Hydrochloric+acid

Hydrochloric acid is a a solution of HCl in water. It is highly corrosive acid. It is a strong mineral acid. It is found naturally in gastric acid. Uses: it has many industrial uses, and is used for pickling of steel, producing organic and inoganic compounds and ph neutralization. Concentrated hydrochloric acid (fuming hydrochloric acid) forms acidic mists. Both the mist and the solution have a corrosive effect on human tissue, with the potential to damage respiratory organs, eyes, skin, and intestines.

Gastric acid is one of the main secretions of the stomach. It consists mainly of hydrochloric acid and acidifies the stomach content to a pH of 1 to 2.

Chloride (Cl−) and hydrogen (H+) ions are secreted separately in the stomach fundus  region at the top of the stomach by  parietal cells  of the  gastric mucosa  into a secretory network called  canaliculi  before it enters the stomach lumen.

Gastric acid acts as a barrier against microorganisms  to prevent infections and is important for the digestion of food. Its low pH denatures proteins  and thereby makes them susceptible to degradation by  digestive enzymes  such as  pepsin. The low pH also activates the enzyme precursor pepsinogen  into the active enzyme pepsin by self-cleavage. After leaving the stomach, the hydrochloric acid of the chyme  is neutralized in the  duodenum  by  sodium bicarbonate.

The stomach itself is protected from the strong acid by the secretion  of a thick  mucus  layer, and by  secretin  induced buffering with  sodium bicarbonate. Heartburn or  peptic ulcers  can develop when these mechanisms fail. Drugs of the antihistaminic  and  proton pump inhibitor  classes can inhibit the production of acid in the stomach, and  antacids  are used to neutralize existing acid.



Chemistry
Hydrogen chloride (HCl) is a monoprotic acid , which means it can  dissociate  (//i.e.,// ionize) only once to give up one H+ ion (a single  proton  ). In aqueous hydrochloric acid, the H+ joins a water molecule to form a hydronium  ion, H3O+:

HCl + H2O → H3O+ + Cl− The other ion formed is Cl−, the chloride ion. Hydrochloric acid can therefore be used to prepare salts called //chlorides//, such as sodium chloride. Hydrochloric acid is a strong acid , since it is essentially completely dissociated in water.

Monoprotic acids have one acid dissociation constant , //K//a, which indicates the level of dissociation in water. For a strong acid like HCl, the //K//a is large. Theoretical attempts to assign a//K//a to HCl have been made. When chloride salts such as NaCl are added to aqueous HCl they have practically no effect on pH , indicating that Cl− is an exceedingly weak  conjugate base  and that HCl is fully dissociated in aqueous solution. For intermediate to strong solutions of hydrochloric acid, the assumption that H+ molarity  (a unit of  concentration  ) equals HCl molarity is excellent, agreeing to four significant digits.

Of the six common  strong  mineral acids  in chemistry, hydrochloric acid is the monoprotic acid least likely to undergo an interfering  oxidation-reduction  reaction. It is one of the least hazardous strong acids to handle; despite its acidity, it consists of the non-reactive and non-toxic chloride ion. Intermediate-strength hydrochloric acid solutions are quite stable upon storage, maintaining their concentrations over time. These attributes, plus the fact that it is available as a pure reagent , make hydrochloric acid an excellent acidifying reagent.

Hydrochloric acid is the preferred acid in titration  for determining the amount of  bases. Strong acid titrants give more precise results due to a more distinct endpoint. Azeotropic or "constant-boiling" hydrochloric acid (roughly 20.2%) can be used as a  primary standard  in  quantitative analysis , although its exact concentration depends on the  atmospheric pressure  when it is prepared.

Hydrochloric acid is frequently used in chemical analysis  to prepare ("digest") samples for analysis. Concentrated hydrochloric acid dissolves many metals and forms oxidized metal chlorides and hydrogen gas, and it reacts with basic compounds such as calcium carbonate  or  copper(II) oxide , forming the dissolved chlorides that can be analyzed.