# What is the difference between hydrogen chloride and hydrochloric acid?

My teacher insists that hydrogen chloride is a misnomer, and that the proper nomenclature demands HCl to be named hydrochloric acid. However, I saw the name hydrogen chloride used in my textbook, but it was never further explained.

• The two are not identical. Hydrogen chloride is the anhydrous gas. Hydrochloric acid is an aqueous solution of hydrogen chloride. // PS - Forget arguing with the teacher. It isn't worth it... – MaxW Nov 7 '16 at 3:52
• @MaxW That is a very stupid and egoistic advise, to not argue with teachers. How will they ever learn? And the classmates and future pupils no less? – Karl Nov 7 '16 at 14:31
• @Karl It depends on your situation. In my experience, if you are not extremely friendly with a teacher, it is impractical to argue straight out with them even if you are being polite. Some people just don't want to hear it. – Widow Maven Nov 8 '16 at 0:41

Hydrogen chloride is a gas. It is the molecule made up of a hydrogen and a chlorine atom bonded by a single bond. It comes in gas cylinders for use in chemistry.

Hydrochloric acid is a solution (no, not to your problem of a stubborn teacher). It is composed of water molecules and hydrogen chloride molecules. In terms of mass percentage, concentrated hydrochloric acid is often $37~\%\ \ce{HCl}$ in water. It comes in glass bottles (often brown glass for ease of bottle use; the chemical company does not have to distinguish between compounds that can live in clear bottles and those that must live in brown ones) for use in chemistry.

Hydrogen chloride can also be dissolved in other solvents such as ether. In this case too, it may be termed hydrochloric acid, although a specification of the solvent should be added.

Whether or not either of the two names is a misnomer depends on what you are addressing. Using hydrogen chloride for the liquid solution is as wrong as using hydrochloric acid for the gas.

• In ether, the Sigma Aldrich choice is actually "hydrogen chloride in ether." – Zhe Nov 8 '16 at 20:44
• Does HCl gas ionize in ether and even if it does my book says that "An acid is a compound which dissociates in aqueous solution to produce H+ ions as the only positively charged ions" – MrAP Dec 29 '16 at 2:51
• @MrAP That’s using the Arrhenius definition. By the Brønsted-Lowry one, HCl is acidic in etheric solution (the ether oxygen acts as a base). – Jan Dec 29 '16 at 14:18
• It is true for all solvents by Lowry-Bronsted definition or it is true only for ether? – MrAP Dec 29 '16 at 20:24
• @MrAP For all solvents that are Brønsted bases. – Jan Dec 29 '16 at 22:21

Pure HCl(g) is a covalent bonded compound and does not break into ions and is neutral to litmus and is not acidic. In case of HCl acid it is a monobasic acid and exhibits acidic properties. Secondly HCl gas has smooth reaction with alkali metals whereas HCl acid has explosive reaction with alkali metals.