# Carbon and its Compounds Class 10 Important Questions Science Chapter 4

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## Carbon and its Compounds Class 10 Important Questions with Answers Science Chapter 4

### Carbon and its Compounds Class 10 Important Questions Very Short Answer Type

Question 1.
How many covalent bonds are there in a molecule of ethane (C2H6)?  (CBSE 2011)
There are 7 covalent bonds in a molecule of ethane.

Question 2.
Write the electron dot structure of ethane molecule (C2H4).   (CBSE 2011)

Question 3.
Write the electron dot structure of ethane molecule (C2H6).   (CBSE 2011)

Question 4.
Draw the structure of butanone molecule, CH3COC2H5.   (CBSE 2011)

Question 5.
Draw the structure of the hexanal molecule, C5H11CHO.    (CBSE 2011)

Question 6.
Butanone is a four carbon per molecule compound. Name the functional group present in it.   (CBSE 2011)
Ketone

Question 7.
Name the following compound:   (CBSE 2011)

1-Hexyne is IUPAC name of the compound.

Question 8.
Name the functional group present in each of the following organic compounds:
(i) C2H5Cl
(ii) C2H5OH   (CBSE 2012)
(i) (- Cl) Halogen (Chloro)
(ii) (- OH) Alcohol

Question 9.
Name the functional group present in each of the following compounds:
(i) HCOOH
(ii) C2H5CHO   (CBSE 2012)
(i) – COOH (Carboxylic acid)
(ii) – CHO (Aldehyde)

Question 10.
Name the functional group present in each of the following organic compounds:
(i) CH3COCH3
(ii) C2H5COOH   (CBSE 2012)

(ii) Carboxylic acid (—COOH)

Question 11.
Write the name and formula of the second member of the carbon compounds having functional group —OH.   (CBSE 2012)

Question 12.
Write the name and formula of the first member of the carbon compounds functional group —CHO.   (CBSE 2012)

Question 13.
Write the name and formula of the first member of the carbon compounds having functional group —COOH.   (CBSE 2012)

Question 14.
Write the name and formula of the 2nd member of the series of carbon compounds whose general formula is C2H2n+1OH   (CBSE 2012)
Ethanol, C2H5OH or CH3CH2OH

Question 15.
Write the name and formula of the 2nd member of the series of carbon compounds whose general formula is CnH2n.   (CBSE 2012)
C3H6, H2C = CH – CH3.
Propene is second member of series whose general formula is CnH2n.

Question 16.
Write the name and formula of the 2nd member of homologous series having general formula CnH2n.   (Delhi 2015)
Propene C3H6

Question 17.
Name the process by which unsaturated fats are changed to saturated fats.    (Foreign 2015)
Hydrogenation.

Question 18.
Write the number of covalent bonds in the molecule of ethane.   (AI 2015)
Seven.

Question 19.
Write the next homologue of each of the following:    (Delhi 2016)
(i) C2H4
(ii) C4H6
(i) C3H6
(ii) C5H8

Question 20.
Which element exhibits the property of catenation to maximum extent and why?   (Foreign 2016)
Carbon, Due to strong C—C bond.

Question 21.
Write the name and structure of an alcohol with three carbon atoms in its molecule.   (AI 2016)

Question 22.
While cooking, if bottom of the vessel is getting blackened on the outside, what does is mean? (Delhi 2017)
It means fuel is not burning completely.

### Carbon and its Compounds Class 10 Important Questions Short Answer Type

Question 1.
(a) Complete the following equations:

(b) Write the name of the following:
(i) CH3CH2COOH
(ii) CH3CH2Br
(c) Draw the electron dot structure of ethene(C2H4).   (CBSE 2008C)
(a)

(b) (i)Propanoic acid
(ii) Bromoethane
(c) Electron dot structure of ethene

Question 2.
(a) Name the compound CH3CH2OH and identify its functional group.
(b) Give a chemical test to distinguish between ethanol and ethanoic acid.
(c) Name the product formed when an organic acid reacts with an alcohol in presence of an acid catalyst. What is the name assigned to this type of reaction? (AI 2008C)
(a) CH3CH2OH – Ethanol; Functional group: alcohol (-OH)

(b) Take ethanol and ethanoic acid in two different test tubes. Add sodium carbonate/ sodium hydrogen carbonate solution in both the test tubes, the test tube which will produce brisk effervescence of CO2 gas will contain ethanoic acid. Ethanol do not evolve CO2 gas when reacted with Na2CO3/NaHCO3.

(c) When an organic acid reacts with an alcohol in presence of an acid as catalyst, it produces fruity smelling compound called ester. Such a reaction is called esterification.
Example:

Question 3.
(a) Give a chemical test to distinguish between saturated and unsaturated hydrocarbons.
(b) (i) Name the products formed when ethanol burns in air.
(ii) What two forms of energy are liberated on burning alcohol?
(c) Why is the reaction between methane and chlorine considered a substitution reaction?   (AI 2008C)
(a) On adding bromine water, the unsaturated hydrocarbon decolourises the bromine
water but the saturated hydrocarbon will not decolourise bromine water.

(b) (i) Ethanol burns in air to produce carbon dioxide and water.
C2H5OH + 3O2 → 2CO2 + 3H2O + heat + light
(ii) Two forms of energy obtained are heat energy and light energy.

(c) When methane reacts with chlorine, the hydrogen atom of methane is replaced by chlorine atom step by step and hence it is termed as substitution reaction.
CH4 + Cl2 → CH3Cl + HCl

Question 4.
(a) Name the compound CH3COOH and identify its functional group.
(b) Give a chemical test to identify this compound.
(c) Name the gas evolved when this compound acts on solid sodium carbonate. How would you identify this gas?  (AI 2008C)
(a) Ethanoic acid, functional group is —COOH (Caboxylic group)
(b) Take few drops of ethanoic acid in a test tube and add sodium hydrogen carbonate solution to it. Brisk effervescence of CO2 gas is formed which turns lime water milky.
(c) CO2 gas is evolved. To identify the gas, pass it through freshly prepared limewater, it turns milky due to the formation of milky white precipitate of CaCO3.
Ca(OH)2 + CO2 → CaCO3 + H2O

Question 5.
Give reason for the following observations:
(a) The element carbon forms a very large number of compounds.
(b) Air holes of a gas burner have to be adjusted when the heated vessels get blackened by the flame.
(c) Use of synthetic detergents causes pollution of water.  (CBSE 2009)
(a) Carbon forms large number of compounds due to its property of catenation,
i.e. self linking. They form isomeric compounds i.e. compounds with same molecular formula but different structural formula.
(b) The vessels blacken due to deposits of black carbon particles on it which is caused due to incomplete combustion of fuel. Air holes are adjusted so that air enters through the holes and helps in complete combustion of the fuel.
(c) Synthetic detergent is non-biodegradable, it remains in the water thereby causing water pollution.

Question 6.
(a) What is a ‘homologous series’ of substances?
(b) In an organic compound, which part largely determine its physical and chemical properties?
(c) Write a chemical equation to represent the reaction of ethanol with acidified
solution of potassium dichromate. (AI 2009)
(a) Homologous series is a series of organic compounds having same general formula, all members of the compounds show same chemical properties and slight variation in physical properties.
(b) Functional group.

Question 7.
(a) What is vinegar?
(b) Describe with a chemical equation, what happens when sodium hydrogen carbonate reacts with ethanoic acid.  (AI 2009)
(a) The 5% – 10% aqueous solution of acetic acid is called vinegar.
(b)

Ethanoic acid reacts with sodium bicarbonate to produce brisk effervescence of CO2 gas and sodium acetate.

Question 8.
(a) Write the names of the functional groups in:

(b) Describe a chemical test to distinguish between ethanol and ethanoic acid.
(c) Write a chemical equation to represent what happens when hydrogen gas is passed through an unsaturated hydrocarbon in the presence of nickel as a catalyst.   (Foreign 2009)
(a) (i) Ketone
(ii) Aldehyde
(b) On adding Na2CO3/NaHCO3, the test tube containing ethanoic acid produces brisk effervescence of CO2 gas. Alcohol will not show any reaction.
CH3COOH + NaHCO3 → CH3COONa + CO2 + H2O
C2H5OH + NaHCO3 → No reaction

Question 9.
What is an ‘esterification’ reaction? Describe an activity to show esterification.   (CBSE 2011)
When carboxylic acid reacts with alcohol in the presence of cone. H2SO4, pleasant fruity smelling compound, ester is formed. This reaction is called esterification.

Activity:
(i) Take 1 ml of ethanol in a test tube. Add 1 ml of acetic acid in this test tube.

(ii) Add few drops of conc. H2SO4 in the mixture
(iii) Heat the content on water bath for 5 minutes.
(iv) Smell the resulting mixture formed.

Question 10.
Out of HCl and CH3COOH, which one is a weak acid and why? Describe an activity to support your answer.   (CBSE 2011)
Acetic acid (CH3COOH) is a weaker acid because it does not dissociate completely into its ions in aqueous solution.

Activity:
Add zinc metal in HCl and CH3COOH taken in different test tubes. The hydrogen gas will be evolved faster in HCl and slowly in CH3COOH. It shows acetic acid is a weak acid.

Alternative Method:
If we use pH paper, the colour of pH paper will be dark red in HCl and light red in CH3COOH which shows HCl is a strong acid and CH3COOH is a weak acid.

Question 11.
Write chemical equations for what happens when
(i) sodium metal is added to ethanoic acid.
(ii) solid sodium carbonate is added to ethanoic acid.
(iii) ethanoic acid reacts with a dilute solution of sodium hydroxide.   (CBSE 2011)
(i) H2 gas is evolved.

(ii) Brisk effervescence due to carbon dioxide gas is formed.

(iii) Sodium ethanoate and water are formed.

Question 12.
Describe two examples of different oxidations of ethanol. Name the products obtained in each case.   (CBSE 2011)
(i) When ethanol is heated with copper at 573 K, ethanal is formed.

(ii) When ethanol is oxidised with alkaline potassium permanganate solution, ethanoic acid is formed

Question 13.
Write a chemical equation in each case to represent the following types of chemical reactions of organic compounds:
(i) Oxidation reactions
(iii) Substitution reactions.   (CBSE 2011)
(i) Oxidation reaction:

(iii) Substitution reaction:

Question 14.
What are isomers? Draw the structures of two isomers of butane, C4H10. Why can’t we have isomers of first three members of alkane series?  (CBSE 2012)
Those compounds, which have same molecular formula but different structural fomulae are called isomers.

In first three members of alkane series, branching is not possible. Therefore, we cannot have isomers.

Question 15.
Define homologous series of organic compounds. List its two characteristics. Write the name and formula of the first member of the series of alkenes.   (CBSE 2012)
The series of organic compounds having same functional group and similar chemical properties is called homologous series.
Each member differs from successive member by -CH2- group. The difference in molecular weight between two successive members is 14 u.

Characteristics:

• It has same general formula, from which, all members can be derived.
• They have similar chemical properties.
C2H4, CH2=CH2, Ethene is first member of alkene series.

Question 16.
Complete the following equations:
(i) CH4 + O2

(iii) CH3COOH + NaOH →     (CBSE 2012)
(i) CH4 + 2O2 → CO2(g) + 2H2O(l)

(iii) CH3COOH + NaOH → CH3COONa + H2O

Question 17.
Why homologous series of carbon compounds are so called? Write chemical formula of two consecutive members of a homologous series and state the part of these compounds that determines their
(i) physical properties, and
(ii) chemical properties.      (CBSE 2012)
The series consists of members of same family with similar chemical properties therefore, called homologous series.
CH3OH, and CH3CH2OH are two consecutive members of homologous series of alcohols.
Alkyl group – CH3 and – CH2CH3 part determines physical properties. Functional group – OH determines chemical properties of the compounds.

Question 18.
Name the oxidising agent used for the conversion of ethanol to ethanoic acid. Distinguish between ethanol and ethanoic acid on the basis of
(i) litmus test,
(ii) reaction with sodium hydrogen carbonate.   (CBSE 2012)
Alkaline potassium permanganate or Acidified potassium dichromate.
(i) Ethanol will not affect litmus paper. Ethanoic acid turn blue litmus paper red.
(ii) Ethanol will not react with sodium hydrogen carbonate. Ethanoic acid will give brisk effervescence due to colourless, odourless carbon dioxide gas.

Question 19.
Distinguish between esterification and saponification reactions of organic compounds with the help of the chemical equation for each. What is the use of
(i) esters and
(ii) saponification process?   (CBSE 2012)
Esterification: It is a process in which alcohol and carboxylic acid combine in the presence of cone. H2SO4 to form ester.

Saponification: When an ester reacts with sodium hydroxide, sodium salt of acid and alcohol is formed.

Uses:
(i) Esters are used as perfumes and as artificial flavouring agents in cold drinks and ice creams.
(ii) Saponification process is used in the manufacture of soaps.

Question 20.
What is meant by functional group in carbon compounds ? Write in tabular form the structural formula and the functional group present in the following compounds : (Foreign 2015)
(i) Ethanol
(ii) Ethanoic acid
An atom or a group of atoms/heteroatoms which determine the chemical properties of an organic compound.

Question 21.
With the help of an example, explain the process of hydrogenation. Mention the essential conditions for the reaction and state the change in physical property with the formation of the product.   (Delhi 2015)

Addition of hydrogen to the molecule of an unsaturated hydrocarbon/compounds is hydrogenation. Essential condition for hydrogenation is the presence of a catalyst like Ni/Pd/Pt.

Change observed in the physical property during hydrogenation is the change of the unsaturated compound from the liquid state to the corresponding saturated compound in the solid-state and its boiling or melting point will increase.

Question 22.
What is the difference between the molecules of soaps and detergents, chemically? Explain the cleansing action of soaps.   (Delhi 2015)
Soaps are sodium or potassium salts of long chain carboxylic acids.
Detergents are ammonium or sulphonate salts.

Soap molecule has two ends, the charged end that gets attracted towards water is called hydrophilic and the long carbon chain that repels water is called hydrophobic tail. When soap is dissolved in water, the carbon chain i.e., hydrophobic end gets attracted towards the oil, dirt and grease. The hydrophilic end stays away from this. The micelle formation takes place.

The tail entangles dirt, oil or grease, if required, the agitation is done. Lot of rinsing is done with water so that water molecules attract charged (Na+) end and carries the soap molecules with dirt attached to it and clean the clothes, utensils, etc.

Question 23.
Explain why carbon forms compounds mainly by covalent bond. Explain in brief two main reasons for carbon forming a large number of compounds. Why does carbon form strong bonds with most other elements?   (Delhi 2015)
Carbon has 4 electrons in its outermost shell, and needs to gain or lose 4 electrons to attain noble gas configuration.
Losing or gaining 4 electrons is not possible due to energy considerations; hence it shares electrons to form covalent bonds.

Two reasons for large number of carbon compounds :
Catenation: The unique ability of carbon to form bonds with other atoms of carbon giving rise to long chains of different types of compounds.

Tetravalency : Since carbon has a valency of 4, it is capable of bonding with four other atoms of carbon or atoms of elements like oxygen, hydrogen, nitrogen, sulphur, chlorine, etc.

The reason for the formation of strong bonds by carbon is its small size which enables the nucleus to hold on to the shared pairs of electrons strongly.

Question 24.
Write the molecular formula of the following compounds and draw their electron-dot structures : (Foreign 2015)
(i) Ethane
(ii) Ethene
(iii) Ethyne

Question 25.
List two tests for experimentally distinguishing between an alcohol and a carboxylic acid and describe how these tests are performed.  (AI 2015)
(a) Acid test: Reaction with carbonates/hydrogen carbonates.
Take samples of alcohol and carboxylic acid in 2 test tubes, and add sodium carbonate or sodium bicarbonate solution to each. The compound which will produce brisk effervescence of CO2 gas will be acid.

(b) Alcohol test: Take small amount of ethanol and ethanoic acid in test tube A and B. Add 5% solution of alkaline potassium permanganate drop by drop to this solution and warm the test tube.
The colour of potassium permanganate will disappear in test tube containing alcohol.

Question 26.
Draw the electron-dot structure for ethyne. A mixture of ethyne and oxygen is burnt for welding. In your opinion, why cannot we use a mixture of ethyne and air for this purpose?  (AI 2015)

In pure oxygen, ethyne undergoes complete combustion and high temperature suitable for welding is attained. Whereas air contains less percentage /amount of oxygen which results in incomplete combustion of ethyne and the temperature required for welding is not attained.

Question 27.
An aldehyde as well as a ketone can be represented by the same molecular formula, say C3H6O. Write their structures and name them. State the relation between the two in the language of science.  (AI 2016)

Isomers (same molecular formula but different structural formula/different functional group).

Question 28.
What are covalent compounds? Why are they different from ionic compounds? List their three characteristic properties. (Delhi 2016)
Covalent compounds are those compounds which are formed by sharing of electrons between two atoms which contain covalent bonds.
Covalent compounds are different from ionic compounds because the ionic compounds are formed by the transfer of electrons.

Three characteristics of covalent compounds:

1. Generally have low melting and boiling points.
2. Generally insoluble or less soluble in water but soluble in organic solvents.
3. Do not conduct electricity. (Or any other characteristic)

Question 29.
When ethanol reacts with ethanoic acid in the presence of cone. H2SO4, a substance with fruity smell is produced. Answer the following:  (Delhi 2016)
(i) State the class of compounds to which the fruity smelling compounds belong. Write the chemical equation for the reaction and write the chemical name of the product formed.
(ii) State the role of conc. H2SO4 in this reaction.
(i) Esters
Chemical equation:

Product’s chemical name – Ethyl ethanoate

(ii) Conc. H2SO4 acts as a dehydrating agent (Helps in the removal of water formed in the reaction).

Question 30.
Write the name and molecular formula of an organic compound having its name suffixed with ‘ol’ and having two carbon atoms in its molecule. Write balanced chemical equation to indicate what happens when this compound is heated with excess cone. H2SO4 and the name of main product formed. Also state the role of conc. H2SO4 in the reaction.   (Foreign 2016)
Ethanol; C2H5OH / C2H6O

Role of conc. H2SO4 – dehydrating agent.

Question 31.
An organic compound ‘P’ is a constituent of wine. ‘P’ on reacting with acidified K2Cr2O7 forms another compound ‘Q’. When a piece of sodium is added to ‘Q’ a gas ‘R’ evolves which burns with a pop sound. Identify P, Q and R and write the chemical equations of the reactions involved.   (Foreign 2016)
P – Ethanol, Q – Ethanoic acid, R – Hydrogen

Question 32.
Write chemical equation of the reaction of ethanoic acid with the following:   (AI 2016)
(a) Sodium;
(b) Sodium hydroxide;
(c) Ethanol

### Carbon and its Compounds Class 10 Important Questions Long Answer Type

Question 1.
(a) Why does carbon form compounds mainly by covalent bonding?
(b) List any two reasons for carbon forming a very large number of compounds.
(c) An organic acid ‘X’ is a liquid which often freezes during wintertime in cold countries, 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.   (CBSE 2008)
(a) Carbon forms compounds mainly by covalent bonding because carbon has small size, so neither it can lose four electrons easily, because very high amount of energy will be required, nor it can gain four electrons as 6 parotons cannot hold 10 electrons. Hence, it shares four electrons forming covalent bonds.

(b) (i) Due to catenation – Self linking property
(ii) Tetravalency of carbon – Forms compounds with other elements.

(c) (i) ‘X’ is CH3COOH, it freezes during winter in cold countries.
‘Y is ester CH3COOC2H5

Question 2.
(a) What is homologous series of compounds? List any two characteristics of a homologous series.
(b) (i) What would be observed on adding 5% solution of alkaline potassium
permanganate solution drop by drop to some warm ethanol taken in a test tube?
(ii) Write the name of the compound formed during the chemical reaction.
(c) How would you distinguish experimentally between an alcohol and a carboxylic acid on the basis of a chemical property?   (CBSE 2008)
(a) Organic compounds when arranged in series having same general formula and similar chemical properties is called homologous series.

Two characteristics of homologous series.

1. Each successive member differ by – CH2 group, 14 u.
2. The method of preparation and chemical properties of members of homologous
series is same.

(b) (i) The colour of KMnO4 will get discharged because ethanol gets oxidised to
form ethanoic acid.
$$\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}+2(\mathrm{O}) \stackrel{\text { alk. } \mathrm{KMnO}_{4}}{\longrightarrow} \mathrm{CH}_{3} \mathrm{COOH}+\mathrm{H}_{2} \mathrm{O}$$
(ii) Ethanoic acid, CH3COOH

(c) On adding sodium bicarbonate solution to both the test tubes containing ethanol and ethanoic acid the test tube containing carboxylic acid (ethanoic acid) will show brisk effervescence due to formation of CO2 gas. Alcohol will not react with sodium bicarbonate.

Question 3.
(a) What is a functional group in a carbon compound?. Identify the functional group present in CH3COOH and C2H5OH.
(b) State the principle on which the cleansing action of soap is based. (Foreign 2008)
(a) The atom or group of atoms which determines the properties of a compound is called functional group.
C2H2OH has (- OH) alcoholic group
CH3COOH has (- COOH) carboxylic functional group

(b) Cleansing action of soap depends on its structure, it has two ends hydrophobic which attracts dirt, oil or grease and hydrophilic end which attracts water.

The dirt is carried by hydrophobic portion which is attached to hydrophilic end which gets attached to water and is washed away.

Question 4.
(a) What is homologous series? Give one example.
(b) What will happens if ethanoic acid reacts with ethanol in the presence of an acid as a catalyst? Name the reaction. Write the chemical reaction for this reaction.
(c) Why are soaps ineffective in hard water?  (CBSE 2008C)
(a) Homologous series is series of compounds having same functional group and same chemical properties. When members of the series are arranged in ascending order, two successive members differ by -CH2 group and mass 14 u.
Example:

(b) Ethanol reacts with ethanoic acid to produce a fruity smelling compound called ester, the cone, sulphuric acid is used as dehydrating agent which removes water. Such reaction is called esterification.

(c) Hard water contains salts of Ca and Mg. Soap molecule reacts with these salts to produce white precipitate called scum, which is insoluble in water and the cleansing action of soap becomes ineffective.

Question 5.
(a) The structural formula of an easter is

Write the structural formula of the corresponding alcohol and the acid.
(a) (i) Mention the experimental conditions involved in obtaining ethene from ethanol.
(ii) Write the chemical equation for the above reaction.
Explain the cleansing action of soap.   (Foreign 2009)
(a) CH3COOH and CH3CH2OH
(b) (i) Ethanol when heated in presence of cone. H2SO4, it gets dehydrated to form ethene at 160°C – 170°C.

Question 6.
(a) Distinguish between esterification and saponification reactions of organic compounds.
(b) With a labelled diagram describe an activity to show the formation of an ester.  (AI 2009)
Esterification: Reaction in which carboxylic acid reacts with alcohol in presence of cone. H2SO4 to form a fruity smelling compound called ester.

Saponification: It is a reaction in which an ester reacts with alkali solution to form a compound called soap.

(b) Activity to show the formation of an ester: Take a test tube and add ethanol, acetic acid and few drops of cone. H2SO4 in it. Warm it over a water bath, i.e., keeping the test tube in a beaker containing water. Pleasant, fruity smelling compound called ester is formed.

Question 7.
(a) State two properties of carbon which lead to a very large number of carbon compounds.
(b) Why does micelles formation take place when soap is added to water? Why are micelles not formed when soap is added to ethanol?   (CBSE 2011)
(a) (i) Catenation
(ii) Tetravalency

(b) Soap has hydrophobic tail (hydrocarbon) which attracts towards oil or dirt and hydrophilic part dissolves in water. When large number of molecular ions of soaps get aggregated then to keep hydrophic tail away from water and closer to oil there tails of molecules point at the centre of a sphere and hydrophilic part at the surface of sphere which causes the micelle formation.

Micelles are not formed in ethanol because hydrocarbon part gets dissolved in ethanol thus, it does not suspend around oil particles. Hence, micelles are not formed in ethanol.

Question 8.
Explain isomerism. State any four characteristics of isomers. Draw the structures of possible isomers of butane, C4H10.   (CBSE 2011)
Isomerism is a phenomenon due to which some compounds have same molecular formula but different structural fomulae.

Characteristics:

• They differ in structural formula
• They differ in melting point
• They differ in boiling point.
• They differ in solubility in same solvent.

Question 9.
There are two isomers of butane, C4H10.

Give reasons for the following:
(i) Element carbon forms compounds mainly by covalent bonding.
(ii) Diamond has a high melting point.
(iii) Graphite is a good conductor of electricity.
(iv) Acetylene burns with a sooty flame.
(v) Kerosene does not decolourise bromine water while cooking oils do.  (CBSE 2011)
(i) It is because carbon has four valence electrons, it cannot gain or lose four electrons because high energy is needed. It can only share four electrons.
(ii) It is due to strong covalent bonds and compact structure of diamond.
(iii) It is due to presence of free electrons in graphite because each carbon is linked to three other carbon atoms.
(iv) It is due to high percentage of carbon, it burns with sooty or smoky flame.
(v) Kerosene oil is mixture of saturated hydrocarbons while cooking oils are unsaturated hydrocarbons therefore bromine undergoes addition reaction with cooking oils and gets decolourised.

Question 10.
List in tabular form three physical and two chemical properties on the basis of which ethanol and ethanoic acid can be differentiated.   (CBSE 2012)
Physical properties:

 Ethanol Ethanoic acid 1. It has specific smell 1. It has vinegar like smell. 2. It has burning taste 2. It is sour in taste 3. It does not freeze in winters 3. It freezes in winters

Chemical properties:

 Ethanol Ethanoic acid 1. It does not react with NaHCO3 1. It gives CO2 with NaHCO3 2. It burns with blue flame 2. It does not bum with blue flame 3. It does not affect blue litmus 3. It turns blue litmus red

Question 11.
What are the hydrocarbons? Write the name and general formula of (i) saturated hydrocarbons, (ii) unsaturated hydrocarbons, and draw the structure of one hydrocarbon of each type. How can an unsaturated hydrocarbon be made saturated?   (CBSE 2012)
Hydrocarbons are the compounds of carbon and hydrogen.
(i) Alkanes, CnH2n+2 are saturated hydrocarbons.

(ii) Alkenes, CnH2n and Alkynes, CnH2n-2 are unsaturated hydrocarbons.

Unsaturated hydrocarbons can be made saturated by hydrogenation.

Question 12.
What are detergents chemically? List two merits and two demerits of using detergents for cleansing. State the reason for the suitability of detergents for washing, even in the case of water having calcium and magnesium ions. (CBSE 2012)
Detergents chemically are ammonium or sulphonate salts with long carbon chain
Merits:

1. They work well with hard water.
2. They are more effective than soaps.

Demerits:

1. They are expensive.
2. Some of them having branching and are non-biodegradable, therefore create water pollution.
Detergents are suitable for hard water having Mg2+ and Ca2+ ions because they do not form insoluble salts with Mg2+ and Ca2+ ions.

Question 13.
Both soap and detergent are some type of salts. What is the difference between them? Describe in brief the cleansing action of soap. Why do soaps not form lather in hard water? List two problems that arise due to the use of detergents instead of soaps.  (AI 2015)
Soaps are sodium or potassium salts of long chain carboxylic acids.
Detergents are ammonium or sulphonate salts with long carbon chain.

Cleansing action of soap:
Soap molecule has two ends, the charged end that gets attracted towards water is called hydrophilic and the long carbon chain that repels water is called hydrophobic tail. When soap is dissolved in water, the carbon chain i.e., hydrophobic end gets attracted towards the oil, dirt and grease. The hydrophilic end stays away from this. The micelle formation takes place.

The tail entangles dirt, oil or grease, if required, the agitation is done. Lot of rinsing is done with water so that water molecules attract charged (Na+) end and carries the soap molecules with dirt attached to it and clean the clothes, utensils, etc.

Problems due to the use of detergents are:

• It leads to water or soil pollution.
• It can also cause skin problems.

Question 14.
Elements forming ionic compounds attain noble gas electronic configuration by either gaining or losing electrons from their valence shells. Explain giving reason why carbon cannot attain such a configuration in this manner to form its compounds. Name the type of bonds formed in ionic compounds and in the compounds formed by carbon. Also explain with reason why carbon compounds are generally poor conductors of electricity.  (Foreign 2015)
Carbon has 4 electrons in its outermost shell. It cannot lose 4 electrons to form C4+ because very high energy is required to remove 4 electrons.
It cannot gain 4 electrons to form C4- ions because it is difficult for 6 protons to hold on to 10 electrons.

Ionic/Electrovalent bonds are formed in ionic compounds. Covalent bonds are formed in carbon compounds. There are no free electron or charged particle in carbon compound hence they are poor conductors of electricity.

Question 15.
(a) Give a chemical test to distinguish between saturated and unsaturated hydrocarbon.
(b) Name the products formed when ethane burns in air. Write the balanced chemical equation for the reaction showing the types of energies liberated.
(c) Why is reaction between methane and chlorine in the presence of sunlight considered a substitution reaction?   (Delhi 2016)
(a) Pass the vapours of the given samples of saturated and unsaturated hydrocarbons into bromine water taken in two separate test tubes. The one which discharges the colour of bromine water is that of unsaturated hydrocarbon and the other represents saturated hydrocarbon (or any other test).

(b) On burning ethane in air, the products obtained are carbon dioxide and water, along with heat and light.
2C2H6(g) + 7O2(g) → 4CO2(g) + 6H2O(l) + Heat + Light

(c) It is considered a substitution reaction because the hydrogen atoms of methane (CH4) are replaced by chlorine atoms one by one.

Question 16.
(a) You have three unlabelled test tubes containing ethanol, ethanoic acid and soap solution. Explain the method you would use to identify the compounds in different test tubes by chemical tests using litmus paper and sodium metal.
(b) Give the reason for formation of scum when soaps are used with hard water.  (Foreign 2016)