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Chemical substances
Arsenic triiodide

Arsenic triiodide

Last updated: March 19, 2023

Arsenic triiodide is an inorganic compound with formula AsI₃.

Table of contents

Names

List of substance names

Nomenclature

Name

Typical name: Arsenic triiodide

Compositional nomenclature: Arsenic triiodide; Arsenic(III) iodide

Substitutive nomenclature: Triiodoarsane

Additive nomenclature: Triiodidoarsenic

Other names: Triiodoarsine; Arsenous iodide

Formulae and structures

List of formulae

Formula name

Formula

Typical formula: AsI₃

Molecular formula: AsI₃

Compositional formula: AsI₃

Structural formula

Structural formula with no lone pair

Lewis structure

Colored Lewis structure

Properties

List of substance properties

Item

Value

Name: Arsenic triiodide

Formula: AsI₃

Appearance: Orange red solid

Odor: Pungent odor

Molar mass: 455.62 g/mol

Density: 4.73 g/cm³^[1]
Solid

Melting point: 140.9 °C^[1]

Boiling point: 424 °C^[1]

Constituents

Constituent atoms

Atom	Name	Oxidation state	Number
As	Arsenic	+3	1
I	Iodine	−1	3

Ratio of atoms

Atom	Atomic weight	Number	Atomic ratio	Weight ratio
As	74.922	1	25.00%	16.44%
I	126.90	3	75.00%	83.56%

Thermodynamic properties

Phase transition properties

Item

Value

Enthalpy of fusion: 21.8 kJ · mol⁻¹^[2]
at 141°C

Enthalpy of vaporization: 59.3 kJ · mol⁻¹^[1][2]
at 424°C

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	−58.2^[3]	−59.4^[3]	213.05^[3]	105.77^[3]
Gas	–	–	388.34^[3]	80.63^[3]

Solubility

Qualitative solubility

Reactive

Slowly reactive: H₂OWater

Miscible

Very soluble

Soluble: CH₂I₂Diiodomethane
CS₂Carbon disulfide
H₂OWater
C₆H₆^[1]Benzene
C₆H₅CH₃^[1]Toluene

Slightly soluble: H₂O^[1]Water
C₂H₅OH^[1]Ethanol
C₂H₅OC₂H₅^[1]Diethyl ether

Very slightly soluble

Insoluble

Solubility in diiodomethane (g/100 g)^[4]

12°C
17.4

Solubility in water (g/100 g)^[4]

25°C
6

Solubility in carbon disulfide (g/100 g)^[4]

25°C
5.2

Solubility curve (g/100 g)

Preparations

Reaction of nonmetal and nonmetal

The reaction of arsenic and iodine yields arsenic triiodide.

Reaction of arsenic and iodine ◆ Δ_rG −118.8 kJ/mol K 6.50 × 10²⁰ pK −20.81: 2AsArsenic + 3I₂Iodine
⟶
2AsI₃Arsenic triiodide

Chemical reactions

Reaction with oxidizing species

The reaction of arsenic triiodide and oxidizing species yields a variety of products.

Reaction of arsenic triiodide and oxygen ◆ Δ_rG −1327.0 kJ/mol K 3.02 × 10²³² pK −232.48: 4AsI₃Arsenic triiodide + 5O₂Oxygen
⟶
2As₂O₅Diarsenic pentaoxide + 6I₂Iodine

Reaction of arsenic triiodide and nitric acid ◆ Δ_rG −528.9 kJ/mol K 4.56 × 10⁹² pK −92.66: 2AsI₃Arsenic triiodide + 10HNO₃Nitric acid
⟶
As₂O₅Diarsenic pentaoxide + 3I₂Iodine + 10NO₂↑Nitrogen dioxide + 5H₂OWater

Reaction of arsenic triiodide and nitric acid ◆ Δ_rG −1503.5 kJ/mol K 2.52 × 10²⁶³ pK −263.40: 6AsI₃Arsenic triiodide + 10HNO₃Nitric acid
⟶
3As₂O₅Diarsenic pentaoxide + 9I₂Iodine + 10NO↑Nitrogen monoxide + 5H₂OWater

Reaction of arsenic triiodide and potassium permanganate ◆ Δ_rG −3178.3 kJ/mol K 6.52 × 10⁵⁵⁶ pK −556.81: 8AsI₃Arsenic triiodide + 10KMnO₄Potassium permanganate
⟶
4As₂O₅Diarsenic pentaoxide + 7I₂Iodine + 10MnO₂Manganese(IV) oxide + 10KIPotassium iodide

Reaction with reducible species

The reaction of arsenic triiodide and reducible species yields a variety of products.

Reaction of arsenic triiodide and iron(III) oxide: 3AsI₃Arsenic triiodide + 4Fe₂O₃Iron(III) oxide
⟶
3FeAsO₄Iron(III) arsenate + 2FeIron + 3FeI₃Iron(III) iodide

Reaction of arsenic triiodide and iron(III) oxide: 2AsI₃Arsenic triiodide + 6Fe₂O₃Iron(III) oxide
⟶
2FeAsO₄Iron(III) arsenate + 3I₂Iodine + 10FeOIron(II) oxide

Reaction with reducing species

The reaction of reducing species and arsenic triiodide yields a variety of products.

Reaction of sodium and arsenic triiodide ◆ Δ_rG −798.8 kJ/mol K 8.78 × 10¹³⁹ pK −139.94: 3NaSodium + AsI₃Arsenic triiodide
⟶
3NaISodium iodide + AsArsenic

Reaction of hydrogen and arsenic triiodide ◆ Δ_rG 129.0 kJ/mol K 0.25 × 10⁻²² pK 22.60: 3H₂Hydrogen + 2AsI₃Arsenic triiodide
⟶
2AsArsenic + 6HIHydrogen iodide

Reaction of hydrogen and arsenic triiodide ◆ Δ_rG 133.4 kJ/mol K 0.43 × 10⁻²³ pK 23.37: 3H₂Hydrogen + AsI₃Arsenic triiodide
⟶
AsH₃Arsine + 3HIHydrogen iodide

Reaction of hydrogen sulfide and arsenic triiodide ◆ Δ_rG 229.7 kJ/mol K 0.57 × 10⁻⁴⁰ pK 40.24: 3H₂SHydrogen sulfide + 2AsI₃Arsenic triiodide
⟶
3SSulfur + 2AsArsenic + 6HIHydrogen iodide

Reaction of hydrogen sulfide and arsenic triiodide ◆ Δ_rG 234.1 kJ/mol K 0.97 × 10⁻⁴¹ pK 41.01: 3H₂SHydrogen sulfide + AsI₃Arsenic triiodide
🔥
⟶
3SSulfur + AsH₃Arsine + 3HIHydrogen iodide

Precipitation reaction

The reaction of mercury(II) chloride and arsenic triiodide yields mercury(II) iodide and arsenic trichloride.

Reaction of mercury(II) chloride and arsenic triiodide ◆ Δ_rG −169.3 kJ/mol K 4.57 × 10²⁹ pK −29.66: 3HgCl₂Mercury(II) chloride + 2AsI₃Arsenic triiodide
💧
⟶
3HgI₂↓Mercury(II) iodide + 2AsCl₃Arsenic trichloride

Electrolysis of aqueous solution

Electrolysis of aqueous arsenic triiodide yields a variety of products.

Electrolysis of aqueous arsenic triiodide with water as oxidizing agent ◆ Δ_rG 522.1 kJ/mol K 0.34 × 10⁻⁹¹ pK 91.47: 2AsI₃Arsenic triiodide + 5H₂OWater
💧⚡
⟶
As₂O₅Diarsenic pentaoxide + 3I₂Iodine + 5H₂↑Hydrogen

Electrolysis of aqueous arsenic triiodide with water as oxidizing agent ◆ Δ_rG 533.0 kJ/mol K 0.42 × 10⁻⁹³ pK 93.38: 2AsI₃Arsenic triiodide + 8H₂OWater
💧⚡
⟶
2H₃AsO₄Arsenic acid + 3I₂Iodine + 5H₂↑Hydrogen

Electrolysis of aqueous arsenic triiodide without water as reactant ◆ Δ_rG 118.8 kJ/mol K 0.15 × 10⁻²⁰ pK 20.81: 2AsI₃Arsenic triiodide
💧⚡
⟶
2AsArsenic + 3I₂Iodine

Electrolysis of aqueous arsenic triiodide with water as non-redox agent ◆ Δ_rG 308.5 kJ/mol K 0.90 × 10⁻⁵⁴ pK 54.05: 2AsI₃Arsenic triiodide + 3H₂OWater
💧⚡
⟶
AsH₃↑Arsine + 3I₂Iodine + H₃AsO₃Arsenous acid

Electrolysis of aqueous arsenic triiodide with water as non-redox agent ◆ Δ_rG 510.6 kJ/mol K 0.35 × 10⁻⁸⁹ pK 89.45: 4AsI₃Arsenic triiodide + 3H₂OWater
💧⚡
⟶
2AsH₃↑Arsine + 6I₂Iodine + As₂O₃Diarsenic trioxide

References

List of references

1
James G. Speight (2017)
Lange's Handbook of Chemistry, 17th edition
https://www.accessengineeringlibrary.com/content/book/9781259586095
McGraw Hill Education
- Amazon
Citation list
- ^ Density, 4.73 g/cm³ - p.33
- ^ Melting point, 140.9 °C - p.33
- ^ Boiling point, 424 °C - p.33
- ^ Enthalpy of vaporization, 59.3 kJ · mol⁻¹ - p.297
- ^ Qualitative solubility, Soluble in benzene - p.33
- ^ Qualitative solubility, Soluble in toluene - p.33
- ^ Qualitative solubility, Slightly soluble in water - p.33
- ^ Qualitative solubility, Slightly soluble in ethanol - p.33
- ^ Qualitative solubility, Slightly soluble in diethyl ether - p.33
2
John R. Rumble Jr, David R. Lide, Thomas J. Bruno (2019)
CRC Handbook of Chemistry and Physics 100th Edition
https://www.routledge.com/CRC-Handbook-of-Chemistry-and-Physics/book-series/CRCHANCHEPHY
CRC Press
- Amazon
Citation list
- ^ Enthalpy of fusion, 21.8 kJ · mol⁻¹ - p.6-153
- ^ Enthalpy of vaporization, 59.3 kJ · mol⁻¹ - p.6-138
3
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
4
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

Δ_rG	−118.8 kJ/mol
K	6.50 × 10²⁰
pK	−20.81

Δ_rG	−1327.0 kJ/mol
K	3.02 × 10²³²
pK	−232.48

Δ_rG	−528.9 kJ/mol
K	4.56 × 10⁹²
pK	−92.66

Δ_rG	−1503.5 kJ/mol
K	2.52 × 10²⁶³
pK	−263.40