Hydrogen cyanide is written HCN. With school atomic masses the molar mass is 27 g/mol. Hydrogen cyanide is a linear molecule of hydrogen, carbon, and nitrogen.
H₂O
WaterNH₃
AmmoniaCO₂
Carbon DioxideH₂O₂
Hydrogen PeroxideSO₂
Sulfur DioxideNO₂
Nitrogen DioxideHCl
Hydrochloric AcidH₂SO₄
Sulfuric AcidHNO₃
Nitric AcidCH₄
MethaneC₂H₆
EthaneC₃H₈
PropaneC₄H₁₀
ButaneC₂H₄
EthyleneC₂H₂
AcetyleneC₆H₆
BenzeneC₇H₈
TolueneC₁₀H₈
NaphthaleneC₆H₁₂
CyclohexaneCH₃OH
MethanolC₂H₅OH
EthanolCH₃COOH
Acetic AcidHCHO
FormaldehydeCH₃COCH₃
AcetoneC₄H₁₀O
Diethyl EtherC₂H₇N
EthylamineC₂H₅NO
AcetamideC₆H₁₂O₆
GlucoseC₆H₁₂O₆
FructoseC₁₂H₂₂O₁₁
SucroseCO(NH₂)₂
UreaC₂₇H₄₆O
CholesterolC₉H₈O₄
AspirinC₈H₉NO₂
AcetaminophenC₁₃H₁₈O₂
IbuprofenC₈H₁₀N₄O₂
CaffeineC₆H₆N₂O
NicotinamideC₆H₈O₆
Ascorbic AcidC₁₆H₁₈N₂O₄S
Penicillin GC₂H₆O₂
Ethylene GlycolC₈H₈
StyreneC₂H₃Cl
Vinyl ChlorideC₃H₅NO
AcrylamideC₆H₁₁NO
CaprolactamLiCl
Lithium chlorideNa₂O
Sodium oxideNaCl
Sodium chlorideMgF₂
Magnesium fluorideAlCl₃
Aluminum chlorideCaO
Calcium oxideCaC₂
Calcium carbideKNO₃
Potassium nitrateMg₃(PO₄)₂
Magnesium phosphateAl₂(SO₄)₃
Aluminum sulfateMg(OH)₂
Magnesium hydroxideNH₄Cl
Ammonium chlorideNH₄OH
Ammonium hydroxideCuO
Copper(II) oxideCu₂O
Copper(I) oxideFeSO₄
Iron(II) sulfateFe₂(SO₄)₃
Iron(III) sulfatePbCO₃
Lead(II) carbonateMgO
Magnesium oxideAl₂S₃
Aluminum sulfideLiF
Lithium fluoride(NH₄)₂S
Ammonium sulfideKF
Potassium fluorideNiCl₂
Nickel(II) chlorideKCN
Potassium cyanideCH₃COONa
Sodium acetateCaCO₃
Calcium carbonateNa₃P
Sodium phosphideBeBr₂
Beryllium bromideFeO
Iron(II) oxideHg₂Cl₂
Mercury(I) chlorideHg(NO₃)₂
Mercury(II) nitrateCH₃COOCu
Copper(I) acetateSiO₂
Silicon dioxideP₄O₁₀
Tetraphosphorus decaoxideN₂O₅
Dinitrogen pentoxideCO
Carbon monoxideHF
Hydrogen fluoridePCl₅
Phosphorus pentachlorideCF₄
Carbon tetrafluorideSF₆
Sulfur hexafluorideNBr₃
Nitrogen tribromideN₂O
Dinitrogen monoxideN₂O₃
Dinitrogen trioxideCS₂
Carbon disulfideCl₂O₇
Dichlorine heptoxideBF₃
Boron trifluorideCCl₄
Carbon tetrachlorideSO₃
Sulfur trioxideSiCl₄
Silicon tetrachlorideP₂S₅
Diphosphorus pentasulfideBCl₃
Boron trichloridePBr₃
Phosphorus tribromideCBr₄
Carbon tetrabromideNF₃
Nitrogen trifluorideOF₂
Oxygen difluorideNCl₃
Nitrogen trichlorideH₂S
Hydrogen sulfidePH₃
PhosphineBeCl₂
Beryllium chlorideHCN
Hydrogen cyanideClF₃
Chlorine trifluorideXeF₂
Xenon difluorideLinear
Linear
Hydrogen cyanide is a linear molecule of hydrogen, carbon, and nitrogen. Carbon sits at the center, with a single bond to hydrogen and a triple bond to nitrogen. It boils near room temperature and its vapor is highly toxic. It should be kept distinct from the salt potassium cyanide.
Properties
Molar mass
27.03 g/mol
Boiling point
25.6 °C
Bond type
Covalent
Geometry
Linear
Uses
Linear VSEPR example · Cyanide naming comparison
Exam note
Systematic name
Hydrogen cyanide
Compound class
It is a polar covalent molecule with a linear shape.
Formula unit
Carbon is sp hybridized. The H–C single bond and the C≡N triple bond lie on the same line.
Watch the formula
With school atomic masses the molar mass is 27 g/mol: 1 (H) + 12 (C) + 14 (N). The formula is written HCN; the salt KCN is ionic and a different substance. The molecule is linear but still polar, because the ends are different; the dipoles do not cancel as they do in CO₂. The vapor is highly toxic.
Molar mass calculation
Masses given in the question come first. When none are given, school values put the total at 27 g/mol.
+
+
= 27 g/mol
HCN
The same count with periodic-table atomic masses gives 27.026 g/mol.
| Element | Atom count | Contribution (g/mol) | Mass % |
|---|---|---|---|
| Carbon (C) | 1 | 12.011 | 44.4 |
| Hydrogen (H) | 1 | 1.008 | 3.7 |
| Nitrogen (N) | 1 | 14.007 | 51.8 |
| Total | 27.026 | 100 |
Common questions
What is hydrogen cyanide?
Hydrogen cyanide is a linear molecule of hydrogen, carbon, and nitrogen. Carbon sits at the center, with a single bond to hydrogen and a triple bond to nitrogen. It boils near room temperature and its vapor is highly toxic. It should be kept distinct from the salt potassium cyanide.
What is the formula of hydrogen cyanide?
Hydrogen cyanide is written HCN. The systematic name is Hydrogen cyanide. Carbon is sp hybridized. The H–C single bond and the C≡N triple bond lie on the same line.
What is the molar mass of hydrogen cyanide?
Hydrogen cyanide has a molar mass of 27.026 g/mol from the atomic masses on the periodic table. With school atomic masses the total is 27 g/mol, counting 1 carbon, 1 hydrogen and 1 nitrogen.
What is hydrogen cyanide used for?
Hydrogen cyanide is used for linear VSEPR example and cyanide naming comparison.
What should you watch for with hydrogen cyanide on an exam?
With school atomic masses the molar mass is 27 g/mol: 1 (H) + 12 (C) + 14 (N). The formula is written HCN; the salt KCN is ionic and a different substance. The molecule is linear but still polar, because the ends are different; the dipoles do not cancel as they do in CO₂. The vapor is highly toxic.