General Information

Acetic acid, also known as ethanoic acid, is an organic chemical compound, giving vinegar its sour taste and pungent smell. Its structural formula is represented as CH₃COOH. Pure, water-free acetic acid (glacial acetic acid) is a colourless liquid that absorbs water from the environment (hygroscopy), and freezes below 16.7 °C (62 °F) to a colourless crystalline solid. Acetic acid is corrosive, and its vapour causes irritation to the eyes, a dry and burning nose, sore throat and congestion to the lungs. It is a weak acid because at standard conditions for temperature and pressure the dissociated acid exists in equilibrium with the undissociated form in aqueous solutions, in contrast to strong acids, which are fully dissociated.

Acetic acid is one of the simplest carboxylic acids (the second-simplest, next to formic acid). It is an important chemical reagent and industrial chemical that is used in the production of polyethylene terephthalate mainly used in soft drink bottles; cellulose acetate, mainly for photographic film; and polyvinyl acetate for wood glue, as well as synthetic fibres and fabrics. In households diluted acetic acid is often used in descaling agents. In the food industry acetic acid is used under the food additive code E260 as an acidity regulator.

The global demand of acetic acid is around 6.5 million tonnes per year (Mt/a), of which approximately 1.5 Mt/a is met by recycling; the remainder is manufactured from petrochemical feedstocks or from biological sources.

Chemical Properties

Acidity
The hydrogen (H) atom in the carboxyl group (−COOH) in carboxylic acids such as acetic acid can be given off as an H+ ion (proton), giving them their acidic character. Acetic acid is a weak, effectively monoprotic acid in aqueous solution, with a pKa value of 4.8.

Chemical reactions
Acetic acid is corrosive to many metals including iron, magnesium, and zinc, forming hydrogen gas and metal salts called acetates. Metal acetates can also be prepared from acetic acid and an appropriate base, as in the popular "baking soda + vinegar" reaction.

Mg(s) + 2CH₃COOH(aq) → (CH₃COO)₂Mg(aq) + H₂(g) NaHCO₃(s) + CH₃COOH(aq) → CH₃COONa(aq) + CO₂(g) + H₂O(l)

Acetic acid undergoes the typical chemical reactions of a carboxylic acid, notably the formation of ethanol by reduction, and formation of derivatives such as acetyl chloride via nucleophilic acyl substitution. Acetates when heated with arsenic trioxide form cacodyl oxide, which can be detected by its malodorous vapours.

Biochemistry
The acetyl group, derived from acetic acid, is fundamental to the biochemistry of virtually all forms of life. Unlike some longer-chain carboxylic acids (the fatty acids), acetic acid does not occur in natural triglycerides.

Acetic acid is produced and excreted by certain bacteria, notably the Acetobacter genus and Clostridium acetobutylicum.
Acetic acid, when complexed with coenzyme A, is central to the metabolism and biosynthetic processes of almost all forms of life. It results naturally from the action of certain bacteria in foods or liquids containing sugars or ethanol.

As an example of its importance in biology, acetic acid is produced in the human body after the consumption of alcoholic beverages. The ethanol is first converted into acetaldehyde, which is then converted into acetic acid by the enzyme acetaldehyde dehydrogenase and converted further to acetyl-CoA by acetate-CoA ligase.

Physical Properties
Pure acetic acid is a colourless, corrosive, flammable liquid that freezes at 16.6 °C. It is called glacial acetic acid because it freezes with long ice-like crystals.

In aqueous solution, acetic acid can lose the proton of its carboxyl group, turning into the acetate ion CH₃COO−. The pKa of acetic acid is about 4.8 at 25 °C, meaning that about half of the acetic acid molecules are in the acetate form at a pH of 4.8. A 1.0 M solution has a pH of 2.4.

In its gaseous state, acetic acid consists of pairs of dimers held together by hydrogen bonds. As a result, the ideal gas law does not accurately describe the behaviour of acetic acid vapour, since it does not take intermolecular interactions into account. The dimers look like this:

Preparation
Of old, all acetic acid was made by a fermentation process, still amounting to approximately 10% of world production. About 75% of all acetic acid made for industrial use is made by methanol carbonylation, explained below.

Historic method: fermentation
Vinegar is manufactured by fermenting various starchy, sugary, or alcoholic foodstuffs with Acetobacter bacteria. Commonly used feeds include apple cider, wine, and grain, malt, rice or potato mashes. This is very similar to some processes for making kombucha or kvass. The vinegar is then distilled from the fermentation broth. Most nations have laws that the acetic acid found in food vinegar must be produced by fermentation rather than by non-biological means. Vinegar is usually 4%–8% acetic acid by volume.

Industrial preparation: catalysed methanol carbonylation
Most virgin acetic acid is produced by the carbonylation of methanol. In this process, methanol and carbon monoxide react to produce acetic acid according to the chemical equation

:CH₃OH + CO + CH₃COOH

Because both methanol and carbon monoxide are commodity raw materials, standard methanol carbonylation long appeared to be an attractive method for acetic acid production, and patents on such processes were granted as early as the 1920s. However, the high pressures needed (200 atm or more) discouraged at the time commercialisation of these routes. The first commercial methanol carbonylation process, which used a cobalt catalyst, was developed by BASF in the early 1960s. In 1968, a rhodium-based catalyst was discovered that could operate efficiently at lower pressure with almost no by-products. The first plant using this catalyst was built by Monsanto in 1970, and rhodium-catalysed methanol carbonylation became the dominant method of acetic acid production (see Monsanto process). In the late 1990s, BP Chemicals commercialised an iridium-catalysed process, CativaTM, which now operates on many production plants.

Alternative preparation method
When butane is heated with air in the presence of various metal ions, including those of manganese, cobalt, and chromium, peroxides form and then decompose to produce acetic acid according to the chemical equation

         : 2C₄H₁₀ + 5O₂ → 4CH₃COOH + 2H₂O

Typically, the reaction is run at a combination of temperature and pressure designed to be as hot as possible while still keeping the butane a liquid. Typical reaction conditions are 150 °C and 55 atm. Several side products may also form, including butanone, ethyl acetate, formic acid, and propionic acid. These side products are also commercially valuable, and the reaction conditions may be altered to produce more of them if this is economically useful.

Under similar conditions and using similar catalysts as are used for butane oxidation, acetaldehyde can be oxidised by the oxygen in air to produce acetic acid

        :2CH₃CHO + O₂ → 2CH₃COOH

Using modern catalysts, this reaction can have an acetic acid yield greater than 95%. The major side products are ethyl acetate, formic acid, and formaldehyde, all of which have lower boiling points than acetic acid and are readily separated by distillation.

• dilute ethanoic acid is used as a preservative in the preparation of pickles.
• it is used for making cellulose acetate which is an important artificial fibre.
• it is used in the manufacture of acetone and esters used in perfumes.
• it is used in the preparation of dyes.
• it is used to coaggulate rubber from latex.
• it is used for making white lead which is used as a white paint.
• it is used as a chemical reagent in chemistry lab

Safety
Concentrated acetic acid is corrosive and has to be handled with appropriate care, since it can cause skin burns, permanent eye damage, irritation to the mucous membranes and can cause acidic burns or blisters to appear several hours after exposure. Latex gloves offer no protection, so specially resistant gloves, such as those made of nitrile rubber, should be worn when handling the compound.

Dilute acetic acid, in the form of vinegar, is harmless and has been consumed for millennia. However, ingestion of stronger solutions is dangerous. It can cause severe damage to the digestive system, and a potentially lethal change in the acidity of the blood.

Acetic acid poses no known cancer risk.

Short Description

Frequently Asked Questions:

(1) How do I find the number of moles of acetic acid?

Ans. :- You have provided very few specifics on your actual experiment so it will be difficult to help you very much other than to give you the basic idea.

You need to write out the chemical reaction which is taking place…a neutralization reaction between the acetic acid and the base you are titrating it with. Find the number of moles of base needed to neutralize 1 mole of the acid from the chemical reaction. Compare this figure with the number of moles of base needed in your experiment to reach the end point (should be obvious from the graph). How many times more/less of the base did you use in your experiment? This same multiple can be used to find the number of moles of base in your initial solution.

Remember,
When finding concentration,
Molarity = moles of solute / Liters of solution
Molality = moles of solute / kilograms of solvent
You can also re-arrange these equations to solve for unknown quantities when working backwards.

Ans. :- First calculate the moles of acetic acid, then the weight of acetic acid, then divide by the weight of vinegar.

1. moles of acetic acid is equivalent to moles of NaOH required to neutralize it:
moles of NaOH = volume x molarity (note molarity is expressed in moles per liter)
moles of NaOH = 0.03084 liters * 0.128 Moles/liter = 0.0039475 moles.

2. wt of acetic acid corresponding to 0.0039475 moles:
mw of acetic acid (CH₃COOH) =
2*12.01 + 4*1 + 2*16.00=60.02 grams/mole

wt= 60.02 grams/mole*0.0039475 moles=0.2369 grams

3. % acetic acid = wt of acetic acid/total wt of sample *100
% acetic acid = 0.2369 grams/5.441 grams * 100= 4.35%

Ans.:- Normality of NaOH =? (needed to calculate the % acetic acid)

assume 0.1 N NaOH

mL NaOH x N of NaOH = milliequivalents of acetic acid

12.54 mL x 0.10 = 1.254 meg of Acetic Acid
1 meq of acetic acid = 0.060 gram

1.254 meq x 0.060 = 0.07524 grams acetic acid
0.07524 gm acetic acid / 10.05 gm vinegar = 0.749%

Ans.:- The Ka = [H₃0+] [CH₃COO-] / [CH₃COOH]

The Ka is equal to the molar concentration of the hydronium ion times the molar concentration of the acetate ion divided by the molar concentration of the unionized acetic acid.

Since the amount of [H₃0+] is equal to [CH₃COO-] you can also write the numerator as [H₃0+]^2.

The negative log of [H₃0+] is the pH, so you can measure the pH and determine the [H₃0+]. Then square it to get [H₃0+]^2.

For example, if the pH is 6 then the [H₃0+] is 10^-6 and [H₃0+]^2 would be 10^-12. {Remember 10^a x 10^b = 10^(a+b)}.

Then you can calculate the Ka by dividing the calculated value for [H₃0+]^2 and dividing it by the original molar concentration of [CH₃COOH], which is effectively not changed.

Ans.:- 26.13ml. of NaOH at 0.1006 moles per litre gives a total of 0.02613 * 0.1006 = 0.002628678 moles of NaOH.

The reaction of the equation is

CH₃COOH + NaOH -> CH₃COONa + H₂O

So one mole of acetic acid reacts with one mole of NaOH. Therefore, there must have been 0.002628678 moles of CH₃COOH in your 25ml. of diluted vinegar.

Multiply by 40 (= 1000 / 25) to get 0.10514712 moles of acetic acid in one litre of the diluted vinegar, or 1.0514712 moles in one litre of the undiluted vinegar.

The molecular mass of acetic acid = 12 + 3 * 1 + 12 + 16 + 16 + 1 = 60g/mole, meaning that there must have been 6.31g. of acetic acid per litre in the original sample

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