NCERT Exemplar Class 10 Science Solutions Chapter 4 Carbon And Its Compounds

Question 2. Which of the following statements are usually correct for carbon compounds? These
(i) are good conductors of electricity
(ii) are poor conductors of electricity
(iii) have strong forces of attraction between their molecules
(iv) do not have strong forces of attraction between their molecules
(a) (i) and (iii) (b) (ii) and (iii)
(c) (i) and (iv) (d) (ii) and (iv)

Answer:(d)
Solution:
Carbon predominantly forms covalent compounds, due to valency 4. Generally, carbon is a poor conductor of electricity as its compounds are predominantly covalent in nature. The forces of attraction in between their molecules are weak as they are not covalent in nature.
Statements (ii) and (iv) are correct.
Therefore, option (d) is correct.

Question 3. A molecule of ammonia $(NH_3)$has
(a) only single bonds
(b) only double bonds
(c) only triple bonds
(d) two double bonds and one single bond
Answer:(a)
Solution:
A molecule of ammonia (NH3) has only single bonds and these are covalent bonds.

Therefore, option (a) is correct.

Question 4. Buckminsterfullerene is an allotropic form of
(a) phosphorus
(b) sulphur
(c) carbon
(d) tin
Answer:(c)
Solution:
Buckminsterfullerene is an allotrope of carbon-containing clusters of 60 carbon atoms joined together to form spherical molecules. Its formula is C60, (C-Sixty)
It has 20 hexagons and 12 pentagons. Other allotropic forms of carbon are graphite, diamond, coal, coke…etc.

Therefore, option (c) is correct.

Question 5. Which of the following are correct structural isomers of butane?

(a) (i) and (iii)
(b) (ii) and (iv)
(c) (i) and (ii)
(d) (iii) and (iv)
Answer:(c)
Solution: Structural isomers: two or more organic compounds having the same molecular formulas but different structures.
Butane: $C_4H_{10}$

Structure (i) is n-butane. It is a structural isomer of butane.
Structure (iii) is iso-butane. It is a structural isomer of butane.
Other structures, i.e., (ii) and (iv) have different molecular formulas, hence incorrect
Therefore, option (c) is correct.

Question 6. $CH_{3}-CH_{2}-OH\xrightarrow[Heat]{Alkaline KMnO_{4}}CH_{3}-COOH$
In the above given reaction, alkaline $KMnO_4$ acts as
(a) reducing agent
(b) oxidizing agent
(c) catalyst
(d) dehydrating agent
Answer:(b)
Solution: Here ethanol is converted to ethanoic acid.
$KMnO_4$ acts as an oxidizing agent as it removes hydrogen from $CH_3CH_2OH$ and adds one oxygen to it.
Therefore, option (b) is correct.

Question 7. Oils on treating with hydrogen in the presence of palladium or nickel catalyst form fats. This is an example of
(a) Addition reaction
(b) Substitution reaction
(c) Displacement reaction
(d) Oxidation reaction
Answer: (a)
Solution:
Oils are unsaturated compounds containing double bonds. Unsaturated compounds are the only ones that can undergo addition reactions.
The reaction is known as the hydrogenation reaction. For example:

Hydrogenation reactions are addition reactions.
Therefore, option (a) is correct.

Question 8. In which of the following compounds, $-OH$ is the functional group?
(a) Butanone
(b) Butanol
(c) Butanoic acid
(d) Butanal
Answer: (b)
Solution:
(a) Butanone: $C_4H_8O$

The functional group is $-C=O$
(b) Butanol: $CH_3-CH_2-CH_2-CH_2-OH$
The general formula of alcohols is $C_nH_{(2n+1)}- OH.$
For Butanol, n = 4
Butanol Formula = $C_4H_9OH$
The functional group is $-OH$.
(c) Butanoic acid: $C_4H_8O_2$
The functional group is $-COOH.$
(d) Butanal: $C_4H_8O$
The functional group is $-CHO$.
Therefore, option (b) is correct.

Question 9. The soap molecule has a
(a) hydrophilic head and a hydrophobic tail
(b) hydrophobic head and a hydrophilic tail
(c) hydrophobic head and a hydrophobic tail
(d) hydrophilic head and a hydrophilic tail
Answer: (a)
Solution:
A soap molecule is made up of two parts: A long hydrocarbon part and a short ionic part $-COO-Na^+$ group. The long hydrocarbon chain is hydrophobic (water repelling) and the ionic portion is hydrophilic (water-attracting).

Therefore, option (a) is correct.

Question 10. Which of the following is the correct representation of electron dot structure of nitrogen?

Answer: (d)

The electronic configuration of N (atomic number 7) is 2, 5
Therefore, it needs three more electrons to complete its octet. Each nitrogen atom shares three electrons to form a molecule of $N_{2}$ as:
$N\equiv N$
Hence the correct electron dot structure is:

Therefore, option (d) is correct.

Question 11. Structural formula of ethyne is

Answer: (a)
Ethyne: $C_2H_2$
‘eth’ shows the presence of two carbon atoms and ‘yne' shows the presence of a triple bond,
Thus, the ethyne structure is:
$H-C\equiv C-H$
It is also known as acetylene.
Therefore, option (a) is correct.

Question 12. Identify the unsaturated compounds from the following
(i) Propane
(ii) Propene
(iii) Propyne
(iv) Chloropropane
(a) (i) and (ii) (b) (ii) and (iv)
(c) (iii) and (iv) (d) (ii) and (iii)
Answer:

A hydrocarbon in which the two carbon atoms are connected by a ‘double bond’ or ‘triple bond' is categorized as unsaturated hydrocarbon
(i) Propane: $C_3H_8$

(ii) Propene: $C_3H_6$

(iii) Propyne: $C_3H_4$
$CH_3-C\equiv CH$
(iv) Chloropropane: $C_3H_7Cl$


So, Propene and propyne have double bonds and triple bonds respectively which means they are unsaturated.
Propane and chloropropane are saturated hydrocarbons which contain only single bonds.
Therefore, option (d) is correct.

Question 13. Chlorine reacts with saturated hydrocarbons at room temperature in the
(a) absence of sunlight
(b) presence of sunlight
(c) presence of water
(d) presence of hydrochloric acid
Answer: (b)
Chlorine reacts with saturated hydrocarbon at room temperature in the presence of sunlight,
$CH_{4}+Cl_{2}\overset{sunlight}{\rightarrow}CH_{3}Cl+HCl$
$CH_3Cl+Cl_{2}\overset{sunlight}{\rightarrow}CH_{2}Cl_{2}+HCl$
$CH_2Cl_{2}+Cl_{2}\overset{sunlight}{\rightarrow}CHCl_{3}+HCl$
$CHCl_{3}+Cl_{2}\overset{sunlight}{\rightarrow}CCl_{4}+HCl$
Therefore, option (b) is correct.

Question 14. In the soap micelles
(a) the ionic end of soap is on the surface of the cluster while the carbon chain is in the interior of the cluster.
(b) ionic end of soap is in the interior of the cluster and the carbon chain is out of the cluster.
(c) both ionic end and carbon chain are in the interior of the cluster
(d) both ionic end and carbon chain are on the exterior of the cluster
Answer:

A group of soup molecules aggregated in a spherical arrangement surrounding the dirt or oil in the soap solution in water is called a ‘micelle’. In a soap micelle, the soap molecules are arranged readily with hydrocarbon ends directed towards the center and ionic ends directed outwards.

Therefore, option (a) is correct.

Question 15. Pentane has the molecular formula $C_5 H_{12}$. It has
(a) 5 covalent bonds
(b) 12 covalent bonds
(c) 16 covalent bonds
(d) 17 covalent bonds
Answer:

Structure of pentane:



It contains 16 covalent bonds.
Therefore, option (c) is correct.

Question 16. Structural formula of benzene is

Answer: (c)
Benzene molecules contains alternate single and double bonds in hexagonal carbon chains. Each carbon is attached to a hydrogen atom which makes the formula of benzene $C_6H_6$ in structure.

Therefore, option (c) is correct.

Question 17. Ethanol reacts with sodium and forms two products. These are
(a) sodium ethanoate and hydrogen
(b) sodium ethanoate and oxygen
(c) sodium ethoxide and hydrogen
(d) sodium ethoxide and oxygen
Answer: (c)
Ethanol reacts with sodium to form sodium ethoxide and releases hydrogen gas.
$C_2H_5OH + 2Na \rightarrow 2C_2H_5O^{-}Na^{+} + H_2$
Therefore, option (c) is correct.

Question 18. The correct structural formula of butanoic acid is:

Answer: (d)
Butanoic acid formula = $C_4H_8O_2$
$C_3H_7COOH$
The general formula of carboxylic acid is $R-COOH$ where R is an alkyl group.
General formula of carboxylic acid = $C_{n-1}H_{2n-1}COOH$
Butanoic acid means 4 carbons

Therefore, option (d) is correct.

Question 19. Vinegar is a solution of
(a) 50% – 60% acetic acid in alcohol
(b) 5% – 8% acetic acid in alcohol
(c) 5% – 8% acetic acid in water
(d) 50% – 60% acetic acid in water
Answer: (c)
Vinegar: $CH_3COOH$
Vinegar is 5%-8% solution of acetic acid in water.
It is also known as acetic acid.

Therefore, option (c) is correct.

Question 20. Mineral acids are stronger acids than carboxylic acids because
(i) mineral acids are completely ionised
(ii) carboxylic acids are completely ionised
(iii) mineral acids are partially ionised
(iv) carboxylic acids are partially ionised
(a) (i) and (iv) (b) (ii) and (iii)
(c) (i) and (ii) (d) (iii) and (iv)
Answer: (a)
Solution:
Mineral acids are strong acids that ionizes almost completely and carboxylic acids are weak acids as they don’t ionize easily and only a small percentage of it get ionized.
Therefore, option (a) is correct.

Question 21. Carbon forms four covalent bonds by sharing its four valence electrons with four univalent atoms, e.g. hydrogen. After the formation of four bonds, carbon attains the electronic configuration of
(a) helium
(b) neon
(c) argon
(d) krypton
Answer: (b)
Electronic configuration of carbon (C) = 2, 4
When it forms four covalent bonds by sharing its four valence electrons with hydrogen, it forms CH₄

So it has a total of 10 electrons which is the configuration of Neon.
Therefore, option (b) is correct.

Question 22. The correct electron dot structure of a water molecule is

Answer: (c)
The oxygen atom has 6 valence electrons, out of which 2 are involved in bonding with the 2 hydrogen atoms. Therefore water molecule has 2 bonded pairs of electrons and 2 lone pairs.

Hence the answer is

Therefore, option (c) is correct.

Question 23 Which of the following is not a straight chain hydrocarbon?

Answer: (d)

We can see that all the carbon atoms are attached by covalent bonds in a continuous straight chain.
But in structure (d), 5 carbons in a chain with another carbon connected to 2^nd carbon from the right.
Therefore, option (d) is correct.

Question 24. Which among the following are unsaturated hydrocarbons?

(a) (i) and (iii)

(b) (ii) and (iii)
(c) (ii) and (iv)

(d) (iii) and (iv)
Answer: (c)
Unsaturated hydrocarbons have double or triple bonds in their structures.
We can see that structure (ii) has a triple bond.
Structure (iv) has a double bond
Therefore, option (c) is correct.

Question 25. Which of the following does not belong to the same homologous series?
(a) $CH_4$
(b) $C_2 H_6$
(c) $C_3 H_8$
(d) $C_4 H_{8}$
Answer: (d)
A homologous series is a group of organic compounds having similar structures and similar chemical properties in which the successive compounds differ by $CH_2$ group.
So, a homologous series of alkanes is
Methane $CH_4$
Ethane $C_2 H_6$
Propane $C_3 H_8$
Butane $C_4 H_{8}$
So, $C_4H_8$ does not belong to the homologous series
Therefore, option (d) is correct.

Question 26. The name of the compound $CH_3 - CH_2 - CHO$ is
(a) Propanal
(b) Propanone
(c) Ethanol
(d) Ethanal
Answer: (a)
The functional group present in $CH_3 - CH_2 - CHO$ is an aldehyde.
The compound has 3 carbons so -Prop is the prefix
Aldehyde has a suffix of -al
Prefix + an + Suffix = Propanal
Therefore, option (a) is correct.

Question 27. The heteroatoms present in
$CH_3 - CH_2 - O - CH_2 - CH_2Cl$ are
(i) oxygen
(ii) carbon
(iii) hydrogen
(iv) chlorine
(a) (i) and (ii)

(b) (ii) and (iii)

(c) (iii) and (iv)

(d) (i) and (iv)
Answer: (d)
Atoms other than C and H, if present in organic compounds, are called heteroatoms.
Oxygen and chlorine are the elements found in the given compound apart from carbon and hydrogen.
Therefore, option (d) is correct.

Question 28. Which of the following represents saponification reaction?
(a) $CH_3COONa + NaOH \overset{CaO}{\rightarrow} CH_4 + Na_2CO_3$
(b) $CH_3COOH + C_2H_5OH \overset{H_2SO_{4}}{\rightarrow}CH_3 COOC_2H_5 + H_2O$
(c) $2CH_3COOH + 2Na \rightarrow 2CH_3COONa + H_2$
(d) $CH_3COOC_2H_5 + NaOH \rightarrow CH_3 COONa + C_2H_5OH$

Answer: (d)
When an ester is heated with sodium hydroxide solution, ester gets hydrolyzed (breaks down) to form the parent alcohol and sodium salt of carboxylic acid. This process is called saponification. Equation (d) has alcohol and sodium salt of carboxylic acid.
Therefore, option (d) is correct.

Question 29. The first member of alkyne homologous series is
(a) ethyne
(b) ethene
(c) propyne
(d) methane
Answer: (a)
A homologous series is a group of organic compounds having similar structures and similar chemical properties in which the successive compounds differ by $CH_2$ group.
The general formula of alkyne is $C_nH_{2n-2}$ where n is the number of carbon atoms. The first member of the alkyne homologous series is ethyne $C_2H_2$ as you need 2 carbons minimum to have a carbon connected with a double bond.
Therefore, option (a) is correct.

Question 31. Write the names of the following compounds

Answer:

(a) Pentane —e + oic acid = Pentanoic acid
The structure has 5 carbons and a carboxylic acid group.
(b) Butane—ane + yne = Butyne
The structure has 5 carbons and a triple bond.
(c) Heptane —e +al = Heptanal
As the structure has 7 carbons and aldehyde group
(d) Pentane —e + ol = Pentanol
As the structure has 5 carbon atoms and one alcohol group

Question 32. Identify and name the functional groups present in the following compounds.

Answer:

(a) —OH (alcohol)
(b)
(carboxylic acid)
(c)
(ketone)
(d) —C= C—
(alkene)

Question 33. A compound X is formed by the reaction of a carboxylic acid $C_2H_4O_2$ and an alcohol in presence of a few drops of $H_2SO_4$. The alcohol on oxidation with alkaline $KMnO_4$ followed by acidification gives the same carboxylic acid as used in this reaction. Give the names and structures of:
(a) carboxylic acid, (b) alcohol and (c) the compound X. Also write the reaction.
Answer:

Carboxylic acid is ethanoic acid

Alcohol is ethanol

X is ethyl ethanoate

Reaction involved:
$CH_{3}COOH(l)+C_{2}H_{5}OH(l)\overset{Conc. H_{2}SO_{4}}{\rightarrow}CH_{3}COOC_{2}H_{5}(l)+H_{2}O(l)$

Question 34. Why detergents are better cleansing agents than soaps? Explain.
Answer:

Detergents are better cleansing agents than soaps because they can be used even with hard water. The charged ends of detergents do not form insoluble precipitates with calcium and magnesium ions in hard water but soap doesn’t work in hard water. Hard water contains Ca²⁺ and Mg²⁺ ions which react with soap to form Insoluble salts of calcium and magnesium.
Detergents have a stronger cleansing action than soaps and are more soluble in water than soaps.

Question 35. Name the functional groups present in the following compounds
(a) $CH_3 CO CH_2 CH_2 CH_2 CH_3$
(b) $CH_3 CH_2 CH_2 COOH$
(c) $CH_3 CH_2 CH_2 CH_2 CHO$
(d) $CH_3 CH_2 OH$
Answer:

(a) Ketone

(b) Carboxylic acid, —COOH

(c) Aldehyde, —CHO
(d) Alcohol, —OH

Question 36. How is ethene prepared from ethanol? Give the reaction involved in it.
Answer:

Ethene is prepared by the dehydration of ethyl alcohol in the presence of $conc. H_{2}SO_{4}$ at $160^{\circ}C$.
$C_2H_5OH \overset{conc. H_{2}SO_{4}}{\rightarrow} CH_2 = CH_2 + H_2O$

Question 37. Intake of small quantity of methanol can be lethal. Comment.
Answer:

Methanol is very poisonous because it gets oxidized to methanol (formaldehyde) in the liver. Methanal reacts aggressively with the components of cells and causes the protoplasm to get coagulated (In the same way, as an egg gets coagulated on boiling). Methanol also affects the optic nerve causing blindness.
$CH_{3}OH+[O]\xrightarrow[H_{2}SO_{4}]{Na_{2}Cr_{2}O_{7}}CH_{2}O+H_{2}O$

Question 38. A gas is evolved when ethanol reacts with sodium. Name the gas evolved and also write the balanced chemical equation of the reaction involved.

Answer:

When ethanol reacts with sodium, the gas evolved is hydrogen.
$2C_2H_5OH + 2Na \rightarrow 2C_2H_5O^-Na^+ + H_2$

Question 39. Ethene is formed when ethanol at 443 K is heated with excess of concentrated sulphuric acid. What is the role of sulphuric acid in this reaction? Write the balanced chemical equation of this reaction.
Answer:

When ethanol is heated with excess of concentrated sulphuric acid at $170^{\circ}C$, it gets dehydrated to form ethene.
The reaction is as follows:
$CH_3CH_2OH \overset{Conc. H_{2}SO_{4}}{\rightarrow} CH_2 = CH_2 + H_2O$
Concentrated sulphuric acid removes water from ethanol, thereby, acting as a dehydrating agent.

Question 40. Carbon, Group (14) element in the Periodic Table, is known to form compounds with many elements.
Write an example of a compound formed with
(a) chlorine (Group 17 of Periodic Table)
(b) oxygen (Group 16 of Periodic Table)
Answer:

(a) Carbon forms carbon tetrachloride when reacted with chlorine in the presence of sunlight.
Carbon tetrachloride: $CCl_4$
(b) Carbons form carbon dioxide or carbon monoxide when reacted with oxygen based on the availability of oxygen.
Carbon dioxide: $CO_2$
Carbon monoxide: CO

Question 41. In electron dot structure, the valence shell electrons are represented by crosses or dots.
(a) The atomic number of chlorine is 17. Write its electronic configuration
(b) Draw the electron dot structure of chlorine molecule.
Answer:

(a) Electronic configuration of CI (atomic number 17)
2 8 7
(b) The electron dot structure of chlorine molecule is

Question 42. Catenation is the ability of an atom to form bonds with other atoms of the same element. It is exhibited by both carbon and silicon. Compare the ability of catenation of the two elements. Give reasons.
Answer:

Both carbon (C) and silicon (Si) have similar valence shell electronic configuration
C (atomic number 6) – Electronic configuration 2, 4
Si (atomic number 14) – Electronic configuration 2, 8, 4
Both have four electrons in the valence shell and hence show the phenomenon of catenation.
Carbon exhibits catenation much more than silicon or any other element due to its smaller size which makes the C—C bonds strong while the Si—Si bonds are comparatively weaker due to their large size.
Thus, due to the greater strength of C—C over Si—Si bonds, carbon shows catenation to a greater extent than silicon.

Question 43. Unsaturated hydrocarbons contain multiple bonds between the two C-atoms and show addition reactions. Give the test to distinguish ethane from ethene.
Answer:

When an unsaturated hydrocarbon reacts with bromine the double or triple bonds between the carbons get broken and bromine gets attached to those carbons.
Conformation test:
Ethane when burnt in the air will give a clear flame whereas ethene will give lots of smoke.
$2 C_2H_6 + 7O_2 \rightarrow 4CO_2 + 6H_2O$
$C_{2}H_{4}(g)+3O_{2}(g) \rightarrow 2CO_{2}(g)+2H_{2}O(l)+Smoke$

Question 44. Match the reactions given in Column (A) with the names given in column (B).

Answer:

A – iv
B – i
C – ii
D – iii
Solution:
Addition reaction - a reaction in which one molecule combines with another to form a larger molecule with no other products.
$CH_2 = CH_2 + H_2 \overset{Ni}{\rightarrow} CH_3 - CH_3$
Substitution reaction – in which one functional group in a chemical compound is replaced by another functional group.
$CH_4 + Cl_2 \overset{sunlight}{\rightarrow} CH_3Cl + HCl$
Neutralization reaction – in which an acid and base react to give salt and water
$CH_3COOH+NaOH \rightarrow CH_3COONa+H_2O$
Esterification reaction – in which an organic acid reacts with an alcohol to form an ester and water
$CH_3OH + CH_3COOH \overset{H^{+}}{\rightarrow} CH_3COOCH_3 + H_2O$

Question 45. Write the structural formulae of all the isomers of hexane.
Answer:

(a) Hexane

(b) 2-methyl pentane

(c) 2,2-dimethyl butane

(d) 2,3-dimethyl butane

(e) 3-methyl pentane

Question 46. What is the role of metal or reagents written on arrows in the given chemical reactions?
(a)
(b) $CH_{3}COOH +CH_{3}CH_{2}OH \overset{Conc. H_{2}SO_{4}}{\rightarrow} CH_{3}COOC_{2}H_{5}+H_{2}O$
(c) $CH_{3}CH_{2}OH\xrightarrow[Heat]{Alk. KMnO_{4}} CH_{3}COOH$
Answer:

(a) Nickel (Ni) acts as the catalyst during the reaction. It first absorbs the hydrogen molecule on its surface as hydrogen atoms and then the alkene molecule side by side. The two hydrogen atoms then add across the double bond of the alkene to form the addition product, i.e., 2, 3- dimethyl butane.
(b) Conc. $H_{2}SO_{4}$ increases the rate of the forward reaction by removing $H_{2}O$ formed during the reaction. In other words, conc. $H_{2}SO_{4}$ acts as a dehydrating agent.
(c) Alkaline $KMnO_{4}$ acts as an oxidizing agent and oxidizes ethanol to ethanoic acid

Question 48. (a) What are hydrocarbons? Give examples.
(b) Give the structural differences between saturated and unsaturated hydrocarbons with two examples each.
(c) What is a functional group? Give examples of four different functional groups.
Answer:

a) Hydrocarbons are compounds made of carbon and hydrogen.
Example- Methane: $CH_4$
Ethene: $CH_2 = CH_2$
Benzene: $C_6H_6$
b) In saturated hydrocarbons, all the bonds of carbon are single bonds but in unsaturated hydrocarbon compounds, the carbon chain has either a double bond or triple bond or both in some cases.
Example
Saturated hydrocarbons:
Methane

Ethane

Unsaturated hydrocarbons:
Ethene

Ethyne
$H-C\equiv C-H$
Propene

c) A functional group is a substituent or moiety in a molecule that causes the molecule's characteristic chemical reactions.
Example:
Alcohol -OH
Carboxylic Acid -COOH
Chlorine -Cl
Fluorine -F
Iodine -I
Aldehyde -CHO
Cyanide -CN

Question 49. Name the reaction which is commonly used in the conversion of vegetable oils to fats. Explain the reaction involved in detail.
Answer:

The conversion of vegetable oil to fat is called a hydrogenation reaction.
Vegetable oils (unsaturated hydrocarbons) are treated with hydrogen and passed over nickel and palladium at 200$^{\circ}C$. The unsaturated compounds turn into saturated.
Example:
$H_{2}C=CH_{2}+H_{2}\overset{Ni}{\rightarrow}C_{2}H_{6}$
This process is used in industries to convert oils to vanaspati ghee as it is more stable and has a lot of shelf-life.

Question 50. (a) Write the formula and draw electron dot structure of carbon tetrachloride.
(b) What is saponification? Write the reaction involved in this process.
Answer:

a) Carbon tetrachloride
CCl₄

(b) When an ester is heated with sodium hydroxide solution, ester gets hydrolyzed (breaks down) to form the parent alcohol and sodium salt of carboxylic acid.
Example:
$CH_3COOCH_3 + NaOH \rightarrow CH_3COONa + CH_3OH$

Question 51. Esters are sweet-smelling substances and are used in making perfumes. Suggest some activity and the reaction involved for the preparation of an ester with well labeled diagram.
Answer:

Reaction Set up:
Take 1 mL ethanol (absolute alcohol) 1 mL glacial acetic acid and a few drops of concentrated sulphuric acid in a test tube.
Warm the test tube in a water bath for at least five minutes.
Pour the contents of the test tube into a beaker containing 20-50 mL of water and smell the resulting mixture.
The sweet smell confirms the presence of an ester.

Reaction mixture:
Ethanoic acid + Alcohol in the presence of concentrated Sulphuric Acid
Reaction:
$CH_3COOH + CH_3CH_2OH \overset{H_{2}SO_4}{\rightarrow}CH_3COOC_2H_5 + H_2O$
Confirmation test for ester formation is a sweet smell.

Question 52. A compound C (molecular formula, $C_2H_4O_2$) reacts with Na - metal to form a compound R and evolves a gas which burns with a pop sound. Compound C on treatment with an alcohol A in presence of an acid forms a sweet smelling compound S (molecular formula, $C_3H_6O_2$). On addition of NaOH to C, it also gives R and water. S on treatment with NaOH solution gives back R and A. Identify C, R, A, S and write down the reactions involved.
Answer:

Since Compound C has two oxygen atoms it can be an ester or carboxylic acid.
Given that the gas evolved (on the reaction with sodium) burns with a pop sound in an indication that the evolved gas is hydrogen.
Compound R is going to be a salt with sodium being the positive ion and the rest of the compound C which lost hydrogen must be negatively charged. This is only possible with carboxylic acid and not ester.
So C is a carboxylic acid and based on the number of carbons it is Ethanoic acid.
Compound C is $CH_3COOH.$
Compound R is $CH_3COONa.$.
Compound A is $CH_3OH$.
Compound S is $CH_3COOCH_3$
Reactions involved:
$2CH_3 COOH + 2Na \rightarrow 2CH_{3}COONa+H_{2}$
(C) (R)
$CH_3COOH + CH_{3}OH \rightarrow CH_3COOCH_{3}+H_2O?$
(C) (A) (R)
$CH_3COOOH +NaOH\rightarrow CH_{3}COONa?+H_{2}O$
(C) (R)
$CH_3COOCH_{3}+NaOH\rightarrow CH_{3}COONa +CH_{3}OH?$
(R) (A)

Question 53. Look at Figure 4.1 and answer the following questions
(a) What change would you observe in the calcium hydroxide solution taken in tube B?
(b) Write the reaction involved in test tubes A and B respectively.
(c) If ethanol is given instead of ethanoic acid, would you expect the same change?
(d) How can a solution of lime water be prepared in the laboratory?

Answer:

(a) Calcium hydroxide or Limewater $(Ca(OH)_2)$ taken in tube B turns milky when carbon dioxide passes through it as it forms Calcium carbonate $(CaCO_3)$
$Ca(OH)_2 (aq) + CO_2 (g) \rightarrow CaCO_3 (s) + H_2O (l)$
(b) Test Tube A
Sodium Carbonate reacts with ethanoic acid to form sodium ethanoate, carbon dioxide, and water
$Na_2CO_3 + CH_3COOH \rightarrow CH_3COONa + CO_2 + H_2O$
Test Tube B
Calcium hydroxide turns milky white due to the formation of Calcium carbonate (CaCO3) when Carbon dioxide is passed through it.
$Ca(OH)_2 (aq) + CO_2 (g) \rightarrow CaCO_3 (s) + H_2O (l)$
(c) No change will take place when we take ethanol instead of ethanoic acid.
$CH_3CH_2OH + Na_2CO_3 \rightarrow \text{ NO REACTION}$
(d) Take a small piece of Calcium oxide in a test tube. Add water to it, part of it gets dissolved but the majority of it gets suspended. So pass the complete solution into a filter paper and collect it in a test tube and this solution is lime water.
$CaO + H_2O \rightarrow Ca(OH)_2$

Question 54. How would you bring about the following conversions? Name the process and write the reaction involved.
(a) ethanol to ethene.
(b) propanol to propanoic acid.
Write the reactions.
Answer:

(a) When Ethanol is reacted with concentrated Sulphuric acid in the presence of heat it will lead to the removal of water molecules and form ethene. This type of reaction is called dehydrogenation reaction.
$CH_3CH_2OH \overset{conc. H_{2}SO_{4}}{\rightarrow} CH_2=CH_2 + H_2O$
(b) When propanol is heated in the presence of potassium permanganate, it will convert to propanoic acid. This type of reaction is called an oxidation reaction.
$CH_3CH_2CH_2OH \overset{Alk. KMnO_{4}}{\rightarrow} CH_3CH_2COOH$

Question 55. Draw the possible isomers of the compound with molecular formula $C_3H_6O$ and also give their electron dot structures.
Answer:

For $C_3H_6O$
1) Propanal

2) Acetone

3) Methoxyethane
$H_{2}C=CH-O-CH_{3}$
4) trans-1-propenol

5) cis-1-propenol

6) 2-propen-2-ol

7) 2-propen-1-ol

8) oxacyclobutane

9) cyclopropanol

10 and 11) Enantiomers of methyl oxirane:

(S)-Methyloxirane (R)-Methyloxirane

Question 56. Explain the given reactions with the examples
(a) Hydrogenation reaction
(b) Oxidation reaction
(c) Substitution reaction
(d) Saponification reaction
(e) Combustion reaction
Answer:

(a) Hydrogenation reaction is the addition of hydrogen to the unsaturated molecule of a hydrocarbon.
Oils are unsaturated compounds containing double bonds. Unsaturated compounds are the only ones which can undergo addition reaction.
The reaction is known as the hydrogenation reaction. For example:

Hydrogenation reactions are additional reactions

(b) Oxidation reaction: A reaction in which an organic compound is reacted with an oxidizing agent where hydrogen is removed or oxygen is added to the compound.
For example:
Alcohol $\rightarrow$ Aldehyde/Ketone $\rightarrow$ Carboxylic acid
$CH_{3}CH_{2}OH \overset{Alk. KMnO_{4}}{\rightarrow}CH_{3}COOH$

(c) Substitution reaction is when an atom or group of atoms is replaced with another atom or group of atoms.
$CH_4 + Cl_2 \overset{hv}{\rightarrow} CH_3Cl + HCl$
(d) When an ester is heated with sodium hydroxide solution, it gets hydrolyzed (breaks down) to form the parent alcohol and sodium salt of carboxylic acid.
Example:
$CH_3COOCH_3 + NaOH \overset{Alk. KMnO_{4}}{\rightarrow} CH_3COONa + CH_3OH$
(e) Combustion Reaction is where an organic compound reacts with oxygen to form carbon dioxide and water vapor.
$CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O + Heat + Light$

Question 57. An organic compound A on heating with concentrated $H_2SO_4$ forms a compound B which on addition of one mole of hydrogen in presence of Ni forms a compound C. One mole of compound C on combustion forms two moles of $CO_2$ and 3 moles of $H_2O$. Identify the compounds A, B and C and write the chemical equations of the reactions involved.
Answer:

As the compound on combustion forms two moles of carbon dioxide and 3 moles of water, it means that 2 carbon atoms and 6 hydrogen atoms are present. So the molecular formula is C₂H₆ (ethane).
$C_2H_6 + 3.5 O_2 \rightarrow 2CO_2 + 3H_2O$
Compound A is ethanol (CH3CH2OH). On dehydrogenation, it gives ethene.
$C_2H_5OH \overset{Hot conc. H_{2}SO_{4}}{\rightarrow}C_{2}H_{4}+H_{2}O$
Compound B is ethene $(CH_2=CH_2)$
The compound C is obtained by the addition of 1-mole hydrogen in the presence of nickel to B which means C is ethane
$C_{2}H_{4}+H_{2}\overset{Ni}{\rightarrow}C_{2}H_{6}$
Compound C is $CH_3-CH_3$
$C_{2}H_{6}+7O_{2}\rightarrow4CO_{2}+6H_{2}O+Heat+Light$