Acetic Acid

An Introduction to Acetic Acid Structure (CH3COOH) 

Acetic acid with the chemical formula of CH3COOH is also known as ethanoic acid. It is a colourless liquid with the characteristic of a pungent smell. This organic compound is soluble in water and more acidic than H2O but less acidic than mineral acids. 5-8% acetic acid in water is called vinegar and is used widely as preservatives in pickles. 

The structure of CH3COOH in solid-state exists in a chain of molecules, and they are connected through hydrogen bonds with each other. The undiluted version of it is also known as glacial acetic acid because it has a melting point of 16⁰ C and hence often gets frozen in winter when weather is cold. 

Structure of Acetic Acid

Acetic acid is the second simplest form of a carboxylic acid-containing methyl group with CH3 chemical name and is connected to carboxylic acid group (COOH). In another way, we can say that it is the acetyl group (CH3CO) connected to hydroxyl group (OH). 

The structure of CH3COOH reveals that it contains sp2 hybridisation. Ethanoic acid behaves as dimer while in liquid and vapour state because of intermolecular hydrogen bonding. This following figure shows the structure.

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Apart from that, to draw the Lewis structure of acetic acid first, you have to figure out the number of valence electrons. As for this organic compound, carbon, oxygen and hydrogen have 4, 6 and 1 valence electrons, respectively. Therefore total number of electron valence will be= 2(4) +2(6) +4(1) = 24. 

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If you look at the Lewis structure, you will see that there is one double bond and six single bonds. Also, each oxygen molecule contains two lone pairs of electrons. Also, keep in the mind that each dash refers to two electrons and each lone pair means two electrons. 

  1. Physical

Properties of CH3COOH


Chemical formula


C2H2O2


Appearance


Colourless liquid


Odour


Pungent, vinegar like


Molar mass


60.052 g·mol−1


Solubility 


Miscible 


Melting point


16⁰ to 17⁰ C


Boiling point


118⁰ to 119⁰ C


  1. Chemical

Acidity (Reaction with metals, Alkalis) 

1. Ethanoic acid is known to react with active metals like Na to liberate hydrogen. This reaction is similar to that of ethanol. 

CH3COOH + Na--CH3COONa+H2

 2. Acetic acid reacts with NaOH to form salt and water. 

CH3COOH + NaOHCH3COONa + H2O 

3. CH3COOH also reacts with sodium carbonate and sodium hydrogen carbonate, which are weaker bases and releases CO2

Na2 CO3 + 2 CH3COOH → 2 CH3COONa + CO2 + H2O

CH3COOH + NaHCO3 ↓ NaCH3COO + H2O + CO2

Acid Chlorides

It reacts with thionyl chloride and produces acetyl chloride. 

CH3COOH + SOCl2---------> CH3COCl + HCl + SO2

Acid Anhydride

Acetic acid reacts with an acid chloride in the presence of a base and releases acetic anhydride. 

CH3CO2H → CH2 =C=O + H2O

CH3CO2H + CH2=C=O → (CH3CO)2O

Ester

When any alcohol reacts with any carboxylic acid, it produces esters. When acetic acid reacts with ethyl alcohol, it leads to the formation of ethyl ethanoate.  

CH3COOH + C2H5OH ------- CH3COOC2H5 + H2O

CH3COOH as Solvent

Acetic acid is a polar protic solvent. It is an acid solvent as it can donate an H+ ion to the substance to be dissolved. It is often used in reactions like Friedel-Crafts Alkylation. Using it, terephthalic acid can be produced. 

Acetic Acid Preparation 

Ethanoic acid is prepared industrially primarily via carbonylation. This process takes place in the following steps

1. CH3OH + HI → CH3I + H2O

2. CH3I + CO → CH3COI

3. CH3COI + H2O → CH3COOH + HI

Other Methods

Acetaldehyde Oxidation

2 CH3CHO + O2 → 2 CH3CO2H

Under some conditions and using catalysts, acetic acid can be formed. In this reaction, several significant by-products are produced for example formic acid, ethyl acetate, etc.

Ethylene Oxidation

In the presence of palladium catalyst, we can get acetic acid from ethylene.

C2H4 + O2 → CH3CO2H

Oxidative Fermentation

In the presence of sufficient oxygen, acetic acid bacteria can produce ethanoic acid from foodstuffs. 

C2H5OH + O2 → CH3COOH + H2O

Anaerobic Fermentation 

C6H12O6 → 3 CH3COOH

Some anaerobic bacteria like Acetobacterium can transform sugar directly into acetic acid.  

Apart from these methods, researchers are also trying to produce acetic acid through the oxidation of waste gases from industrial processes. 

Baking Soda and CH3COOH Reaction

The reaction between sodium bicarbonate and acetic acid produces carbon dioxide gases. It is usually used in chemical volcanoes.  

The overall chemical equation is as follows:

NaHCO3(s) + CH3COOH (l) → CO2(g) + H2O(l) + Na+(aq) + CH3COO-(aq)

Where, s = solid, g = gas, l = liquid, aq = aqueous or water solution.

You can write this reaction in other way as well,

NaHCO3 + HC2H3O2 → NaC2H3O2 + H2O + CO2

However, this reaction is not responsible for the dissociation of the NaC2H3O2 in water.

The chemical reaction typically takes place in two steps. In which the first one is a double displacement reaction where acetic acid of the vinegar reacts with sodium bicarbonate to produce carbonic acid and sodium acetate

NaHCO3 + HC2H3O2 → NaC2H3O2 + H2CO2

Since Carbonic acid is unstable, it goes through a decomposition reaction to release carbon dioxide gas

H2CO3 → H2O + CO2

The carbon dioxide leaves the solution in bubbles form. Since these bubbles weigh more than air, the carbon dioxide collects on the surface of the beaker or overflows. In this baking soda volcano, usually, detergent is used to collect the gas which forms bubbles and appears to a great extent like lava from a 'volcano.' Nonetheless, a solution of diluted sodium acetate still stays even after the reaction. However, if we boil off the water from this solution, there remains a supersaturated sodium acetate solution. It is called "hot ice" that crystallised spontaneously and releases heat and produces a solid that is more like water ice.

The baking soda and vinegar reaction release carbon dioxide that has different uses apart from forming a chemical volcano. It is then collected and utilised as a chemical fire extinguisher.

Did You Know

· November 1st is observed as National Vinegar Day. 

· This name vinegar directly came from French “vin aigre” meaning “sour wine”. 

Application of Acetic Acid

  • CH3COOH is massively used in numerous industries. 

  • Commercially, acetic acid is used in manufacturing vinegar, ester, and several polymeric materials. 

  • It has been noted, apple cider vinegar reduces high concentration of blood sugars and also helps in losing weight.

  • Farmers sometimes spray acetic acid on livestock silage to fight fungal and bacterial growth. 

  • Before examining white blood cells, it is also used to lyse red blood cells.

  • In the production of camphor, perfume and cooking ingredients, acetic acid acts as a solvent.

  • For photographic emulsion development, it is also often used as a stop bath.  

Health Hazards

Acetic acid can prove to be hazardous for health if not used with precautions. As it is highly corrosive to eyes and skin, proper safety measures should be followed while handling this chemical. It includes wearing gloves, splash goggles etc. 

Also, though drinking apple cider vinegar is good for health, excessive intake of it may lead to stomach upset, damage of throat and teeth, etc. 

Acetic acid can be harmful to aquatic organisms as well. If it mixes with water, it makes the water acidic and inappropriate for living creatures.  

Trivia

People have been using acetic acid for centuries now, mostly as vinegar. However, it is believed that an Islamic alchemist Jabir ibn Hayyan Geber first extracted CH3COOH from vinegar. In 1700, a German chemist Georg Ernst Stahl (1660–1734) extracted acetic acid from vinegar by distillation.

About 1.4 million metric tons of CH3COOH is produced in the United States every year. The major part of it is used as raw material for the production of plastics. 

Test Your Knowledge

1. From which spirit is vinegar produced?

  1. Malted grain

  2. Fruit juices

  3. Ethanol

  4. Ale

2. Which ethanol is oxidised into acetic acid aerobically?

  1. Acetobacter

  2. Gluconobacter

  3. Both a) and b)

  4. Lactobacillus

Answers: 1-c), 2-c). 

For more study material on chemistry topics like the structure of CH3COOH and other chemical compounds like ethanol, benzene, etc., check out Vedantu’s website regularly. Now you can also download our Vedantu app for enhanced access to these study materials and online interactive sessions for doubt clearing.

FAQ (Frequently Asked Questions)

1. What is the formula of acetic acid?

The formula of acetic acid is CH3COOH.

2. What do you mean by Acetic acid fermentation?

Acetic acid fermentation refers to an oxidation process by which alcohol is transformed into acetic acid with the help of genus acetobacter bacteria.  

What is the pH of CH3COOH?

1.0 M CH3COOH has a pH of about 2.4. 

4. Which vinegar contains the highest percentage of acetic acid?

Generally, white vinegar contains the highest percentage of acetic acid that is almost 7%. Other than that, relatively milder vinegar like red wine vinegar and balsamic vinegar contains about 6% of acetic acid.