Acids

Acids: The Definitions

Under the Arrhenius definition, acids are substances that produce protons (H+ ions) when in an aqueous solution (which has water as its solvent). For example, when HCl (hydrochloric acid) dissociates in water, it produces H+ (aq) and Cl- (aq), which increases the concentration of protons in the solution.

For more information, check out these websites:

• https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Acids_and_Bases/Acid/Arrhenius_Concept_of_Acids_and_Bases

• https://www.intechopen.com/books/corrosion/the-arrhenius-acid-and-base-theory

Under the Bronsted-Lowry Definition, acids were proton (H+) donors. Let's take the example with HCl again:

HCl (aq) + H2O(l) --> H3O (+) + Cl- (aq)

Here, HCl donated its proton to water to from hydronium cation (H3O+).

Here are some more resources to explore:

• https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Acids_and_Bases/Acid/Bronsted_Concept_of_Acids_and_Bases

• https://courses.lumenlearning.com/suny-mcc-introductorychemistry/chapter/bronsted-lowry-acids-and-bases/

But what if a compound doesn't contain a hydrogen atom (H) but still acts like an acid? Lewis came up with the answer. He defined a an acid as a substance that accepts a pair of electrons. This would apply to compounds like AlCl3 or BCl3, which are acidic in nature but do not contain hydrogen.

Here are some resources to check out on Lewis acids:

• https://chemed.chem.purdue.edu/genchem/topicreview/bp/ch11/lewis.php

• https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Acids_and_Bases/Acid/Lewis_Concept_of_Acids_and_Bases

Other Properties

If one were to taste an acid (and yes there are non-hazardous acids, depending on concentration, for human consumption!), it would taste "sour". Indeed, the term "acid" is related to the Latin for "sour". Unfortunately, acids tend to have the bad habit of corroding surfaces with which they come in contact. Hydrochloric acid (HCl) can corrode your skin, for example.

Under the pH scale, acids have a pH less than 6 (commonly) or 7 (by definition).

Examples of Acids:

Acids can be found in substances like:

• Limes/Lemons/oranges/grape/tomato (juice)

• Black coffee

• Urine

• Stomach fluids

• Yogurt

• Vinegar

• Batteries

• Insecticides (boric acid)

• Lactic acid (produced when you exercise)

Chemical formulas of acids include:

Strong acids:

• HCl (hydrochloric acid)

• HBr (hydrobromic acid)

• HI (hydroiodic acid)

• H2SO4 (sulfuric acid)

• HNO3 (nitric acid)

• HClO4 (perchloric acid)

• and more...

Weak acids:

• Cations of strong bases (i.e. Na+)

• HF (hydrofluoric acid)

• HC2H3O2 (acetic acid)

• H3PO4 (phosphoric acid)

• H2CO3 (carbonic acid)

• and more...

Typically, these are used in laboratory settings only due to their hazardous properties.