Question

What is the chemical formula for iron (II) hydroxide?

Answer 1

Hint: Chemical formula of any compound represents the number of atoms involved. It tells us the exact stoichiometric composition of that compound. The chemical formulas of various compounds are written according to the rules and norms set by IUPAC.

Complete answer:
The chemical formulas of compounds are written in such a manner, so that they can compensate for the valences present in the atoms of the element. For instance, one negative charge of any ion cannot form a compound with an element having a charge of positive two. Therefore, those negative ions are taken in a quantity of two, and the whole numbers are written as subscript for their respective amounts.
We have been given iron (II) hydroxide, which is also called ferrous hydroxide. The respective formula for iron is, Fe and that of hydroxide is OH. As we know the cation is always named first, so iron is the cation and hydroxide is the anion.
The chemical name written as iron (II) represents that the valence of iron is +2, so it will be in form of $F{{e}^{2+}}$ , and as we know hydroxides have a formula, $O{{H}^{-}}$. So, to balance the +2 charge on ferrous, 2 hydroxide ions are needed. Therefore the formula becomes, $Fe{{(OH)}_{2}}$ .
Hence, the chemical formula for iron (II) hydroxide is $Fe{{(OH)}_{2}}$.

Note:
Iron is one of the transition elements. Transition elements have various valences, so their valence or charges are written in their chemical names. For instance, iron exist as ferrous with +2 charge and as ferric with +3 charge, so their hydroxides will be named as iron (II) hydroxide and iron (III) hydroxide and their formula will be written as $Fe{{(OH)}_{2}}$and $Fe{{(OH)}_{3}}$ respectively.