Why is it at all necessary to understand the chemistry of oxalic acid? Let us find out. Imagine a salad made with some leafy greens, tomatoes and almonds. Also some soy yoghurt, sweet potato-beet root smoothie with some raspberry toppings.
Now can you guess about a common link between the food items that I have just stuffed in? And your answer is- High oxalic acid/oxalate content.
Often we end up consuming around 200 - 300 mg of oxalates daily. Although people prone to kidney stone risks or kidney-related disorders are often recommended by doctors to lower their oxalate intake to 50-100 mg per day depending on the severity of the case.
Hence it is important to understand the chemistry of this acid!
TABLE OF CONTENTS
Oxalic Acid is the simplest dicarboxylic acid with the IUPAC name Ethanedioic Acid and a molecular formula of HOOC - COOH. It is also known as Oxiric acid. It is a colourless crystalline acid which dissolves in water, forming a colourless solution.
Since 1745, salts of oxalic acid were extracted from wood sorrel by Dutch scientist Herman Boerhaave. However, later in the year 1773, François Pierre Savary isolated oxalic acids from these salts. Finally, oxalic acid was prepared synthetically in a laboratory in the year 1776.
Approximately 120,000 tonnes of oxalic acid are produced every year across the globe for usage.
The formula of oxalic acid is H2C2O4 and is a diprotic acid. Its conjugate base is called oxalate, (C2O4)2-.
Oxalic acid can also exist in the form of dihydrate H2C2O4. 2H2O It can exist as a dimer as well owing to hydrogen bond formation.
In this reaction, the - CHOH. CHOH units present in the sucrose break up forming the di-carboxylic group of oxalic acid.
Firstly, sodium formate is heated at 400' C to give the following product:
The sodium oxalate obtained is then dissolved in an aqueous solution of Ca(OH)2. Calcium oxalate precipitates out of the solution.
The calcium oxalate solid is with a calculated amount of dilute sulphuric acid in order to liberate oxalic acid. The reaction can be represented as follows:
Calcium sulphate precipitate is filtered out and oxalic acid is crystallized from the filtrate as a dihydrate.
Since It is a dibasic acid, = 2
Equivalent mass of Oxalic acid dihydrate is given by =
Oxalic acid consists of two carboxyl groups. Hence it gives most of the reactions of the carboxylic acid group twice owing to two - COOH groups.
When glycerol is heated with oxalic acid at around 530K, allyl alcohol is produced.
Q1. What is the significance of oxalic acid in industries?
Answer: Oxalic acid is greatly used as an acid rinse in laundries, where it is effective in removing rust and ink stains owing to its reducing nature. Also because it converts most insoluble iron compounds into a soluble complex ion.
Q2. Oxalic acid is made to react with conc. H2SO4 and the resultant mixture is made to pass through KOH solution. Which of the following will come out of the solution unchanged?
Answer: Option A is correct. Oxalic acid on being treated with conc. H2SO4 produces carbon dioxide, carbon monoxides along with the removal of water. KOH being a strong base, preferably absorbs CO2.
Hence the gas which comes out finally is CO. So Option A is correct.
Q3. IUPAC name of Oxalic acid is?
A. Ethanoic Acid
B. Ethanedioic Acid
C. Oxiric Acid
D. Butanedioic Acid
Answer: Option B is correct. Since the long chain has 2 carbon atoms and a functional group is - COOH present at both these two positions, So Ethanedioic acid is the answer.
Q.4 Oxalic acid can be obtained in the presence of nitric acid, by oxidation of :
A. Ethylene Glycol
C. Ethanedioic acid
Answer: On oxidation of carbohydrates by strong oxidizing agents like nitric acid, in presence of catalyst like V2O5, oxalic acid is produced. Hence Option B is the answer.
Question 1. Is oxalic acid polar or non-polar?
Answer: Two carboxylic acid groups are present in oxalic acid (HOOC - COOH). These groups are polar as it has a tendency to donate 2 H+ ions and form the conjugate base. Also, it can form hydrogen bonds with molecules of water. Oxalic acid is therefore an ideal water-solute. In fact, it is polar and is thus soluble in all polar solvents.
Question 2. What are the natural sources of oxalic acid?
Answer: The most common sources are leafy greens like spinach, cabbage, broccoli, and brussels sprouts; tomatoes, soy milk, soy yoghurt, almonds, nuts, and raspberries etc.
Question 3. Is oxalic acid weak or strong?
Answer: Oxalic acid is an organic acid and hence a weak acid as compared to mineral acids. It is weaker than H3O+ but stronger than acetic acid, nitrous acid and benzoic acid due to the two carboxyl group present in the molecule.
Question 4. Is oxalic acid anyhow linked with kidney stones?
Answer: It is estimated that approximately 80% of kidney stones, globally, are composed of calcium oxalate (Ca - Ox) mixed with calcium phosphate. A large number of people with potential risk of kidney stones are recommended by doctors to lower their oxalate intake levels to 50 - 100 mg per day.
Question 5. How can we eliminate oxalates from the body?
Answer: It is possible, by increasing the amount of calcium in the diet. A diet rich in calcium intake will help to reduce the amount of oxalate being absorbed by the human body. And as a result, stones are less likely to form.
|Preparation and chemical reactions of ethanoic acid||Preparation and chemical reactions of Benzoic acid|
|Uses of carboxylic acid||Acid derivatives - Structure and chemical properties|