Importance:
The chapter “Carbon and Its Compounds” is a key topic in chemistry and usually carries a weightage of about \(7\) to \(10\ \)marks in examinations.
This chapter enables students to:
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Understand the role of organic compounds in daily life.
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Classify and name organic compounds using IUPAC rules.
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Identify functional groups.
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Learn the preparation, properties, and uses of ethanol and ethanoic acid.
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Understand the composition and cleansing action of soaps and detergents.
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Differentiate between soaps and detergents.
Question distribution:
- Part I ( \(1\) mark) - One question
- Part IV ( \(7\) mark) - One question
(Note: The exact mark distribution may vary slightly across examinations.)
Learning objectives:
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Recognising the versatility of carbon: Recognise how carbon’s ability to form four covalent bonds leads to a wide variety of organic compounds, such as hydrocarbons, alcohols, acids, etc.
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Classification of organic compounds: Learn to classify compounds based on the type of carbon chain, atoms present (heteroatoms), and functional groups, enhancing the ability to identify and differentiate organic molecules.
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Mastering IUPAC nomenclature: Understand the systematic naming of organic compounds based on IUPAC rules, including hydrocarbons and functionalised compounds, improving the precision of chemical communication.
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Relating the uses of organic compounds in daily life: Relate how compounds like ethanol, ethanoic acid, soaps, and detergents play an essential role in our everyday lives, from cleaning products to food preservation
Organic (Covalent) compounds:
All carbon compounds are made up of covalent bonds. These are the compounds that are referred to as organic compounds. Everything in this world has a unique characteristics, and organic compounds are no exception. Some of them are as follows:
- Organic compounds have a complex structure and a high molecular weight.
- Organic compounds are mostly insoluble in water but soluble in organic solvents like ether, carbon tetrachloride, toluene, etc.
- Organic compounds are highly inflammable.
- When compared to inorganic compounds, organic compounds have lower melting and boiling points.
- They show the phenomenon of isomerism, where the same molecular formula can correspond to different organic compounds with varying physical and chemical properties.
- Organic compounds are volatile in nature.
Classification of organic compounds
Classification of hydrocarbons:
Hydrocarbons are organic compounds that are made up of only carbon and hydrogen atoms.
|
Number
of
carbon atoms
|
Alkane
(\(C_nH_{2n + 2}\))
|
Alkene
(\(C_nH_{2n}\))
|
Alkyne
(\(C_nH_{2n – 2}\)).
|
|
\(1\)
|
Methane
(\(CH_4\))
|
-
|
-
|
|
\(2\)
|
Ethane
(\(C_2H_6\))
|
Ethene
(\(C_2H_4\))
|
Ethyne
(\(C_2H_2\))
|
|
\(3\)
|
Propane
(\(C_3H_8\))
|
Propene
(\(C_3H_6\))
|
Propyne
(\(C_3H_4\))
|
|
\(4\)
|
Butane
(\(C_4H_{10}\))
|
Butene
(\(C_4H_8\))
|
Butyne
(\(C_4H_6\))
|
|
\(5\)
|
Pentane
(\(C_5H_{12}\))
|
Pentene
(\(C_5H_{10}\))
|
Pentyne
(\(C_5H_8\))
|
Special features of carbon:
- Catenation: Ability of carbon atoms to bond with themselves forming chains and rings.
- Tetravalency: Carbon has four valence electrons and forms four covalent bonds.
Bromine water test: Used to detect unsaturation.
Test for unsaturation
Functional group:
A functional group is an atom or group of atoms in a molecule that determines its chemical properties.
Classes of organic compounds based on functional group
Homologous series:
A homologous series is a group or class of organic compounds that have the same general formula and similar chemical properties but differby a −\(CH_2\) group and thus by \(14 amu\) in molecular mass.
Consider the members of the alkanes listed in the below table. The following are their condensed structural formulas:
|
Name
|
Molecular
formula
|
| Methane | \(CH_4\) |
| Ethane | \(CH_3CH_3\) |
| Propane | \(CH_3CH_2CH_3\) |
| Butane | \(CH_3(CH_2)_2CH_3\) |
| Pentane |
\(CH_3(CH_2)_3CH_3\)
|
If you look at the preceding series, each successive member has one more methylene (\(CH_2\)) group than the preceding member, which is why they are called homologs.
PYQ - Homologous series
Nomenclature of organic compounds:
Therefore, the International Union of Pure and Applied Chemistry (IUPAC) developed a standard nomenclature system, enabling scientists worldwide to communicate clearly using a compound's structure-based name.
Components of an IUPAC name:
Organic compounds on naming with IUPAC consist of \(3\) parts:
1. Root word: It specifies the number of carbon atoms in the compound's parent chain as well as the pattern of their arrangement.
Root words of hydrocarbons:
|
Number
of
carbon atoms
|
Root word
|
|
\(1\)
|
Meth-
|
|
\(2\)
|
Eth-
|
|
\(3\)
|
Prop-
|
|
\(4\)
|
But-
|
|
\(5\)
|
Pent-
|
|
\(6\)
|
Hex-
|
|
\(7\)
|
Hept-
|
|
\(8\)
|
Oct-
|
|
\(9\)
|
Non-
|
|
\(10\)
|
Dec-
|
2. Prefix: It represents the substituents or branches in the parent chain.
Prefix for IUPAC Name:
|
Substituent
|
Prefix used
|
|
\(-F\)
|
Fluoro
|
|
\(-Cl\)
|
Chloro
|
|
\(-Br\)
|
Bromo
|
|
\(-I\)
|
Iodo
|
|
\(-NH_2\)
|
Amino
|
|
\(-CH_3\)
|
Methyl
|
|
\(-CH_2CH_3\)
|
Ethyl
|
3. Suffix: It is further divided into primary and secondary suffix.
- Primary suffix: If all of the bonds between the parent chain's carbon atoms are single, the suffix 'ane' must be used and the suffixes ‘ene' and ‘yne' are used for compounds with double and triple bonds, respectively.
- Seconday suffix: The compound's functional group is described by the secondary suffix.
PYQ - IUPAC nomenclature
|
Class of the compound
|
Functional group
|
Suffix used
|
|
Alcohol
|
\(-OH\)
|
-ol
|
|
Aldehyde
|
\(-CHO\)
|
-al
|
|
Ketone
|
\(-C=O\)
|
-one
|
|
Carboxylic acid
|
\(-COOH\)
|
-oic acid
|
Let us now see the IUPAC rules for naming organic compounds:
- Find the longest chain of carbon atoms to determine the parent name (root word).
- Start counting the carbon atoms in the parent chain at the closest end of the substituent or functional group. These are known as locant numbers. If both a functional group and a substituent are present, the functional group takes precedence.
- In the case of alkenes and alkynes, find the double or triple bond and use its locant number followed by a dash and a primary suffix.
- If the compound contains a functional group, find it and use the locant number followed by a dash and a secondary suffix.
- When the primary and secondary suffixes are combined, the primary suffix's terminal 'e' is removed.
- Identify the substituent using a number followed by a dash and a prefix to specify its location and identity.
Let us try to name the linear and substituted hydrocarbons in a systematic manner using IUPAC rules:
Step 1: There is a seven-membered carbon chain; hence, the root word is ‘Hept’.
Step 2: There is a substituent. So, the carbon chain is numbered from the left end, which is closest to the substituent.
The correct way of numbering the carbon atoms
Step 3: All are single bonds between the carbon atoms, and thus the suffix is ‘ane’.
Step 4: The substituent is a methyl group compound located at the third carbon atom. So, its locant number is \(3\). Thus, the prefix is ‘\(3-Methyl\)’.
Hence, the name of the given compound is \(\text{3-Methyl + hept + ane = 3-Methyl heptane}\).
The below are some of the IUPAC names of various classes of compound:
IUPAC names of various classes of compounds
Ethanol (\(C_2H_5OH\)):
Ethanol, commonly referred to as alcohol, is a simple organic compound with the molecular formula \(C_2H_5OH\). It is a colourless, volatile liquid with a pleasant odour and a burning taste. Found in alcoholic beverages and medicinal syrups, ethanol holds significant industrial and domestic importance.
Skeletal structure of ethanol
Chemical properties of ethanol (\(C_2H_5OH\)):
i. Dehydration to ethene: \(CH_3CH_2OH \xrightarrow [443K]{Conc H_2SO_4} CH_2=CH_2 + H_2O\)
ii. Reaction with sodium: \(2CH_3CH_2OH + 2Na \rightarrow 2C_2H_5ONa + H_2\)
iii. Oxidation:
iv. Dehydrogenation: \(CH_3CH_2OH \xrightarrow [573K]{Cu} CH_3CHO + H_2\)
v. Esterification: \(CH_3CH_2OH + CH_3COOH \xrightarrow {Conc H_2SO_4} CH_3COOC_2H_5 + H_2O\)
vi. Combustion: \(CH_3CH_2OH + 3O_2 \rightarrow 2CO_2 + 3H_2O\)
PYQ - Esterification
Ethanoic acid (\(CH_3COOH\)):
Ethanoic acid is a key carboxylic acid, widely used in food and industry. When pure, it forms ice-like crystals and is called glacial acetic acid.
Skeletal structure of ethanoic acid
Chemical properties of ethanoic acid:
i. Reaction with metal: \(2CH_3COOH + 2Na \rightarrow 2CH_3COONa + H_2\)
ii. Reaction with carbonates and bicarbonates: \(2CH_3COOH + NaCO_3 \rightarrow 2CH_3COONa + CO_2 + H_2O\)
iii. Reaction with base: \(CH_3COOH + NaOH \rightarrow CH_3COONa + H_2O\)
iv. Decarboxylation (removal of \(CO_2\)): \(CH_3COOH \xrightarrow {NaOH /CaO} CH_4+ Na_2CO_3\)
Soaps:
Soaps are sodium or potassium salts of long-chain carboxylic acids, called fatty acids. Soap generally requires the use of two major raw materials:
- Fat
- Alkali
Sodium hydroxide is the most common alkali used in soap production. Potassium hydroxide is yet another alternative. A potassium-based soap is far more water-soluble than a sodium-based soap.
Based on the above features, there are two types of soaps:
- Hard soap: Soaps made by saponifying oils or fats with caustic soda (sodium hydroxide) are referred to as hard soaps. They are typically used for washing.
- Soft soap: Soaps that are made by saponifying oils or fats with potassium salts are referred to as soft soaps. They are employed in the cleansing of the body.
The alkaline hydrolysis of esters (using alkali like sodium hydroxide) is known as saponification. The chemical equation of saponification is
\(CH_3COOCH_3 + NaOH → CH_3COONa + CH_3OH\)
Cleansing action of soap:
- A soap molecule is made up of two chemically distinct parts that interact with water in different ways. It has one polar end with a short head carboxylate group (\(-COONa\)) and one non-polar end with a long tail made of the hydrocarbon chain.
- The polar end is hydrophilic (water-loving) in nature, and it is drawn to water. The non-polar end is hydrophobic (hates water) in nature, and it is attracted to dirt or oil on the cloth but not to water. As a result, the hydrophobic part of the soap molecule traps the dirt while the hydrophilic part makes the entire molecule water-soluble.
-
When soap or detergent is dissolved in water, the molecules form clusters known as 'micelles'. Their long hydrocarbon chains bind to the oil and dirt. As a result, the dirt is surrounded by the non-polar end of the soap molecules. The micelles are water-soluble because of the charged carboxylate end of the soap molecules. As a result, the soap washes away the dirt.
Cleansing action of soap
Effect of hard water on soap and rise of detergents:
The presence of calcium and magnesium ions (\(Ca^{2+}\) and \(Mg^{2+}\)) in hard water limits the cleaning action of soap. When combined with soap, hard water forms a thin layer (precipitates of metal ions) known as scum, which leaves a deposit on the clothes or skin and is difficult to remove. This can cause the fabric to deteriorate over time and eventually ruin the clothes. To overcome this problem, synthetic detergents were developed.
Unlike soaps (which are sodium salts of fatty acids), detergents are usually sodium salts of sulphonic acids or alkyl hydrogen sulphates. These do not form scum with hard water ions, allowing detergents to maintain their cleaning action in both hard and acidic water.
Difference between soaps and detergents:
|
Soap
|
Detergent
|
| The sodium salt of long-chain fatty acids makes up the soap. | Sodium salts of sulphonic acids make up the detergent. |
| \(-COO^-Na^+\) is the ionic part of the soap. | \(-SO_3^-Na^+\) is the ionic part of the detergent. |
| Soap is manufactured from animal fats or vegetable oils. | Detergents are obtained from hydrocarbons extracted from crude oil. |
| The effectiveness of soap reduces in hard water. | Detergents are effective in hard water. |
| Soap forms a scum in hard water. | Detergents do not form scum in hard water. |
| Soap has a poor foaming capacity. | Detergents have a rich foaming capacity. |
| They are biodegradable. | They are mostly non-biodegradable. |
Have you ever noticed the term "TFM" mentioned on the soap cover?:
What is TFM in Soaps?
TFM (Total Fatty Matter) indicates the quality of a soap. According to Indian standards:
-
Bathing bars: TFM between 40% and 60%
-
Toilet soaps: TFM between 60% and 76%
Higher TFM means better moisturising, gentler cleansing, and overall superior soap quality.
So next time you see those stubborn stains disappear or your shampoo lather up, remember it’s all clever molecules working behind the scenes. Understanding soaps and detergents isn’t just about cleaning, it’s about unlocking the science in everyday magic.