Home
Chemical substances
Potassium selenite

Potassium selenite

Last updated: March 19, 2023

Potassium selenite is an inorganic compound with formula K₂SeO₃.

Table of contents

Names

List of substance names

Nomenclature

Name

Typical name: Potassium selenite

Compositional nomenclature: Potassium selenite

Additive nomenclature: Potassium trioxidoselenate(2−)

Formulae and structures

List of formulae

Formula name

Formula

Typical formula: K₂SeO₃

Compositional formula: K₂SeO₃

Structural formula

Structural formula with no lone pair

Other structural formulas

Lewis structure

Colored Lewis structure

Properties

List of substance properties

Item

Value

Name: Potassium selenite

Formula: K₂SeO₃

Appearance: Colorless solid

Odor: Odorless

Molar mass: 205.165 g/mol

Density: –

Melting point: –

Boiling point: –

Constituents

Constituent ions

Ion	Name	Charge number	Number
K⁺	Potassium ion	1	2
SeO₃²⁻	Selenite ion	-2	1

Constituent atoms

Atom	Name	Oxidation state	Number
K	Potassium	+1	2
Se	Selenium	+4	1
O	Oxygen	−2	3

Ratio of atoms

Atom	Atomic weight	Number	Atomic ratio	Weight ratio
K	39.0983	2	33.33%	38.11%
Se	78.971	1	16.67%	38.49%
O	15.999	3	50.00%	23.39%

Thermodynamic properties

Phase transition properties

Item

Value

Enthalpy of fusion: –

Enthalpy of vaporization: –

Enthalpy of vaporization at 25°C: –

Enthalpy of other transition: –

Standard thermodynamic properties

State	Standard enthalpy of formation Δ_fH° kJ · mol⁻¹	Standard Gibbs energy of formation Δ_fG° kJ · mol⁻¹	Standard molar entropy S° J · K⁻¹ · mol⁻¹	Standard molar heat capacity at constant pressure C_p° J · K⁻¹ · mol⁻¹
Crystalline solid	−982.0^[1]	–	–	–
Ionized aqueous solution	−1013.8^[1]	−936.3^[1]	218.0^[1]	–

Solubility

Qualitative solubility

Reactive

Miscible

Very soluble: H₂OWater

Soluble

Slightly soluble

Very slightly soluble

Insoluble

Solubility in water (g/100 g)^[2]

0°C	10°C	20°C	30°C	40°C	60°C	100°C
169	186	203	217	217	220	217

Solubility curve (g/100 g)

Preparations

Chemical reactions

Electrolytic dissociation

Electrolytic dissociation of potassium selenite yields potassium ion and selenite ion.

Electrolytic dissociation of potassium selenite: K₂SeO₃Potassium selenite
⟶
2K⁺Potassium ion + SeO₃²⁻Selenite ion

Reaction with strong acid

The reaction of potassium selenite and strong acid yields salt of strong acid and selenous acid.

Reaction of potassium selenite and hydrogen chloride ◆ Δ_rG −56.4 kJ/mol K 7.60 × 10⁹ pK −9.88: K₂SeO₃Potassium selenite + 2HClHydrogen chloride
⟶
2KClPotassium chloride + H₂SeO₃Selenous acid

Reaction of potassium selenite and hydrogen bromide ◆ Δ_rG −56.4 kJ/mol K 7.60 × 10⁹ pK −9.88: K₂SeO₃Potassium selenite + 2HBrHydrogen bromide
⟶
2KBrPotassium bromide + H₂SeO₃Selenous acid

Reaction of potassium selenite and hydrogen iodide ◆ Δ_rG −56.4 kJ/mol K 7.60 × 10⁹ pK −9.88: K₂SeO₃Potassium selenite + 2HIHydrogen iodide
⟶
2KIPotassium iodide + H₂SeO₃Selenous acid

Reaction of potassium selenite and perchloric acid ◆ Δ_rG −56.4 kJ/mol K 7.60 × 10⁹ pK −9.88: K₂SeO₃Potassium selenite + 2HClO₄Perchloric acid
⟶
2KClO₄Potassium perchlorate + H₂SeO₃Selenous acid

Reaction of potassium selenite and hydrogen chloride: K₂SeO₃Potassium selenite + 2HClHydrogen chloride
⟶
2KClPotassium chloride + SeO₂Selenium dioxide + H₂OWater

Reaction with reducing species

The reaction of reducing species and potassium selenite yields a variety of products.

Reaction of hydrogen and potassium selenite ◆ Δ_rG −265.1 kJ/mol K 2.78 × 10⁴⁶ pK −46.44: 3H₂Hydrogen + K₂SeO₃Potassium selenite
⟶
K₂SePotassium selenide + 3H₂OWater

Reaction of sodium and potassium selenite ◆ Δ_rG −627.3 kJ/mol K 7.91 × 10¹⁰⁹ pK −109.90: 6NaSodium + K₂SeO₃Potassium selenite
⟶
3Na₂OSodium oxide + K₂SePotassium selenide

Reaction of hydrogen sulfide and potassium selenite ◆ Δ_rG −128.8 kJ/mol K 3.67 × 10²² pK −22.56: 3H₂SHydrogen sulfide + K₂SeO₃Potassium selenite
⟶
3SSulfur + K₂SePotassium selenide + 3H₂OWater

Reaction of sodium and potassium selenite ◆ Δ_rG −584.7 kJ/mol K 2.72 × 10¹⁰² pK −102.44: 8NaSodium + K₂SeO₃Potassium selenite
⟶
Na₂SeSodium selenide + 3Na₂OSodium oxide + 2KPotassium

Reaction of hydrogen sulfide and potassium selenite ◆ Δ_rG −73.1 kJ/mol K 6.41 × 10¹² pK −12.81: H₂SHydrogen sulfide + K₂SeO₃Potassium selenite
⟶
K₂SO₃Potassium sulfite + H₂SeHydrogen selenide

Reaction with oxidizing species

The reaction of potassium selenite and oxidizing species yields a variety of products.

Reaction of potassium selenite and oxygen ◆ Δ_rG −159.6 kJ/mol K 9.14 × 10²⁷ pK −27.96: 2K₂SeO₃Potassium selenite + O₂Oxygen
⟶
2K₂SeO₄Potassium selenate

Reaction of potassium selenite and nitric acid ◆ Δ_rG −11.0 kJ/mol K 8.46 × 10¹ pK −1.93: K₂SeO₃Potassium selenite + HNO₃Nitric acid
🔥
⟶
K₂SeO₄Potassium selenate + HNO₂Nitrous acid

Reaction of potassium selenite and nitric acid ◆ Δ_rG −56.3 kJ/mol K 7.30 × 10⁹ pK −9.86: 3K₂SeO₃Potassium selenite + 2HNO₃Nitric acid
⟶
3K₂SeO₄Potassium selenate + 2NO↑Nitrogen monoxide + H₂OWater

Reaction of potassium selenite and potassium permanganate ◆ Δ_rG −28.6 kJ/mol K 1.02 × 10⁵ pK −5.01: 4K₂SeO₃Potassium selenite + 2KMnO₄Potassium permanganate
🔥
⟶
4K₂SeO₄Potassium selenate + K₂OPotassium oxide + Mn₂O₃Manganese(III) oxide

Reaction of potassium selenite and potassium permanganate ◆ Δ_rG −6.2 kJ/mol K 1.22 × 10¹ pK −1.09: 3K₂SeO₃Potassium selenite + 2KMnO₄Potassium permanganate
🔥
⟶
3K₂SeO₄Potassium selenate + K₂OPotassium oxide + 2MnO₂Manganese(IV) oxide

Reaction with oxidizing species under acidic condition

The reaction of potassium selenite, oxidizing species, and hydrogen ion yields a variety of products.

Reaction of potassium selenite and potassium permanganate under acidic condition ◆ Δ_rG −631.1 kJ/mol K 3.66 × 10¹¹⁰ pK −110.56: 5K₂SeO₃Potassium selenite + 2KMnO₄Potassium permanganate + 6H⁺Hydrogen ion
⟶
5K₂SeO₄Potassium selenate + 2K⁺Potassium ion + 2Mn²⁺Manganese(II) ion + 3H₂OWater

Reaction of potassium selenite and potassium permanganate under acidic condition ◆ Δ_rG −487.7 kJ/mol K 2.76 × 10⁸⁵ pK −85.44: 3K₂SeO₃Potassium selenite + 2KMnO₄Potassium permanganate + 2H⁺Hydrogen ion
⟶
3K₂SeO₄Potassium selenate + 2K⁺Potassium ion + 2MnO₂Manganese(IV) oxide + H₂OWater

Reaction of potassium selenite and hydrogen peroxide under acidic condition ◆ Δ_rG −580.5 kJ/mol K 5.00 × 10¹⁰¹ pK −101.70: 4K₂SeO₃Potassium selenite + 3H₂O₂Hydrogen peroxide + 2H⁺Hydrogen ion
⟶
3K₂SeO₄Potassium selenate + 2K⁺Potassium ion + H₂SeO₃Selenous acid + 3H₂OWater

Reaction with oxidizable species under acidic condition

The reaction of oxidizable species, potassium selenite, and hydrogen ion yields a variety of products.

Reaction of copper and potassium selenite under acidic condition ◆ Δ_rG −15.8 kJ/mol K 5.86 × 10² pK −2.77: 3CuCopper + K₂SeO₃Potassium selenite + 6H⁺Hydrogen ion
🔥
⟶
3Cu²⁺Copper(II) ion + K₂SePotassium selenide + 3H₂OWater

Reaction of copper and potassium selenite under acidic condition ◆ Δ_rG −210.6 kJ/mol K 7.86 × 10³⁶ pK −36.90: 2CuCopper + K₂SeO₃Potassium selenite + 6H⁺Hydrogen ion
⟶
2Cu²⁺Copper(II) ion + SeSelenium + 2K⁺Potassium ion + 3H₂OWater

Reaction of potassium iodide and potassium selenite under acidic condition ◆ Δ_rG −102.5 kJ/mol K 9.06 × 10¹⁷ pK −17.96: 4KIPotassium iodide + K₂SeO₃Potassium selenite + 6H⁺Hydrogen ion
⟶
6K⁺Potassium ion + 2I₂Iodine + SeSelenium + 3H₂OWater

Reaction of potassium iodide and potassium selenite under acidic condition ◆ Δ_rG −261.4 kJ/mol K 6.24 × 10⁴⁵ pK −45.80: 8KIPotassium iodide + 3K₂SeO₃Potassium selenite + 14H⁺Hydrogen ion
⟶
14K⁺Potassium ion + 4I₂Iodine + 2SeSelenium + H₂SeO₃Selenous acid + 6H₂OWater

Reaction with oxidizing species under neutral condition

The reaction of potassium selenite, oxidizing species, and water yields a variety of products.

Reaction of potassium selenite and potassium permanganate under neutral condition ◆ Δ_rG −328.0 kJ/mol K 2.90 × 10⁵⁷ pK −57.46: 3K₂SeO₃Potassium selenite + 2KMnO₄Potassium permanganate + H₂OWater
⟶
3K₂SeO₄Potassium selenate + 2KOHPotassium hydroxide + 2MnO₂Manganese(IV) oxide

Reaction of potassium selenite and potassium permanganate under neutral condition ◆ Δ_rG −350.4 kJ/mol K 2.44 × 10⁶¹ pK −61.39: 4K₂SeO₃Potassium selenite + 2KMnO₄Potassium permanganate + H₂OWater
⟶
4K₂SeO₄Potassium selenate + 2KOHPotassium hydroxide + Mn₂O₃Manganese(III) oxide

Reaction of potassium selenite and chlorine under neutral condition ◆ Δ_rG −160.2 kJ/mol K 1.16 × 10²⁸ pK −28.07: 2K₂SeO₃Potassium selenite + Cl₂Chlorine + H₂OWater
⟶
K₂SeO₄Potassium selenate + 2KClPotassium chloride + H₂SeO₃Selenous acid

Reaction of potassium selenite and chlorine under neutral condition ◆ Δ_rG −32.0 kJ/mol K 4.04 × 10⁵ pK −5.61: K₂SeO₃Potassium selenite + Cl₂Chlorine + H₂OWater
⟶
K₂SeO₄Potassium selenate + 2HClHydrogen chloride

Reaction with reducible species

The reaction of potassium selenite and reducible species yields a variety of products.

Reaction of potassium selenite and manganese(IV) oxide ◆ Δ_rG −22.4 kJ/mol K 8.40 × 10³ pK −3.92: K₂SeO₃Potassium selenite + 2MnO₂Manganese(IV) oxide
🔥
⟶
K₂SeO₄Potassium selenate + Mn₂O₃Manganese(III) oxide

Reaction of potassium selenite and manganese(IV) oxide ◆ Δ_rG 30.6 kJ/mol K 0.44 × 10⁻⁵ pK 5.36: K₂SeO₃Potassium selenite + MnO₂Manganese(IV) oxide
🔥
⟶
K₂SeO₄Potassium selenate + MnOManganese(II) oxide

Reaction of potassium selenite and iron(III) oxide: K₂SeO₃Potassium selenite + Fe₂O₃Iron(III) oxide
🔥
⟶
K₂SeO₄Potassium selenate + 2FeOIron(II) oxide

Reaction of potassium selenite and iron(III) oxide ◆ Δ_rG 124.2 kJ/mol K 0.17 × 10⁻²¹ pK 21.76: K₂SeO₃Potassium selenite + 3Fe₂O₃Iron(III) oxide
🔥
⟶
K₂SeO₄Potassium selenate + 2Fe₃O₄Iron(II,III) oxide

Reaction with oxidizable species

The reaction of oxidizable species and potassium selenite yields a variety of products.

Reaction of iron(II) oxide and potassium selenite: 9FeOIron(II) oxide + K₂SeO₃Potassium selenite
🔥
⟶
3Fe₃O₄Iron(II,III) oxide + K₂SePotassium selenide

Reaction of iron(II) oxide and potassium selenite: 6FeOIron(II) oxide + K₂SeO₃Potassium selenite
🔥
⟶
3Fe₂O₃Iron(III) oxide + K₂SePotassium selenide

Reaction of copper and potassium selenite ◆ Δ_rG 110.0 kJ/mol K 0.54 × 10⁻¹⁹ pK 19.27: 3CuCopper + K₂SeO₃Potassium selenite
🔥
⟶
3CuOCopper(II) oxide + K₂SePotassium selenide

Reaction of potassium iodide and potassium selenite ◆ Δ_rG 1342.2 kJ/mol K 0.72 × 10⁻²³⁵ pK 235.14: 4KIPotassium iodide + K₂SeO₃Potassium selenite
🔥
⟶
3K₂OPotassium oxide + 2I₂Iodine + SeSelenium

Reaction of copper and potassium selenite ◆ Δ_rG 61.1 kJ/mol K 0.20 × 10⁻¹⁰ pK 10.70: 6CuCopper + K₂SeO₃Potassium selenite
🔥
⟶
3Cu₂OCopper(I) oxide + K₂SePotassium selenide

Reaction with hardly oxidizable species under acidic condition

The reaction of hardly oxidizable species, potassium selenite, and hydrogen ion yields a variety of products.

Reaction of hydrogen chloride and potassium selenite under acidic condition ◆ Δ_rG 183.3 kJ/mol K 0.77 × 10⁻³² pK 32.11: 4HClHydrogen chloride + K₂SeO₃Potassium selenite + 2H⁺Hydrogen ion
🔥
⟶
2Cl₂Chlorine + SeSelenium + 2K⁺Potassium ion + 3H₂OWater

Reaction of gold and potassium selenite under acidic condition: 4AuGold + 3K₂SeO₃Potassium selenite + 18H⁺Hydrogen ion
🔥
⟶
4Au³⁺Gold(III) ion + 3SeSelenium + 6K⁺Potassium ion + 9H₂OWater

Reaction of sodium chloride and potassium selenite under acidic condition ◆ Δ_rG 183.3 kJ/mol K 0.77 × 10⁻³² pK 32.11: 4NaClSodium chloride + K₂SeO₃Potassium selenite + 6H⁺Hydrogen ion
🔥
⟶
4Na⁺Sodium ion + 2Cl₂↑Chlorine + SeSelenium + 2K⁺Potassium ion + 3H₂OWater

Reaction of sodium chloride and potassium selenite under acidic condition ◆ Δ_rG 388.0 kJ/mol K 0.11 × 10⁻⁶⁷ pK 67.97: NaClSodium chloride + 2K₂SeO₃Potassium selenite + 4H⁺Hydrogen ion
🔥
⟶
NaClO₄Sodium perchlorate + 2SeSelenium + 4K⁺Potassium ion + 2H₂OWater

Reaction of hydrogen chloride and potassium selenite under acidic condition ◆ Δ_rG 388.0 kJ/mol K 0.11 × 10⁻⁶⁷ pK 67.97: HClHydrogen chloride + 2K₂SeO₃Potassium selenite + 4H⁺Hydrogen ion
🔥
⟶
HClO₄Perchloric acid + 2SeSelenium + 4K⁺Potassium ion + 2H₂OWater

Precipitation reaction

When a certain chemical species is present in aqueous solution, it reacts with potassium selenite to form a precipitate.

Reaction of potassium selenite and chromium(VI) oxide: K₂SeO₃Potassium selenite + CrO₃Chromium(VI) oxide
💧
⟶
K₂CrO₄↓Potassium chromate + SeO₂Selenium dioxide

Reaction of calcium chloride and potassium selenite: CaCl₂Calcium chloride + K₂SeO₃Potassium selenite
💧
⟶
CaSeO₃↓Calcium selenite + 2KClPotassium chloride

Reaction of calcium bromide and potassium selenite: CaBr₂Calcium bromide + K₂SeO₃Potassium selenite
💧
⟶
CaSeO₃↓Calcium selenite + 2KBrPotassium bromide

Reaction of calcium iodide and potassium selenite: CaI₂Calcium iodide + K₂SeO₃Potassium selenite
💧
⟶
CaSeO₃↓Calcium selenite + 2KIPotassium iodide

Reaction of potassium selenite and chromic acid: K₂SeO₃Potassium selenite + H₂CrO₄Chromic acid
💧
⟶
K₂CrO₄↓Potassium chromate + H₂SeO₃Selenous acid

Decomposition

Decomposition of potassium selenite yields potassium oxide and selenium dioxide.

Decomposition of potassium selenite: K₂SeO₃Potassium selenite
🔥
⟶
K₂OPotassium oxide + SeO₂Selenium dioxide

Decomposition of potassium selenite ◆ Δ_rG 284.3 kJ/mol K 0.16 × 10⁻⁴⁹ pK 49.81: 4K₂SeO₃Potassium selenite
🔥
⟶
3K₂SeO₄Potassium selenate + K₂SePotassium selenide

Decomposition of potassium selenite ◆ Δ_rG 471.0 kJ/mol K 0.31 × 10⁻⁸² pK 82.52: 3K₂SeO₃Potassium selenite
🔥
⟶
2K₂SeO₄Potassium selenate + K₂OPotassium oxide + SeSelenium

Electrolysis of aqueous solution

Electrolysis of aqueous potassium selenite yields a variety of products.

Electrolysis of aqueous potassium selenite with water as oxidizing agent ◆ Δ_rG 165.5 kJ/mol K 0.10 × 10⁻²⁸ pK 28.99: K₂SeO₃Potassium selenite + H₂OWater
💧⚡
⟶
K₂SeO₄Potassium selenate + H₂↑Hydrogen

Electrolysis of water ◆ Δ_rG 474.258 kJ/mol K 0.82 × 10⁻⁸³ pK 83.09: 2H₂OWater
⚡
⟶
2H₂↑Hydrogen + O₂↑Oxygen

Electrolysis of aqueous potassium selenite without water as reactant ◆ Δ_rG 284.3 kJ/mol K 0.16 × 10⁻⁴⁹ pK 49.81: 4K₂SeO₃Potassium selenite
💧⚡
⟶
3K₂SeO₄Potassium selenate + K₂SePotassium selenide

Electrolysis of aqueous potassium selenite with water as non-redox agent ◆ Δ_rG 149.2 kJ/mol K 0.73 × 10⁻²⁶ pK 26.14: 3K₂SeO₃Potassium selenite + H₂OWater
💧⚡
⟶
2K₂SeO₄Potassium selenate + 2KOHPotassium hydroxide + SeSelenium

Electrolysis of aqueous potassium selenite without water as reactant ◆ Δ_rG 998.2 kJ/mol K 0.13 × 10⁻¹⁷⁴ pK 174.88: 2K₂SeO₃Potassium selenite
💧⚡
⟶
2K₂SePotassium selenide + 3O₂↑Oxygen

References

List of references

1
Janiel J. Reed (1989)
The NBS Tables of Chemical Thermodynamic Properties: Selected Values for Inorganic and C1 and C2 Organic Substances in SI Units
https://doi.org/10.18434/M32124
National Institute of Standards and Technology (NIST)
Citation list
2
Atherton Seidell (1919)
Solubilities of Inorganic and Organic Compounds: A Compilation of Quantitative Solubility Data From the Periodical Literature
D. Van Nostrand Company
- Amazon
Citation list
- ^ Solubility in Water (g/100 g), See the table - p.341

Δ_rG	−103.4 kJ/mol
K	1.30 × 10¹⁸
pK	−18.11

Δ_rG	−425.2 kJ/mol
K	3.10 × 10⁷⁴
pK	−74.49

Δ_rG	−510.2 kJ/mol
K	2.42 × 10⁸⁹
pK	−89.38

Δ_rG	120.9 kJ/mol
K	0.66 × 10⁻²¹
pK	21.18

Potassium selenite

Names

List of substance names

Formulae and structures

List of formulae

Properties

List of substance properties

Constituents

Constituent ions

Constituent atoms

Ratio of atoms

Thermodynamic properties

Phase transition properties

Standard thermodynamic properties

Solubility

Qualitative solubility

Solubility in water (g/100 g)[2]

Solubility curve (g/100 g)

Preparations

Reaction of acid and base

Reaction of base and acidic oxide

Reaction of basic oxide and acid

Reaction of basic oxide and acidic oxide

Reaction of active metal and acid

Reaction of nonmetal and hydroxide base

Decomposition

Chemical reactions

Electrolytic dissociation

Reaction with strong acid

Reaction with reducing species

Reaction with oxidizing species

Reaction with oxidizing species under acidic condition

Reaction with oxidizable species under acidic condition

Reaction with oxidizing species under neutral condition

Reaction with reducible species

Reaction with oxidizable species

Reaction with hardly oxidizable species under acidic condition

Precipitation reaction

Decomposition

Electrolysis of aqueous solution

References

List of references

Related substances

Selenite of alkali metal

Selenium oxoacid salt of potassium

Acid and acidic oxide

Base and basic oxide

Related categories

Classification by constituent

Type of substance

State of substance

Property of substance

Solubility of substance

Color of substance

Odor of substance

Solubility in water (g/100 g)^[2]