CBSE Class 10 Science Carbon and its compound Sure Shot Questions Set 02

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ASSIGNMENT QUESTIONS SET – 2

CHAPTER – 4

CARBON AND ITS COMPOUNDS

Multiple choice questions

Carbon exists in the atmosphere in the form of

1. carbon monoxide only
2. carbon monoxide in traces and carbon dioxide
3. carbon dioxide only
4. coal

Answer: (b) carbon monoxide in traces and carbon dioxide

Which of the following statements are usually correct for carbon compounds? These (i) are good conductors of electricity, (ii) are poor conductors of electricity, (iii) have strong forces of attraction between their molecules, (iv) do not have strong forces of attraction between their molecules.

1. (i) and (iii)
2. (ii) and (iii)
3. (i) and (iv)
4. (ii) and (iv)

Answer: (d) (ii) and (iv)

A molecule of ammonia (NH₃) has

1. only single bonds
2. only double bonds
3. only triple bonds
4. two double bonds and one single bond

Answer: (a) only single bonds

Buckminsterfullerene is an allotropic form of

1. phosphorus
2. sulphur
3. carbon
4. tin

Answer: (c) carbon

Oils on treating with hydrogen in the presence of palladium or nickel catalyst form fats. This is an example of

1. addition reaction
2. substitution reaction
3. displacement reaction
4. oxidation reaction

Answer: (a) addition reaction

In which of the following compounds is −OH the functional group?

1. Butanone
2. Butanol
3. Butanoic acid
4. Butanal

Answer: (b) Butanol

Which of the following are correct structural isomers of butane?

1. (i) and (iii)
2. (ii) and (iv)
3. (i) and (ii)
4. (iii) and (iv)

Answer: (c) (i) and (ii). Structure (i) is n-butane and (ii) is isobutane (2-methylpropane). Structure (iii) is again n-butane drawn bent, and (iv) is cyclobutane.

In the reaction given below, alkaline KMnO₄ acts as
\(\mathrm{CH_3-CH_2-OH}\xrightarrow{\mathrm{Alkaline\ KMnO_4+Heat}}\mathrm{CH_3-COOH}\)

1. reducing agent
2. oxidising agent
3. catalyst
4. dehydrating agent

Answer: (b) oxidising agent

The structural formula of ethyne is

Answer: (a) H−C≡C−H

The soap molecule has a

1. hydrophilic head and a hydrophobic tail
2. hydrophobic head and a hydrophilic tail
3. hydrophobic head and a hydrophobic tail
4. hydrophilic head and a hydrophilic tail

Answer: (a) hydrophilic head and a hydrophobic tail

Which of the following is the correct representation of the electron dot structure of nitrogen?

Answer: (d). Each nitrogen atom has five valence electrons, so two atoms share three pairs (a triple bond) and each keeps one lone pair.

Identify the unsaturated compounds from the following: (i) propane, (ii) propene, (iii) propyne, (iv) chloropropane.

1. (i) and (ii)
2. (ii) and (iv)
3. (iii) and (iv)
4. (ii) and (iii)

Answer: (d) (ii) and (iii)

Chlorine reacts with saturated hydrocarbons at room temperature in the

1. absence of sunlight
2. presence of sunlight
3. presence of water
4. presence of hydrochloric acid

Answer: (b) presence of sunlight

In soap micelles

1. the ionic end of soap is on the surface of the cluster while the carbon chain is in the interior of the cluster
2. the ionic end of soap is in the interior of the cluster and the carbon chain is out of the cluster
3. both the ionic end and the carbon chain are in the interior of the cluster
4. both the ionic end and the carbon chain are on the exterior of the cluster

Answer: (a)

Pentane has the molecular formula C₅H₁₂. It has

1. 5 covalent bonds
2. 12 covalent bonds
3. 16 covalent bonds
4. 17 covalent bonds

Answer: (c) 16 covalent bonds (4 C−C bonds and 12 C−H bonds)

Ethanol reacts with sodium and forms two products. These are

1. sodium ethanoate and hydrogen
2. sodium ethanoate and oxygen
3. sodium ethoxide and hydrogen
4. sodium ethoxide and oxygen

Answer: (c) sodium ethoxide and hydrogen

The structural formula of benzene is

Answer: (c). Benzene is C₆H₆: six carbon atoms in a ring with alternate double bonds and one hydrogen on each carbon.

The correct structural formula of butanoic acid is

Answer: (d). Butanoic acid has four carbon atoms, with the −COOH group on the last one.

Vinegar is a solution of

1. 50–60% acetic acid in alcohol
2. 5–8% acetic acid in alcohol
3. 5–8% acetic acid in water
4. 50–60% acetic acid in water

Answer: (c) 5–8% acetic acid in water

Mineral acids are stronger acids than carboxylic acids because (i) mineral acids are completely ionised, (ii) carboxylic acids are completely ionised, (iii) mineral acids are partially ionised, (iv) carboxylic acids are partially ionised.

1. (i) and (iv)
2. (ii) and (iii)
3. (i) and (ii)
4. (iii) and (iv)

Answer: (a) (i) and (iv)

Carbon forms four covalent bonds by sharing its four valence electrons with four univalent atoms, e.g. hydrogen. After the formation of four bonds, carbon attains the electronic configuration of

1. helium
2. neon
3. argon
4. krypton

Answer: (b) neon (the octet, 2, 8)

The correct electron dot structure of a water molecule is

Answer: (c). Oxygen shares one pair with each hydrogen and keeps two lone pairs.

Which of the following is not a straight chain hydrocarbon?
(a) \(\mathrm{H_3C-CH_2-CH_2-CH_2-\underset{\underset{CH_3}{|}}{CH_2}}\)(b) \(\mathrm{H_3C-CH_2-CH_2-CH_2-CH_2-CH_3}\)(c) \(\mathrm{\overset{\overset{CH_3}{|}}{H_2C}-H_2C-H_2C-\underset{\underset{CH_3}{|}}{CH_2}}\)(d) \(\left.\begin{array}{l}\mathrm{CH_3}\\ \mathrm{H_3C}\end{array}\right\rangle\mathrm{CH-CH_2-CH_2-CH_3}\)

Answer: (d). Here the carbon chain has a branch (two CH₃ groups on one carbon). In (a) and (c) the extra CH₃ only continues the chain.

Which among the following are unsaturated hydrocarbons?
(i) \(\mathrm{H_3C-CH_2-CH_2-CH_3}\)(ii) \(\mathrm{H_3C-C\equiv C-CH_3}\)(iii) \(\mathrm{H_3C-\underset{\underset{CH_3}{|}}{CH}-CH_3}\)(iv) \(\mathrm{H_3C-\underset{\underset{CH_3}{|}}{C}=CH_2}\)

1. (i) and (iii)
2. (ii) and (iii)
3. (ii) and (iv)
4. (iii) and (iv)

Answer: (c) (ii) and (iv)

Which of the following does not belong to the same homologous series?

1. CH₄
2. C₂H₆
3. C₃H₈
4. C₄H₈

Answer: (d) C₄H₈. The others are alkanes (C_nH_2n+2); C₄H₈ is an alkene.

The name of the compound CH₃−CH₂−CHO is

1. Propanal
2. Propanone
3. Ethanol
4. Ethanal

Answer: (a) Propanal

The heteroatoms present in CH₃−CH₂−O−CH₂−CH₂Cl are (i) oxygen, (ii) carbon, (iii) hydrogen, (iv) chlorine.

1. (i) and (ii)
2. (ii) and (iii)
3. (iii) and (iv)
4. (i) and (iv)

Answer: (d) (i) and (iv)

Which of the following represents a saponification reaction?

1. \(\mathrm{CH_3COONa+NaOH}\xrightarrow{\mathrm{CaO}}\mathrm{CH_4+Na_2CO_3}\)
2. \(\mathrm{CH_3COOH+C_2H_5OH}\xrightarrow{\mathrm{H_2SO_4}}\mathrm{CH_3COOC_2H_5+H_2O}\)
3. \(\mathrm{2CH_3COOH+2Na\rightarrow 2CH_3COONa+H_2}\)
4. \(\mathrm{CH_3COOC_2H_5+NaOH\rightarrow CH_3COONa+C_2H_5OH}\)

Answer: (d). Saponification is the alkaline hydrolysis of an ester into the sodium salt of the acid and the alcohol.

The first member of the alkyne homologous series is

1. ethyne
2. ethene
3. propyne
4. methane

Answer: (a) ethyne

Short and long answer questions

Draw the electron dot structure of ethyne and also draw its structural formula.

Answer: Each carbon has 4 valence electrons and each hydrogen has 1. The two carbon atoms share three pairs of electrons, and each carbon shares one pair with a hydrogen atom.
Electron dot structure:

Structural formula:

Why are detergents better cleansing agents than soaps? Explain.

Answer: Soaps form an insoluble scum with the calcium and magnesium salts in hard water, so they do not lather and clean poorly. Detergents are sodium salts of sulphonic acids (or ammonium salts), and they do not form scum with hard water, so they clean well in both soft and hard water.

Name the functional groups present in the following compounds: (a) CH₃COCH₂CH₂CH₂CH₃; (b) CH₃CH₂CH₂COOH; (c) CH₃CH₂CH₂CH₂CHO; (d) CH₃CH₂OH.

Answer: (a) Ketone (>C=O). (b) Carboxylic acid (−COOH). (c) Aldehyde (−CHO). (d) Alcohol (−OH).

How is ethene prepared from ethanol? Give the reaction involved in it.

Answer: Ethanol is heated at 443 K with excess of concentrated sulphuric acid, which removes a molecule of water (dehydration):
\(\mathrm{CH_3CH_2OH}\xrightarrow{\mathrm{Conc.\ H_2SO_4,\ 443\ K}}\mathrm{CH_2=CH_2+H_2O}\)

Intake of a small quantity of methanol can be lethal. Comment.

Answer: In the liver, methanol is oxidised to methanal (formaldehyde), which rapidly combines with the protoplasm of the cells and coagulates it. Methanol also damages the optic nerve, causing blindness, and can cause death.

A gas is evolved when ethanol reacts with sodium. Name the gas evolved and also write the balanced chemical equation of the reaction involved.

Answer: Hydrogen gas is evolved.
\(\mathrm{2CH_{3}CH_{2}OH\,+\,2Na\,}\rightarrow \mathrm{\,2CH_{3}CH_{2}ONa\,+\,H_{2}}\)

Write the names of the following compounds.

Answer: (a) Pentanoic acid.
(b) But-1-yne (butyne).
(c) Heptanal (a seven-carbon aldehyde; the source drawing omitted the hydrogen on the −CHO carbon).
(d) Pentan-1-ol (pentanol).

Identify and name the functional groups present in the following compounds.

Answer: (a) Propan-1-ol: alcohol (−OH).
(b) Propanoic acid: carboxylic acid (−COOH).
(c) Pentan-3-one: ketone (>C=O).
(d) But-1-ene: alkene (a C=C double bond).

A compound X is formed by the reaction of a carboxylic acid C₂H₄O₂ and an alcohol in the presence of a few drops of H₂SO₄. The alcohol on oxidation with alkaline KMnO₄ followed by acidification gives the same carboxylic acid as used in this reaction. Give the names and structures of (a) the carboxylic acid, (b) the alcohol and (c) the compound X. Also write the reaction.

Answer: (a) Ethanoic acid (acetic acid), \(\mathrm{CH_3COOH}\)
(b) Ethanol, \(\mathrm{CH_3CH_2OH}\) (its oxidation gives ethanoic acid)
(c) X = ethyl ethanoate, \(\mathrm{CH_3COOC_2H_5}\)
\(\mathrm{CH_3COOH+CH_3CH_2OH}\xrightarrow{\mathrm{H_2SO_4}}\mathrm{CH_3COOCH_2CH_3+H_2O}\)

Ethene is formed when ethanol at 443 K is heated with excess of concentrated sulphuric acid. What is the role of sulphuric acid in this reaction? Write the balanced chemical equation of this reaction.

Answer: Concentrated sulphuric acid acts as a dehydrating agent (it removes water from ethanol).
\(\mathrm{CH_3CH_2OH}\xrightarrow{\mathrm{Conc.\ H_2SO_4,\ 443\ K}}\mathrm{CH_2=CH_2+H_2O}\)

Carbon, a Group 14 element in the Periodic Table, is known to form compounds with many elements. Write an example of a compound formed with (a) chlorine (Group 17), (b) oxygen (Group 16).

Answer: (a) Carbon tetrachloride, CCl₄.
(b) Carbon dioxide, CO₂ (or carbon monoxide, CO).

In the electron dot structure, the valence shell electrons are represented by crosses or dots. (a) The atomic number of chlorine is 17. Write its electronic configuration. (b) Draw the electron dot structure of the chlorine molecule.

Answer: (a) 2, 8, 7.
(b) Each chlorine atom has 7 valence electrons and shares one pair, so that each attains 8 electrons.

Catenation is the ability of an atom to form bonds with other atoms of the same element. It is exhibited by both carbon and silicon. Compare the ability of catenation of the two elements. Give reasons.

Answer: Carbon shows catenation to a much greater extent than silicon. Carbon forms very long chains, branched chains and rings, because the C−C bond is very strong (small atom). The Si−Si bond is weaker (bigger atom), so silicon forms only short chains of up to about seven or eight atoms, and these are less stable.

Unsaturated hydrocarbons contain multiple bonds between two carbon atoms and show addition reactions. Give the test to distinguish ethane from ethene.

Answer: Add bromine water (or alkaline KMnO₄) to both. Ethene adds bromine and decolourises the brown bromine water (or the purple KMnO₄), whereas ethane does not change the colour.

Write the structural formulae of all the isomers of hexane.

Answer: Hexane (C₆H₁₄) has five isomers:
1. n-Hexane: \(\mathrm{CH_3-CH_2-CH_2-CH_2-CH_2-CH_3}\)
2. 2-Methylpentane: \(\mathrm{CH_3-\underset{\underset{CH_3}{|}}{CH}-CH_2-CH_2-CH_3}\)
3. 3-Methylpentane: \(\mathrm{CH_3-CH_2-\underset{\underset{CH_3}{|}}{CH}-CH_2-CH_3}\)
4. 2,2-Dimethylbutane: \(\mathrm{CH_3-\underset{\underset{CH_3}{|}}{\overset{\overset{CH_3}{|}}{C}}-CH_2-CH_3}\)
5. 2,3-Dimethylbutane: \(\mathrm{CH_3-\underset{\underset{CH_3}{|}}{CH}-\underset{\underset{CH_3}{|}}{CH}-CH_3}\)

What is the role of the metal or reagents written on the arrows in the given chemical reactions? (a) (CH₃)₂C=C(CH₃)₂ + H₂ →(Ni) (CH₃)₂CH−CH(CH₃)₂; (b) CH₃COOH + CH₃CH₂OH →(conc. H₂SO₄) CH₃COOC₂H₅ + H₂O; (c) CH₃CH₂OH →(alkaline KMnO₄, heat) CH₃COOH.

Answer: (a) Nickel is a catalyst for the addition of hydrogen (hydrogenation).
(b) Concentrated sulphuric acid acts as a catalyst and as a dehydrating agent in the esterification.
(c) Alkaline KMnO₄ is an oxidising agent, which oxidises ethanol to ethanoic acid.

A salt X is formed and a gas is evolved when ethanoic acid reacts with sodium hydrogencarbonate. Name the salt X and the gas evolved. Describe an activity and draw the diagram of the apparatus to prove that the evolved gas is the one which you have named. Also, write the chemical equation of the reaction involved.

Answer: The salt X is sodium ethanoate (sodium acetate) and the gas is carbon dioxide.
Activity: take a little sodium hydrogencarbonate in a test tube and add ethanoic acid. Brisk effervescence occurs. Pass the gas through a delivery tube into a second test tube containing lime water. The lime water turns milky, which shows that the gas is carbon dioxide.

\(\mathrm{CH_{3}COOH\,+\,NaHCO_{3}\,}\rightarrow \mathrm{\,CH_{3}COONa\,+\,H_{2}O\,+\,CO_{2}}\)

What are hydrocarbons? Give examples.

Answer: Compounds made up of only carbon and hydrogen are hydrocarbons. Examples: methane (CH₄), ethene (C₂H₄), ethyne (C₂H₂).

Give the structural differences between saturated and unsaturated hydrocarbons with two examples each.

Answer: Saturated hydrocarbons have only single bonds between carbon atoms, for example methane CH₄ and ethane C₂H₆. Unsaturated hydrocarbons have at least one double or triple bond between carbon atoms, for example ethene CH₂=CH₂ and ethyne HC≡CH.

What is a functional group? Give examples of four different functional groups.

Answer: An atom or group of atoms which makes a carbon compound react in a particular way and decides its properties is a functional group. Examples: alcohol (−OH), aldehyde (−CHO), ketone (>C=O), carboxylic acid (−COOH).

Name the reaction which is commonly used in the conversion of vegetable oils to fats. Explain the reaction involved in detail.

Answer: The reaction is hydrogenation. Unsaturated vegetable oils, which have double bonds, are heated with hydrogen in the presence of a nickel catalyst. Hydrogen adds across the double bonds and converts the oil into a saturated fat (vanaspati ghee), which is solid at room temperature.

Write the formula and draw the electron dot structure of carbon tetrachloride.

Answer: Formula: CCl₄. Carbon shares one electron pair with each of four chlorine atoms, and each chlorine keeps three lone pairs.

What is saponification? Write the reaction involved in this process.

Answer: The alkaline hydrolysis of an ester (a fat or oil) with sodium hydroxide to form soap (the sodium salt of a fatty acid) and glycerol is called saponification.
\(\mathrm{Ester + NaOH \longrightarrow Sodium\ salt\ of\ acid\ (soap) + Alcohol\ (glycerol)}\)
For example: \(\mathrm{CH_3COOC_2H_5 + NaOH \longrightarrow CH_3COONa + C_2H_5OH}\)

Esters are sweet-smelling substances and are used in making perfumes. Suggest some activity and the reaction involved for the preparation of an ester with a well labelled diagram.

Answer: Take 1 mL of ethanol and 1 mL of glacial ethanoic acid in a test tube and add a few drops of concentrated sulphuric acid. Warm the mixture in a water bath for about five minutes. Then pour it into a beaker of water. A sweet, fruity smell of the ester (ethyl ethanoate) is noticed.

\(\mathrm{CH_3COOH+C_2H_5OH}\xrightarrow{\mathrm{Conc.\ H_2SO_4}}\mathrm{CH_3COOC_2H_5+H_2O}\)

A compound C (molecular formula C₂H₄O₂) reacts with Na metal to form a compound R and evolves a gas which burns with a pop sound. Compound C on treatment with an alcohol A in the presence of an acid forms a sweet-smelling compound S (molecular formula C₃H₆O₂). On addition of NaOH to C, it also gives R and water. S on treatment with NaOH solution gives back R and A. Identify C, R, A, S and write down the reactions involved.

Answer: C = ethanoic acid, CH₃COOH; R = sodium ethanoate, CH₃COONa; A = methanol, CH₃OH; S = methyl ethanoate, CH₃COOCH₃.
\(\mathrm{2CH_{3}COOH\,+\,2Na\,}\rightarrow \mathrm{\,2CH_{3}COONa\,+\,H_{2}}\)
\(\mathrm{CH_3COOH+CH_3OH}\xrightarrow{\mathrm{H^+}}\mathrm{CH_3COOCH_3+H_2O}\)
\(\mathrm{CH_{3}COOH\,+\,NaOH\,}\rightarrow \mathrm{\,CH_{3}COONa\,+\,H_{2}O}\)
\(\mathrm{CH_{3}COOCH_{3}\,+\,NaOH\,}\rightarrow \mathrm{\,CH_{3}COONa\,+\,CH_{3}OH}\)

Draw the possible isomers of the compound with molecular formula C₃H₆O and also give their electron dot structures.

Answer: The two isomers are propanal (an aldehyde, CH₃CH₂CHO) and propanone (a ketone, CH₃COCH₃).
Propanal:


Propanone:

How would you bring about the following conversions? Name the process and write the reaction involved. (a) ethanol to ethene; (b) propanol to propanoic acid. Write the reactions.

Answer: (a) Dehydration: heat ethanol with excess concentrated sulphuric acid at 443 K. \(\mathrm{CH_3CH_2OH}\xrightarrow{\mathrm{Conc.\ H_2SO_4,\ 443\ K}}\mathrm{CH_2=CH_2+H_2O}\)
(b) Oxidation: heat propanol with alkaline potassium permanganate (followed by acidification) or acidified potassium dichromate. \(\mathrm{CH_3CH_2CH_2OH}\xrightarrow{\mathrm{Alkaline\ KMnO_4,\ heat}}\mathrm{CH_3CH_2COOH}\)

Explain the given reactions with examples: (a) hydrogenation reaction; (b) oxidation reaction; (c) substitution reaction; (d) saponification reaction; (e) combustion reaction.

Answer: (a) Addition of hydrogen to unsaturated hydrocarbons in the presence of Ni: \(\mathrm{CH_2=CH_2+H_2}\xrightarrow{\mathrm{Ni}}\mathrm{CH_3-CH_3}\)
(b) Addition of oxygen (or removal of hydrogen): \(\mathrm{CH_3CH_2OH}\xrightarrow{\mathrm{Alkaline\ KMnO_4}}\mathrm{CH_3COOH}\)
(c) Replacement of a hydrogen atom by another atom: \(\mathrm{CH_4+Cl_2}\xrightarrow{\mathrm{Sunlight}}\mathrm{CH_3Cl+HCl}\)
(d) Alkaline hydrolysis of an ester: \(\mathrm{CH_{3}COOC_{2}H_{5}\,+\,NaOH\,}\rightarrow \mathrm{\,CH_{3}COONa\,+\,C_{2}H_{5}OH}\)
(e) Burning in oxygen to give carbon dioxide, water, heat and light: \(\mathrm{CH_{4}\,+\,2O_{2}\,}\rightarrow \mathrm{\,CO_{2}\,+\,2H_{2}O}\)

An organic compound A on heating with concentrated H₂SO₄ forms a compound B, which on addition of one mole of hydrogen in the presence of Ni forms a compound C. One mole of compound C on combustion forms two moles of CO₂ and 3 moles of H₂O. Identify the compounds A, B and C and write the chemical equations of the reactions involved.

Answer: C gives 2 CO₂ and 3 H₂O, so C is ethane, C₂H₆. B is ethene (it adds H₂ to give ethane) and A is ethanol (dehydration gives ethene).
\(\mathrm{CH_3CH_2OH}\xrightarrow{\mathrm{Conc.\ H_2SO_4,\ heat}}\mathrm{CH_2=CH_2+H_2O}\)
\(\mathrm{CH_2=CH_2+H_2}\xrightarrow{\mathrm{Ni}}\mathrm{CH_3CH_3}\)
\(\mathrm{2C_{2}H_{6}\,+\,7O_{2}\,}\rightarrow \mathrm{\,4CO_{2}\,+\,6H_{2}O}\)

Define allotropy.

Answer: The existence of an element in two or more different forms in the same physical state, which differ in physical properties but have similar chemical properties, is called allotropy. Example: diamond, graphite and fullerene are allotropes of carbon.

What is vinegar?

Answer: Vinegar is a 5–8% solution of ethanoic (acetic) acid in water.

What is combustion?

Answer: The burning of a substance in oxygen with the release of heat and light is combustion. Carbon compounds burn in oxygen to give carbon dioxide and water.

How can you differentiate saturated and unsaturated hydrocarbons on the basis of burning behaviour?

Answer: Saturated hydrocarbons burn with a clean blue flame in a good supply of air. Unsaturated hydrocarbons burn with a yellow, sooty flame because the carbon is not burnt completely.

Give two advantages of synthetic detergents over soaps.

Answer: They can be used with hard water without forming scum, and they work in acidic water also. (They also have a stronger cleansing action.)

What are substitution reactions?

Answer: Reactions in which one atom or group of atoms in a molecule is replaced by another atom or group are substitution reactions. Example: \(\mathrm{CH_{4}\,+\,Cl_{2}\,}\rightarrow \mathrm{\,CH_{3}Cl\,+\,HCl}\) (in sunlight).

Differentiate between diamond and graphite.

Answer: Diamond: each carbon is joined to four other carbon atoms in a rigid three-dimensional structure; it is very hard, transparent, a bad conductor of electricity and has a very high melting point.
Graphite: each carbon is joined to three others in flat hexagonal layers which can slide over one another; it is soft and slippery, black and a good conductor of electricity.

Discuss the method of preparation of soap in the laboratory.

Answer: Take about 20 mL of vegetable oil (castor or coconut oil) in a beaker and add 30 mL of 20% sodium hydroxide solution. Heat the mixture with constant stirring for some time (until a paste forms). Add 5–10 g of common salt (NaCl) to the mixture and stir. The soap separates out as a solid; filter it off, wash it with a little cold water and let it dry.

Write five ill effects of alcohol drinking.

Answer: It damages the liver, affects the brain and the nervous system, weakens the heart, can lead to addiction and accidents, and affects the family and social life. (Any five.)

Differentiate between ionic compounds and covalent compounds.

Answer: Ionic compounds are formed by transfer of electrons, are hard crystalline solids with high melting and boiling points, are soluble in water and conduct electricity when molten or dissolved.
Covalent compounds are formed by sharing of electrons, are usually liquids or gases (or soft solids) with low melting and boiling points, are usually insoluble in water and do not conduct electricity.

Give some important properties of ethanol (ethyl alcohol).

Answer: Ethanol is a colourless liquid with a pleasant smell and burning taste, soluble in water in all proportions, and boils at 351 K. It burns with a blue flame, reacts with sodium to give hydrogen, is oxidised to ethanoic acid, and gives ethene on dehydration.

Give five main advantages of synthetic detergents over soaps.

Answer: 1. Work in hard water without forming scum.
2. Work in acidic water also.
3. Have a stronger cleansing action.
4. Lather more easily.
5. Can be made in large quantities from petroleum products, and do not need fats and oils.

Write important uses of (a) ethanol and (b) ethanoic acid.

Answer: (a) Ethanol is used as a solvent for paints and varnishes, in medicines (tincture of iodine, cough syrups), as a fuel mixed with petrol (power alcohol), and in alcoholic drinks.
(b) Ethanoic acid is used as vinegar to preserve food and pickles, as a solvent, and in the making of dyes, perfumes, plastics and medicines.

What happens when ethanol reacts with (i) sodium, (ii) potassium permanganate solution?

Answer: (i) Hydrogen gas is released and sodium ethoxide is formed: \(\mathrm{2CH_{3}CH_{2}OH\,+\,2Na\,}\rightarrow \mathrm{\,2CH_{3}CH_{2}ONa\,+\,H_{2}}\)
(ii) Alkaline KMnO₄ oxidises ethanol to ethanoic acid; the purple colour of the permanganate disappears: \(\mathrm{CH_3CH_2OH}\xrightarrow{\mathrm{Alkaline\ KMnO_4,\ heat}}\mathrm{CH_3COOH}\)

An organic acid X is a liquid which often freezes during winter time in cold countries and has the molecular formula C₂H₄O₂. On warming it with ethanol in the presence of a few drops of concentrated sulphuric acid, a compound Y with a sweet smell is formed. (i) Identify X and Y. (ii) Write a chemical equation for the reaction involved.

Answer: (i) X is ethanoic acid (glacial acetic acid) and Y is ethyl ethanoate.
(ii) \(\mathrm{CH_3COOH+C_2H_5OH}\xrightarrow{\mathrm{Conc.\ H_2SO_4}}\mathrm{CH_3COOC_2H_5+H_2O}\)

Write the names of the following: (i) an alkaline earth metal belonging to the third period; (ii) the alkali metal atom having the largest atomic radius; (iii) the halogen atom belonging to the fourth period; (iv) the element having the lowest ionisation energy; (v) the element having the second lowest electronegativity.

Answer: (i) Magnesium. (ii) Francium (the largest among the common ones is caesium). (iii) Bromine. (iv) Caesium (francium is similar, but it is radioactive and very rare). (v) Caesium (francium has the lowest value).

An organic compound X of molecular formula C₂H₄O₂ gives brisk effervescence with sodium hydrogencarbonate. Give the name and molecular formula of X with the balanced equation.

Answer: X is ethanoic acid (acetic acid), CH₃COOH.
\(\mathrm{CH_{3}COOH\,+\,NaHCO_{3}\,}\rightarrow \mathrm{\,CH_{3}COONa\,+\,H_{2}O\,+\,CO_{2}}\)

Soaps are not considered as effective cleansing agents. Why?

Answer: In hard water, soap reacts with the calcium and magnesium salts to form an insoluble scum, which wastes soap and does not clean well.

How do the melting and boiling points of hydrocarbons change with the increase in molecular mass?

Answer: They increase, because the forces of attraction between the larger molecules are stronger.

Write down the relevant chemical equation involved in decolourisation.

Answer: The decolourisation of bromine water by ethene (an unsaturated hydrocarbon): \(\mathrm{CH_{2}=CH_{2}\,+\,Br_{2}\,}\rightarrow \mathrm{\,CH_{2}Br-CH_{2}Br}\) (brown bromine water turns colourless). The question as printed in the source does not say which reaction is meant.

A compound X has the molecular formula C₃H₄. One mole of X reacts with 2 moles of hydrogen to yield a compound Y. Deduce the structures of X and Y.

Answer: C₃H₄ fits C_nH_2n−2, so X is an alkyne: propyne, CH₃−C≡CH. It adds 2 moles of hydrogen to form propane, CH₃CH₂CH₃ (Y).

What is a dehydration reaction? Give one example.

Answer: A reaction in which a molecule of water is removed from a compound. Example: \(\mathrm{CH_3CH_2OH}\xrightarrow{\mathrm{Conc.\ H_2SO_4}}\mathrm{CH_2=CH_2+H_2O}\)

What is hydrolysis?

Answer: The breaking down of a compound by water (or by acid or alkali) is hydrolysis. Example: an ester splits into an acid and an alcohol.

Why doesn't soap form micelles in ethanol as it does in water?

Answer: Micelles form in water because the hydrocarbon tails are hydrophobic and gather together in the interior. Ethanol is an organic solvent, so the hydrocarbon tails dissolve in it and do not need to aggregate; hence no micelles form.

Three elements X, Y and Z belong to Group 17 but to the 2nd, 3rd and 4th periods respectively. The number of valence electrons in X is 7. Find the number of valence electrons in Y and Z. (The source asked for "X and Z".)

Answer: All the elements in a group have the same number of valence electrons, so Y and Z (and X) have 7 valence electrons each.

What is the use of the oxyacetylene flame?

Answer: It gives a very hot flame (about 3000 °C) and is used for welding and cutting metals.

What is observed on adding a 5% solution of alkaline potassium permanganate drop by drop to some warm ethanol taken in a test tube?

Answer: The purple colour of the permanganate disappears at first, because ethanol is oxidised to ethanoic acid. When more permanganate is added than the ethanol can use, the purple colour remains.

Write the name of the compound formed during the chemical reaction.

Answer: The question is incomplete in the source: the reaction it refers to is missing, so it cannot be answered.

How would you distinguish experimentally between an alcohol and a carboxylic acid on the basis of a chemical property?

Answer: Add sodium hydrogencarbonate to each. The carboxylic acid gives brisk effervescence of carbon dioxide, but the alcohol does not.

Why are vegetable oils healthy as compared to vegetable ghee? How are vegetable oils converted into vegetable ghee? Name the process.

Answer: Vegetable oils are unsaturated and are healthier, while ghee has saturated fats, which are harmful for the heart. Oils are converted to ghee by hydrogenation: hydrogen is passed through the oil in the presence of nickel catalyst.

When acetic acid reacts with X, a salt is formed which on reaction with soda lime gives a gas Y. Identify X and Y.

Answer: X is sodium hydroxide (NaOH), which gives sodium acetate. Heating sodium acetate with soda lime gives methane gas (Y).
\(\mathrm{CH_{3}COOH\,+\,NaOH\,}\rightarrow \mathrm{\,CH_{3}COONa\,+\,H_{2}O}\)
\(\mathrm{CH_3COONa+NaOH}\xrightarrow{\mathrm{CaO}}\mathrm{CH_4+Na_2CO_3}\)

"Alkenes form a homologous series." Explain.

Answer: Alkenes have the same functional group (C=C), the same general formula C_nH_2n, similar chemical properties, and each member differs from the next by a CH₂ group, with a gradual change in physical properties. So they form a homologous series.

Why is ethanoic acid called glacial acetic acid?

Answer: Pure ethanoic acid freezes at 290 K (about 17 °C), which is just below the room temperature in cold regions. It then turns into ice-like crystals, so it is called glacial acetic acid.

Why is the conversion of ethanol to ethanoic acid an oxidation reaction?

Answer: Because ethanol gains oxygen (and loses hydrogen) to form ethanoic acid. Gain of oxygen is oxidation.

A mixture of ethyne and oxygen is burnt for welding. Can you tell why a mixture of ethyne and air is not used?

Answer: Ethyne burns completely in pure oxygen and produces a very hot flame. With air, the oxygen supply is limited and the burning is incomplete, so the flame is sooty and not hot enough for welding.

Why is the conversion of ethanol to ethanoic acid considered an oxidation reaction?

Answer: Because ethanol gains oxygen (and loses hydrogen) to form ethanoic acid. Gain of oxygen is oxidation.

Who was the first to suggest the classification of chemical compounds into inorganic and organic compounds?

Answer: Berzelius (a Swedish chemist), who proposed the vital force theory.

Why are the compounds of carbon studied as a separate branch of chemistry?

Answer: Carbon forms millions of compounds because of catenation and tetravalency, which is far more than all other elements together, and these compounds have their own distinct properties and reactions.

Compounds like calcium carbide, carbon monoxide, carbon dioxide and calcium carbonate are considered as inorganic compounds although they have carbon atoms in their molecules. Give a reason.

Answer: They are obtained from minerals and non-living sources, and their properties are similar to those of inorganic compounds.

Why do compounds like B−B, Si−Si and S−S not exist in nature in long chains like carbon?

Answer: The bonds between these atoms are much weaker than the C−C bond, so they cannot form long, stable chains (catenation is poor in them).

What is "Buckminsterfullerene"? Why is it called so?

Answer: It is an allotrope of carbon in which 60 carbon atoms are joined in a hollow football-like cage (C₆₀). It is named after the American architect Buckminster Fuller, whose geodesic dome has the same shape.

Name the first organic compound obtained from an inorganic source in the laboratory. Who synthesised it?

Answer: Urea, synthesised by Friedrich Wöhler in 1828 from the inorganic compound ammonium cyanate.

(a) phosphorus

(b) sulphur

(b) Substitution reaction

(c) Displacement reaction

(d) Oxidation reaction

(a) Butanone (b) Butanol

(c) Butanoic acid (d) Butanal

8. In the below given reaction, alkaline KMnO4 acts as

(a) reducing agent

(c) catalyst

(d) dehydrating agent

19. Vinegar is a solution of

(c) argon

(d) krypton