CBSE Class 10 Science Carbon and its Compounds VBQs Set 05

Question. Write the chemical equation to explain what happens when ethanol is heated with alkaline solution of potassium permanganate. Mention two physical properties and two uses of ethanol.
Answer: \( CH_3CH_2OH \xrightarrow{\text{Alkaline } KMnO_4 + \text{heat}} CH_3COOH \).
Physical properties: Colorless liquid, characteristic smell. Uses: As a fuel, in medicines like cough syrups.

Question. Write chemical equations to describe two examples of different oxidations of ethanol. List two uses of ethanol.
Answer: 1. Complete combustion: \( C_2H_5OH + 3O_2 \to 2CO_2 + 3H_2O \). 2. Controlled oxidation: \( C_2H_5OH \xrightarrow{\text{Alkaline } KMnO_4} CH_3COOH \).
Uses: Solvent, antiseptic.

Question. Write the chemical equations to show what happens when
(i) sodium hydroxide is added to ethanoic acid?
(ii) solid sodium hydrogen carbonate is added to ethanoic acid?
(iii) ethanol reacts with sodium?
Answer: (i) \( CH_3COOH + NaOH \to CH_3COONa + H_2O \)
(ii) \( CH_3COOH + NaHCO_3 \to CH_3COONa + H_2O + CO_2 \)
(iii) \( 2C_2H_5OH + 2Na \to 2C_2H_5ONa + H_2 \)

Question. Write the chemical equation for the following:
(i) Combustion of methane
(ii) Oxidation of ethanol
(iii) Hydrogenation of ethene
(iv) Esterification reaction
(v) Saponification reaction
Answer: (i) \( CH_4 + 2O_2 \to CO_2 + 2H_2O \)
(ii) \( C_2H_5OH \xrightarrow{\text{Alkaline } KMnO_4} CH_3COOH \)
(iii) \( C_2H_4 + H_2 \xrightarrow{Ni} C_2H_6 \)
(iv) \( CH_3COOH + C_2H_5OH \to CH_3COOC_2H_5 + H_2O \)
(v) \( CH_3COOC_2H_5 + NaOH \to CH_3COONa + C_2H_5OH \)

Question. (i) What happens when a small piece of sodium is dropped in ethanol? Write the equation for this reaction.
(ii) Why is glacial acetic called so?
(iii) What happens when ethanol is heated at 443 K in the presence of conc. \( H_2SO_4 \)? Write the role of conc. \( H_2SO_4 \) in this case.
(iv) Write an equation showing saponification.
Answer: (i) Hydrogen gas is evolved: \( 2C_2H_5OH + 2Na \to 2C_2H_5ONa + H_2 \).
(ii) Because it freezes into ice-like crystals at low temperatures (around 16.5°C).
(iii) It forms ethene; conc. \( H_2SO_4 \) acts as a dehydrating agent.
(iv) \( CH_3COOC_2H_5 + NaOH \to CH_3COONa + C_2H_5OH \).

Question. (a) What is a homologous series? Explain with an example.
(b) Define the following terms giving one example of each.
(i) Esterification (ii) Addition reaction
Answer: (a) Series of compounds with same functional group and similar chemical properties (e.g., Alkanes).
(b) (i) Reaction of acid + alcohol to form ester. (ii) Reaction where atoms are added to unsaturated bonds.

Question. (a) Carry out following conversions :
(i) Ethanol to ethene
(ii) Ethanol to ethanoic acid
(b) Differentiate between addition reaction and substitution reaction. Give one example of each.
Answer: (a) (i) Heat with conc. \( H_2SO_4 \). (ii) Heat with alkaline \( KMnO_4 \).
(b) Addition: \( C_2H_4 + H_2 \to C_2H_6 \); Substitution: \( CH_4 + Cl_2 \to CH_3Cl + HCl \).

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 and name of the product formed when this compound reacts with
(i) sodium metal
(ii) hot concentrated sulphuric acid.
Answer: Ethanol, \( C_2H_5OH \). Uses: Fuel, solvent. (i) Sodium ethanoate and \( H_2 \). (ii) Ethene and \( H_2O \).

Question. (a) Define the term isomer.
(b) Two compounds have same molecular formula \( C_3H_6O \). Write the name of these compounds and their structural formula.
(c) How would you bring the following conversions :
(i) Ethanol to ethene
(ii) Propanol to propanoic acid?
Answer: (a) Same molecular formula, different structure. (b) Propanal and Propanone. (c) (i) Conc. \( H_2SO_4 \). (ii) Alkaline \( KMnO_4 \).

Question. A carbon compound ‘P’ on heating with excess conc. \( H_2SO_4 \) forms another carbon compound ‘Q’ which on addition of hydrogen in the presence of nickel catalyst forms a saturated carbon compound ‘R’. One molecule of ‘R’ on combustion forms two molecules of carbon dioxide and three molecules of water. Identify P, Q and R and write chemical equations for the reactions involved.
Answer: P = Ethanol \( (C_2H_5OH) \), Q = Ethene \( (C_2H_4) \), R = Ethane \( (C_2H_6) \).
Equations: \( C_2H_5OH \xrightarrow{H_2SO_4} C_2H_4 \xrightarrow{H_2/Ni} C_2H_6 \). Combustion: \( 2C_2H_6 + 7O_2 \to 4CO_2 + 6H_2O \).

Soaps and Detergents

Question. Several factories were pouring their wastes in rivers A and B. Water samples were collected from these two rivers. It was observed that sample collected from river A was acidic while that of river B was basic. The factories located near A and B are
(a) Soaps and detergents factories near A and alcohol distillery near B.
(b) Soaps and detergents factories near B and alcohol distillery near A.
(c) Lead storage battery manufacturing factories near A and soaps and detergents factories near B.
(d) Lead storage battery manufacturing factories near B and soaps and detergents factories near A.
Answer: (c) Lead storage battery manufacturing factories near A and soaps and detergents factories near B.

Question. (a) A compound ‘X’ undergoes addition reaction with \( H_2 \) to form a compound ‘Y’ having molecular mass 30 g mol⁻¹. ‘X’ decolorises bromine water and burns with a smoky flame. Identify ‘X’ and ‘Y’ and write chemical equations of the reactions involved.
(b) Write the structural formulae of (i) Butanone, and (ii) Pentanoic acid.
(c) Would you be able to check if water is hard by using a detergent ? Give reason to justify your answer.
Answer: (a) X = Ethene \( (C_2H_4) \), Y = Ethane \( (C_2H_6) \). \( C_2H_4 + H_2 \to C_2H_6 \).
(b) (i) \( CH_3-CO-CH_2-CH_3 \), (ii) \( CH_3-CH_2-CH_2-CH_2-COOH \).
(c) No, because detergents form lather with both hard and soft water.

Question. (a) Carry out the following conversions giving complete conditions for the reaction to take place in each case :
(i) Ethanoic acid from Ethanol
(ii) Ethane from Ethene
(iii) Ester from Ethanoic acid and ethanol
Also state the names given to all the above conversions.
(b) Detergents are preferred over soaps. Why? (Give one reason)
Answer: (a) (i) Oxidation, (ii) Hydrogenation, (iii) Esterification.
(b) Detergents work effectively in hard water, unlike soaps.

Question. Soaps and detergents are both, types of salts. State the difference between the two. Write the mechanism of the cleansing action of soaps. Why do soaps not form lather (foam) with hard water? Mention any two problems that arise due to the use of detergents instead of soaps.
OR
What is the difference between the molecules of soaps and detergents, chemically? Explain the cleansing action of soaps.
Answer: Soaps are sodium salts of long chain carboxylic acids; detergents are sodium salts of alkyl hydrogen sulphates. Cleansing action involves micelles where hydrophobic tails attach to oil. Soaps form scum with \( Ca^{2+}/Mg^{2+} \) in hard water. Detergents are non-biodegradable and cause water pollution.

Question. What are micelles? Why does it form when soap is added to water? Will a micelle be formed in other solvents such as ethanol also? State briefly how the formation of micelles help to clean the clothes having oily spots.
Answer: Micelles are clusters of soap molecules. Hydrophilic head attracts water, hydrophobic tail attracts oil. Micelles do not form in ethanol as soap dissolves in it. Micelles trap oil in the center, allowing it to be washed away with water.

Question. (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 of formation of scum when soaps are used with hard water.
Answer: (a) Ethanoic acid turns blue litmus red. Ethanol and ethanoic acid react with Na to give \( H_2 \). Soap solution is basic and turns red litmus blue.
(b) Soap reacts with calcium and magnesium ions to form insoluble precipitates called scum.

Questions

Question. Which of the following is not observed in a homologous series? Give reason for your choice.
(a) Change in chemical properties
(b) Difference in –CH₂ and 14 u molecular mass
(c) Gradation in physical properties
(d) Same functional group
Answer: (a) Change in chemical properties

Question. The table shows the electronic structures of four elements.
Element P: 2, 6
Element Q: 2, 8, 1
Element R: 2, 8, 7
Element S: 2, 8, 8
(a) Identify which element(s) will form covalent bonds with carbon.
(b) “Carbon reacts with an element in the above table to form several compounds.” Give suitable reason.
Answer: (a) P and R. (b) Carbon exhibits catenation and tetravalency.

Question. The number of carbon compounds is more than those formed by all other elements put together. Justify the statement by giving two reasons.
Answer: Due to (1) Catenation and (2) Tetravalency.

Question. Give a test that can be used to confirm the presence of carbon in a compound. With a valency of 4, how is carbon able to attain noble gas configuration in its compounds?
Answer: Burning producing \( CO_2 \) (turns lime water milky). Carbon attains noble gas configuration by sharing its 4 valence electrons (covalent bonding).

A & R Questions

In the following questions a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following.
(a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
(b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
(c) Assertion is correct statement but reason is wrong statement.
(d) Assertion is wrong statement but reason is correct statement.

Question. Assertion : Both aldehydes and ketones contain carbonyl group.
Reason : In aldehydes, the functional group is attached to at least one hydrogen atom.
(a) A
(b) B
(c) C
(d) D
Answer: (b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.

Question. Assertion : n-Butane has higher m.pt. than its lower alkane, propane.
Reason : Melting points of alkanes do not show regular variation with increase in molecular size.
(a) A
(b) B
(c) C
(d) D
Answer: (b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.

Multiple Choice Questions

Question. Complete the given passage by choosing the correct option.
The element carbon occurs in different forms in nature with widely varying physical properties. Both diamond and graphite are formed by carbon atoms, the difference lies in the manner in which the carbon atoms are bonded to one another. In diamond, each carbon atom is bonded to (i) other carbon atoms forming a rigid (ii) structure. In graphite, each carbon atom is bonded to (iii) other carbon atoms in the same plane giving a (iv) array.
(a) (i) four (ii) hexagonal (iii) three (iv) three-dimensional
(b) (i) three (ii) three-dimensional (iii) four (iv) hexagonal
(c) (i) four (ii) three-dimensional (iii) three (iv) hexagonal
(d) (i) three (ii) hexagonal (iii) four (iv) three-dimensional
Answer: (c) (i) four (ii) three-dimensional (iii) three (iv) hexagonal

Question. Identify the incorrect statement(s).
(i) Diamond is the hardest substance known while graphite is smooth and slippery.
(ii) Diamond is made up of billions of carbon atoms. Each carbon atom is bonded to four other carbon atoms in a tetrahedral manner to form a giant lattice. All carbon atoms are bonded by strong covalent bonds.
(iii) Graphite is a poor conductor of electricity unlike other non-metals.
(iv) Graphite has a giant covalent structure that is made up of layers of carbon atoms. In each layer, each carbon atom is bonded to three other carbon atoms to form hexagonal rings of carbon atoms.
(a) (i) and (iii)
(b) Only (iii)
(c) (ii) and (iv)
(d) (i), (ii) and (iv)
Answer: (b) Only (iii)

Question. Which of the following statements is not correct?
(a) A common functional group is present in different members of a homologous series.
(b) Two consecutive members of a homologous series differ by a \( -CH_3 \) group.
(c) The members of a homologous series can be represented by one general formula.
(d) Different members of a homologous series have similar chemical properties.
Answer: (b) Two consecutive members of a homologous series differ by a \( -CH_2 \) group.

Question. Ethanol on complete oxidation gives
(a) carbon dioxide and water
(b) acetaldehyde
(c) acetic acid
(d) acetone.
Answer: (c) acetic acid

VSA Type Questions

Question. The name of an organic compound is propene. What information can be derived from its name? Explain your answer.
Answer: It is an alkene as its IUPAC name ends in ‘-ene’. It contains a carbon-carbon double bond. It has three carbon atoms in each molecule, as indicated by the prefix ‘prop-’.

Question. An organic compound burns with a sooty flame. Is it a saturated or an unsaturated compound?
Answer: It is an unsaturated compound. Unsaturated compounds have a higher percentage of carbon compared to saturated compounds. Consequently, they undergo incomplete combustion in air, producing a yellow flame with significant soot.

Question. \( -CHO \) group cannot be present in the middle of a chain. Justify.
Answer: The \( -CHO \) group (aldehyde) contains a carbon atom bonded to an oxygen atom by a double bond and to a hydrogen atom. For this carbon atom to be positioned in the middle of a chain, it would need to bond to two other carbon atoms; however, it only has one remaining valency. Thus, it must always be at the end of a chain.

SA I Type Questions

Question. Answer the following :
(a) Why are some of the carbon compounds called saturated while other unsaturated compounds?
(b) Which of these two are more reactive?
Answer: (a) Saturated compounds are those in which all carbon-carbon bonds are single bonds. Unsaturated compounds contain at least one carbon-carbon double or triple bond. (b) Unsaturated compounds are more reactive than saturated compounds.

Question. A compound X has molecular formula \( C_3H_6 \). One mole of X reacts with one mole of bromine to yield a compound Y. Deduce the structures of X and Y.
Answer: X is propene \( (CH_3-CH=CH_2) \) and Y is 1,2-dibromopropane \( (CH_3-CHBr-CH_2Br) \).

Question. What is meant by ‘word root’ in IUPAC name? Give word roots for compounds containing up to ten carbon atoms.
Answer: The word root indicates the number of carbon atoms in the longest continuous chain. Word roots are: \( C_1 \): Meth, \( C_2 \): Eth, \( C_3 \): Prop, \( C_4 \): But, \( C_5 \): Pent, \( C_6 \): Hex, \( C_7 \): Hept, \( C_8 \): Oct, \( C_9 \): Non, \( C_{10} \): Dec.

Question. Give condensed formula for (a) cyclohexane and (b) benzene.
Answer: (a) Cyclohexane: \( C_6H_{12} \) (b) Benzene: \( C_6H_6 \).

Question. Why is the cleansing action of detergents considered more effective than soaps?
Answer: Detergents are effective in both soft and hard water, whereas soaps react with calcium and magnesium ions in hard water to form insoluble precipitates (scum), which reduces their cleaning efficiency.

Question. What is scum? How is it formed?
Answer: Scum is an insoluble white precipitate formed when soap molecules react with the calcium and magnesium salts present in hard water.

SA II Type Questions

Question. Explain the reaction of ethene and ethyne with bromine water. How is this reaction used as a test for unsaturation?
Answer: Ethene and ethyne are unsaturated hydrocarbons. They react with bromine water, which is reddish-brown, through an addition reaction that decolourises the solution. This process serves as a test for unsaturation because saturated hydrocarbons do not decolourise bromine water under normal conditions.

Question. What is combustion? Give some reactions to show that carbon in all its forms and compounds undergo combustion.
Answer: Combustion is a chemical process where a substance reacts rapidly with oxygen, releasing heat and light. Examples include:
\( C + O_2 \to CO_2 + \text{heat} + \text{light} \)
\( CH_4 + 2O_2 \to CO_2 + 2H_2O + \text{heat} + \text{light} \)
\( C_2H_5OH + 3O_2 \to 2CO_2 + 3H_2O + \text{heat} + \text{light} \)

Question. (a) (i) What would be observed on adding 5% solution of alkaline potassium permanganate drop by drop to some warm ethanol taken in a test tube?
(ii) Write the name of the compound formed during the chemical reaction.
(b) How would you distinguish experimentally between an alcohol and a carboxylic acid on the basis of a chemical property?
Answer: (a) (i) Initially, the pink color of the potassium permanganate disappears. (ii) Ethanoic acid (acetic acid) is produced. (b) Sodium bicarbonate \( (NaHCO_3) \) can be used; a carboxylic acid reacts with it to produce brisk effervescence of carbon dioxide gas, whereas an alcohol does not react.

Question. An organic compound A having molecular formula \( C_2H_4O_2 \) reacts with sodium metal and evolves a gas B which readily catches fire. A also reacts with ethanol in the presence of concentrated sulphuric acid to form sweet smelling substance C used in making perfumes.
(i) Identify the compounds A, B and C.
(ii) Write balanced chemical equations to represent
(a) the evolution of B from compound A
(b) the conversion of compound A into compound C.
Answer: (i) A is Ethanoic acid \( (CH_3COOH) \), B is Hydrogen gas \( (H_2) \), and C is Ethyl ethanoate \( (CH_3COOC_2H_5) \).
(ii) (a) \( 2CH_3COOH + 2Na \to 2CH_3COONa + H_2 \)
(b) \( CH_3COOH + C_2H_5OH \xrightarrow{\text{Conc. } H_2SO_4} CH_3COOC_2H_5 + H_2O \)

Question. What is meant by saponification? Give an example.
Answer: Saponification is the alkaline hydrolysis of an ester to produce an alcohol and the sodium or potassium salt of the carboxylic acid (soap). For example:
\( CH_3COOC_2H_5 + NaOH \to CH_3COONa + C_2H_5OH \).

LA Type Questions

Question. Name the functional groups present in the following compounds :
(i) \( CH_3CH_2CH_2OH \)
(ii) \( CH_3COCH_2CH_3 \)
(iii) \( CH_3CH_2CHO \)
(iv) \( CH_3CH_2CH_2COOH \)
(v) \( CH_3COOC_2H_5 \)
Answer: (i) Alcohol \( (-OH) \); (ii) Ketone \( (>C=O) \); (iii) Aldehyde \( (-CHO) \); (iv) Carboxylic acid \( (-COOH) \); (v) Ester \( (-COOR) \).

Question. Give the structures and IUPAC names of straight chain alkanes with molecular formula
(i) \( C_4H_{10} \)
(ii) \( C_5H_{12} \)
(iii) \( C_6H_{14} \)
Answer: (i) \( CH_3-CH_2-CH_2-CH_3 \) (Butane); (ii) \( CH_3-CH_2-CH_2-CH_2-CH_3 \) (Pentane); (iii) \( CH_3-CH_2-CH_2-CH_2-CH_2-CH_3 \) (Hexane).

Question. Write chemical equations for the reactions of ethanoic acid with
(i) sodium carbonate
(ii) potassium
(iii) soda lime
(iv) ethanol in the presence of conc. \( H_2SO_4 \).
Answer: (i) \( 2CH_3COOH + Na_2CO_3 \to 2CH_3COONa + H_2O + CO_2 \)
(ii) \( 2CH_3COOH + 2K \to 2CH_3COOK + H_2 \)
(iii) \( CH_3COOH + NaOH \xrightarrow{CaO, \Delta} CH_4 + Na_2CO_3 \)
(iv) \( CH_3COOH + C_2H_5OH \xrightarrow{\text{Conc. } H_2SO_4} CH_3COOC_2H_5 + H_2O \)

Question. Write the structural formulae for
(i) 2-Methyl-2-butene
(ii) 2-Methylpropene
(iii) Methyl propyl ether
(iv) 2,2-Dimethyl propane
(v) 4,6-Dimethyl hept-2-ene
Answer: (i) \( CH_3-C(CH_3)=CH-CH_3 \); (ii) \( CH_2=C(CH_3)_2 \); (iii) \( CH_3-O-CH_2-CH_2-CH_3 \); (iv) \( C(CH_3)_4 \); (v) \( CH_3-CH=CH-CH_2-CH(CH_3)-CH_2-CH(CH_3)_2 \).

Question. A hydrocarbon has three carbon atoms. Write down its molecular formulae as
(i) alkene
(ii) alcohol derivative
(iii) aldehyde derivative
(iv) ketone derivative
(v) acid derivative.
Answer: (i) \( C_3H_6 \); (ii) \( C_3H_7OH \); (iii) \( C_2H_5CHO \); (iv) \( CH_3COCH_3 \); (v) \( C_2H_5COOH \).