Brønsted-Lowry’s acid-base theory: Acid is a substance which gives a proton (protondonor) and base is a substance which accepts a proton (protonacceptor).
Acid-base indicator is a weak acid or weak base, such as litmus, methyl orange or phenolphthalein, which changes colour when it gains or loses an H+ ion.
Acid-base titration is an analytical technique in volumetric analysis, where an acid of known concentration is used to neutralise a known volume of a base, and the observed volume of the acid required is used to determine the unknown concentration of the base. An acid-base indicator is used to determine the end-point of the titration.
Brøsted acid is a material that gives up hydrogen ions in a chemical reaction.
Brønsted base is a material that accepts hydrogen ions in a chemical reaction.
Acid is a type of compound that contains hydrogen and dissociates in water to produce positive hydrogen ions. The reaction for an acid HA is commonly written:
In fact, the hydrogen ion (the proton) is solvated, and the complete reaction is:
This definition of acids comes from the Arrhenius theory. Such acids tend to be corrosive substances with a sharp taste, which turn litmus red and produce colour changes with other indicators. They are referred to as protonic acids and are classified into strong acids, which are almost completely dissociated in water, (e.g. sulphuric acid and hydrochloric acid), and weak acids, which are only partially dissociated (e.g. acetic acid and hydrogen sulphide). The strength of an acid depends on the extent to which it dissociates, and is measured by its dissociation constant.
In the Lowry-Brønsted theory of acids and bases (1923), the definition was extended to one in which an acid is a proton donor (a Brønsted acid), and a base is a proton acceptor (a Brønsted base). An important feature of the Lowry-Brønsted concept is that when an acid gives up a proton, a conjugate base is formed that is capable of accepting a proton.
Similarly, every base produces its conjugate acid as a result of accepting a proton.
For example, acetate ion is the conjugate base of acetic acid, and ammonium ion is the conjugate acid of ammonia.
As the acid of a conjugate acid/base pair becomes weaker, its conjugate base becomes stronger and vice versa.
A further extension of the idea of acids and bases was made in the Lewis theory. In this, a G. N. Lewis acid is a compound or atom that can accept a pair of electrons and a Lewis base is one that can donate an electron pair. This definition encompasses "traditional" acid-base reactions, but it also includes reactions that do not involve ions, e.g.
in which NH3 is the base (donor) and BCl3 the acid (acceptor).
Conjugated acid is a particle that develops after a base receives a proton.
Conjugated base is a particle which is left after a molecule of acid releases a proton.
Deoxyribonucleic acid (DNA) is a nucleic acid with 2-deoxy-D-ribose as the sugar in its nucleotides. DNA contains encoded genetic information, specifically templates for the synthesis of all of an organism’s proteins and enzymes.
DNA was first identified in the 1869 by Swiss chemist Friedrich Miescher (1844-1895). In 1953, American biologist James Dewey Watson (1928-) and English physicist Francis Harry Compton Crick (1916–2004) had discovered that DNA occurs in the cell as a double helix, with two long strands of the molecule wound around each other, and further that the chemical structure of the molecule dictates that adenine (A) always aligns or pairs with thymine (T), and cytosine (C) always pairs with guanine (G). It is this base pairing that allows DNA in a cell to copy itself, and transfer its information to a new cell. The diameter of the helix is 2.0 nm and there is a residue on each chain every 0.34 nm in the z direction. The angle between each residue on the same strand is 36°, so that the structure repeats after 10 residues (3.4 nm) on each strand.
Ligand field theory is a description of the structure of crystals containing a transition metal ion surrounded by nonmetallic ions (ligands). It is based on the construction of molecular orbitals involving the d-orbitals of the central metal ion and combinations of atomic orbitals of the ligands.
Generalic, Eni. "Bronsted-Lowry%E2%80%99s acid-base theory." Croatian-English Chemistry Dictionary & Glossary. 29 June 2022. KTF-Split. {Date of access}. <https://glossary.periodni.com>.
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