Introduction
The hydronium ion is an important
factor when dealing with chemical
reactions that occur in aqueous solutions. Its concentration
relative to hydroxide is a direct measure of the pH of
a solution. It can be formed when an acid is present in water or simply in pure
water. It's chemical formula is H3O+. It can also be
formed by the combination of a H+ ion with an H2O
molecule. The hydronium ion has a trigonal pyramidal geometry and is
composed of three hydrogen atoms and one oxygen atom. There is a lone
pair of electrons on the oxygen giving it this shape. The bond angle between
the atoms is 113 degrees.
H2O(l) ↔ OH-(aq)+ H+(aq)
As H+ ions are formed, they
bond with H2O molecules in the solution to form H3O+
(the hydronium ion). This is because hydrogen ions do not exist in aqueous
solutions, but take the form the hydronium ion, H3O+. A
reversible reaction is one in which the reaction goes both ways. In other
words, the water molecules dissociate while the OH- ions combine
with the H+ ions to form water. Water has the ability to attract H+
ions because it is a polar
molecule. This means that it has a partial charge, in this case the charge is
negative. The partial charge is caused by the fact that oxygen is more electronegative
than hydrogen. This means that in the bond between hydrogen and oxygen, oxygen
"pulls" harder on the shared electrons thus causing a partial
negative charge on the molecule and causing it to be attracted to the positive
charge of H+ to form hydronium. Another way to describe
why the water molecule is considered polar is through the concept of dipole moment.
The electron geometry of water is tetrahedral
and the molecular geometry is bent.
This bent geometry is asymmetrical, which causes the molecule to be polar and
have a dipole moment, resulting in a partial charge.
Figure 1. The picture above illustrates
the electron density of hydronium. The red area represents oxygen; this is the
area where the electrostatic potential is the highest and the electrons are
most dense.
An overall reaction for the dissociation of water to form hydronium can
be seen here:
2H2O(l) ↔ OH-(aq)+ H3O+(aq)
With Acids
Hydronium not only forms as a result of the dissociation of water, but also
forms when water is in the presence of an acid. As the acid dissociates,
the H+ ions bond with water molecules to form hydronium,
as seen here when hydrochloric acid is in the presence of water:
HCl(aq) + H2O → H3O+(aq) + Cl-(aq)
pH
The pH of a solution depends
on its hydronium concentration. In a sample of pure water, the
hydronium concentration is 1x10-7 moles per liter (0.0000001 M). The
equation to find the pH of a solution using its hydronium concentration is:
pH = -log [H3O+]
or log [H3O+]= -pH
Using this equation, we find the pH of
pure water to be 7. This is considered to be neutral on the pH scale.
The pH can either go up or down depending on the change in hydronium concentration.
If the hydronium concentration increases, the pH decreases, causing the
solution to become more acidic. This happens when an acid is introduced. As H+ ions
dissociate from the acid and bond with water, they form hydronium ions, thus
increasing the hydronium concentration of the solution. If the hydronium
concentration decreases, the pH increases, resulting in a solution that is less
acidic and more basic. This is caused by the OH- ions that
dissociate from bases. These ions bond with H+ ions from the
dissociation of water to form H2O rather than hydronium ions.
A variation of the equation can be used to calculate the hydronium
concentration when a pH is given to us:
[H3O+] = 10-pH
would u like tell me benefits of amide?
BalasHapusok vebria,,,,
BalasHapusI'll tell about it, but not so well because I'm still study too. hehehe :-D
You can read in my blog the title is AMIDE USEFULNESS IN LIFE, in here we can know that nylons are condensation copolymers formed by reacting equal parts of a diamine and a dicarboxylic acid, so that amides are formed at both ends of each monomer in a process analogous to polypeptide biopolymers. Chemical elements included are carbon, hydrogen, nitrogen, and oxygen.
Nylon 5,10, made from pentamethylene diamine and sebacic acid, was studied by Carothers even before nylon 6,6 and has superior properties, but is more expensive to make. In keeping with this naming convention, "nylon 6,12" (N-6,12) or "PA-6,12" is a copolymer of a 6C diamine and a 12C diacid. Similarly for N-5,10 N-6,11; N-10,12, etc. Other nylons include copolymerized dicarboxylic acid/diamine products that are not based upon the monomers listed above. For example, some aromatic nylons are polymerized with the addition of diacids like terephthalic acid (→ Kevlar, Twaron) or isophthalic acid (→ Nomex), more commonly associated with polyesters. There are copolymers of N-6,6/N6; copolymers of N-6,6/N-6/N-12; and others. Because of the way polyamides are formed, nylon would seem to be limited to unbranched, straight chains. But "star" branched nylon can be produced by the condensation of dicarboxylic acids with polyamines having three or more amino groups.