Question

Which description of ethanoic acid is correct?
(A) A clear, colourless and odourless liquid
(B) A colourless liquid with a distinctive odour
(C) A soft white solid with a distinctive odour
(D) A transparent solid with a low melting point

Answer 1

Hint: In order to describe a certain organic compound, we must forst see to which homologous series it belongs. After finding the functional groups and the homologous series, we can predict many physical and chemical properties of the compound, which is otherwise impossible as there are an infinite number of organic compounds that can be formed.

Complete step by step solution:
-To find about the physical description of an organic compound, we first need to find the functional group present in that compound as that is the key to finding about the properties of that given compound, both physical and chemical.
-We see from the name ethanoic acid, the root word is –eth. This suggests that the number of carbon chains present in the compound are 2. The root words for different number of carbon chains can be shown as-

No. of C atoms in chain	Word root	No. of C atoms in chain	Word root
1	Meth	8	Oct
2	Eth	9	Non
3	Prop	10	Dec
4	But	11	Undec
5	pent	20	Icos
6	Hex	30	Triacont
7	Hept	100	cent

-Now, we need to see what else we can find out from the name given. The name is ethanoic acid. This means that the suffix is –oic acid. This stands for the functional group –COOH. Thus, we can finally find the molecular formula by the name of the compound which is written as $C{{H}_{3}}COOH$ .
-Some of the general names of ethanoic acid are ethylic acid, methane carboxylic acid, vinegar acid. It is the main substituent present in vinegar and so it is called vinegar acid. Due to this fact, we can say that the odour of ethanoic acid is vinegar-like pungent smell.
-As there are only 2 carbon chains in the compound, we can completely say that this compound is not solid as the intermolecular force of attraction is less in the compound. There is no colour pigment in acids and so ethanoic acid will also be colourless.
-Thus, ethanoic acid is a clear, colourless liquid with pungent odour. It reacts with alcohols to form esters. It is also used in the manufacture of acetic acid anhydride. It is fully soluble in water.
-On heating, ethanoic acids decompose into methane and carbon-dioxide.
     \[C{{H}_{3}}COOH\xrightarrow{\Delta }C{{H}_{4}}+C{{O}_{2}}\]
Another set of products that can be formed by heating the acid are ethene and water.
     \[C{{H}_{3}}COOH\xrightarrow{\Delta }{{H}_{2}}C=C=O+{{H}_{2}}O\]
-Since it is an acid, it reacts with bases to give salt and water. Some examples can be shown as
     \[C{{H}_{3}}COOH+KOH\to C{{H}_{3}}COOK+{{H}_{2}}O\]

Note: Acetic acid is mainly used in vinegar and for the production of vinyl acetate monomer which is used in paints and adhesives. It is also used as an antiseptic and for the manufacture of rubber and rayon fibre. But it must be kept in mind that ethanoic acid is not used as an acid as it is a weak acid. It does not readily lose hydrogen ions like in other strong acids.