Oxalic Acid Formula: Structure, Molar Mass, Preparation, Uses

Our elders encourage us to consume a sufficient amount of green leafy vegetables. This is because, in addition to being high in fibre, green leafy vegetables are a good source of oxalic acid. Oxalic acid is the most basic dicarboxylic acid and is commonly used as a primary standard solution in acid-base titrations. The oxalic acid formula is represented as \({({\rm{COOH}})_2}\).

The IUPAC name of oxalic acid is ethandioic acid. It is known as the simplest dicarboxylic acid. In this article, we will provide detailed information on Oxalic Acid. Scroll down to learn more!

Oxalic Acid Formula

The IUPAC name of oxalic acid is ethandioic acid. It belongs to the carboxylic acid functional group with the condensed formula \({{\rm{C}}_2}{{\rm{H}}_2}{{\rm{O}}_4}.\) Its chemical formula is \({({\rm{COOH}})_2}\) Which is the crystalline form. However, the molecular formula of hydrated oxalic acid is \({({\rm{COOH}})_2} \cdot 2{{\rm{H}}_2}{\rm{O}}.\)

Molar Mass of Oxalic Acid

The molar mass of Oxalic acid, \({({\rm{COOH}})_2}\),  is:

\(2({\rm{The}}\,{\rm{atomic}}\,{\rm{mass}}\,{\rm{of}}\,{\rm{carbon}}) + 2({\rm{The}}\,{\rm{atomic}}\,{\rm{mass}}\,{\rm{of}}\,{\rm{hydrogen}}){\rm{ + 4}}\left( {{\rm{Atomic}}\,{\rm{mass}}\,{\rm{of}}\,{\rm{Oxygen}}} \right)\)

\( = 2(12.01) + 2(1.007) + 4(15.999) = 90.03\;{\rm{g}}\;{\rm{mo}}{{\rm{l}}^{ – 1}}\)

Hence, one mole of oxalic acid weighs \(90.03\) grams.

Hybridisation of Oxalic Acid

Oxalic acid is the simplest dicarboxylic acid. Oxalic acid, also known as ethanedioic acid, consists of a double carboxylic acid group \(( – {\rm{COOH}})\) attached through single bonds. There are two \({\rm{O}} – {\rm{H}}\) and \({\rm{C}} – {\rm{O}} – {\rm{H}}\) single bonds each and two \( – {\rm{CO}}\) double bonds. There are seven sigma bonds and two pi bonds.

It has two hydrogen atoms, two carbon atoms, and four oxygen atoms. The chemical structure of oxalic acid is as shown below.

The two carbon atoms of oxalic acid have similar hybridisation. This is because both have the same group attached to two of their ends.

The steric number of the carboxylic carbon atom \(=\) Number of atoms attached \(+\) Lone pairs

\( = 3 + 0 = 3\)

The carbon atoms (\({{\rm{C}}_1}\) and \({{\rm{C}}_2}\)) of oxalic acid is \({\rm{s}}{{\rm{p}}^2}\) hybridised \(\left( {1{\rm{s}} + 2{\rm{P}} = 3{\rm{s}}{{\rm{p}}^2}} \right)\). The atomic orbitals of the carbon atom undergo intermixing to form \({3{\rm{s}}{{\rm{p}}^2}}\) hybridised orbitals.

There are two lone pairs on the oxygen atom of the carbonyl group and that of the hydroxyl group. The hydroxyl oxygen allows one of its lone pair electrons to conjugate with the pi system of the carbonyl group. This makes the carboxyl group planar in structure.

Lewis Structure of Oxalic Acid

The electron dot structures or the Lewis structures are the two-dimensional diagrams used to represent valence electrons between atoms of the molecule. Bonding, as well as nonbonding electrons (lone pairs) present in the outermost shell of an atom, can be represented using Lewis structures.

In Oxalic acid, there are two hydrogen atoms, four oxygen atoms, and two carbon atoms. Hence, the total number of valence electrons in Oxalic acid is: \(\left( {{4^*}2{\rm{C}}} \right) + \left( {{1^*}2{\rm{H}}} \right) + \left( {{6^*}4{\rm{O}}} \right) = 34\) electrons.

The \(34\) valence electrons are distributed over \({\rm{C}},\,{\rm{H}}\) and \({\rm{O}}\), with Carbon atom as the central atom. The distribution occurs so that the \({\rm{C}}\) and \({\rm{O}}\) atoms satisfy the octet rule and hydrogen satisfies its duplet. The remaining electrons are present as lone pairs.

The two bonding electrons will form a single bond, and four bonding electrons will form a double bond. Hence, the Lewis structure of oxalic acid can be drawn as:

Preparation of Oxalic Acid

The preparation of oxalic acid by various methods are explained below:

Laboratory Preparation of Oxalic Acid

Oxalic acid can be prepared by the oxidation of sugar using nitric acid in the presence of vanadium pentoxide as the catalyst.

Industry Preparation of Oxalic Acid

Oxalic acid is usually manufactured by heating sodium formate with sodium hydroxide to form sodium oxalate. It is then converted to calcium oxalate and treated with sulfuric acid to obtain oxalic acid.

Physical Properties of Oxalic Acid

The physical properties of oxalic acid are as follows:

1. Oxalic acid is an odourless, colourless crystalline white solid.
2. The density of oxalic acid is \(1.9\;{\rm{g}}/{\rm{mL}}.\)
3. It has a melting point of \(190\,^\circ {\rm{C}}\) and is commonly found in the hydrated form \({({\rm{COOH}})_2} \cdot 2{{\rm{H}}_2}{\rm{O}}.\)
4. It is water-soluble and forms an acidic solution in water.

Chemical Properties of Oxalic Acid

The chemical properties of oxalic acid are as follows:

1. Anhydrous oxalic acid is hydrophilic and readily absorbs water.
2. It is the strongest and simplest dicarboxylic acid and reacts like a typical carboxylic acid, forming the acid chloride and ester derivatives.
3. It is an excellent reducing agent and can reduce the manganese from \(+7\) oxidation state to \(+2\) oxidation state. This property is often used for quantitative analysis of potassium permanganate.
   \(5{{\rm{C}}_2}{{\rm{H}}_2}{{\rm{O}}_4} + 2{\rm{KMn}}{{\rm{O}}_4} + 3{{\rm{H}}_2}{\rm{S}}{{\rm{O}}_4} \to {{\rm{K}}_2}{\rm{S}}{{\rm{O}}_4} + 2{\rm{MnS}}{{\rm{O}}_4} + 8{{\rm{H}}_2}{\rm{O}} + 10{\rm{C}}{{\rm{O}}_2}\)
4. Oxalic acid can react with phosphorus pentachloride to generate phosphorus oxychloride.
5. Upon heating metals with oxalic acid, oxalic acid salt is formed that can lose carbon monoxide and form carbonates. The carbonates can further be heated to decompose into oxide and carbon dioxide. The oxalic acid salt of nickel, cobalt and silver can produce metal instead of nonmetal oxide.
6. It acts as an excellent chelating ligand for various metal cations.

Uses of Oxalic Acid

The uses of oxalic acid are as follows:

1. Oxalic acid can be used as a reducing agent, bleaching agent, mordant for dyeing and printing industry.
2. It is also used in refining of rare metals.
3. It is used as analytical reagent, laboratory reagents, chromatography analysis reagent and dye intermediates.
4. Oxalic acid is used in the production of drugs such as antibiotics.

Oxalic Acid Dihydrate Formula

The molecular formula of oxalic acid dihydrate is \({({\rm{COOH}})_2}.\,2{{\rm{H}}_2}{\rm{O}}\)  with a molecular weight of \(126.07\;{\rm{g}}/{\rm{mol}}.\)

Oxalic acid dihydrate is a reducing agent and can give away \(2\) protons (hydrogen ions) to a base. It is used to reduce populations of naturally occurring microorganisms and as a buffer solution in chromatographic separation.

Equivalent Weight of Oxalic Acid (Calculation)

Oxalic acid is a dibasic acid which can donate two \({{\rm{H}}^ + }\) ions. Therefore, the equivalent weight of oxalic acid can be calculated with the help of the following formula:

\({\rm{Equivalent}}\,{\rm{weight}} = \frac{{{\rm{Molecular}}\,{\rm{weight}}}}{{{\rm{Number}}\,{\rm{of}}\,{\rm{equivalent}}\,{\rm{moles}}}}\)

As \(1\) mole of oxalic acid can release \(2\) moles of \({{\rm{H}}^ + }\) ions and neutralise \(2\) moles of \({\rm{O}}{{\rm{H}}^ – }\) ions, the number of equivalent moles here is equal to \(2\). Thus, the equivalent weight of oxalic acid can be calculated as follows:

Equivalent weight of oxalic acid \(=\) molecular mass of oxalic acid \(/2 = 126\;{\rm{g}}/2 = 63\) grams.

Therefore, the equivalent weight of oxalic acid is \(63\) grams.

Summary

Oxalic acid is a dibasic acid with two ionisable \({{\rm{H}}^ + }\) ions. It is one of the commonly used primary standard solutions, used in titration. Hence, it’s important to learn its structure and related properties. Oxalic acid is utilised in the production of drugs like antibiotics. In this article, we learned the chemical formula, chemical structure and properties of oxalic acid. We also learnt its laboratory and industrial preparation along with its uses.

FAQs on Oxalic Acid

Q.1. What is the molecular formula of oxalic acid?
Ans: The molecular formula of oxalic acid is \({{\rm{C}}_2}{{\rm{H}}_2}{{\rm{O}}_4}\). It can also be written as \({({\rm{COOH}})_2}\).

Q.2. What is oxalic acid?
Ans: Oxalic acid is a dibasic acid with a molecular formula \({{\rm{C}}_2}{{\rm{H}}_2}{{\rm{O}}_4}\). It is also represented as \({({\rm{COOH}})_2}\) and has a molecular weight of \(90.03\;{\rm{g}}\;{\rm{mo}}{{\rm{l}}^{ – 1}}\). Its dihydrate form has the molecular formula \({({\rm{COOH}})_2} \cdot 2{{\rm{H}}_2}{\rm{O}}\).

Q.3. What is oxalic acid used for?
Ans: Oxalic acid can be used as a reducing agent, bleaching agent, mordant for the dyeing and printing industry, and in rare metals refining. It is also used as an analytical reagent, laboratory reagents, chromatography analysis reagent, and in production drugs such as antibiotics.

Q.4. What acid is \({{\rm{C}}_2}{{\rm{H}}_2}{{\rm{O}}_{\rm{4}}}\)?
Ans: \({{\rm{C}}_2}{{\rm{H}}_2}{{\rm{O}}_4}\) is a dibasic acid known as oxalic acid. It is a weak acid and can release two \({{\rm{H}}^ + }\) ions.

Q.5. Which vegetable contains oxalic acid?
Ans: Tomatoes are rich in oxalic acids.

Q.6. How do you neutralise oxalic acid?
Ans: Oxalic acid is a weak acid that can be neutralised by using baking soda.

We hope this detailed article on the oxalic acid formula is helpful to you. If you have any queries on this page or in general about oxalic acid, ping us through the comment box below and we will get back to you as soon as possible.