"Muriatic" is not a word you're likely to have read or heard unless you're a student of the history of science or otherwise a serious chemistry fan. Therefore, muriatic acid isn't something you're likely to be familiar with — at least not by that name. But muriatic acid uses are many, as you'll see.
The modern and overwhelmingly more common name for the same substance is hydrochloric acid, and if you have ever worked with it purposefully, you're aware of its effects.
Hydrochloric or muriatic acid has the chemical formula HCl and is considered a strong acid. Because it is inexpensive and easy to obtain in sizable quantities, this substance is a mainstay in industry, academic laboratories and various other settings. Muriatic acid for pools is still labeled and sold as such on a widespread basis, but for the most part, the less-creative but easier-to-remember name has taken over. Muriatic acid uses include cleaning concrete such as pool decks or sidewalks, hence its availability in home improvement stores.
Hydrochloric acid, in addition to most likely aiding in aspects of your own digestion even as you read this, is used in the production of metals, petroleum products, pharmaceuticals and much more.
Its chemical versatility makes it an extremely common reagent in chemical reactions, and it is easy to produce in mass quantities at a reliably precise concentration. Read on so you can completely "digest" all there is to know about this versatile aqueous solution.
What Are Acids and Bases?
An acid is a molecule that donates a proton (H+, or a hydrogen ion) in aqueous solution, i.e., when it is mixed with water. H2O molecules can accept these protons to become hydronium ions (H3O+) as protons do not exist alone for long if there is anything for them to combine with. A base is a molecule that accepts a proton or, equivalently from a chemistry standpoint, donates hydroxide (OH-) ions in solution.
The molecule or element remaining when an acid donates a proton is called the conjugate base of the acid. In the case of HCl, this is therefore a chloride ion (Cl−). Cl alone is the element chlorine, a halogen.
The reaction of muriatic acid gas with water in aqueous solution is given by
HCl(g) + H2O(l) ⟶ H3O+(aq) + Cl−(aq)
This reaction goes nearly to completion under most conditions (that is, almost all of the HCl is dissolved) because hydrochloric acid is a strong acid.
History and Discovery of Muriatic Acid
Hydrochloric acid was discovered by the alchemist Jabir ibn Hayyan sometime around the year 800 C.E., or over 1,200 years ago. Alchemy is today understood to be a "pseudoscience," but its practitioners nevertheless worked with real substances, and occasionally got useful results.
- The name muriatic acid comes from the Latin for "briny," as in salty; concentrated salt water is a reagent in one of the processes used to manufacture hydrochloric acid.
At the time of its discovery, the world was many centuries away from understanding what acids even were. But any substance with the properties of muriatic acid quickly and forcefully demonstrated was certain to assume great importance to civilization, and this is exactly what happened with HCl.
Properties of Muriatic Acid
Hydrogen chloride on its own exists as a colorless and odorless gas at room temperature, but that is in a vacuum. In air, HCl forms thick white fumes because it reacts readily with the water molecules.
Hydrochloric acid is very corrosive and extremely toxic. If you handle this substance, regardless of the molarity (a measure of concentration), you should wear eye and skin protection.
HCl has a molecular weight (MW) of 36.46 grams per mole (g/mol). Over 95 percent of this mass is consumed by the chlorine atom, yet an equal number of H and Cl atoms exist in the acid's conjugated (intact) form. It is not readily combustible, so despite its other hazards to biological systems, it is highly unlikely to catch fire.
Production of Muriatic Acid
HCl can be synthesized in a number of ways. One common industrial synthesis involves the combustion of hydrogen gas and chlorine gas inside a chamber into which the gases are introduced under pressure through a nozzle.
The hydrochloric acid gas thus produced is then gradually and carefully cooled to the liquid state and diluted to whatever concentration the specifications demand. This reaction is represented by the formula:
H2 + Cl2 ⟶ 2HCl
HCl can also be produced industrially by the reaction of sodium chloride and sulfuric acid:
2NaCl + H2SO4 ⟶ 2HCl + Na2SO4
HCl can also be synthesized from sodium chloride, sulfur dioxide, air and water vapor:
4NaCl + 2SO2 + 2H2O + O2 ⟶ 2Na2SO4 + 4HCl
Muriatic Acid Uses
The same properties that make HCl dangerous to work with unless care is taken are advantageous in certain settings. Just as knives are potentially very dangerous but also extremely useful and universal tools, hydrochloric acid's corrosive qualities can be put to use in carefully controlled settings.
The following list is a survey of some of the main uses of hydrochloric acid in modern society. Note that it is usually still labeled "muriatic acid" when sold for use with swimming pools (see below).
Steel and metal production: The steel and metal industry use muriatic acid to "pickle" steel to remove surface oxides. Most steel is also cleaned in acid before galvanizing, tinning and other coating applications.
Pharmaceutical production: The pharmaceutical industry puts HCl to use in a variety of roles. It can serve as a catalyst or as reactant in chemical reactions. It is excellent for helping precisely control pH; this is important for some drugs to be able to adequately access certain physiologic spaces (e.g., blood, lymphatic fluid), as some of these are more acidic than others.
Food additives and food processing: The food industry uses hydrochloric acid in a variety of products, although the vast majority of it is the production of the common "sweet" food ingredient high fructose corn syrup (HFCS). HCl is also used to produce vitamin supplements.
Water treatment: One of muriatic acid's uses is to regulate the pH of pool water and that of similar settings (e.g., "hot tubs") as well as the acidity of industrial waste water, so that it does minimal damage to the aquatic life in the waterways into which it is disposed.
Petroleum and natural gas production: The petroleum (oil and gas) industry uses muriatic acid to acidify oil and gas wells. The lower pH boosts oil and gas production by dissolving the minerals in the bedrock separating drillers from their quarry.
These minerals, calcium carbonate and magnesium carbonate, give way to produce pores in the oil-containing rocks. Muriatic acid is also found in fluids designed for hydraulic fracturing (“fracking”) rock shale formations to access natural gas and oil.
Muriatic Acid Reaction Demonstration
Many metals react with HCl to produce chlorides of those metals and liberate hydrogen gas in the process. This occurs via a substitution reaction or single-displacement reaction, wherein a reactive metal takes the place of the hydrogen ion that is bonded to the chloride ion.
An example is the reaction of elemental magnesium with HCl to produce magnesium chloride and the aforementioned H2 gas:
Mg(s) + 2 HCl(aq) ⟶ MgCl2(aq) + H2(g)