The concept of acids and bases has been known since the 18th century’s. For the first time, in 1884 a Swiss scientist, Svante August Arrhenius, suggested a theory of acid-base. Arrhenius argued that in water, dilute acids and bases will experience a decomposition into ions. Acid is a substance in water to release hydrogen ions (H).While the base is a substance in water to release hydroxide ions (OH-).
HA (aq) -> H (aq) A-(aq)
Acid hydrogen ion
B (aq) H2O (l) -> BH (aq) OH-(aq)
This theory is quite rational, but after a while, the chemists argue that the H ions can hardly stand alone in solution. This is because the H ions are ions with ionic radii are very small. Therefore, the H ions are bound in a molecule of water and as Other oxonium ions are (H3O). So that the correct reaction to acid compounds in water are as follows.
HA (aq) H2O (aq) -> H3O (aq) A-(aq)
However, more often written ion H3O H, so that the writing becomes as follows.
HA (aq) -H2O-> H (aq) A-(aq)
Type of acid and alkaline compounds
a. Acid compounds
Based on the number of H ions that can be removed, acid compounds can be classified into several types, namely
1) Acid monoprotik, namely acid compounds that can be
release of H ions. Examples of HCl, HBr, HNO3, and
2) Acid poliprotik, are compounds that can release acid
more than one H ion. These acids can be divided into two, namely acid and diprotik
a) Acid diprotik is acid compounds that can release two H ions. Examples of H2SO4, H2CO3 and H2S.
b) Acid triprotik is acid compounds that can release three H ions. Example H3PO4.Based on the ability of acidic compounds to react with water to form H, acidic compounds can be divided into:
1) binary acid, the acid-containing elements of H and non-metallic elements other (non-metal hydride). Examples of HCl, HBr, and HF.
2) oxy acid, the acid-containing elements of H, O, and other elements. Examples of HNO3, H2SO4, HClO3.
3) organic acids, namely acid classified as organic compounds. Examples of CH3COOH and HCOOH.
b. Alkali compounds
Basic compounds can be sorted by the number of-OH groups that can be removed, namely alkaline monohidroksi and polyol.
1) A base monohidroksi are basic compounds that can release one OH-ion. Example NaOH, KOH, and NH4OH.
2) A base polyol is the basic compounds that can release more than one OH-ion. These bases can be divided into
a) dihydroxy bases, namely basic compounds which can release two OH-ions.Examples of Mg(OH)2 and Ba(OH)2.
b) A base trihidroksi is alkaline compound that releases three OH-ions. Examples of Fe(OH)3 and Al(OH)3.
c. The nature of acids and bases
At first, a substance classified as acid or alkaline based on the solution properties of substances in water. The nature of acid or alkaline a substance can be identified by taste. A substance is said as if giving a sour taste sour, while a substance said to be basic if it’s bitter and feel slippery. However, the introduction of this method is risky because of possible chemical compounds that are toxic.
To identify the nature of a solution can be found by using the acid-base indicator. Acid-base indicator is a substance that gives a different color in acid solution and base solution. With the difference that color, acid-base indicator can be used to find out what a substance including acid or alkaline.
One of the practical acid-base indicator used is the litmus. Litmus derived from species of lichens that can be shaped
solution or paper. Frequently used form of litmus
paper, because it is more difficult to oxidize and produce
obvious color changes.
There are two kinds of litmus paper, namely
1) red litmus paper
Red litmus paper turned blue in alkaline solution and the solution of acid or neutral color does not change (still red).
2) blue litmus paper
Blue litmus paper turned red in acid solution and the solution of alkaline or neutral color does not change (remains blue).