Question

The formate ion, HCO2-, is formed when formic acid dissolves in water. A number of possible resonance structures for this ion are shown. Which of these structures are valid and which are invalid?

 

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Answer 1

Concepts and reason

Resonance structures are Lewis structures which are obtained due to the motion of lone pair or pi-electron cloud in the structure.

These structures are electronically equivalent and indicated by double headed arrow $\left( \leftrightarrow \right)$

Fundamentals

Resonance structures : Resonance structure are structures which are indicating the same molecule but differ in their electrinical geometry.

Let A, B, and C are resonance structures, indicated as follows.

${\rm{A}}\, \leftrightarrow \,{\rm{B}}\, \leftrightarrow \,{\rm{C}}$

Charge on every cannonical structutre (resonanse strucure) shoud be equal.

Given ion is formate ion $\left( {{\rm{HC}}{{\rm{O}}_{\rm{2}}}^{\rm{ - }}} \right)$

Given that this formate ion produced by dissolving the formic acid in water.

Complete reaction is as follows:

${\rm{HCOOH + }}{{\rm{H}}_{\rm{2}}}{\rm{O}}\longrightarrow{{}}{\rm{HCO}}{{\rm{O}}^{\rm{ - }}}{\rm{ + }}{{\rm{H}}_{\rm{3}}}{{\rm{O}}^{\rm{ + }}}$

Lewis structure of the formate ion is shown below.

Formate ion structure is shown below:

Resonance structure for this formate ion is as follows:

Therefore, only two possible resonance structures are there for formate ion.

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