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#### Question 1:

Carbon exists in the atmosphere in the form of
(a) carbon monoxide only
(b) carbon monoxide in traces and carbon dioxide
(c) carbon dioxide only
(d) coal

The amount of carbon present in the atmosphere is quite meagre. The atmosphere has 0.03% of carbon dioxide.

Hence, the correct answer is option (c).

#### Question 2:

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
(a) (i) and (iii)
(b) (ii) and (iii)
(c) (i) and (iv)
(d) (ii) and (iv)

Cabon forms covalently bonded molecules which are seen to have strong bonds within the molecule but intermolecular forces are weak. Since the electrons are shared between atoms and no charged particles are formed, such covalent compounds are generally poor conductors of electricity.

Hence, the correct answer is option (d).

#### Question 3:

A molecule of ammonia (NH3) has
(a) only single bonds
(b) only double bonds
(c) only triple bonds
(d) two double bonds and one single bond

Three hydrogen atoms share their electrons with one nitrogen atom to form a molecule of ammonia, ${\mathrm{NH}}_{3}$. This allows nitrogen and hydrogen atom to attain the electronic configuration of the nearest noble gas Ne and He, respectively. The shared pair of electron is said to contribute a single covalent bond. So there are 3 single covalent bonds in ammonia.

Hence, the correct answer is option (a).

#### Question 4:

Buckminsterfullerene is an allotropic form of
(a) phosphorus
(b) sulphur
(c) carbon
(d) tin

Buckminster fullerene is an allotropic form of carbon. Carbon atoms are arranged in the shape of a football in this.

Hence, the correct answer is option (c).

#### Question 5:

Which of the following are correct structural isomers of butane?

(a) (i) and (iii)
(b) (ii) and (iv)
(c) (i) and (ii)
(d) (iii) and (iv)

We see that compound (i) and compound (ii) have the same formula C4H10. Such compounds with identical molecular formula but different structures are called structural isomers.

Hence, the correct answer is option (c).

#### Question 6:

In the above given reaction, alkaline KMnO4 acts as
(a) reducing agent
(b) oxidising agent
(c) catalyst
(d) dehydrating agent

In this reaction, alkaline potassium permanganate is adding oxygen to ethanol and hence, oxidising it to acetic acid. Substances that are capable of adding oxygen to others are known as oxidising agents.

Hence, the correct answer is option (b).

#### Question 7:

Oils on treating with hydrogen in the presence of palladium or nickel catalyst form fats. This is an example of
(b) Substitution reaction
(c) Displacement reaction
(d) Oxidation reaction

Unsaturated hydrocarbons add hydrogen in the presence of catalysts such as palladium or nickel to give saturated hydrocarbons. This addition 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.

Hence, the correct answer is option (a).

#### Question 8:

In which of the following compounds, — OH is the functional group?
(a) Butanone
(b) Butanol
(c) Butanoic acid
(d) Butanal

Suffix for the compounds having a functional group  — OH is 'ol'. So, C4H9OH is butanol.

Hence, the correct answer is option (b).

#### Question 9:

The soap molecule has a
(a) hydrophilic head and a hydrophobic tail
(b) hydrophobic head and a hydrophilic tail
(c) hydrophobic head and a hydrophobic tail
(d) hydrophilic head and a hydrophilic tail.

The soap molecule has two ends, one is the hydrophilic head, that is, it interacts with water, while the other end is the hydrophobic tail, that is, it interacts with hydrocarbons.

Hence, the correct answer is option (a).

#### Question 10:

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

Two nitrogen atoms are bonded through three single covalent bonds to form a nitrogen molecule and one lone pair of electrons remain over each nitrogen atoms.

Hence, the correct answer is option (d).

#### Question 11:

Structural formula of ethyne is

The formula of ethyne is C2H2. There is one triple bond between carbon atoms.

Hence, the correct answer is option (a).

#### Question 12:

Identify the unsaturated compounds from the following
(i) Propane
(ii) Propene
(iii) Propyne
(iv) Chloropropane
(a) (i) and (ii)
(b) (ii) and (iv)
(c) (iii) and (iv)
(d) (ii) and (iii)

Those compounds in which valencies of all the atoms are satisfied by single bonds only, are called saturated compounds and those compounds in which valencies of all the atoms can not be satisfied by single bonds only, are called unsaturated compounds. Such compounds of carbon have double or triple bonds between the atoms to satisfy valencies. Propane (C3H8) and chloropropane (C3H7Cl) are saturated compounds while propene (C3H6) and propyne (C3H4) are unsaturated compounds.

Hence, the correct answer is option (d).

#### Question 13:

Chlorine reacts with saturated hydrocarbons at room temperature in the
(a) absence of sunlight
(b) presence of sunlight
(c) presence of water
(d) presence of hydrochloric acid

In the presence of sunlight, chlorine is added to saturated 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.

Hence, the correct answer is option (b).

#### Question 14:

In the soap micelles
(a) the ionic end of soap is on the surface of the cluster while the carbon chain is in the interior of the cluster.
(b) ionic end of soap is in the interior of the cluster and the carbon chain is out of the cluster.
(c) both ionic end and carbon chain are in the interior of the cluster
(d) both ionic end and carbon chain are on the exterior of the Cluster

Soaps are molecules in which the two ends have differing properties, one is hydrophilic, that is, it interacts with water, while the other end is hydrophobic, that is, it interacts with hydrocarbons. Clusters of molecules in which the hydrophobic tails are in the interior of the cluster and the ionic ends are on the surface of the cluster are called a micelle.

Hence, the correct answer is option (a).

#### Question 15:

Pentane has the molecular formula C5 H12. It has
(a) 5 covalent bonds
(b) 12 covalent bonds
(c) 16 covalent bonds
(d) 17 covalent bonds

There are 16 covalent bonds in the structure of pentane.

Hence, the correct answer is option (c).

#### Question 16:

Structural formula of benzene is

The formula of benzene is C6H6. It has three alternate pi bonds in the ring of carbon atoms.

Hence, the correct answer is option (c).

#### Question 17:

Ethanol reacts with sodium and forms two products. These are
(a) sodium ethanoate and hydrogen
(b) sodium ethanoate and oxygen
(c) sodium ethoxide and hydrogen
(d) sodium ethoxide and oxygen

When ethanol reacts with sodium, sodium ethoxide and hydrogen gas are produced.

Hence, the correct answer is option (c).

#### Question 18:

The correct structural formula of butanoic acid is

Formula of butanoic acid is C3H7COOH.

Hence, the correct answer is option (d).

#### Question 19:

Vinegar is a solution of
(a) 50% – 60% acetic acid in alcohol
(b) 5% – 8% acetic acid in alcohol
(c) 5% – 8% acetic acid in water
(d) 50% – 60% acetic acid in water

5-8% solution of acetic acid in water is called vinegar.

Hence, the correct answer is option (c).

#### Question 20:

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
(a) (i) and (iv)
(b) (ii) and (iii)
(c) (i) and (ii)
(d) (iii) and (iv)

Mineral acids like sulphuric acid, hydrochloric acid etc. are completely ionised. Hence, they are strong acids. Carboxylic acids are partially ionised, they are weak acids.

Hence, the correct answer is option (a).

#### Question 21:

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
(a) helium
(b) neon
(c) argon
(d) krypton

Carbon shares its valence electrons with other atoms of carbon or with atoms of other elements. The shared electrons belong to the outermost shells of both the atoms and lead to both atoms attaining the noble gas configuration. After sharing four electrons with four univalent atoms, carbon attains the electronic configuration of the noble gas Neon (2,8).

Hence, the correct answer is option (b).

#### Question 22:

The correct electron dot structure of a water molecule is

The central atom in water molecule is oxygen. It has 6 electrons in its valence shell and shares one electron each from the two hydrogen atoms.

Hence, the correct answer is option (c).

#### Question 23:

Which of the following is not a straight chain hydrocarbon?

In the hydrocarbon (d), branching takes place at carbon-2.

Hence, the correct answer is option (d).

#### Question 24:

Which among the following are unsaturated hydrocarbons?

(a) (i) and (iii)
(b) (ii) and (iii)
(c) (ii) and (iv)
(d) (iii) and (iv)

Compounds (i) and (iii) are saturated compounds because the valencies of all the atoms are satisfied by single bonds between them. Compounds (iv) and (ii) are unsaturated compounds because there are double and triple bonds between the carbon atoms to satisfy their valencies.

Hence, the correct answer is option (c).

#### Question 25:

Which of the following does not belong to the same homologous series?
(a) CH4
(b) C2 H6
(c) C3 H8
(d) C4 H8

The succeeding members of the homologues series differ by a $—{\mathrm{CH}}_{2}—$ unit. The general formula for the alkane is CnH2n+2. Methane (CH4), ethane (C2H6) and propane (C3H8)  are members of homologues series for alkanes while butene (C4H8) is the fourth member of homologues series for alkene.

Hence, the correct answer is option (d).

#### Question 26:

The name of the compound CH3 — CH2 — CHO is
(a) Propanal
(b) Propanone
(c) Ethanol
(d) Ethanal

We use the root word 'prop' for three carbon atoms and suffix 'al' for the aldehyde functional group.

Hence, the correct answer is option (a).

#### Question 27:

The heteroatoms present in
CH3 — CH2 — O — CH2— CH2 Cl are
(i) oxygen
(ii) carbon
(iii) hydrogen
(iv) chlorine
(a) (i) and (ii)
(b) (ii) and (iii)
(c) (iii) and (iv)
(d) (i) and (iv)

In a hydrocarbon chain, one or more hydrogens can be replaced by other elements, such that the valency of carbon remains satisfied. The element replacing hydrogen is referred to as a heteroatom. In this compound, oxygen and chlorine are heteroatoms.

Hence, the correct answer is option (d).

#### Question 28:

Which of the following represents saponification reaction?
(a)
(b)
(c) 2CH3COOH + 2Na → 2CH3 COONa + H2
(d) CH3COOC2H5 + NaOH → CH3 COONa + C2 H5OH

On treating with sodium hydroxide, which is an alkali, the ethyl acetate, which is an ester, is converted to alcohol and sodium acetate (salt of carboxylic acid). This reaction is known as saponification because it is used in the preparation of soap.

Hence, the correct answer is option (d).

#### Question 29:

The first member of alkyne homologous series is
(a) ethyne
(b) ethene
(c) propyne
(d) methane

The general formula for an alkyne is CnH2n-2. So, the first member of this series is C2H2 (ethyne).

Hence, the correct answer is option (a).

#### Question 30:

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

#### Question 31:

Write the names of the following compounds

(a) Pentanoic acid
(b) Butyne
(c) Heptanal
(d) Pentanol

#### Question 32:

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

(a) Alcohol
(b) Carboxylic acid
(c) Ketone
(d) Alkene

#### Question 33:

A compound X is formed by the reaction of a carboxylic acid C2H4O2 and an alcohol in 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) carboxylic acid, (b) alcohol and (c) the compound X. Also write the reaction.

When ethanoic acid (C2H4O2)  reacts with absolute ethanol (C2H6O) in the presence of an acid catalyst, the ester is formed. So, compound X is ethyl ethanoate.

Ethanol on oxidation with alkaline KMnO4 gives ethanoic acid.

(a) Ethanoic acid is the carboxylic acid which is used in this reaction.

(b) Ethanol

(c) Compound x is ethyl ethanoate (ester).

#### Question 34:

Why detergents are better cleansing agents than soaps? Explain.

Detergents are sodium salts of sulphonic acids or ammonium salts with chlorides or bromide ions etc. Detergents have long hydrocarbon chains. The charged ends of these compounds do not form insoluble precipitates with the calcium and magnesium ions in hard water but soap reacts with calcium and magnesium ions present in the hard water to form insoluble substance called scum. Thus, detergents are better cleansing agents than soaps, they remain effective even in hard water.

#### Question 35:

Name the functional groups present in the following compounds
(a) CH3 CO CH2 CH2 CH2 CH3
(b) CH3 CH2 CH2 COOH
(c) CH3 CH2 CH2 CH2 CHO
(d) CH3 CH2 OH

(a) >CO represents functional group of ketone.
(b) -COOH represents functional group of carboxylic acid.
(c) -CHO represents functional group of aldehyde.
(d) -OH represents functional group of alcohol.

#### Question 36:

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

Ethene is prepared from ethanol by heating it at 443 K with excess concentrated sulphuric acid.

The concentrated sulphuric acid acts as a dehydrating agent which removes water from ethanol.

#### Question 37:

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

Intake of small quantity of methanol can be lethal because methanol is oxidised to methanal in the liver and methanal reacts rapidly with the components of the cell. It coagulates the protoplasm, in much the same way an egg is coagulated by cooking.

#### Question 38:

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

Hydrogen gas is evolved when ethanol reacts with sodium.

#### Question 39:

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.

In this reaction, sulphuric acid acts as a dehydrating agent which removes water from alcohol.

#### Question 40:

Carbon, 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 of Periodic Table)
(b) oxygen (Group 16 of Periodic Table)

(a) Carbon tetrachloride (CCl4)
(b) Carbon monoxide (CO)

#### Question 41:

In 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 chlorine molecule.

(a) The electronic configuration of chlorine is 2, 8, 7.

(b)

#### Question 42:

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.

Catenation is shown by carbon as well as silicon but silicon does not exhibit the property of catenation to the extent seen in carbon compounds. Carbon shows catenation to large extent (forms chains containing 20 or more carbon atoms, and the C-C bond is very strong and hence stable) whereas silicon shows catenation to small extent only (forms chains containing up to 7 or 8 silicon atoms, with weak Si-Si bond and hence, these compounds are very reactive). Silicon does not combine with so many elements to form thousands of covalent compounds just like carbon does.

#### Question 43:

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

On burning, ethane ( saturated hydrocarbon ) generally gives a clean flame while ethene ( unsaturated hydrocarbon ) gives a yellow flame with lots of black smoke.

#### Question 44:

Match the reactions given in Column (A) with the names given in column (B).

 Column (A) Column (B) (a) ${\mathrm{CH}}_{3}\mathrm{OH}+{\mathrm{CH}}_{3}\mathrm{COOH}\stackrel{{\mathrm{H}}^{+}}{\to }{\mathrm{CH}}_{3}{\mathrm{COOCH}}_{3}+{\mathrm{H}}_{2}\mathrm{O}$ (i) Addition reaction (b) (ii) Substitution reaction (c) (iii) Neutralisation reaction (d) CH3COOH + NaOH → CH3COONa + H2O (iv) Esterification reaction

#### Question 45:

Write the structural formulae of all the isomers of hexane.

#### Question 46:

What is the role of metal or reagents written on arrows in the given chemical reactions?

(a)   This reaction represents hydrogenation of unsaturated hydrocarbons. Nickel acts as a catalyst in this reaction.
(b) This is esterification reaction. Concentrated sulphuric acid acts as a catalyst as well as dehydrating agent in this reaction.
(c) In this reaction, alkaline potassium permanganate is adding oxygen to alcohol. Hence, it acts as an oxidising agent.

#### Question 47:

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 chemical equation of the reaction involved.

When ethanoic acid reacts with sodium hydrogencarbonate, it gives rise to a salt (sodium acetate), carbon dioxide and water.

Hence, the salt X is sodium acetate and the gas is carbon dioxide.

Activity:

On passing this evolved gas through freshly prepared lime water, calcium carbonate is formed which makes lime water milky.

The turning of lime water into milky is a standard test of carbon dioxide.

#### Question 48:

(a) What are hydrocarbons? Give examples.
(b) Give the structural differences between saturated and unsaturated hydrocarbons with two examples each.
(c) What is a functional group? Give examples of four different functional groups.

(a) Those carbon compounds which contain only carbon and hydrogen are called hydrocarbons. For example, methane, ethane, ethene etc.
(b) Those hydrocarbons which are linked by single bonds only are called saturated hydrocarbons. For example, methane, ethane, propane etc.

Those hydrocarbons which have double or triple bonds are called unsaturated hydrocarbons. For example, ethene, propene, ethyne etc.

(c) The functional group may be defined as an atom or group of atoms joined in a specific manner which is responsible for the characteristic chemical properties of the organic compounds. The examples are the hydroxyl group (-OH), aldehyde group (-CHO), carboxylic acid group (-COOH), ketones group ( >CO) etc.

#### Question 49:

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

Addition reaction is used in the conversion of vegetable oils to fats. Hydrogen is added to vegetable oils (unsaturated hydrocarbons) in the presence of catalyst such as palladium or nickel to give fats (saturated hydrocarbons).

Note : Animal fats generally contain saturated fatty acids which are unhealthy while vegetable oils contain unsaturated fatty acids which are healthy.

#### Question 50:

(a) Write the formula and draw electron dot structure of carbon tetrachloride.
(b) What is saponification? Write the reaction involved in this process.

(a) The formula for carbon tetrachloride is CCl4.

(b) When an ester is treated with an alkali, it gives alcohol and sodium ethanoate (sodium salt of carboxylic acid).

This reaction is known as saponification because it is used in the preparation of soap.

#### Question 51:

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 well labeled diagram.

Esters are commonly formed by the reaction of an acid and an alcohol. The following activity can be performed for the preparation of an ester:
Take 1 ml ethanol and 1 ml glacial acetic acid in a test tube. Put some drops of conc. sulphuric acid in the test tube. Warm this in a water bath for few minutes ( at least 5 mins). Pour this into a beaker containing 20-50 ml of water and smell the mixture. If it smells sweet, that means, ester has been formed. Esters are sweet-smelling substances which are used in making perfumes and as flavouring agents.

#### Question 52:

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 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.

Compound C is ethanoic acid. When it reacts with sodium metal, it forms sodium ethanoate and hydrogen gas is evolved which burns with a pop sound. Hence, compound R is sodium ethanoate.

Ethanoic acid on treatment with methanol in the presence of an acid forms an ester which is a sweet-smelling compound.

Hence, alcohol A is methanol and compound S is methyl ethanoate.

On addition of NaOH to ethanoic acid, it gives sodium ethanoate and water.

Methyl ethanoate on treatment with NaOH solution gives back sodium ethanoate and methanol.

#### Question 53:

Look at Figure 4.1 and answer the following questions

(a) What change would you observe in the calcium hydroxide solution taken in tube B?
(b) Write the reaction involved in test tubes A and B respectively.
(c) If ethanol is given instead of ethanoic acid, would you expect the same change?
(d) How can a solution of lime water be prepared in the laboratory?

(a) Calcium hydroxide solution taken in tube B becomes milky because of the formation of calcium carbonate.
(b) In test tube A, ethanoic acid reacts with sodium carbonate to give sodium acetate, water, carbon dioxide.

In test tube B, when carbon dioxide is passed through lime water, it turns milky.

(c) If ethanol is given instead of ethanoic acid, the same change would not be expected because ethanol does not react with sodium carbonate.

(d) Lime water is obtained on dissolving quick lime in water. A lot of heat is produced in this reaction.

#### Question 54:

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.

(a)  When ethanol is heated at 443 K with excess concentrated sulphuric acid, it gives ethene.

This process is known as dehydration because concentrated sulphuric acid is a dehydrating agent which removes water from ethanol.

(b) When propanol is treated with alkaline potassium permanganate or acidified potassium dichromate, it is converted to propanoic acid.

Alkaline KMnO4 or acidified K2Cr2O7 is an oxidising agent which is adding oxygen to propanol. Hence, it is an oxidation reaction.

#### Question 55:

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

The possible isomers of this compound are propanone and propanal.

#### Question 56:

Explain the given reactions with the examples
(a) Hydrogenation reaction
(b) Oxidation reaction
(c) Substitution reaction
(d) Saponification reaction
(e) Combustion reaction

(a) When hydrogen is added to unsaturated hydrocarbons in the presence of a catalyst such as palladium or nickel to give saturated hydrocarbons, this reaction is called hydrogenation. It is commonly used in converting vegetable oils to animal fats.

(b) When oxygen is added to the starting material, it is called oxidation. For example, alcohols are converted to carboxylic acid on treating them with oxidising agents such as alkaline potassium permanganate or acidified potassium dichromate. Oxidising agents are capable of adding oxygen to other substances.

(c) When one type of atom or a group of atoms takes the place of another, it is called substitution reaction. For example, chlorine can replace the hydrogen atoms one by one from saturated hydrocarbons when it is added in the presence of sunlight.

(d) When ester is treated with sodium hydroxide, it gives alcohol and sodium salt of carboxylic acid. This reaction is known as saponification because it is used in the preparation of soap.

(e) When a substance burns in oxygen, it is called combustion. Most carbon compounds release a large amount of heat and light on burning.

#### Question 57:

An organic compound A on heating with concentrated H2SO4 forms a compound B which on addition of one mole of hydrogen in 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.

When ethanol (compound A) is heated with concentrated sulphuric acid, it forms ethene and water,

Hence, compound B is ethene. When hydrogen is added to ethene in the presence of nickel catalyst, it forms saturated compound ethane.

Hence, compound C is ethane. On combustion, ethane forms carbon dioxide and water.

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