It is important that the student knows how to perform the assembling the formula of basesas it is a very requested aspect in Inorganic Chemistry and in the study of solutions, since the bases are substances widely used in various chemical processes, such as in neutralization reactions.
To carry out the assembling the formula of a base, it is essential that we know which components are present in a base, whose general formula is YOH, in which:
Y is a cation, which can be any metal or ammonium (NH4+);
OH is the hydroxide, a monovalent anion (OH-1).
However, to carry out the assembling the formula of a base, we must know its name, which is constructed from the following naming rule:
Hydroxide + de + element name
In this rule, the term hydroxide refers to the OH anion, and the element is the cation (cation charge always depends on the nox element) that is accompanying it in the base formula.
Knowing any cation (element) (Y+x) and the hydroxide anion (OH-1), a base formula assembly it is given by the inversion of their charges, so that the charge of the cation (+x) becomes the numerical index (x) of the anion (after a parenthesis) and that the charge of the anion (-1) becomes the numerical index (1) of the cation.
Y+x + OH-1→ Y1(OH)x
Thus, it is evident that what differs one base from another is the element that accompanies the OH group and the numerical index in front of this group. The following are some examples of assembling the base formula:
1st Example: aluminum hydroxide
On this basis, we have the following components:
the aluminum cation (Al+3): which has a fixed nox +3, as it is located in family IIIA of periodic table;
the hydroxide anion (OH-1): common to inorganic bases.
Finally, just cross the ion charges, so that the -1 of the hydroxide is the index (1) of aluminum, and the +3 of aluminum is the index (3) of the hydroxyl, as follows:
Al1(OH)3 or Al(OH)3
2nd Example: Calcium hydroxide
On this basis, we have the following components:
the calcium cation (Ca+2): which has a fixed nox +2, as it is located in the IIA family (alkaline earth metals) from the periodic table;
the hydroxide anion (OH-1): common to inorganic bases.
Finally, just cross the ion charges, so that the -1 of the hydroxide is the index (1) of the calcium, and the +2 of the calcium is the index (2) of the hydroxyl, as follows:
Here1(OH)2 or Ca(OH)2
3rd Example: Gold hydroxide I
On this basis, we have the following components:
the gold cation I (Au+1): which has nox +1, as indicated in the given name;
the hydroxide anion (OH-1): common to inorganic bases.
Finally, just cross the ion charges, so that the -1 of the hydroxide is the index (1) of the gold (Au), and the +1 of the gold is the index (1) of the hydroxyl, as follows:
Au1oh1 or AuOH
4th Example: Titanium Hydroxide IV
On this basis, we have the following components:
the titanium IV cation (Zn+4): which has nox +4, as indicated in the given name;
the hydroxide anion (OH-1): common to inorganic bases.
Finally, just cross the ion charges, so that the -1 of the hydroxide is the index (1) of titanium (Ti), and the +4 of titanium is the index (4) of the hydroxyl, as follows:
You1(OH)4 or Ti(OH)4
5th Example: zinc hydroxide
On this basis, we have the following components:
the zinc cation (Zn+2): which has fixed nox +2;
the hydroxide anion (OH-1): common to inorganic bases.
Finally, just cross the ion charges, so that the -1 of the hydroxide is the index (1) of zinc, and the +2 of the zinc is the index (2) of the hydroxyl, as follows:
Zn1(OH)2 or Zn(OH)2
Mother Diogo Lopes Dias
Source: Brazil School - https://brasilescola.uol.com.br/quimica/montagem-formula-das-bases.htm
