not by students.
Glassware should be clean and dry before use.
When an experiment is completed, the students should discard leftover materials, and rinse all glassware in water.
Cleaning is best done immediately after use as this prevents the staining of work surfaces and the hardening of materials on the glass.
Strong cleaning solvents should be used by the teacher, not by students.

Potassium ferricyanide, K3Fe(CN)6
Potassium ferricyanide, potassium hexacyanoferrate (III), Toxic if ingested
Decomposition of ferricyanides, potassium ferricyanide: 3.30.12
Potassium ferricyanide (III), K3Fe(CN)6.3H2O, (powder K3Fe(CN)6), red prussiate, potassium hexacyanoferrate (III),
potassium ferric cyanide, ruby red, monoclinic crystals, heat decomposes then melts, r.d. 1.89, case-hardening agent, forms good
crystals, used in redox experiments, chemical analysis uses characteristic colour reactions, heating with concentrated sulfuric acid forms
carbon monoxide gas (in dyeing, etching blueprint paper, fertilizer).
Potassium ferricyanide is Highly toxic, boiling with dilute acids forms cyanide gas.
Potassium ferricyanide with concentrated ammonia solution may explode.

Potassium ferrocyanide, K4Fe(CN)6.3H2O
Potassium ferrocyanide, potassium ferrous cyanide, potassium hexacyanoferrate (II), potassium hexacyanoferrate (II)-3-water, yellow
prussiate of potash, prussiate of potassium, Environment danger, Toxic if ingested, coordination compound, yellow monoclinic crystals
or powder, r.d. 1.85, case hardening agent, used to detect Fe3+ ions, efflorescent, anhydrous at 100oC, direct heating of the solid forms
cyanogen gas.
Highly toxic, heating with concentrated sulfuric acid forms carbon monoxide gas,
Highly toxic, boiling with dilute acids forms cyanide gas (CN)2.
Highly toxic, Mixtures with nitrite salts are explosive.

Potassium hydrogen carbonate, KHCO3
Potassium hydrogen carbonate, potassium bicarbonate (impure potassium bicarbonate "American saleratus"), colourless, odourless,
white granules, r.d. 2.17, used in buffers, baking powder, aerated waters, antacid medicines, carbon dioxide fire extinguishers, some
detergents, laboratory reagent.
Potassium hydrogen carbonate occurs as calcinite mineral.

Potassium hydrogen tartrate (KHC4H4O7)
Potassium hydrogen tartrate, cream of tartar, potassium bitartrate, HOOC(CHOH)2COOK, KO2CCH(OH)CH(OH)CO2H,
potassium L-tartrate monobasic, potassium hydrogen L-tartrate, tartaric acid monopotassium salt, L(+)-Tartaric acid monopotassium
salt, potassium hydrogen L-tartrate, tartaric acid monopotassium salt, potassium bitartrate, potassium hydrogen tartrate, tartar, acid
potassium tartrate, beeswing, argol.
Potassium hydrogen tartrate is a white crystalline acid salt, purified form of brown crystals argol from deposits in wine vats, used in
baking powder.

Beeswing
Beeswing is the filmy, veined "crust" in old port, which has finally fermented in the bottle.
Common names: Cream of tartar, Potassium hydrogen tartrate (KHC4H4O7), potassium bitartrate.

Argol
Argol, tartar (beeswing), acid potassium tartrate, white crystalline acid salt, purified form of brown crystals argol,
(used in baking powder, from deposits in wine vats, the "crust" in crusted port that has finally fermented in the bottle).
Common names: Cream of tartar, Potassium hydrogen tartrate (KHC4H4O7), potassium bitartrate.

Potassium hydroxide, KOH
Potassium hydroxide, KOH, caustic potash, potash lye, Extremely corrosive to skin, eyes
Potassium hydroxide, Solution > 4M (24%), Extremely corrosive to skin, eyes
Potassium hydroxide, Solution < 4M (24%), Extremely corrosive to skin, eyes
Potassium hydroxide, Solution > 1M (6%), Extremely corrosive to skin, eyes
Potassium hydroxide, Solution < 1M (6%), Corrosive to skin, eyes
Potassium hydroxide, Solution > 0.1M (0.5%), Corrosive to skin, eyes
Potassium hydroxide, Solution < 0.1M (0.5%), Not hazardous
Potassium hydroxide 2 M solution, dissolve 110 g of KOH sticks in 1 L water
Alkalis, Safety instructions: 5.3.3
Bases, properties of bases, alkalis: 12.7.0
Potassium hydroxide with chlorazol black (study of fungi): 6.9
Prepare iodic acid, HIO3, and potassium iodate, KIO3: 12.19.6.3
Prepare potash alum from its constituent salts: 12.14.1
Prepare soap: 12.12.1
Reactions of chlorine with alkalis, bleaching powder: 13.4.15
Respiration is a form of combustion: 8.6.5.

Potassium hydroxide, KOH, caustic potash, lye, potash, white pellets, KOH "sticks" or rods in water, lumps, flakes, sticks, very
deliquescent, absorbs CO2 and SO2 from air better than sodium hydroxide because more soluble, used to prepare soft soap and
alkaline storage cells, heat from dissolving in water, r.d. 2.044, m.p. 380oC, E525, potassium lye, damages eyes and body tissues.
KOH, solid, flake, pellets, 1 M analytical reagent, caustic potash
Potassium hydroxide, as a solid or concentrated solution is extremely corrosive to the skin and eyes.
Always wear safety glasses when handling potassium hydroxide, even with dilute concentrations.
If potassium hydroxide enters the eye, rinse the eye instantly with water.
Solutions of potassium hydroxide on the skin feel soapy because fats in the skin are broken down to form anions of fatty acids,
e.g. stearate, palmitate and oleate that give the solution a slippery feel.
When potassium hydroxide dissolves in water, a large amount of heat is released.
It sometimes causing the solution to boil violently if it has NOT been stirred, so always stir solutions in that potassium hydroxide is
dissolving to dissipate heat and to provide a uniform concentration throughout the solution.
Potassium hydroxide solutions boil at a higher temperature than pure water.
Hygroscopic so keep in sealed plastic container.
It is more corrosive to eyes than acids.

Potassium hydrogen phosphate, K2HPO4
Potassium hydrogen phosphate, K2HPO4, potassium hydrogen orthophosphate, dipotassium hydrogen phosphate (V),
di-potassium monohydrogen phosphate, di-potassium hydrogen orthophosphate,
Microbiology chemicals, K2HPO4 (MERCK No. 5099, SIGMA No. P 3786)
Food additive, culture nutrient
Micro-organisms and water pollution: 4.3.11
Prepare solutions of known concentration: 5.4.1.0 (See Dipotassium hydrogen orthophosphate in table)
Buffer reagent, phosphate buffer reagent (potassium hydrogen phosphate): 9.2.25.

Potassium iodide, KI
See: Potassium iodide (Commercial)
Potassium iodide, KI, Potassium iodide paper, Potassium iodide powder pillows
Potassium iodide, For 0.1 M solution, 16.6 g in 1 L water
Potassium iodide crystals, KI, photography, ingredient of iodized "table salt"
Iodine clock reaction, hydrogen peroxide, potassium iodide: 17.1.6
Potassium iodide with hydrogen peroxide, reverse colour change: 17.3.5
Coloured precipitates, double decomposition reactions: 12.2.1c
Electrolysis of potassium iodide solution, electrolytic writing: 15.5.23
Iodine solution, tests for starch: 1.6
Potassium iodide with potassium iodate (rate of reaction depends on concentration): 17.5.4.2
Reactions of copper (II) ions, Cu2+: 12.7.2
Tincture of iodine, I2.

Potassium iodide, KI, colourless solution, white crystals or granules, r.d. 3.12, m.p. 698oC, lightly deliquescent in moist air, bitter taste,
separated from potassium iodate by fractional crystallization, becomes yellow when iodine lost to air (chemical analysis, photography,
additive to prepare iodized "table salt" to iodine deficiency, e.g. goitre), (in tincture of iodine medicine, solvent for iodine to form the
brown triiodide ion I3-, KI3 (aq), used as a test for starch).
Detects presence of Pb2+ ions when yellow precipitate of lead iodide forms.
If KI solutions become yellow from iodine formation add sodium hydrogen sulfite solution to make solution colourless again.

Potassium iodate, KIO3
Potassium iodate, potassium iodate (V) powder, potassium iodate (VII), potassium periodate, Toxic, may ignite with combustibles or
organic compounds
Prepare iodic acid, HIO3, and potassium iodate, KIO3: 12.19.6.3
Table salt and rock salt: 19.1.16.

Potassium iodate, white, monoclinic crystals or granules, slightly deliquescent, r.d. 3.89, m.p. 560oC, oxidizing agent (ingredient of
iodized "table salt", analytical reagent), store out of light (potassium iodate is potassium salt of iodic acid).
It may ignite combustibles or organic compounds and produce toxic fumes.
Violent reaction with aluminium, magnesium, carbon, sulfur, phosphorus.
Violent reaction with sodium bisulfite if water added.
Potassium iodate forms toxic fumes with concentrated sulfuric acid.

Potassium nitrate, KNO3
Potassium nitrate, nitre (US niter), saltpetre (US saltpeter), formerly sodium carbonate, potassium nitrate (V), nitrate of potash
Potassium nitrate, colourless crystals or white powder, Preservative E249, For 0.1 M solution, 10.l g in 1 L water, Oxidizing
Ammonium nitrate cold pack: 14.2.4
Reactions of ammonium salts and potassium salts with water: 14.2.1
Combustible solids: 3.5.10
Combustion of potassium nitrate, fire line on paper, string fuse: 14.2.6
Decomposition of nitrates: 3.30.4
Low cost: from garden stores as potassium nitrate or "saltpeter" fertilizer, from pottery stores, test reagents
Micro-organisms and water pollution: 4.3.11
Prepare potassium nitrate from manure: 3.9.1
Potassium nitrate with water: 14.2.5
Prince Rupert's Drops, tempered glass, toughened glass: 34.5.2.9
Refrigerants: 14.2.7
Solubility and temperature, solubility of salts in water: 3.10
Solubility of different salts and temperature: 7.7.5

Potassium nitrate, KNO3, "saltpetre", (US saltpeter) (occurs as nitre, niter, Bengali saltpetre), colourless, odourless, trigonal or rhombic
crystals or white granules, r.d. 2.11, m.p. 333oC, Preservative E252, strong oxidizing agent that decomposes at 400oC to lose O2,
(nitrate of potash fertilizer, fireworks, food preservative, explosives, e.g. gunpowder), E252.
Potassium nitrate is a powerful oxidizing agent and forms explosive mixtures with most combustible materials.
Potassium nitrate has relatively low toxicity, and can be safely used in aqueous solution.
Do NOT mix potassium nitrate with charcoal, sulfur, red phosphorus or active metals, e.g. Na, powdered Al, Mg, cyanides, sulfides,
thiosulfates, ammonium salts, acetates, household sugar or combustible material, because these mixtures may be explosive.
The demonstration of explosives is NOT permitted in schools.
If testing production of oxygen from heated solid and lighted splint is accidentally dropped into molten salt, explosion may occur.
Gunpowder (black powder, black gunpowder), a mixture of potassium nitrate, charcoal and sulfur,
the explosive propellant formerly used in firearms now superseded for modern firearms by smokeless powder, a mixture of potassium
salts.
Common names: Saltpetre, saltpeter (used as stump remover, agricultural fertilizer, meat preserver.)

Potassium nitrite, KNO2
Potassium nitrite, potassium nitrite (III), Toxic if ingested
Potassium nitrite, Solution <1%, Not hazardous
Potassium nitrite, KNO2, white to yellow deliquescent solid, m.p. 440oC, explodes above 600oC, used to detect presence of amino
groups inorganic compounds, reacts with acids to form toxic nitrogen dioxide gas, that reacts with oxygen in the air to form highly toxic
nitrogen dioxide gas.

Potassium perchlorate, KClO4
"Blaster Balls", potassium perchlorate + sulfur, exothermic reaction, (toy product)
Potassium perchlorate, Toxic, skin irritant, Violent explosive mixture with combustible, Not permitted in schools
Potassium perchlorate should not be used or stored in a school science laboratory.
Prepare potassium perchlorate by fractional crystallization, KClO4: 12.19.8.5

Potassium permanganate, KMnO4
Acidified potassium permanganate (VII) reactions, oxidizing agent in titrations: 15.2.4.4
Colour change of diluted potassium permanganate: 3.3.1
Ethanedioic acid-2-water (oxalic acid) with potassium manganate (VII), autocatalysis: 17.3.3
Potassium manganate (VII) oxidizes iron (II) to iron (III): 15.2.4.1
Potassium manganate (VII) oxidizes glycerol to carbon dioxide and water: 15.2.4.2
Potassium manganate (VII) solution liberates chlorine from hydrochloric acid: 15.2.4.3
Potassium permanganate, Condy's crystals (Agriculture): 16.6.11
Movement of ions, potassium permanganate solution: 3.4.1
Oxidation of glycerol by potassium permanganate: 12.12.4
Permanganates, hazards: 3.7.12
Prepare chlorine with hydrochloric acid / potassium manganate (VII): 13.4.1.2
Prepare ethanal with potassium manganate (VII): 16.3.2.2
Prepare oxygen gas with potassium manganate (VII): 3.49.4
Prepare potassium permanganate: 12.8.3
Reduce potassium manganate (VII) with hydrogen sulfide: 3.43.2
Reduce potassium manganate (VII) with sulfur dioxide: 3.51.2
Tests for alcohols, potassium manganate (VII): 16.1.3.1.1a
Tests for saturated hydrocarbons, acidified potassium manganate (VII) solution: 16.4.9.0.

Potassium permanganate, KMnO4, potassium manganate (VII), Condy's crystals (OXD 1490), Toxic
Potassium permanganate, KMnO4, potassium manganate (VII) (OXD 1490), Condy's crystals, Toxic if ingested, 0.2 M, 0.02 M,
analytical reagent, purple red crystals, dark purple, bronze with metallic sheen, odourless, rhombic crystals, r.d. 2.7, heat decomposes,
distinct sweet bitter taste, common strong oxidizing agent and disinfectant, chemistry analytical reagent, MnO4- ion.
Potassium permanganate is a powerful oxidizing agent that forms dangerously combustible or even explosive mixtures with oxidizable
materials, or combustible materials, e.g. red phosphorus, cyanides, thiosulfates acetates, sugar, charcoal, sulfur, phosphorus,
ammonium salts, active metal powders, organic compounds.
The solid is also spontaneously flammable on contact with glycerine, ethylene glycol and other organic compounds.
It forms violently explosive manganese heptoxide on mixing with concentrated sulfuric acid.
Oxygen gas is formed on heating the solid, but toxic fine particles of manganese oxides are produced simultaneously, so if the reaction
occurs in a test tube, place a plug of glass wool in the end of the tube to trap particles.
Do NOT use sulfuric acid for drying oxygen gas from decomposition of potassium permanganate, because the acid could accidentally
mix with the salt and react explosively.
For preparing oxygen gas, it is safer to use hydrogen peroxide and potassium permanganate, or hydrogen peroxide with manganese
dioxide catalyst.
If potassium permanganate is used for preparation of chlorine gas by reaction with hydrochloric acid, be sure that the solid is covered
with a layer of water and that hydrochloric acid is used, NOT sulfuric acid.
Acidified solutions are used as an oxidant in organic chemistry for the oxidation of aldehydes or alcohols.
Neutral solutions are used to distinguish between alkanes and alkenes.
Dilute aqueous solutions of potassium permanganate are relatively harmless and have been used medicinally for mouthwashes and
bactericides.
Potassium manganate (VII) is NOT a primary standard, so make up an approximate concentration and titrate it against an ethanoic
acid solution of known concentration.
Potassium manganate (VII) crystals are so dark it is difficult to see if all have dissolved when making up a solution.
Bottles of potassium manganate (VII) solution may have a brown precipitate around the top of manganese (IV) oxide, formed when
manganate (VII) ions react with water in the air.
Used to stain wood and furniture.
For water treatment, used for oxidation of Fe2+ --> Fe3+, and Mn2+ --> Mn4+, remove tastes and odours, disinfectant, control
nuisance organisms, control DBD (dielectric barrier discharge), of ozone.
Used as topical fungicide and antiseptic.
Solution of 1 g per litre controls powdery mildew and black spot plant diseases.
However, pink staining causes problems.
Potassium permanganate, Solution < 25%, Not hazardous
Low cost: from aquarium suppliers as crystals or aqueous solution, in test reagents, water purification suppliers.

Potassium persulfate, K2S2O8
Potassium persulfate, potassium peroxydisulfate, Toxic, skin irritant, white crystalline solid, mixture with combustibles burns fiercely,
solid decomposes on standing below 100oC.

Potassium sodium tartrate, C4H4KNaO6
Potassium sodium tartrate, potassium sodium tartrate-4-water, sodium potasium L-tartrate, Rochelle salt
Piezoelectricity (voltage produced by mechanical stress to crystals): 32.1.2.1
Hydrogen peroxide with potassium sodium tartrate, cobalt (II) chloride catalyst, visible activated complex: 17.3.1.4.

Rochelle salt, KNaC4H4O6.4H2O
Rochelle salt, potassium sodium tartrate tetrahydrate, Seignette salt, Seidlitz powder, is a double salt of tartaric acid
It has a saline cooling taste as a laxative, and the large deliquescent monoclinic crystals are piezoelectric and used in "crystal"
phonograph pickups.
E337
9.142.1
Prepare Fehling's solution: 9.142.1
Tests for proteins, biuret test: 16.6.5.

Potassium sulfate, K2SO4
Potassium sulfate, powder K2SO4, sulfate of potash fertilizer
Artificial gemstones, potassium sulfate, aluminium sulfates: 12.10.2.6.1

Potassium sulfate, K2SO4, sulfate of potash fertilizer, E515, white crystalline powder, prepared with potassium carbonate or potassium
hydroxide with sulfuric acid.
Potassium sulfate, For 0.1 M solution, 17.4 g in 1 L water
Fertilizer as source of potassium iron instead of KCl for chlorine-sensitive plants.

Potassium sulfide, K2S
Potassium sulfide, E225 (preservative, antioxidant)
Potassium sulfide, K2S, Highly toxic if ingested, releases hydrogen sulfide gas, Not permitted in schools
Potassium sulfide, liver of sulfur: Alkaline mixture of mainly potassium polysulfides that turns silver black
Potassium sulfide, liver of sulfur, sulfurated potash, red-yellow to brown-red, deliquescent, analytical reagent and epilatory,
(depilatory, hair removing), dusts may explode.

Potassium thiocyanate, KSCN
Potassium thiocyanate, KSCN, potassium isothiocyanate, potassium sulfocyanate, Toxic if ingested
Potassium thiocyanate, colourless prisms, r.d. 1.89, m.p. about 173oC, deliquescent
Potassium thiocyanate, dilute solutions, Not hazardous
Thiocyanate (thiocyanato), S-CN-, monodentate ligand
Group III Insoluble hydroxides, Fe(OH)3, Cr(OH)3, Al(OH)3: 12.11.7.3

3.9.1 Prepare potassium nitrate from manure
The mineral form of potassium nitrate, nitre, saltpetre (UK), saltpeter (US) cannot be made in any considerable quantity in less than
six or eight months.
Use rotted manure ("black earth"), old mortar or wood ashes mixed with straw.
Each week, add the richest kinds of liquid manure, e.g. urine, dung water, water from privies, cesspools, drain to keep the heap moist,
but not wet.
Drain off any superfluous liquid to a tank to be used in later watering the heaps.
Turn the whole heap turned over every month to hasten the process of nitrification.
During the last few months of the process, heaps must be kept moist by water only.
As the heap ripens, the nitre is brought to the surface by evaporation, as a white efflorescence, detectable by the taste.
A more accurate method is by leaching a small quantity of the earth, and boiling to dryness, and weighing the salt.

2. Repeated leaching with water to produce a ley is used to get as strong a solution as possible, and extract most of the nitre.
After the sixth leaching, the earth is considered as sufficiently exhausted.
The leys thus obtained are used upon fresh earth until the solution is of sufficient density to bear an egg when it then contains about a
pound of salt to a gallon of liquid.

3. The ley contains, nitrate of potash (nitre, potassium nitrate), nitrate of lime, nitrate of magnesia, sodium chloride and potassium
chloride.
To convert all other nitrates into nitrate of potash, add wood ashes.
The potash of the ashes takes all the nitric acid of the other nitrates forming the nitrate of potash (nitre), and the lime and magnesia are
precipitated as an insoluble sediment.
Also, the ashes can be mixed with the nitrified earth and leached together or the saltpetre ley filtered through wood ashes, or the ley of
ashes added to the saltpetre ley.

4. Put the ley in a boiler.
The ley still contains common salt (sodium chloride), and other impurities.
However, nitre, it is much more soluble than common salt in boiling water, but much less soluble in cold water.
As the boiling proceeds and the solution becomes more concentrated, the common salt is precipitated in small crystals as a sandy
sediment to be raked out.
Remove organic matter rising as scum.
Leave the boiler to cool when the concentration has reached almost the point of saturation, determined by letting fall a drop of the
boiling liquid upon a cold metallic surface so that if it quickly crystallizes it is time to stop the boiling.
As the ley cools, most of the nitre separates as crystals, which sink to the bottom.
Remove the crystals and return the mother liquor to the boiler, or used in watering the heaps.
The crude saltpetre still contains 15-20% of impurities, mainly sodium chloride, potassium chloride and organic matter.

5. Refining
Starting with saturated solution of nitre, add glue that seizes upon the organic matter and rises as scum to be removed.
Continue the boiling until the liquid is clear, then cooled and constantly stirred until most of the nitre is deposited in very fine,
needle-like crystals, called saltpetre flour.
Wash off all adhering mother liquor.
The nitre is now dried by gentle heat and constant stirring, and may be considered quite pure, and fit for the manufacture of gunpowder.

6. Analysis
1. A saturated solution of any salt will not dissolve any more of that salt, but will freely dissolve other salts.
2. Nitre mixed with charcoal and heated is converted into carbonate of potash but common salt is not affected.
However if saltpetre is mixed with charcoal alone and then heated the reaction is violent and explosive.
To moderate the violence, the saltpetre is mixed with common salt, which does not interfere with the reaction.
Use one part crude saltpetre, four parts common salt, and one-half part charcoal, heated in an iron spoon, until reaction ceases.
The nitre is now changed into carbonate of potash to be dissolved in water and filtered then estimated by the quantity of sulfuric of
known strength necessary to neutralize it completely.
3. A strong hot solution of nitre crystallizes on cooling, and that the temperature at which crystals begin to deposit depends upon how
much nitre is in the solution, whatever the presence of impurities.
In a saturated solution of nitre, one hundred parts by weight of water at 32F contains 13.32 parts of nitre.

12.8.3 Prepare potassium permanganate
1. Potassium permanganate, dark purple crystals, blue metallic sheen, specific gravity 2.7, melting point 240oC, soluble in water,
sulfuric acid and acetone.
Used as an oxidizing agent, a disinfectant, as an anti-algal agent, in metal cleaning, in tanning, bleaching, and as a preservative for fresh
flowers and fruits.
2. Put 10 g of potassium hydroxide on a sand tray and heat gently to melt.
Add 1 g of potassium chlorate, mixing with a glass rod.
Add 7.5 g of manganese dioxide very gradually and continuing to stir.
When all has been added heat to bright red heat for fifteen minutes.
Leave to cool, break off the melt and grind to a fine powder in a mortar.
Transfer the powder to a 500 mL flask, add 200 mL of water and heat on a gauze.
During the boiling pass carbon dioxide into the solution.
At first the solution is green and contains potassium manganate:
6KOH + 3MnO2 + KClO3 --> 3K2MnO4 + KCl + 3H2O
Later it becomes purple potassium permanganate:
3K2MnO4 + 2CO2 --> 2KMnO4 + MnO2 + 2K2CO3
After boiling for ten minutes let cool and pour off through glass wool in a filter.
Wash the flask and return the filtrate to it.
Boil for a further ten minutes while carbon dioxide passes through, withdraw a drop of solution and place on a filter paper.
If the drop has a green centre continue the process until complete.
Finally cool and filter.
Transfer the solution to a large evaporating basin and evaporate until crystals appear, then set aside to crystallize.

12.14.0 Potassium
Potassium, K (Dutch potasch, potasschen, potash) (Latin: kalium, K), metal, potassium rod stored in mineral oil, AAS solution
Toxic if ingested or contacts skin
Potassium is a soft and shiny white alkali metal, highest metal in the reactivity series so does not occur in the free state, 2.5% of the
earth's crust, available as the metal in liquid paraffin and is used widely in chemistry, is the " K" in the common fertilizer NPK, usually
as K2O.
Reacts with dilute HCl or H2SO4 to form H2 and metal ion, reacts with concentrated oxidizing acids, HNO3 or H2SO4 to produce high
oxidation number ions, and sulfur dioxide SO2 or nitrogen dioxide, NO2, reacts with cold water and reacts with air to form peroxides.
Potassium has less concentration in extra cellular fluids than in intracellular fluids where it is the primary cation.
Potassium ions are lost in sweat along with sodium ions.
Potassium metal is banned in many school systems.
Potassium reacts violently with water to form hydrogen gas that may ignite or explode.
Destroy potassium safely with 2-methylpropan-2-ol.
Potassium forms a crust of yellow oxide that may explode when cut.
For school science experiments use sodium or lithium instead of potassium.
Atomic number: 19, Relative atomic mass: 39.0983, r.d. 0.86, m.p. = 63.7oC, b.p. = 774oC.
Specific heat capacity: 753 J kg-1 K-1.

12.14.01 Potassium safety
Potassium metal is banned in many school systems.
Potassium reacts violently with water to form hydrogen gas that may ignite or explode.
Destroy potassium safely with 2-methylpropan-2-ol.
Potassium forms a crust of yellow oxide that may explode when cut.
Use sodium or lithium instead of potassium.

12.14.1 Prepare potash alum from its constituent salts
Potash alum, K2SO4.Al2(SO4)3.24H2O,
Aluminium sulfate can form a double salt with the sulfate of a monovalent metal.
With potassium sulfate it forms potash alum, K2SO4.Al2(SO4)3.24H2O.
In other alums where Na or (NH4) = X, they have the formula: X2SO4.Al2(SO4)3.24H2O.
In other alums, the sulfate of other trivalent metals, Y, are substituted for aluminium sulfate, and they have the formula:
X2SO4.Y2(SO4)3.24H2O, i.e. X+.Y3+.2SO42-.12H2O.
The molecular weight of potassium sulfate = 174.
The molecular weight of hydrated aluminium sulfate Al2SO4.8H2O = 666.
So equi-molecular weights of these sulfates = 174: 666 = 1.45 g : 5.6 g.
Crystal-growing competitions often use potash alum and require competitors to grow the best single crystal of potash alum judged on
the following criteria: clarity, colourlessness, straight and sharp edges, smooth faces, and regular shape.
Dissolve 1.45 g of potassium sulfate in 15 mL of water.
Dissolve 5.6 g of aluminium sulfate crystals in 20 mL of hot water.
Mix the two solutions and leave until the next day.
Select a crystal with a regular shape and let it to grow in the solution.
Dissolve the rest of the crystals in the minimum of water and leave to form new crystals.

12.14.2 Prepare potash alum with aluminium foil.
Potash alum, K2SO4.Al2(SO4)3.24H2O
Dissolve 1 g of potassium hydroxide pellets in 40 mL of water and add upwards of 1 g of aluminium foil.
When action ceases, excess magnesium must be left over.
2l + 2KOH + 2H2O --> 2KAlO2 + 3H2
Pour off the liquid and slowly add dilute sulfuric acid to it until litmus paper shows the solution is slightly acidic.
Heat the solution to evaporate it to a small volume, then leave to cool.
Filter off the crystals, then wash and dry them.
2KAlO2 + 4H2SO4 --> K2SO4 + Al2(SO4)3 + 4H2O.

12.14.4 Prepare chrome alum
Chrome alum, KCr(SO4)2, K2SO4.Cr2(SO4)3.24H2O, Cr2(SO4)3.K2SO4.24H2O
1. Reducing action of ethanol on potassium dichromate in acid solution.
Heat 7.5 g of potassium dichromate (VI) in 50 mL of water and leave to cool.
Add 6 mL of concentrated sulfuric acid, stand in ice and stir with a thermometer until cooled to 35oC.
Slowly add by drops 5 mL of ethanol and keep stirring so temperature remains below 50oC.
Leave the solution until the next day in a refrigerator.
Separate crystals from the remaining solution, wash with deionized water and dry with filter paper.
Choose a good crystal to grow in the solution of potash alum to form an overgrowth.
K2Cr2O7 + 4H2SO4 + 3CH3CH2OH --> K2SO4 + Cr2(SO4)3 + 7H2O + 3CH3.CHO (acetaldehyde)
Cr2O72- + 8H+ + 3CH3CH2OH --> 2Cr3+ + 7H2O + 3CH3.CHO (omitting the spectator ions).

2. Dissolve 60 g of potassium chromium sulfate in 100 ml water.
Stir common alum (aluminium potassium sulfate) into warm water until it will no longer dissolve.
Mix the two solutions to form deep violet-blue crystals.
Use a seed crystal in a saturated solution of chrome alum to form large diamond-shaped crystals, similar to potash alum.

3. Mix same molar concentrations of solutions of potassium sulfate and chromium (III) sulfate then allow to crystallize from a
saturated solution on a piece of weighted cotton.
If the solution is evaporated instead of leaving for crystallization, a mixture of crystals of potassium sulfate and chromium (III) sulfate
forms.

12.14.4.1 Properties of chrome alum
Chrome alum is also known as potassium chromium (III) sulfate, chromium (III) potassium sulfate,
chromium (III) potassium sulfate-12-water, chromium (III) potassium sulfate dodecahydrate.
It is a potassium double sulfate of chromium with formula [Cr2(SO4)3, K2SO4, 24H2O], [K2SO4, Cr2(SO4)3, 24H2O],
[CrK(SO4)2, 12H2O], so it is similar to potash alum.
It can be used in dyeing and in tanning leather.

See 12.5.0: Chromium ions in solution, [Cr(H2O)6]3+
1. Chrome alum crystals are soluble in water to form an violet-blue acid solution, about pH 3.

2. Boil a dilute solution of chrome alum in a test-tube.
The violet-blue colour of the solution turn green but when allowed to cool and stand the violet-blue colour returns.

3. Add washing soda solution, Na2CO3.10H2O, to a violet-blue solution of chrome alum in a test-tube.
A light green gelatinous precipitate of the hydrogen carbonate forms or a light blue precipitate forms with bubbles of carbon dioxide.
Add drops of hydrogen peroxide to the test-tube and boil the contents.
A yellow solution of sodium chromate forms.
Filter paper wetted with the yellow solution turns green in sulfur dioxide gas.

4. Add dilute ammonia to a solution of chrome alum.
A light green precipitate of chromium hydroxide forms.
This precipitate, like aluminium hydroxide, has a great attraction for dyes and is used as a mordant to make dyes stick to cloth.
Add small amount of ammonia
Cr(H2O)63+ --> Cr(H2O)3(OH)3
blue chrome alum --> light green neutral complex of chromium hydroxide
Add excess ammonia that replaces water as a ligand
Cr(H2O)3(OH)3 --> Cr(NH3)63+
light green chromium hydroxide --> violet hexaamminechromium (III) ion
(in test-tube violet over green precipitates).

5. Oxidize chromium (III) ions to chromium (VI) ions
Add excess sodium hydroxide solution to hexaaquachromium (III) ion solution to form green hexahydroxochromate (III) ion solution.
Cr(H2O)63+ --> Cr(H2O)3(OH)3
Heat with hydrogen peroxide solution to form bright yellow chromate (VI) ion solution.

12.14.5 Superphosphate production
See 6.42: Artificially-prepared fertilizers
Superphosphate fertilizer, a mixture of monobasic and dibasic calcium phosphate and calcium sulfate.
It is produced by concentrated sulfuric acid with phosphate rock.
Ca3(PO4)2 + 2H2SO4
Ca(H2PO4)2 + 2CaSO4
Wear goggles if superphosphate dust is produced.
Dispose of superphosphate in the garbage to landfill.

15.2.4.1 Potassium permanganate (VII) oxidizes iron (II) to iron (III)
Add potassium permanganate solution and drops of dilute sulfuric acid to iron (II) sulfate solution.
The manganate (VII) ions (MnO4-) are reduced to manganese (II) ions (Mn2+).
The iron (II) ions (Fe2+) are oxidized to iron (III) ions (Fe3+).
MnO4- (aq) + 8H+ (aq) + 5e--> Mn2+ (aq) + 4H2O (l)
5Fe2+ (aq) --> 5Fe3+ (aq) + e-
MnO4- (aq) + 8H+ (aq) + 5Fe2+ (aq) --> Mn2+ (aq) + 4H2O (l) + 5Fe3+ (aq)
Under alkaline conditions, MnO2 is precipitated, a reaction used in water treatment.
MnO4- + 2H2O + 3e- --> MnO2 + 4OH-.

15.2.4.2 Potassium permanganate (VII) oxidizes glycerol to carbon dioxide and water
Put 3 g of fine crystal potassium permanganate on a coffee in lid on sand.
Make a hole in the centre of the potassium permanganate and pour 1 mL glycerol (propane-1, 2, 3-triol) into the hole.
Boil then cool the glycerol first if it has already absorbed water.
Observe a bright pink flame and steam given off.
Dissolve the residue in water and note a green solution [Mn (VI)] and brown solid [Mn (IV)].

15.2.4.3 Potassium permanganate solution liberates chlorine from hydrochloric acid
Do this experiment in a fume cupboard.
Add potassium permanganate solution to 2 cm of concentrated hydrochloric acid solution in a test-tube with damp filter paper over
the edge of the opening.
Chlorine gas is given off.
Be careful! The damp filter paper becomes bleached.
2MnO4- (aq) + 16H (aq)+ + 10Cl- --> 2Mn2+ (aq) + 8H2O (l) + 5Cl2 (g)
10Cl- (aq) - 10e- --> 5Cl2 (chloride ion oxidized)
2MnO4- (aq) + 16H+ (aq) + 10e- --> 2Mn2+ (aq) + 6H2O (l) (permanganate ion reduced).

15.2.4.4 Acidified potassium permanganate (VII) reactions
Potassium permanganate (VII) is an oxidizing agent in titrations.
1. Prepare acidified potassium manganate (VII) solution by mixing 10 mL of 0.02 M potassium manganate (VII) solution with 20 ml.
of dilute sulfuric acid.
It is an oxidizing agent and irritating to the skin and eyes.
Wash any splashes off the skin.
It should be diluted further to give a pale pink solution to ensure that decolorization occurs readily.
For disposal, add sodium metabisulfite with stirring to the acidified potassium manganate (VII) solution residue until the solution is
colourless.
Flush to foul water drain.

2. Put potassium manganate (VII) solution in the burette.
Put the other solution in the receiving flask, acidified with dilute sulfuric acid, not hydrochloric acid.
Potassium manganate (VII) becomes colourless as it drops into the solution in the receiving flask until at the end point a slight trace of
permanent pink solution indicates excess of manganate (VII) ions.
The half equation for manganate (VII) ions in acidic solution:
MnO4- (aq) + 8H+ + 5e- --> Mn2+ (aq) + 4H2O (l).

3. Acidified potassium manganate (VII) solution oxidizes:
3.1 Iron (II) ions to iron (III) ions
Fe2+ (aq) --> Fe3+ (aq) + e-
5Fe2+ (aq) + MnO4- (aq) + 8H+ (aq) --> 5Fe3+ (aq) + Mn2+ (aq) + 4H2O (l)
3.2 Hydrogen peroxide solution to oxygen.
H2O2 --> O2 + 2H+ + 2e-
3.3 Ethanedioic acid to carbon dioxide (using much heat).
(COOH)2 --> 2CO2 + 2H+ + 2e-
3.4 Sulfate (IV) ions [sulfite ions] to sulfate (VI) ions [sulfate ions].
SO32- + H2O --> SO42- + 2H+ + 2e-
However, potassium manganate (VII) solution cannot be used in solutions containing ions it can oxidize, e.g. Cl-, Br-.