Acid: vị chua, làm thuốc nhuộm đổi màu
Bases: vị đắng, cảm giác nhớt.
Arrhenius: acids làm tăng [H+], bases làm tăng [OH-] trong dung dịch.
Arrhenius: acid + base salt + water.
Problem: định nghĩa này chỉ áp dụng được trong dung dịch nước
The H+ Ion in Water
The H+(aq) ion is simply a proton with no electrons. (H has one proton, one electron, and no neutrons.)
In water, the H+(aq) form clusters.
The simplest cluster is H3O+(aq). Larger clusters are H5O2+ and H9O4+.
Generally we use H+(aq) and H3O+(aq) interchangeably....
The solubility of a partially soluble salt is decreased when a common ion is added.
Consider the equilibrium established when acetic acid, HC2H3O2, is added to water.
At equilibrium H+ and C2H3O2- are constantly moving into and out of solution, but the concentrations of ions is constant and equal.
If a common ion is added, e.g. C2H3O2- from NaC2H3O2 (which is a strong electrolyte) then [C2H3O2-] increases and the system is no longer at equilibrium.
So, [H+] must decrease.
The roles of His181, His184 and Tyr186 in PETN reductase have been
examined by mutagenesis, spectroscopic and stopped-flow kinetics, and by
determination of crystallographic structures for the Y186F PETN reductase
and reduced wild-type enzyme—progesterone complex. Residues His181
and His184 are important in the binding of coenzyme, steroids, nitro-aromatic ligands and the substrate 2-cyclohexen-1-one.