Overview
Carbon and its Compounds explains why one element out of more than a hundred accounts for the overwhelming majority of known compounds. Carbon has atomic number 6 and the electronic configuration 2,4, so it needs four more electrons to attain a noble gas configuration. It cannot realistically gain four electrons, because holding ten electrons around a nucleus of six protons would be very difficult, nor lose four, because removing four electrons would require an enormous amount of energy and leave a cation with six protons holding only two electrons. Carbon therefore shares electrons, forming covalent bonds, and this single fact explains everything that follows: covalent compounds have low melting and boiling points because the molecules are held together by weak forces, and they are generally poor conductors because the bonding produces no ions. Two further properties make carbon unique - catenation, its unmatched ability to link with other carbon atoms in long chains, branched chains and rings, and tetravalency, which lets it bond with four atoms of carbon or of other monovalent elements. The chapter then builds up organic chemistry systematically: saturated and unsaturated hydrocarbons with their general formulas, chains, branches and rings, the idea of a homologous series in which successive members differ by a CH2 unit and a molecular mass of 14 u, functional groups, and IUPAC nomenclature. It closes with the chemical properties of carbon compounds - combustion, oxidation, addition and substitution reactions - with ethanol and ethanoic acid, and with the cleansing action of soaps and detergents through the formation of micelles.
Learning Objectives
- Explain why carbon forms covalent bonds rather than ionic bonds.
- State the general properties of covalent compounds and account for them.
- Describe the structure and properties of diamond, graphite and fullerenes.
- Define catenation and tetravalency and explain why they make carbon unique.
- Distinguish saturated from unsaturated hydrocarbons and write their general formulas.
- Draw the electron dot structures of simple carbon compounds.
- Define a homologous series and state the difference between successive members.
- Identify the common functional groups and name compounds containing them.
- Apply the IUPAC rules to name simple carbon compounds.
- Describe combustion, oxidation, addition and substitution reactions of carbon compounds.
- Describe the properties and reactions of ethanol and ethanoic acid.
- Explain the cleansing action of soap and the formation of a micelle.
- Explain why detergents are used in hard water while soaps are not effective.
Topics in this chapter
7 topics · tap a topic title to jump straight to it.
Bonding in Carbon: The Covalent Bond
The problem carbon faces
The atomic number of carbon is 6. It has therefore four electrons in its outermost shell, and its electronic configuration is 2,4. Carbon needs to gain a noble gas configuration, and there are in principle two ways to do it.
- It could gain four electrons forming C4- anion. But it would be difficult for the nucleus with six protons to hold on to ten electrons, that is, four extra electrons.
- It could lose four electrons forming C4+ cation. But it would require a large amount of energy to remove four electrons leaving behind a carbon cation with six protons in its nucleus holding on to just two electrons.
The solution: sharing
Carbon overcomes this problem by sharing its valence electrons with other atoms of carbon or with atoms of other elements. Not just carbon, but many other elements form molecules by sharing electrons in this manner.
The shared electrons belong to the outermost shells of both the atoms and lead to both atoms attaining the noble gas configuration. The bond formed by the sharing of a pair of electrons between two atoms is known as a covalent bond.
- A single bond is formed when one pair of electrons is shared, as in H2, Cl2, CH4.
- A double bond is formed when two pairs of electrons are shared, as in O2.
- A triple bond is formed when three pairs of electrons are shared, as in N2.
Properties of covalent compounds
Since the electrons are shared between atoms and no charged particles are formed, such covalent compounds are generally poor conductors of electricity.
Covalent compounds have low melting and boiling points. This is because the molecular forces of attraction between the molecules are weak, even though the bond within a molecule is strong. Do not confuse the two: the covalent bond inside the molecule is strong, but the attraction between molecules is weak, and it is the latter that must be overcome to melt or boil the substance.
- Carbon: atomic number 6, configuration 2,4, four valence electrons - it can neither easily gain nor lose four.
- Single bond in H2, Cl2 and CH4; double bond in O2; triple bond in N2.
- Covalent compounds have low melting and boiling points because intermolecular forces are weak, not because the bond is weak.
- Covalent bond: a bond formed by the sharing of a pair of electrons between two atoms
- H2: H-H (single); O2: O=O (double); N2: N(triple bond)N
Allotropes of Carbon
Diamond
In diamond, each carbon atom is bonded to four other carbon atoms forming a rigid three-dimensional structure. Diamond is the hardest substance known.
Diamonds can be synthesised by subjecting pure carbon to very high pressure and temperature. These synthetic diamonds are small but are otherwise indistinguishable from natural diamonds.
Graphite
In graphite, each carbon atom is bonded to three other carbon atoms in the same plane giving a hexagonal array. One of these bonds is a double-bond, and thus the valency of carbon is satisfied. Graphite structure is formed by the hexagonal arrays being placed in layers one above the other.
These layers are held together by weak forces, and this is why graphite is smooth and slippery. Graphite is a very good conductor of electricity as compared to other non-metals.
Compare the two structures and the properties follow directly. Diamond's rigid three-dimensional network of strong bonds makes it the hardest substance; graphite's weakly held layers slide over each other, which is exactly why it lubricates and why a pencil leaves a mark.
Fullerenes
Fullerenes form another class of carbon allotropes. The first one to be identified was C-60 which has carbon atoms arranged in the shape of a football.
Since this looked like the geodesic dome designed by the US architect Buckminster Fuller, the molecule was named fullerene.
Allotropy
All three - diamond, graphite and fullerenes - are made only of carbon atoms, yet they differ completely in hardness, appearance and electrical conductivity. The physical properties of diamond and graphite vary because of the different manner in which the carbon atoms are bonded to one another. This is the phenomenon of allotropy.
- Diamond: each carbon bonded to four others in a rigid three-dimensional structure - the hardest substance known.
- Graphite: each carbon bonded to three others in hexagonal layers held by weak forces - smooth, slippery and a good conductor.
- C-60 fullerene is football-shaped, named after Buckminster Fuller's geodesic dome.
Versatile Nature of Carbon: Catenation and Tetravalency
Why carbon has so many compounds
We have seen the members of two classes of compounds - diamond and graphite. The largest number of compounds formed by carbon is with hydrogen, and these are called hydrocarbons. This unique nature of carbon is because of two features.
Catenation
Carbon has the unique ability to form bonds with other atoms of carbon, giving rise to large molecules. This property is called catenation.
These compounds may have long chains of carbon, branched chains of carbon or even carbon atoms arranged in rings. In addition, carbon atoms may be linked by single, double or triple bonds.
- Compounds of carbon, which are linked by only single bonds between the carbon atoms, are called saturated compounds.
- Compounds of carbon having double or triple bonds between their carbon atoms are called unsaturated compounds.
Silicon forms compounds with hydrogen which have chains of up to seven or eight atoms, but these compounds are very reactive. The carbon-carbon bond is very strong and hence stable. This gives us the large number of compounds with many carbon atoms linked to each other.
Tetravalency
Since carbon has a valency of four, it is capable of bonding with four other atoms of carbon or atoms of some other mono-valent element.
Compounds of carbon are formed with oxygen, hydrogen, nitrogen, sulphur, chlorine and many other elements giving rise to compounds with specific properties which depend on the elements other than carbon present in the molecule.
The consequence
The bonds that carbon forms with most other elements are very strong making these compounds exceptionally stable. One reason for the formation of strong bonds by carbon is its small size. This enables the nucleus to hold on to the shared pairs of electrons strongly.
The bonds formed by elements having bigger atoms are much weaker.
- Catenation: carbon's unique ability to bond with other carbon atoms in long chains, branched chains and rings.
- Saturated compounds have only single carbon-carbon bonds; unsaturated compounds have double or triple bonds.
- Carbon's small size lets the nucleus hold the shared electron pairs strongly, which is why its bonds are so strong.
Hydrocarbons: Saturated, Unsaturated, Chains and Rings
Alkanes
Saturated hydrocarbons are called alkanes. In alkanes all the carbon atoms are linked by single covalent bonds.
The general formula of alkanes is CnH2n+2, where n is the number of carbon atoms.
Alkenes and alkynes
Unsaturated hydrocarbons which contain one or more double bonds are called alkenes. The general formula for alkenes is CnH2n.
Unsaturated hydrocarbons which contain one or more triple bonds are called alkynes. The general formula for alkynes is CnH2n-2.
Chains, branches and rings
Carbon atoms may be arranged in the form of straight chains, branched chains or rings.
Butane, C4H10, can be arranged in two different ways - as a straight chain and as a branched chain. Both have the same molecular formula but different structures; these are structural isomers.
Cyclohexane has the formula C6H12 and its carbon atoms are arranged in a ring. Benzene, C6H6, is another important ring compound.
Straight chain, branched chain and cyclic carbon compounds - all these which contain only carbon and hydrogen are called hydrocarbons.
Homologous series
In carbon compounds, the hydrogen atoms can be replaced by other atoms in accordance with their valencies. The element replacing hydrogen is referred to as a heteroatom. These heteroatoms confer specific properties to the compound, regardless of the length and nature of the carbon chain and hence are called functional groups.
A series of compounds in which the same functional group substitutes for hydrogen in a carbon chain is called a homologous series.
Look at the alkanes: CH4, C2H6, C3H8, C4H10. Each successive member differs from the previous one by a -CH2- unit, and the difference in molecular masses is 14 u.
As the molecular mass increases in any homologous series, a gradation in physical properties is seen. This is because the melting and boiling points increase with increasing molecular mass. Other physical properties such as solubility in a particular solvent also show a similar gradation. But the chemical properties, which are determined solely by the functional group, remain similar in a homologous series.
- Butane C4H10 exists as a straight chain and a branched chain - the same molecular formula, different structures.
- Successive members of a homologous series differ by a -CH2- unit and by 14 u of molecular mass.
- Physical properties change gradually along a homologous series; chemical properties stay similar because the functional group is unchanged.
- Alkanes: CnH2n+2
- Alkenes: CnH2n
- Alkynes: CnH2n-2
- Successive homologues differ by -CH2- and by 14 u in molecular mass
Functional Groups and IUPAC Nomenclature
The common functional groups
- Halo- (chloro, bromo): -Cl, -Br, replacing a hydrogen atom.
- Alcohol: -OH.
- Aldehyde: -CHO.
- Ketone: -CO- (a carbonyl group in the middle of the chain).
- Carboxylic acid: -COOH.
Note that in each of these, a valency of carbon remains free for bonding with the rest of the carbon chain.
The rules of naming
Naming a carbon compound can be done by the following method.
- Identify the number of carbon atoms in the compound. A compound having three carbon atoms would have the name prop-.
- In case a functional group is present, it is indicated in the name of the compound with either a prefix or a suffix.
- If the name of the functional group is to be given as a suffix, and the suffix of the functional group begins with a vowel a, e, i, o, u, then the name of the carbon chain is modified by deleting the final 'e' and adding the appropriate suffix. For example, a three-carbon chain with a ketone group would be named in the following manner: propane - 'e' = propan + '-one' = propanone.
- If the carbon chain is unsaturated, then the final 'ane' in the name of the carbon chain is substituted by 'ene' or 'yne'. For example, a three-carbon chain with a double bond would be called propene and if it has a triple bond, propyne.
Prefixes for carbon number
The stems are: meth- (1), eth- (2), prop- (3), but- (4), pent- (5), hex- (6).
So CH3OH is methanol, C2H5OH is ethanol, CH3COOH is ethanoic acid, and CH3COCH3 is propanone.
- Suffix beginning with a vowel: propane minus 'e' plus '-one' gives propanone.
- Unsaturation changes the ending: propane becomes propene for a double bond and propyne for a triple bond.
- Stems: meth-, eth-, prop-, but-, pent-, hex- for one to six carbon atoms.
- Alcohol -OH; aldehyde -CHO; ketone -CO-; carboxylic acid -COOH; halo -Cl or -Br
- Name = (stem for number of carbons) + (saturation: -ane / -ene / -yne) + (functional group suffix)
Chemical Properties of Carbon Compounds
Combustion
Carbon, in all its allotropic forms, burns in oxygen to give carbon dioxide along with the release of heat and light.
Saturated hydrocarbons will generally give a clean flame while unsaturated carbon compounds will give a yellow flame with lots of black smoke. However, limiting the supply of air results in incomplete combustion of even saturated hydrocarbons giving a sooty flame.
The gas or kerosene stove used at home has inlets for air so that a sufficiently oxygen-rich mixture is burnt to give a clean blue flame. If the bottoms of cooking vessels are getting blackened, it means that the air holes are blocked and fuel is getting wasted.
Oxidation
Carbon compounds can be easily oxidised on combustion. In addition to this complete oxidation, there are reactions in which alcohols are converted to carboxylic acids.
Some substances are capable of adding oxygen to others. These substances are known as oxidising agents. Alkaline potassium permanganate or acidified potassium dichromate are oxidising alcohols to acids.
Addition reaction
Unsaturated hydrocarbons add hydrogen in the presence of catalysts such as palladium or nickel to give saturated hydrocarbons. Catalysts are substances that cause a reaction to occur or proceed at a different rate without the reaction itself being affected.
This reaction is commonly used in the hydrogenation of vegetable oils using a nickel catalyst. Vegetable oils generally have long unsaturated carbon chains while animal fats have saturated carbon chains.
Note that animal fats generally contain saturated fatty acids which are said to be harmful for health. Oils containing unsaturated fatty acids should be chosen for cooking.
Substitution reaction
Saturated hydrocarbons are fairly unreactive and are inert in the presence of most reagents. However, in the presence of sunlight, chlorine is added to hydrocarbons in a very fast reaction.
Chlorine can replace the hydrogen atoms one by one. It is called a substitution reaction because one type of atom or a group of atoms takes the place of another. A number of products are usually formed with the higher homologues of alkanes.
- Saturated hydrocarbons burn with a clean flame; unsaturated ones give a yellow flame with black smoke.
- Blackened cooking vessels mean the air holes are blocked and fuel is being wasted.
- Vegetable oils have unsaturated chains and animal fats saturated ones; unsaturated oils should be chosen for cooking.
- Combustion: C + O2 -> CO2 + heat + light
- CH4 + 2O2 -> CO2 + 2H2O + heat + light
- Oxidation: CH3CH2OH --(alkaline KMnO4 + heat, or acidified K2Cr2O7 + heat)--> CH3COOH
- Addition: R-CH=CH-R + H2 --(Ni catalyst)--> R-CH2-CH2-R
- Substitution: CH4 + Cl2 --(sunlight)--> CH3Cl + HCl
Ethanol, Ethanoic Acid, Soaps and Detergents
Ethanol
Ethanol is a liquid at room temperature. It is commonly called alcohol and is the active ingredient of all alcoholic drinks. In addition, because it is a good solvent, it is also used in medicines such as tincture iodine, cough syrups, and many tonics.
- Reaction with sodium: Alcohols react with sodium leading to the evolution of hydrogen. With ethanol, the other product is sodium ethoxide.
- Reaction to give unsaturated hydrocarbon: Heating ethanol at 443 K with excess concentrated sulphuric acid results in the dehydration of ethanol to give ethene. The concentrated sulphuric acid can be regarded as a dehydrating agent which removes water from ethanol.
Intake of even a small quantity of methanol can be lethal. Methanol is oxidised to methanal in the liver. Methanal reacts rapidly with the components of cells. It causes the protoplasm to get coagulated, in much the same way as an egg is coagulated by cooking. Methanol also affects the optic nerve, causing blindness.
Ethanoic acid
Ethanoic acid is commonly called acetic acid and belongs to a group of acids called carboxylic acids. 5-8% solution of acetic acid in water is called vinegar and is used widely as a preservative in pickles.
The melting point of pure ethanoic acid is 290 K and hence it often freezes during winter in cold climates. This gave rise to its name glacial acetic acid.
- Esterification reaction: Esters are most commonly formed by reaction of an acid and an alcohol. Ethanoic acid reacts with absolute ethanol in the presence of an acid catalyst to give an ester. Esters are sweet-smelling substances. These are used in making perfumes and as flavouring agents. On treating with sodium hydroxide, the ester is converted back to alcohol and sodium salt of carboxylic acid. This reaction is known as saponification because it is used in the preparation of soap.
- Reaction with a base: Ethanoic acid reacts with sodium hydroxide to give a salt, sodium ethanoate (commonly called sodium acetate) and water.
- Reaction with carbonates and hydrogencarbonates: Ethanoic acid reacts with carbonates and hydrogencarbonates to give rise to a salt, carbon dioxide and water.
Soaps and the micelle
The molecules of soap are sodium or potassium salts of long-chain carboxylic acids.
The ionic-end of soap interacts with water while the carbon chain interacts with oil. The soap molecules, thus form structures called micelles where one end of the molecules is towards the oil droplet while the ionic-end faces outside. This forms an emulsion in water and helps in dissolving the dirt when we wash our clothes.
Soap micelles can therefore clean, since the oily dirt will be collected in the centre of the micelle. The micelles stay in solution as a colloid and will not come together to precipitate because of ion-ion repulsion. Thus, the dirt suspended in the micelles is also easily rinsed away.
Why soap fails in hard water
Most dirt is oily in nature and as you know, oil does not dissolve in water. The molecules of soap are sodium or potassium salts of long-chain carboxylic acids.
Have you ever observed while agitating soap solution that some soap remains as scum? Hard water contains calcium and magnesium salts, and soap reacts with these to form an insoluble precipitate called scum. A lot of soap is wasted in the process.
Detergents are generally ammonium or sulphonate salts of long chain carboxylic acids. The charged ends of these compounds do not form insoluble precipitates with the calcium and magnesium ions in hard water. Thus, they remain effective in hard water. Detergents are usually used to make shampoos and products for cleaning clothes.
- Methanol is oxidised to methanal in the liver, coagulating protoplasm and attacking the optic nerve to cause blindness.
- Pure ethanoic acid melts at 290 K and freezes in cold climates - hence the name glacial acetic acid.
- In hard water, soap reacts with calcium and magnesium salts to form scum; detergents do not, so they remain effective.
- 2Na + 2CH3CH2OH -> 2CH3CH2O-Na+ (sodium ethoxide) + H2
- CH3CH2OH --(hot conc. H2SO4, 443 K)--> CH2=CH2 + H2O
- Esterification: CH3COOH + CH3CH2OH --(acid catalyst)--> CH3COOC2H5 + H2O
- Saponification: CH3COOC2H5 + NaOH -> CH3COONa + C2H5OH
- NaOH + CH3COOH -> CH3COONa + H2O
- 2CH3COOH + Na2CO3 -> 2CH3COONa + H2O + CO2
Key Concepts
- Covalent bond
- A bond formed by the sharing of a pair of electrons between two atoms, so that both attain a noble gas configuration.
- Single, double and triple bond
- Bonds formed by sharing one, two or three pairs of electrons respectively - as in H2, O2 and N2.
- Allotropes
- Different forms of the same element in the same physical state, differing in the way the atoms are bonded - diamond, graphite and fullerenes for carbon.
- Diamond
- The allotrope in which each carbon is bonded to four others in a rigid three-dimensional structure; the hardest substance known.
- Graphite
- The allotrope in which each carbon is bonded to three others in hexagonal layers held by weak forces; smooth, slippery and a good conductor of electricity.
- Fullerene
- The allotrope class first identified as C-60, with atoms arranged like a football, named after Buckminster Fuller's geodesic dome.
- Catenation
- Carbon's unique ability to form bonds with other carbon atoms, giving long chains, branched chains and rings.
- Tetravalency
- Carbon's valency of four, which lets it bond with four other carbon atoms or four atoms of a monovalent element.
- Saturated compounds
- Carbon compounds linked by only single bonds between the carbon atoms.
- Unsaturated compounds
- Carbon compounds having double or triple bonds between their carbon atoms.
- Alkane
- A saturated hydrocarbon with the general formula CnH2n+2.
- Alkene
- An unsaturated hydrocarbon containing one or more double bonds, with the general formula CnH2n.
- Alkyne
- An unsaturated hydrocarbon containing one or more triple bonds, with the general formula CnH2n-2.
- Heteroatom
- An element that replaces hydrogen in a carbon compound, conferring specific properties on it.
- Functional group
- An atom or group of atoms that gives a carbon compound its specific chemical properties, regardless of the length of the carbon chain.
- Homologous series
- A series of compounds in which the same functional group substitutes for hydrogen in a carbon chain; successive members differ by -CH2- and 14 u.
- Oxidising agent
- A substance capable of adding oxygen to others, such as alkaline potassium permanganate or acidified potassium dichromate.
- Addition reaction
- The reaction in which unsaturated hydrocarbons add hydrogen in the presence of a palladium or nickel catalyst to give saturated hydrocarbons.
- Catalyst
- A substance that causes a reaction to occur or proceed at a different rate without itself being affected by the reaction.
- Hydrogenation
- The addition of hydrogen to vegetable oils using a nickel catalyst, converting unsaturated chains into saturated ones.
- Substitution reaction
- A reaction in which one type of atom or group of atoms takes the place of another, as when chlorine replaces hydrogen in methane in sunlight.
- Esterification
- The reaction of a carboxylic acid with an alcohol in the presence of an acid catalyst to give a sweet-smelling ester.
- Saponification
- The reaction in which an ester treated with sodium hydroxide gives back an alcohol and the sodium salt of a carboxylic acid; used in making soap.
- Glacial acetic acid
- Pure ethanoic acid, so called because it freezes in cold climates - its melting point is 290 K.
- Micelle
- The structure formed by soap molecules in which the carbon chains point inward towards the oil droplet and the ionic ends face outward into the water.
- Scum
- The insoluble precipitate formed when soap reacts with the calcium and magnesium salts of hard water.
- Detergent
- An ammonium or sulphonate salt of a long-chain carboxylic acid, whose charged ends do not precipitate with calcium and magnesium ions, so it works in hard water.
End-of-Chapter Trial Paper & Test Questions
Topic-wise questions to test your understanding of every concept in this chapter.
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Why does carbon form a very large number of compounds, far more than most other elements? / कार्बन अधिकांश अन्य तत्वों की तुलना में बहुत अधिक संख्या में यौगिक क्यों बनाता है?
Show answer
Because of catenation (the ability of carbon atoms to bond with one another forming long chains, branches and rings) and its tetravalency, which lets it bond with four other atoms forming stable covalent compounds. / कार्बन की श्रृंखलन क्षमता (कार्बन परमाणुओं का आपस में जुड़कर लंबी श्रृंखला, शाखा व वलय बनाना) और चतुर्संयोजकता के कारण, जिससे यह चार अन्य परमाणुओं से जुड़कर स्थायी सहसंयोजी यौगिक बनाता है।
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Define a covalent bond and explain why carbon forms covalent bonds rather than ionic bonds. / सहसंयोजी बंध को परिभाषित करें और बताएं कि कार्बन आयनिक बंध के बजाय सहसंयोजी बंध क्यों बनाता है?
Show answer
A covalent bond is formed by the mutual sharing of electrons between atoms to complete their octets. / सहसंयोजी बंध परमाणुओं के बीच इलेक्ट्रॉनों की पारस्परिक साझेदारी से बनता है ताकि वे अपना अष्टक पूरा कर सकें। Carbon has 4 valence electrons; gaining or losing 4 electrons needs too much energy, so it shares electrons. / कार्बन में 4 संयोजी इलेक्ट्रॉन होते हैं; 4 इलेक्ट्रॉन प्राप्त करने या खोने में बहुत ऊर्जा लगती है, इसलिए यह इलेक्ट्रॉन साझा करता है।
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What are isomers? Draw/describe the two structural isomers of butane (C4H10). / समावयवी क्या हैं? ब्यूटेन (C4H10) के दो संरचनात्मक समावयवी बनाइए/वर्णन कीजिए।
Show answer
Isomers are compounds with the same molecular formula but different structural arrangements. / समावयवी वे यौगिक हैं जिनका अणुसूत्र समान परंतु संरचनात्मक व्यवस्था भिन्न होती है। Butane has n-butane (straight chain CH3-CH2-CH2-CH3) and isobutane (branched, a CH3 group on the middle carbon). / ब्यूटेन के दो समावयवी हैं: n-ब्यूटेन (सीधी श्रृंखला CH3-CH2-CH2-CH3) तथा आइसोब्यूटेन (शाखित, बीच के कार्बन पर CH3 समूह)।
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What is a homologous series? State any two of its characteristics. / समजातीय श्रेणी क्या है? इसकी कोई दो विशेषताएं बताइए।
Show answer
A homologous series is a group of organic compounds having the same general formula and similar chemical properties, where successive members differ by a -CH2- unit. / समजातीय श्रेणी समान सामान्य सूत्र व समान रासायनिक गुणों वाले कार्बनिक यौगिकों का समूह है, जिसमें क्रमागत सदस्य -CH2- इकाई से भिन्न होते हैं। Characteristics: members differ by 14 mass units (CH2) and show a gradation in physical properties like melting/boiling point. / विशेषताएं: सदस्य 14 द्रव्यमान इकाई (CH2) से भिन्न होते हैं तथा गलनांक/क्वथनांक जैसे भौतिक गुणों में क्रमिक परिवर्तन दिखाते हैं।
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Explain the conversion of ethanol to ethanoic acid and name the type of reaction. / एथेनॉल का एथेनॉइक अम्ल में परिवर्तन समझाइए तथा अभिक्रिया का प्रकार बताइए।
Show answer
Ethanol is heated with an oxidising agent such as alkaline KMnO4 or acidified K2Cr2O7, which oxidises it to ethanoic acid. / एथेनॉल को क्षारीय KMnO4 या अम्लीय K2Cr2O7 जैसे ऑक्सीकारक के साथ गर्म किया जाता है, जो इसे एथेनॉइक अम्ल में ऑक्सीकृत कर देता है। This is an oxidation reaction. / यह एक ऑक्सीकरण अभिक्रिया है।
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Why are detergents preferred over soaps for washing in hard water? / कठोर जल में धुलाई के लिए साबुन की तुलना में अपमार्जक क्यों पसंद किए जाते हैं?
Show answer
Soaps react with calcium and magnesium ions in hard water to form an insoluble scum, wasting soap. / साबुन कठोर जल के कैल्शियम और मैग्नीशियम आयनों से क्रिया करके अघुलनशील स्कम बनाते हैं, जिससे साबुन व्यर्थ होता है। Detergents do not form scum with hard water and remain effective, so they clean better. / अपमार्जक कठोर जल के साथ स्कम नहीं बनाते और प्रभावी बने रहते हैं, इसलिए वे बेहतर सफाई करते हैं।
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Explain how soap removes oily dirt, with reference to the structure of a micelle. / मिसेल की संरचना के संदर्भ में बताइए कि साबुन तैलीय गंदगी को कैसे हटाता है।
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A soap molecule has a hydrophobic (oil-loving) tail and a hydrophilic (water-loving) head. / साबुन अणु में एक जलविरोधी (तेल-प्रिय) पूँछ और एक जलरागी (जल-प्रिय) शीर्ष होता है। The tails dissolve into the oil droplet while the heads face the water, forming a micelle that lifts the dirt into water and washes it away. / पूँछें तेल की बूंद में घुल जाती हैं जबकि शीर्ष जल की ओर रहते हैं, जिससे मिसेल बनता है जो गंदगी को जल में उठाकर बहा देता है।
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Why does a candle flame or LPG burn with a clean flame while some carbon compounds burn with a sooty flame? / मोमबत्ती की लौ या LPG स्वच्छ लौ से जलती है जबकि कुछ कार्बन यौगिक कज्जली (धुएँदार) लौ से क्यों जलते हैं?
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Saturated hydrocarbons with sufficient air undergo complete combustion giving a clean blue flame. / पर्याप्त वायु के साथ संतृप्त हाइड्रोकार्बन पूर्ण दहन करते हैं और स्वच्छ नीली लौ देते हैं। Unsaturated compounds or those burning in limited air undergo incomplete combustion, releasing unburnt carbon particles that cause a yellow sooty flame. / असंतृप्त यौगिक या सीमित वायु में जलने वाले यौगिक अपूर्ण दहन करते हैं, जिससे बिना जला कार्बन निकलकर पीली कज्जली लौ देता है।
Related Laws & Principles
Explore allFoundational laws & principles behind this chapter. Each one opens a full page — what it says, why it matters, five practice questions and the mistakes to avoid.