Class 10 Science Chapter 4 Board Questions

(i) Alcoholic group.
(ii) Carboxylic group.

Fourth member is pentane (C₅H₁₀).

Silicon also exhibits the property of catenation. Compound of silicon are not stable.

The two features are: Catenation and tetra-valency.

Butyne (C₄H₆)

Alkaline KMnO₄ or acidified K₂Cr₂O₇ is used for oxidation of ethanol. Ethanoic acid is formed on oxidation.

Carbon tetrachloride is a covalent compound. Such compound does not produced ions. Therefore, carbon tetrachloride is not a good conductor of electricity.

Carbon is found in the atmosphere and earth’s crust. In the atmosphere it is found as CO₂ and in the earth’s crust it is found as mineral like carbonates.
The percentage of carbon in the air is 0.03% and in the earth crust it is present to the extent of 0.02%.

Seven covalent bond.

Compound with the formula CH₂ does not exist.
First member of the series is C₂H₄(Ethene)
Second member of the series is C₃H₆(Propene)

(i) C₃H₆ Propene
(ii) C₅H₈ Pentyne

Methane: CH₄
Ethanol: C₂H₅OH

Covalent compound.

Carbon atom has a small size and this enables its nucleus to hold on the shared pair of electron quite strongly. This is why carbon forms strong bond with most other elements and the compounds formed are exceptionally stable as compared to covalent bond formed by other elements.

Saturated hydrocarbon having to carbon atom is ethane. Its chemical formula is C₂H₆

Silicon forms compound which have chains like carbon. Compound formed by silicon are few and are not so reactive.

(i) Carboxylic acid group
(ii) Ketonic group

C₄H₁₀, C₅H₁₂

The phenomenon in which two or more compounds having same molecular formula may exist with different structural formulae is called isomerism.

The reaction of an esters to react with an acid or base to give back the alcohol and carboxylic acid is called saponification. This is so called because this reaction is used in the preparation of soap.

(i) CH₃CH₂CH₂- C(CH₃)₂-CH₃
2,2-Dimethylpentane

(ii) CH₃CH₂CHO
Propanal

(iii) CH₃CH(OH)CH₃
2-Propanol

(i) Count the number of carbon atoms in the compound and give it the base name accordingly.
(ii) Identifying the functional group in the compound and name the compound by adding the prefix or suffix to the base name.
(iii) If there are only carbon atom single bonds, the ending in the base name will be ‘ane’. If there are double or triple bonds the ending in the base name will be ‘ene’ and ‘yne’ respectively.

Ethanol and ethanoic acid are example of covalent compound.
Difference in properties of covalent and ionic compounds:
(i) Covalent compounds are formed by sharing of electron while ionic compounds are obtained by transfer of electrons.
(ii) Covalent compound do not conduct electricity while ionic compound do.
(iii) There are weaker intermolecular forces in covalent compound compared to ionic compounds.
(iv) Covalent compounds possess lower melting and boiling point compared to ionic compounds.

A mixture of ethyne and oxygen undergoes complete combustion and high temperature is attained suitable for welding. Whereas air is mixture of nitrogen and oxygen. Oxygen can burn ethyne into carbon dioxide and water with the production of heat. Nitrogen does not have the property of burning ethyne. Therefore, less heat will be produced if we burn ethyne and air for welding purposes.

Conversion of an oil into fat by passing hydrogen gas in the presence of nickel as catalyst is called hydrogenation. This is how hydrogenation is carried out.
Conditions: Presence of a catalyst like nickel is essential.
Change in physical properties: Oils are liquid while the fats obtained on hydrogenation are solid that’s why a physical state take place on hydrogenation.

Soap are sodium or potassium salt of long chain carboxylic acids.
Detergents are ammonium and sulphonate salt of long chain carboxylic acids.
Cleaning action of soap: The ionic end of soap dissolves in water while the carbon chain dissolves in oil. Soap molecules form micelle where one end of the soap molecule is linked to the oil droplet while the ionic part faces water. This form an emulsification in water. On adding water this micelles containing dirt are washed away and our clothes are washed clean.

Test 1: Reaction with sodium: Two one ml of the sample in a test tube. Add a small dried pieces of sodium metal into it. If bubbles of hydrogen are seen the sample is alcohol otherwise it is a carboxylic acid. Hydrogen gas burns with pop sound. When a flame is brought near it.

Test 2: Reaction with sodium hydrogen carbonate: Take 2 ml of saturated liquid solution of sodium hydrogen carbonate in a test tube. Add a little of the unknown sample into it and shake. If evolution of carbon dioxide gas take place, then the sample is carboxylic acid otherwise it is an alcohol. Carbon dioxide when pass through lime water turns milky.

(a) 2Na + 2CH₃COOH → 2CH₃COONa + H₂

(b) NaOH + CH₃COOH → CH₃COONa + H₂

(c) C₂H₅OH + CH₃COH → CH₃COOC₂H₅ + H₂

Conversion of an oil into fat by passing hydrogen gas in the presence of nickel as catalyst is called hydrogenation. This is how hydrogenation is carried out.
Conditions: Presence of a catalyst like nickel is essential.
Change in physical properties: Oils are liquid while the fats obtained on hydrogenation are solid that’s why a physical state take place on hydrogenation.

Soap are sodium or potassium salt of long chain carboxylic acids.
Detergents are ammonium and sulphonate salt of long chain carboxylic acids.
Cleaning action of soap: The ionic end of soap dissolves in water while the carbon chain dissolves in oil. Soap molecules form micelle where one end of the soap molecule is linked to the oil droplet while the ionic part faces water. This form an emulsification in water. On adding water this micelles containing dirt are washed away and our clothes are washed clean.

Test 1: Reaction with sodium: Two one ml of the sample in a test tube. Add a small dried pieces of sodium metal into it. If bubbles of hydrogen are seen the sample is alcohol otherwise it is a carboxylic acid. Hydrogen gas burns with pop sound. When a flame is brought near it.

Test 2: Reaction with sodium hydrogen carbonate: Take 2 ml of saturated liquid solution of sodium hydrogen carbonate in a test tube. Add a little of the unknown sample into it and shake. If evolution of carbon dioxide gas take place, then the sample is carboxylic acid otherwise it is an alcohol. Carbon dioxide when pass through lime water turns milky.

(a) 2Na + 2CH3COOH → 2CH3COONa + H2

(b) NaOH + CH3COOH → CH3COONa + H2

(c) C2H5OH + CH3COH → CH3COOC2H5 + H2

Covalent compounds are the compounds that contain covalent bonds in the molecule. A covalent bond is formed by sharing of electron between atoms.
While a covalent compound contains covalent bond the ionic compound is made up of ionic bond which is formed by the transfer of electrons from one atom to the other.
Characteristics of covalent compounds:
(i) These compound show low melting and boiling point because the intermolecular forces are weak.
(ii) Such compounds are poor conductor of electricity.
(iii) Generally insoluble or less soluble in water but soluble in organic solvents.

(i) Fruity smelling compounds belong to the class of ester.
C₂H₅OH + CH₃COOH → CH₃COOC₂H₅ + H₂O
(ii) Conc. H₂SO₄ acts as a dehydrating agent and removing the water formed in the reaction.

A series of compound whose two successive member differ by –CH2 in the molecule formula and which shows similar chemical properties are called homologous series.
Characteristics:
1. Melting and boiling points increase regularly with increase in molecular mass.
2. Solubility in a particular solvent shows a regular gradation.
3. Chemical properties remain the same in homologous series.
Next higher homologue of HCOOH is CH₃COOH. Its name is ethanoic acid or acetic acid.

Carbon has two unique features:
(i) It is tetravalent.
(ii) It has the property of catenation.
The above two feature enables carbon to form a large numbers of compounds with varying size, shape that’s why carbon atom has long chain or even are arranged in branches or rings. Because of tetra-valency carbon atom in its compound are linked by single, double or triple bonds. Carbon atom are also bonded with oxygen, hydrogen, chlorine, nitrogen and sulphur giving rise to compounds with specific properties typical of the element other than carbon present in the molecule.

Saturated hydrocarbons:
A hydrocarbon in which each carbon atom is attached to four other atoms is known as saturated hydrocarbon. The bonds so formed are single covalent bonds. These hydrocarbons are also called alkanes.
Unsaturated hydrocarbons:
Hydrogens containing either a carbon double bond (C=C) or a carbon-carbon triple bond in their molecules are called unsaturated hydrocarbon.

(a) Compound containing carbon and hydrogen are called hydrocarbon example methane (CH₄).
(b) Structural difference- Saturated hydrocarbon have all its carbon connected to each other by only single bond whereas in unsaturated hydrocarbons there are one or more double or triple bonds between two carbon atoms.
Saturated hydrocarbon- methane (CH₄), ethane (C₂H₆).
Unsaturated hydrocarbon- ethene (C₂H₄), ehyne (C₂H₂).

A homologous series in a group or family of compounds which contain the same functional group but have different chains lengths thus these have the same chemical properties but different physical properties but different physical properties that vary in a regular manner.
Characteristics of homologous series are:
(i) It has a general formula in term of number of carbon atoms.
(ii) It has the functional group if any,
(iii) The member of a homologous series that’s why homologous have similar chemical properties.
(iv) Various homologous can be prepared by the general method of preparation for the series.
(v) Two successive (adjacent) homologous differ by 1 carbon atom and 2 hydrogen atoms in their molecular formulae.
(vi) The members of a homologous series show a gradual change in their physical properties with increases in molecular mass.

Soaps are sodium or potassium salts of long chain fatty acids while detergents are ammonium or sulphonate salts of long chain carboxylic acids.
Soaps molecules has two parts. The ionic end of soap dissolves in water while the carbon chain dissolves in oil. Most dirt is oily in nature. Soap molecules form a micelle around dirt (oil) whose outer parts are directed towards water. On adding excess water, the dirt along with the soap molecules is washed away. This is how the cleansing action of soaps is described. Hard water contains chlorides and sulphates of calcium and magnesium which react with soap to form insoluble scum. Therefore, soap is not able to perform its cleansing action.
Detergents are not biodegradable substances. Thus, they may cause water pollution. Detergents are highly basic in nature. They may affect the skin.

(a)
(i) Unsaturated hydrocarbons show addition reaction. This is because unsaturated hydrocarbon contains double or triple bonds. Such compounds are unstable because the four valences of carbon atom are not satisfied by linking to four atoms. They complete the four valences in addition reaction.
(ii) In the conversion of ethanol to ethanoic acid, the number of oxygen atoms increases and the number of hydrogen atoms decreases. Hence, it is an oxidation reaction.
(iii) Alcohol supplied for industrial purpose is cheap. To prevent its use for human consumption, it is made unfit for drinking by adding a poisonous substance like copper sulphate.

(b) CH3CH₂OH → CH₂ = CH₂ + H₂O

(c) Concentrated sulphuric acid acts as a catalyst in the esterification reaction.

Carbon has no tendency to lose electrons easily. Similarly, it has no tendency to gain electrons. It completes its octet buy sharing the electrons other atoms. Therefore, carbon forms compounds mainly by covalent bonds.
Two main resources for carbon forming a large number of compounds are given below:
Catenation: It is the property of carbon to link with other carbon atoms to form straight chain, branched chain or cyclic compounds. Thus, carbon forms a large number of compounds containing 2, 3, 4, 5…. etc., carbon atoms.
Tetravalency; Carbon has four electrons in the outermost shell. It shares these four electrons with four electrons from four other monovalent atoms. Carbon has the tendency to form bonds with hydrogen, oxygen, nitrogen and halogens. This increases the number of compounds of carbon.
Carbon forms strong bonds with most other elements: This is because carbon has a small atomic size. It can hold strongly the four pairs of electrons. That it shares with other atoms. Therefore, it forms strong bonds with other elements.

(a) Saturated hydrocarbons give a clean flame on burning while unsaturated carbon compounds will give a yellow flame with a lot of black smoke.

(b) Ethane burns in air to form carbon dioxide and water.
2C₂H₆ + 7O₂ → 4CO₂ +6H₂O +Heat +Light

(c) Reaction between methane and chlorine in the presence of sunlight is a substitution reaction because hydrogen atoms in methane are successively replaced or substituted by chlorine atoms.

The compounds A, B, C, D are given as under:
A = CH₃COOH
B = CH₃COONa
C = C₂H₅OH
D = CHCOOC₂H₅

The reactions are explained as under:
2CH₃COOH + 2Na → 2CH₃COONa + H₂
CH₃COOH + C₂H₅OH → CH₃COOC₂H₅ + H₂O
CH₃COOC₂H₅ + H₂O → CH₃COOH + C₂H₅OH

The structure of synthetic detergent is similar to that of soaps. They have a long hydrocarbon chain which is water repelling and a short ionic part which is water attracting. The water attracting group in a synthetic detergent usually a sodium sulphonate group (SO₃)⁻ (Na)⁺ or sodium sulphate group(SO₄)⁻ (Na)⁺ The cleaning action of soap and detergent are similar. Thus chemically these they are not different. Difference lies only in the hydrocarbon part. Synthetic detergent made from long chain hydrocarbon obtained from petroleum whereas hydrocarbon part of soap or vegetable oils. In soaps water attracting part is –COONa whereas in detergent it is –SO₃Na. Detergent is being preferred to soap because these form lather even with hard water and have better cleaning action.