4. Carbon and its Compounds

CBSE Class 10 Science Chapter 4. Carbon and its Compounds

Chapter 4. Carbon and its Compounds

CBSE Class 10 Science Chapter 4. Carbon and its Compounds Previous Years Questions and Answers :

Question : State two characteristic feature of carbon which when put together give rise to large number of carbon compounds . [2010 1M]

Answer : Two characteristic features of carbon that, when combined, give rise to a large number of carbon compounds are tetravalency and catenation .

Question : Draw the structure of Butanone molecule, . [2011 1M]

Answer : The structure of Butanone molecule, .

Question : A student added acetic acid to test tubes I , II , III and IV containing the labelled and then brought a burning splinter near the mouth of each test tube .

The splinter would be extinguished when brought near the mouth of test tube . [2011 1M]

(a) I (b) II (c) III (d) IV

Answer : (d) IV

Question : Acetic acid reacts with solid sodium hydrogen carbonate , [2011 1M]

(a) Slowly forming no gas (b) Vigorously with effervescence

Answer : (b) Vigorously with effervescence .Top of Form

Question : Vapours of acetic acid smell : [2011 1M]

(a) Pungent like vinegar (b) Sweet like rose (c) Suffocating like sulphur dioxide (d) Odorless like water

Answer : (a) Pungent like vinegar .

[The vapors of acetic acid have a pungent smell, similar to vinegar. ]

Question : A student takes powder in a test tube and pours some drops of acetic acid in it . He observes : [2012 1M]

(a) No reaction in the test tube

(b) Colourless gas with pungent smell

(d) White fumes with smell of vinegar .

Answer : (d) White fumes with the smell of vinegar.

Question : Hard water required for an experiment is not available in a school laboratory . However , following salts are available in the laboratory . Select the salts which may be dissolved in water to make it hard for the experiment . [2013 1M]

(i) Calcium Sulphate (ii) Sodium Sulphate (iii) Calcium Chloride (iv) Potassium Sulphate (v) Sodium Hydrogen Carbonate (vi) Magnesium Chloride

(a) (i) , (ii) and (iv) (b) (i) , (iii) and (vi) (c) (iii) , (v) and (vi) (d) (ii) , (iv) and (v)

Answer : (b) (i) , (iii) and (vi)

[The salts that may be dissolved in water to make it hard for the experiment are:

(i) Calcium Sulphate (iii) Calcium Chloride (vi) Magnesium Chloride ]

Question : A student takes 2 ml acetic acid in a dry test tube and adds a pinch of sodium hydrogen carbonate to it . He makes the following observations : [2013 1M]

(i) A colourless and odourless gas evolve with a brisk effervescence .

(ii) The gas turns lime water milky when passed through it .

(iii) The gas burns with an explosion when a burning splinter is brought neat it .

(iv) The gas extinguishes the burning splinter which is brought near it .

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

Answer : (b) (ii), (iii), and (iv)

Question : In an experiment to study the properties of ethanoic acid , a student takes about 3 mL of ethanoic acid in a dry test tube .He adds an equal amount of distilled water to it and shakes the test tube well . After some time he is likely to observe that [2014 1M]

(a) a colloid is formed in the test tube (b) the ethanoic acid dissolves readily in water (c) the solution become light orange . (d) water floats over the surface of ethanoic acid .

Answer : (b) the ethanoic acid dissolves readily in water

[ When ethanoic acid (acetic acid) is mixed with water, it readily dissolves in water due to its miscibility. Ethanoic acid is highly soluble in water, forming a homogeneous solution. ]

Question : We need 20% aqueous solution of sodium hydroxide for the study of saponification reaction . When we open the lid of the bottle containing solid sodium hydroxide we observe it in which form ? [2014 1M]

(a) Colourless transparent beads (b) Small white beads (c) White pellets /flakes (d) Fine white powder .

Answer : (c) White pellets/flakes .

[When the lid of the bottle containing solid sodium hydroxide (NaOH) is opened, it is typically observed in the form of white pellets or flakes. ]

Question : While studying saponification reaction , a student measures the temperature of the reaction mixture and also finds its nature using blue/red limus paper . On the basis of his observations the correct conclusion would be [2014 1M]

(a) the reaction is exothermic and the reaction mixture is acidic .

(b) the reaction is endothermic and the reaction mixture is acidic .

(d) the reaction is exothermic and the reaction mixture is basic .

Answer : (d) the reaction is exothermic and the reaction mixture is basic.

[In a saponification reaction, ester reacts with a strong base like sodium hydroxide to produce alcohol and the salt of the carboxylic acid (soap). This reaction is typically exothermic, meaning it releases heat. Additionally, the reaction produces a basic solution. ]

Question : In a locality ,hard water , required for an experiment , is not available . However , the following salts are available in the school laboratory : [2014 1M]

(i) Sodium sulphate (ii) Calcium sulphate (iii) Magnesium chloride (iv) Sodium chloride (v) Calcium chloride (vi) Potassium sulphate

Which of the above salts may be dissolved in water to obtain hard water for the experiment ?

(a) (ii) , (iii) and (v) (b) (i) , (ii) and (v) (c) (i) , (ii) , (iv) and (vi) (d) (iii) and (v) only

Answer : (a) (ii), (iii), and (v)

[ From the given options, the salts that contain calcium and magnesium ions are: (ii) Calcium sulphate (iii) Magnesium chloride (v) Calcium chloride ]

Question : Write the number of covalent bonds in the molecules of butane, . [2015 1M]

Answer : The number of covalent bonds in the molecules of butane () is 13 .

Question : While preparing soap a small quantity of common salt is generally added to the reaction mixture of vegetable oil and sodium hydroxide . Which one of the following may be the purpose of adding common salt ? [2015 1M]

(a) To reduce the basic nature of the soap (b) Top make the soap neutral (c) To enhance the cleansing power of the soap (d) To favour the precipitation of the soap

Answer : (d) To favor the precipitation of the soap.

[ Common salt is added to help precipitate the soap from the reaction mixture. This process is known as salting out, where the addition of salt reduces the solubility of the soap, causing it to separate from the aqueous solution.]

Question : A student takes about 4mL of distalled water in four test tubes marked P , Q , R and S . He then dissolves in each test tube an equal amount of one salt in one test tube , namely sodium sulphate in P , potassium sulphate in Q ,calcium sulphate in R and magnesium sulphate in S . After that he adds an equal amount of soap solution in each test tube . On shaking each of these test tubes well, he observes a good amount of lather (foam) in the test tube marked . [2015 1M]

(a) P and Q (b) Q and R (c) P , Q and S (d) P , R and S

Answer : (a) P and Q

[The formation of lather (foam) with soap solution indicates the presence of hard water. Hard water contains dissolved calcium and magnesium ions, which interfere with the lathering ability of soap due to the formation of insoluble calcium and magnesium salts of fatty acids. ]

Question : When you add sodium hydrogen carbonate to acetic acid in a test tube , a gas liberates immediately with brisk effervescence . Name this gas . Describe the method of testing this gas . [2015 1M]

Answer : The gas liberated is carbon dioxide ().

To test for carbon dioxide, pass it through lime water. Carbon dioxide turns lime water milky due to the formation of calcium carbonate precipitate.

Question : Write the name and structure of an aldehyde with four carbon atoms in its molecule . [2016 1M]

Answer : The name of an aldehyde () is butanal .

Structure :

Question : Write the molecular formula of the and member of the homologous series where the first member is ethyne . [2017 1M]

Answer : The second member of this homologous series is propyne, with the molecular formula .

The third member of this homologous series is butyne, with the molecular formula .

Question : A student requires hard water for an experiment in his laboratory which is not available in the neighbouring area .In the laboratory there are some salts, which when dissolved in distilled water can covert it into hard water . Selwect from the following groups of salts , a group each salt of which when dissolved in distilled water will make it hard . [2017 1M]

(a) Sodium chloride , Potassium chloride

(b) Sodium sulphate , Potassium sulphate

(d) Calcium sulphate , calcium chloride

Answer : (d) Calcium sulphate, calcium chloride .

[ Both calcium sulphate () and calcium chloride () when dissolved in water can contribute calcium ions, thereby making the water hard. ]

Question : Name the function group present in propanone . [2020 1M]

Answer : The functional group present in propanone is ketone .

Question : Assertion (A) : In a homologous series of alcohols, the formula for the second member is and the third member is .

Reason (R) : The difference between the molecular masses of the two consecutive members of a homologous series is 144 . [2020 1M]

(a) Both A and R are true and R is the correct explanation of the Assertion .

(b) Bothe A and R are true but R is not the correct explanation of the Assertion .

(d) A is false but R is true .

Answer : (c) A is true but R is false.

[We know that the molecular formula of ethanol (the second member) is , and the molecular formula of propanol (the third member) is . So, Assertion (A) is true.

The difference between the molecular masses of two consecutive members in a homologous series typically corresponds to the difference in the molecular masses of their basic units (e.g., in aliphatic compounds). For alcohols, this difference is 14 (the molecular mass of ), not 144. ]

Question : Write the name and general formula of a chain of hydrocarbons in which an addition reaction with hydrogen is possible . State the essential condition for an addition reaction . Stating this condition, write a chemical equal giving the name of the reactant and the product of reaction . [2015 2M]

Answer : The name of the hydrocarbon chain where addition reaction with hydrogen is possible is an alkene. The general formula of an alkene is .

The essential condition for an addition reaction is the presence of a suitable catalyst, such as nickel (Ni).

When ethene () reacts with hydrogen () in the presence of a nickel catalyst to form ethane ().

Reaction :

The name of the reactant and the product of the reaction are ethene and ethane respectively .

Question : A student adds a spoon full of powdered sodium hydrogen carbonate to a flask containing ethanoic acid . List two main observations , he must note in his note book , about the reaction that takes place . Also write chemical equation for the reaction . [2016 2M]

Answer : Two main observations the student must note about the reaction between powdered sodium hydrogen carbonate (sodium bicarbonate) and ethanoic acid (acetic acid) are:

(i) The student should observe the evolution of bubbles of a colorless and odorless gas, which is carbon dioxide (). This indicates the release of carbon dioxide gas due to the reaction.

(ii) The student should observe the formation of sodium acetate, which is a clear, colorless solution. This indicates the formation of a salt as a product of the reaction.

When sodium hydrogen carbonate react with ethanoic acid then produces sodium acetate,carbon dioxide and water .

Question : Mention the essential material (chemicals) to prepare soap in the laboratory . Describe in brief the test of determining the nature (acidic/alkaline) of the reaction mixture of saponification reaction . [2017 2M]

Answer : The essential materials for preparing soap in the laboratory include oils or fats (such as cooking oil), sodium hydroxide (NaOH), and water. To determine the nature of the reaction mixture in saponification, take two test tubes with 10 mL of water each. Add a drop of oil to both (A and B). In test tube B, add soap solution. Shake both vigorously for the same time, then observe. If the mixture in B forms an emulsion, it indicates an alkaline nature due to soap formation.

Question : A compound ‘X’ on heating with excess conc. Sulphuric acid at 443K gives an unsaturated compound ‘Y’ . ‘X’ also reacts with sodium metal to evolve a colourless gas ‘Z’ . Identify ‘X’ , ‘Y’ and ‘Z’ . Write the equation of the chemical reaction of formation of ‘Y’ and also write the role of sulphuric acid in the reaction . [2018 2M]

Answer : Heating compound 'X' with excess concentrated sulphuric acid () at 443K produces an unsaturated compound 'Y'.

The compound 'X' is (Ethanol) and the unsaturated compound ‘Y’ is (Ethene)

The compound 'X' reacts with sodium metal (Na) to evolve a colorless gas 'Z'.

The gas is hydrogen () .

Sulphuric acid () acts as a dehydrating agent in this reaction.

[ Note : It removes a molecule of water from the alcohol, leaving behind the unsaturated hydrocarbon (ethene). The sulfuric acid facilitates the elimination of water from the alcohol, promoting the formation of the unsaturated compound.]

Question : In three test tubes A , B and C , three different liquids namely , distilled water , underground water and distilled water in which a pinch of calcium sulphate is dissolved , respectively are taken . Equal amount of soap solution is added to each test tube will the length of the foam (lather) be longest ? Justify your answer . [2019 2M]

Answer : The length of the foam (lather) will be longest in test tube C, which contains distilled water with a pinch of calcium sulphate dissolved in it. This is because calcium and magnesium ions in hard water form insoluble salts with the soap, reducing its lathering ability.

When soap is added to distilled water (test tube A), it lathers relatively well because there are no calcium or magnesium ions present to interfere with the formation of lather.

In underground water (test tube B), which is likely to contain dissolved calcium and magnesium ions, the lathering ability of the soap will be reduced compared to distilled water (test tube A), but not as much as in the presence of a concentrated source of calcium ions like calcium sulphate (test tube C).

Therefore, the presence of calcium sulphate in distilled water (test tube C) will result in the longest length of foam (lather) due to the reduced lathering ability of the soap in the presence of calcium ions.

Question : “Carbon prefers to share its valence electrons with other atoms of carbon or with atoms of other elements rather than gaining or losing the valence electrons in order to attain noble gas configuration .” Give reasons to justify this statement . [2022 2M]

Answer : The statement "Carbon prefers to share its valence electrons with other atoms of carbon or with atoms of other elements rather than gaining or losing the valence electrons in order to attain noble gas configuration" can be justified based on the following reasons:

(i) If carbon were to gain four electrons, forming a anion, it would be challenging for the nucleus with six protons to hold on to ten electrons. The resulting anion would be highly unstable due to the electrostatic repulsion between the extra electrons.

(ii) if carbon were to lose four electrons, forming a cation, it would require a substantial amount of energy to remove four electrons. This process would leave behind a carbon cation with six protons in its nucleus, holding onto just two electrons. Again, this would result in an unstable configuration.

Question : (i) Why are covalent compounds generally poor conductors of electricity ?

(ii) Name the following compound :

(iii) Name the gas evolved when ethanoic acid is added to sodium carbonate . How would you prove the presence of this gas ? [2008 3M]

Answer : (i) Covalent compounds are generally poor conductors of electricity because the electrons are shared between atoms, and no charged particles are formed. As a result, there are no free-moving charged particles (such as ions or electrons) that can carry an electric current through the compound.

(ii)

Propanone

(iii) The gas evolved when ethanoic acid is added to sodium carbonate is carbon dioxide ().

To prove the presence of this gas, pass it through lime water. Carbon dioxide turns lime water milky due to the formation of calcium carbonate precipitate.

Question : Give reasons for the following observations:

(i) The element carbon forms a very large number of compounds .

(ii) Air holes of a gas burner have to be adjusted when the heated vessels get blackened by the flame .

(iii) Use of synthetic detergents cause pollution of water . [2009 3M]

Answer : (i) The element carbon forms a very large number of compounds because of its unique ability to form stable covalent bonds with other carbon atoms, resulting in a wide variety of molecular structures. This property, known as catenation, allows for the formation of extensive and diverse organic compounds.

(ii) The air holes of a gas burner need to be adjusted when the heated vessels get blackened by the flame because incomplete combustion occurs when there is insufficient oxygen. This leads to the formation of carbon particles (soot), which deposit on the vessel's surface, causing blackening.

(iii) Synthetic detergents cause pollution of water due to their non-biodegradable nature. Traditional soap molecules are biodegradable, whereas synthetic detergents are not easily broken down by natural processes. They accumulate in water bodies, disrupting ecosystems and harming aquatic life.

Question : Name the functional group of organic compounds that can be hydrogenated . With the help of suitable example,explain the process of hydrogenation mentioning the conditions of the reaction any one change in physical property with formation of the product . Name any one natural source of organic compounds that are hydrogenated . [2010 3M]

Answer : The functional group of organic compounds that can be hydrogenated is the carbon-carbon double bond, also known as an alkene.

Hydrogenation is a chemical reaction where hydrogen gas () is added across the double bond of an alkene, forming a single bond between the carbons. This reaction is commonly catalysed by metal catalysts such as nickel (Ni).

The chemical reaction is :

One significant change in physical property that occurs during the hydrogenation process is the transition from a gaseous alkene to a liquid alkane. For instance, ethene () is a gas at room temperature and pressure, while ethane (), the product of hydrogenation, is a liquid under the same conditions.

One natural source of organic compounds that are commonly hydrogenated is vegetable oils. Vegetable oils are rich in unsaturated fatty acids, which contain carbon-carbon double bonds in their hydrocarbon chains.

Question : Write chemical equations to show what happens when : [2011 3M]

(i) Ethanol is heated with concentrated sulphuric acid at 443K .

(ii) Ethanol reacts with ethanoic acid in the presence of an acid as a catalyst .

(iii) An ester reacts with a base .

Answer : (i) When ethanol is heated with concentrated sulphuric acid at 443K ,then produces ethene and water .

(ii) When ethanol reacts with ethanoic acid in the presence of an acid () catalyst ,the produces ester .

(iii) When ester react with a base (NaOH) then produces ethanol and sodium acetate .

Question : Complete the following equations : [2012 3M]

(i)

(ii)

(iii)

Answer : (i) heat and light

(ii)

(iii)

Question : Name the oxidizing 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 carbonate . [2013 3M]

Answer : The oxidizing agent used for the conversion of ethanol to ethanoic acid is acidified potassium dichromate () and Alkaline permanganate () .

(i) Litmus test: The distinguish between ethanol and ethanoic acid are :

Ethanol	Ethanoic acid
Ethanol is neutral and does not change the color of litmus paper.	Ethanoic acid is acidic and turns blue litmus paper red.

(ii) Reaction with sodium carbonate:

Ethanol

Ethanoic acid

Ethanol does not react with sodium carbonate.

Ethanoic acid reacts with sodium carbonate to produce carbon dioxide gas, water, and sodium ethanoate.

Question : (i) Difference between alkanes and alkenes . Name and draw the structure of one member of each .

(ii) Alkanes generally burn clean flame. Why ? [2013 3M]

Answer : (i) Difference between Alkanes and Alkenes are :

Alkanes	Alkenes
General formula:	General formula :
Consist of single bonds between carbon atoms	Contain at least one carbon-carbon double bond
Saturated hydrocarbons (contain maximum number of hydrogen atoms per carbon)	Unsaturated hydrocarbons (contain fewer hydrogen atoms per carbon due to double bond)
Relatively unreactive under normal conditions	More reactive compared to alkanes due to the presence of pi bonds
Example :Methane (), Ethane (), Propane (), etc.	Example : Ethene (), Propene ( ), Butene (), etc.

Name and Structure of Alkane : Mathane :

Name and Structure of Alkene : Ethene :

(ii) Alkanes generally burn clean flame because they undergo complete combustion in the presence of sufficient oxygen, producing only carbon dioxide and water. The absence of impurities results in a clean flame during their combustion.

Question : A carboxylic acid (molecular formula ) reacts with an alcohol in the presence of an acid catalyst to form a compound ‘X’ . The alcohol on oxidation with alkaline followed by acidification gives the same carboxylic acid . Write the name and structure of :

(i) carboxylic acid (ii) Alcohol and (iii) the compound ‘X’ . [2014 3M]

Answer : (i) Carboxylic acid: The carboxylic acid with the molecular formula is ethanoic acid (acetic acid) .

Structure :

(ii) Alcohol: Since the carboxylic acid reacts with an alcohol to form a compound 'X', and the final product yields the same carboxylic acid upon oxidation, the alcohol involved must be ethanol () .

Structure :

(iii) Compound 'X': When ethanol () reacts with ethanoic acid () in the presence of an acid catalyst, it forms ethyl ethanoate (), also known as ethyl acetate.

Structure :

Question : Define the term ‘structural ’ .Explain why propane cannot exhibit this property .Draw the structures of possible isomers of butane, . [2014 3M]

Answer : Structural isomers are compounds that have the same molecular formula but different structural arrangements of atoms.

Propane ( ) consists of a chain of three carbon atoms with eight hydrogen atoms attached. There is only one possible way to arrange these atoms in a straight chain for propane, making it unable to form structural isomers. Hence, propane cannot exhibit structural isomerism because there is only one possible arrangement of its atoms within the molecule.

The Structural isomer of butane :

n-butane

Iso-butane

Question : List two tests for experimentally distinguishing between an alcohol and a carboxylic acid and describe how these tests are performed . [2015 3M]

Answer : Two common tests for experimentally distinguishing between an alcohol and a carboxylic acid are :

Acidified Potassium Dichromate(VI) Test:

The orange colour of the dichromate solution will change to blue green.

Sodium Bicarbonate (Sodium Hydrogen Carbonate) Test :

If the compound is a carboxylic acid, it will react with sodium bicarbonate to produce carbon dioxide gas (). Effervescence (bubbling) will be observed, and if you pass the gas through lime water, it will turn milky due to the formation of calcium carbonate ( ).

If the compound is an alcohol, there will be no reaction with sodium bicarbonate, and no effervescence will occur.

Question : Write three different chemical reactions showing the conversion of ethanoic to sodium ethanoate . Write balanced chemical equation in each case . Write the name of the reactants and the products other than ethanoic acid and sodium ethanoate in each case . [2016 3M]

Answer : The three different chemical reactions showing the conversion of ethanoic acid to sodium ethanoate:

Reaction with Sodium Hydroxide (NaOH):

Balanced Equation:

Reactants: Ethanoic acid () and Sodium hydroxide (NaOH)

Products: Sodium ethanoate () and water ()

Reaction with Sodium Bicarbonate ():

Balanced Equation:

Reactants: Ethanoic acid () and Sodium bicarbonate ()

Products: Sodium ethanoate ( ) , Carbon dioxide gas () and Water ()

Reaction with Sodium Carbonate ():

Balanced Equation:

Reactants: Ethanoic acid () and Sodium carbonate ()

Products: Sodium ethanoate () and Carbon dioxide gas () and Water () .

Question : Distinguish between esterification and saponification process . [2017 3M]

Answer : Esterification and saponification are two different chemical processes involving esters and are associated with different reactions and products.

Esterification:

Esterification is a chemical reaction in which an alcohol (or a phenol) reacts with a carboxylic acid to form an ester and water.

Reaction: The general formula for esterification is: Carboxylic acid+Alcohol→Ester+Water

Conditions: Esterification reactions are carried out in the presence of an acid catalyst, such as concentrated sulfuric acid ( ).

Example: The esterification of ethanoic acid and ethanol produces ethyl ethanoate and water:

Saponification:

Saponification is a process in which esters react with a strong base (usually an alkali like sodium hydroxide or potassium hydroxide) to produce a carboxylic acid and an alcohol (or phenol), along with the formation of a salt (soap).

Reaction: The general formula for saponification is:

Ester + Base → Carboxylic acid + Alcohol + Salt (soap)

Conditions: Saponification reactions are typically carried out under basic conditions, and heat may be applied to speed up the reaction.

Example: The saponification of ethyl ethanoate with sodium hydroxide produces sodium ethanoate (soap), ethanol, and sodium hydroxide:

Question : Write the structural formula of ethanol . What happens when it is heated with excess of conc. at 443 K ? Write the chemical equation for the reaction stating the role of conc. in this reaction . [2017 3M]

Answer : The structural formula of ethanol :

When ethanol () is heated with an excess of concentrated sulfuric acid () at 443 K, it undergoes dehydration to form ethene () and water (). This reaction is a classic example of dehydration of alcohols.

The chemical equation for the reaction is:

In this reaction, concentrated sulphuric acid acts as a catalyst and a dehydrating agent. The role of concentrated sulfuric acid is to protonate the hydroxyl group of ethanol, forming a good leaving group (water).

Question : (i) Why are most carbon compounds poor conductors of electricity ?

(ii) Write the name and structure of a saturated compound in which the carbon atoms are arranged in a ring . Give the number of single bonds present in this compound . [2018 3M]

Answer : (i) Most carbon compounds are poor conductors of electricity because the electrons are shared between atoms, and no charged particles are formed. Such covalent compounds lack free-moving charged particles necessary for conducting electricity.

(ii) A saturated compound in which carbon atoms are arranged in a ring is called cyclohexane. Cyclohexane is a cyclic hydrocarbon with the molecular formula . It consists of a ring of six carbon atoms, each bonded to two hydrogen atoms.

Structure :

Question : 3 mL of ethanol is taken in a test tube and warned gently in a water bath . A 5% solution of alkaline potassium permanganate is added first drop by drop to this solution , then in excess .

(i) How is 5% solution of prepared ?

(ii) State the role of alkaline potassium permanganate in this reaction . What happens on adding it in excess ?

(iii) Write chemical equation of this reaction . [2020 3M]

Answer : (i) To prepare a 5% solution of potassium permanganate (), 5 grams of would be dissolved in sufficient water to make a 100 mL solution.

(ii) The role of alkaline potassium permanganate in this reaction is to oxidise ethanol. Potassium permanganate acts as an oxidising agent. When added in excess, it continues to oxidise ethanol until it is completely oxidised.

(iii) The chemical equation for the reaction between ethanol and alkaline potassium permanganate is:

Question : Consider the following organic compounds :

(a) Name the functional group present in their compounds .

(b) Write the general formula for the compounds of this functional group .

(c) State the relationship between these compounds and draw the structure of any other compound having similar functional group . [2022 3M]

Answer : (a) Name of the functional group present in compounds is Aldehyde .

(b) The general formula for aldehydes is .

(c) The relationship between ethanal and propanal is that they are both aldehydes, which means they share the same functional group, – CHO (the aldehyde group).

Structure :

Ethanal

Propanal

Question : (a) Draw the electron dot structure for ethyne .

(b) List two difference between the properties exhibited by covalent compounds and ionic compounds . [2022 3M]

Answer : (a) The electron structure of ethyne :

(b) The difference between of the covalent compounds and ionic compounds are :

Covalent Compounds	Ionic Compounds
Sharing of electrons between atoms	Transfer of electrons from one atom to another
Generally poor conductors of electricity	Conduct electricity when dissolved in water or in molten state .

Question : (i) State two properties of carbon which lead to a very large number of carbon compounds .

(ii) Why does micelle formation take place when soap is added to water ? why are micelles not formed when soap is added to ethanol ? [2011 5M]

Answer : (i) Two properties of carbon which lead to a very large number of carbon compounds are:

(a) Tetravalency: Carbon has the ability to form four covalent bonds with other atoms due to its tetravalency. This allows carbon to form stable molecules with a wide variety of elements, including hydrogen, oxygen, nitrogen, and other carbon atoms.

(b) Catenation: Carbon exhibits the unique property of catenation, which is the ability to form long chains or rings of carbon atoms by bonding with itself. This property allows carbon to form complex and diverse molecular structures, resulting in a vast array of organic compounds with different properties and functionalities.

(ii) Micelle formation occurs when soap is added to water because soap molecules have a hydrophilic end that interacts with water and a hydrophobic end that interacts with hydrocarbons. In water, soap molecules align at the surface with hydrophobic tails protruding out, forming micelles in which the hydrophobic tails are in the interior and the ionic ends are on the surface. This unique orientation allows soap to trap and remove oily dirt, forming a colloid that stays in solution due to ion-ion repulsion.

Micelles are not formed when soap is added to ethanol because ethanol does not provide the same environment for the hydrophilic and hydrophobic interactions required for micelle formation.

Question : List in tabular form three physical and two chemical properties on the basis of which ethanol and ethanoic acid can be differentiated . [2012 5M]

Answer : The three physical properties of ethanol and ethanoic acid are :

Ethanol	Ethanoic acid
(i) Ethanol is a colorless liquid at room temperature.	(i) Ethanoic acid is a colorless liquid at room temperature.
(ii) Ethanol has a characteristic pleasant odor.	(ii) Ethanoic acid has a pungent smell, reminiscent of vinegar.
(iii) Ethanol has a slightly sweet taste.	(iii) Ethanoic acid has a sour, acidic taste.

Two chemical differences between ethanol and ethanoic acid are:

Ethanol	Ethanoic acid
(i) Ethanol contains the hydroxyl functional group (– OH), which is characteristic of alcohols.	(i) Ethanoic acid contains the carboxyl functional group (– COOH), which is characteristic of carboxylic acids.
(ii) Ethanol is a neutral compound and does not exhibit acidic properties.	(ii) Ethanoic acid is a weak acid and can donate a hydrogen ion () in solution, thus exhibiting acidic properties.

Question : (i) Define the term ‘isomers’ .

(ii) Draw two possible isomers of the compound with molecular formula and write their names .

(iii) Give the electron dot structures of the above two compounds . [2013 5M]

Answer : (i) The compounds with identical molecular formula but different structures are called structural isomers.

(ii) Two isomer of propanal are :

Propanal

Propanone

(iii) The electron dot structure of propanal :

The electron dot structure of propanone :

Question : 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 . [2015 5M]

Answer : Soap and detergents are both types of salts, but they have different chemical structures and properties.

Difference between Soap and Detergent are :

Soap	Detergent
(i) Soaps have a hydrophobic tail and a hydrophilic head, making them amphiphilic molecules.	(i) Detergents often have a similar structure but can be tailored for specific purposes.
(ii) Soaps are typically derived from natural sources, such as fats and oils .	(ii) Detergents are synthetic compounds.
(iii) Soaps form insoluble precipitates (scum) in hard water, reducing their effectiveness.	(iii) Detergents are less affected by hard water and can still produce lather.

Cleansing Action of Soap:

The cleansing action of soap involves the formation of micelles. In water, the hydrophilic heads of soap molecules interact with water molecules, while the hydrophobic tails cluster together to form micelles. The hydrophobic tails trap dirt and oil, allowing them to be rinsed away with water.

Soaps do not form lather in hard water because hard water contains calcium and magnesium ions that react with soap molecules to form insoluble precipitates (soap scum). This reduces the effectiveness of the soap and prevents lather formation.

Problems with Detergents:

(i) Many detergents contain synthetic chemicals that may have environmental impacts, such as harming aquatic life.

(ii) Some people may experience skin irritation or allergies due to the synthetic nature of certain detergent compounds.

Question : A carbon compound ‘P’ on heating with excess conc. forms another carbon compound ‘Q’ which on nickel catalyst forms a saturated carbon compound ‘R’ . One molecules of ‘R’ on combustion form two molecules of carbon dioxide and three molecules of water . Identify P , Q and R and write chemical equations involved . [2016 5M]

Answer : (i)

(ii)

(iii) heat and light

P - (Ethanol) , Q - (Ehtene) , R - (Ethane ) .

Question : Why certain compound are called hydrocarbons ? Write the general formula for homologous series of alkanes , alkenes , alkynes and also draw the structure of the first member of each series . Write the name of the reaction that converts alkenes into alkanes and also write a chemical equations to show the necessary conditions for the reaction to occur . [2017 5M]

Answer : The carbon compounds which contain only carbon and hydrogen are called hydrocarbons.

The general formula for the homologous series of hydrocarbons are

Alkanes:

Methane ()

Alkenes:

Ethene ()

Alkynes:

Ethyne ()

The necessary conditions for this reaction are the presence of a catalyst, typically a metal catalyst such as palladium or nickel, and the use of hydrogen gas ().

The chemical equation for the hydrogenation of ethene () to ethane () is :

Question : Write the chemical formula and name of the compound which is the active ingredient of all alcoholic drinks . List its two uses . Write chemical equation an name of the product formed when this compound reacts with (i) Sodium metal (ii) Hot concentrated sulphuric acid . [2019 5M]

Answer : The chemical formula of the compound which is the active ingredient of all alcoholic drinks is ethanol, which has the molecular formula .

Two uses of ethanol are :

(a) Ethanol is the primary component of alcoholic beverages such as beer, wine, and spirits.

(b) Ethanol is used as a solvent in various industries, including pharmaceuticals, cosmetics, and the production of perfumes.

(i) When ethanol reacts with sodium metal, it forms sodium ethoxide and hydrogen gas.

(ii) When ethanol reacts with hot concentrated sulfuric acid, it undergoes dehydration to form ethene (ethylene) and water.

Question : What is methane ? Draw its electron dot structure . Name the type of bonds formed in this compound . Why are such compounds :

(i) Poor conducts of electricity ? and (ii) Have low melting and boiling points ? What happens when this compound burns in oxygen ? [2019 5M]

Answer : Methane is a saturated hydrocarbon with the chemical formula .

Electron dot structure of methane :

The type of bonds formed in methane is covalent bonds. Covalent bonds are formed by the sharing of electrons between atoms, resulting in the formation of molecules.

Reasons why such compounds like methane are poor conductors of electricity and have low melting and boiling points:

(i) Covalent compounds like methane are poor conductors of electricity because the electrons are shared between atoms, and no charged particles are formed. In such compounds, there are no free ions or electrons that can move to carry an electric current.

(ii) Covalently bonded molecules like methane have low melting and boiling points because although they have strong bonds within the molecule, the intermolecular forces (forces between molecules) are weak. Therefore, it takes relatively little energy to break these forces and convert the substance from a solid to a liquid or a liquid to a gas.

When methane burns in oxygen, then produce carbon dioxide () and water () along with heat

Question : Name a cyclic unsaturated carbon compound. [2020 1M]

Answer : The name of a cyclic unsaturated carbon compound is benzene .

Structure of Benzene :