Carbon and its Compounds
Multiple Choice Questions
1. Carbon exists in the atmosphere in the form of
(a) carbon monoxide only
(b) carbon monoxide in traces and carbon dioxide
(c) carbon dioxide only
(d) coal
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Answer
(c) carbon dioxide only
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)
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Answer
(d) (ii) and (iv)
Explanation
Carbon compounds form covalent bonds hence they have very weak force of attraction. Carbon compounds are poor conductors of electricity.
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
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Answer
(a) only single bonds
Explanation
Nitrogen has three electron in its outermost shell and hydrogen has 1.3 hydrogen atoms combine with 1 nitrogen atom to make ammonia. These bonds are single bonds.
4. Buckminsterfullerene is an allotropic form of
(a) phosphorus
(b) sulphur
(c) carbon
(d) tin
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Answer
(c) carbon
Explanation
Diamond, Graphite, Lonsdaleite, C60 (Buckminsterfullerene or buckyball), C540, C70, Amorphouscarbon, and h) single-walled carbon nanotube, or buckytube. Are the allotropes of Carbon.
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)
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Answer
(c) (i) and (ii)
Explanation
Chemical formula of Butane is $C _4 H _{10}$, here option iii) and iv) have 8 hydrogen atoms, hence they are wrong.
6. $CH 3 - CH _2 - OH \xrightarrow{\text{Alkaline} KMnO_4 + \text{Heat} } CH _3-COOH$
In the above given reaction, alkaline $KMnO _4$ acts as
(a) reducing agent
(b) oxidising agent
(c) catalyst
(d) dehydrating agent
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Answer
(b) oxidising agent
Explanation
Two Hydrogen atoms are replaced by an atom of oxygen making oxidation of ethanol. Here addition of oxygen is provided by potassium.
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
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Answer
(a) Addition reaction
Explanation
Here Hydrogen is added to oil, hence it is an addition reaction.
8. In which of the following compounds, $-OH$ is the functional group?
(a) Butanone
(b) Butanol
(c) Butanoic acid
(d) Butanal
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Answer
(b) Butanol
Explanation
Compound with $OH$ Functional group will have a suffix ol in them hence answer is (b) Butanol.
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
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Answer
(a) hydrophilic head and a hydrophobic tail
Explanation
Because of hydrophobic tail Oil and grease is trapped inside a micelle. Hydrophobic head makes the outer surface of micelle. Hence micelle is easily washed by water.
10. Which of the following is the correct representation of electron dot structure of nitrogen?
(a) $: \ddot{N}: \ddot{N}$ :
(b) $: \dot{N}:: \dot{N}$ :
(c) $: \ddot{N}: \dot{N}$ :
(d) $: N: \vdots N:$
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Answer
d)
Explanation
In this structure Nitrogen atoms gets 8 electron whereas in other options it is different.
11. Structural formula of ethyne is
(a) $H-C \equiv C-H$
(b) $H_3-C \equiv C-H$
(c) 
(d) 
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Answer
a)
Explanation
Chemical formula of Ethyne is $C _2H _2$, Hence answer is a)
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)
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Answer
(d) (ii) and (iii)
Explanation
Propene has double bond and Propyne is having triple bond. Hence they are unsaturated compounds.
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
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Answer
(b) presence of sunlight
Explanation
In presence of sunlight Chlorine reacts with Hydrocarbons and displaces Hydrogen atoms.
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
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Answer
(a) the ionic end of soap is on the surface of the cluster while the carbon chain is in the interior of the cluster.
Explanation
A micelle is a spherical aggregate soap molecules in soap solution. In the soap micelles the ionic end of soap is on the surface of the cluster while the carbon chain is in the interior of the cluster.
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
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Answer
(c) 16 covalent bonds
16. Structural formula of benzene is
Show Answer
Answer
c)
Explanation
Chemical formula of Benzene is C6H6. In option call the arms of carbon atoms are occupied hence it is the right answer.
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
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Answer
(c) sodium ethoxide and hydrogen
Explanation
$2 Na+2 CH_3 CH_2 OH \longrightarrow 2 CH_3 CH_2 ONa+H_2$
18. The correct structural formula of butanoic acid is
Show Answer
Answer
d)
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
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Answer
(c) 5\% - 8\% acetic acid in water
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)
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Answer
(a) (i) and (iv)
Explanation
Mineral acids are completely ionized whereas carboxylic acids are partially ionized. Hence mineral acids are stronger than carboxylic acids.
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
Show Answer
Answer
(b) neon
Explanation
After sharing four valence electrons with univalent atoms. Electronic configuration of Carbon becomes 2.8 which is same as electronic configuration of Neon.
22. The correct electron dot structure of a water molecule is
(a) $H \cdot \ddot{O} \cdot H$
(b) $H: \ddot{O} \cdot H$
(c) $H: \ddot{O: H}$
(d) $H: O: H$
Show Answer
Answer
c)
Explanation
Option c) represents complete octet configuration . Hence it is the right answer.
23. Which of the following is not a straight chain hydrocarbon?
(a) $H_3 C-CH_2-CH_2-CH_2-\underset{\substack{| \\ CH_3}}{CH_2}$
(b) $H_3 C-CH_2-CH_2-CH_2-CH_2-CH_3$
(c) $H_2\stackrel{\substack{CH_3 \\ |} }{C} H_2C-H_2C-\underset{\substack{| \\ CH_3} }{C}H_2$
(d) $\substack{CH_3 \\ H_3C } \substack{\backslash \\ /} CH-CH_2-CH_2-CH_3$
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Answer
d)
24. Which among the following are unsaturated hydrocarbons?
(i) $H_3 C-CH_2-CH_2-CH_3$
(ii) $H_3 C-C \equiv C-CH_3$
(iii) $\begin{gathered}H_3 C-CH-CH_3 \\ | \\ CH_3\end{gathered}$
(iv) $\begin{gathered}H_3 C-C=CH_2 \\ | \\ CH_3\end{gathered}$
(a) (i) and (iii)
(b) (ii) and (iii)
(c) (ii) and (iv)
(d) (iii) and (iv)
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Answer
(c) (ii) and (iv)
Explanation
Option (ii and (iv having double and triple bonds, hence they are unsaturated hydrocarbons.
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) $C_4 H_8$
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Answer
(d) $C_4 H_8$
Explanation
General formula for $C_4 H_8$ is $C_n H _{2 n}$ and for other option it is $C_n H _{2 n+2}$
26. The name of the compound $CH _3-CH _2-CHO$ is
(a) Propanal
(b) Propanone
(c) Ethanol
(d) Ethanal
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Answer
(a) Propanal
Explanation
This compound has 3 carbon atoms and an aldehyde which add suffix al to 3 carbon compound.
27. The heteroatoms present in $CH _3-CH _2-O-CH _2-CH _2 Cl$ 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)
Show Answer
Answer
(d) (i) and (iv)
Explanation
Oxygen and chlorine are not among essential components of Hydrocarbon hence they are heteroatoms.
28. Which of the following represents saponification reaction?
(a) ${CH}_3 {COONa}+{NaOH} \rightarrow {CH}_4+{Na}_2 {CO}_3$
(b) ${CH}_3 {COOH}+{C}_2 {H}_5 {OH} \rightarrow {CH}_3 {COOC}_2 {H}_5+{H}_2$
(c) $2 {CH}_3 {COOH}+2 {Na} \rightarrow 2 {CH}_3 {COONa}+{H}_2$
(d) ${CH}_3 {COOC}_2 {H}_5+{NaOH} \rightarrow {CH}_3 {COONa}+{C}_2 {H}_5 {OH}$
Show Answer
Answer
(d) ${CH}_3 {COOC}_2 {H}_5+{NaOH} \rightarrow {CH}_3 {COONa}+{C}_2 {H}_5 {OH}$
Explanation
Saponification is a reaction in which ethanol and sodium ethanoate are produced upon treatment of ester with an alkali.
29. The first member of alkyne homologous series is
(a) ethyne
(b) ethene
(c) propyne
(d) methane
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Answer
(b) ethene
Short Answer Questions
30. Draw the electron dot structure of ethyne and also draw its structural formula
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Answer
Molecular formula= $C 2 H _2$
Electronic Formula
$ =H \cdot \cdot c \vdots \vdots c \cdot \cdot H $
Structural formula $=H-C \equiv C-H$
31. Write the names of the following compounds
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Answer
a) Pentanoic acid
b) Butyne
c) Heptanal
d) Pentanol
32. Identify and name the functional groups present in the following compounds.
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Answer
a) Alcohol
b) Carboxylic acid
c) Ketone
d) Alkene
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.
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Answer
Carboxylic acid $=CH _3 COOH$ ethanoic acid
Alchohol $=CH_3 CH_2 OH$ ethanol
$X=CH_3 COOCH_2 CH_3$ ethyl ethanoate
34. Why detergents are better cleansing agents than soaps? Explain.
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Answer
Detergents are better than soaps because detergents are ammonium or sulphonate salts of long chain carboxylic acids. Charged ends of theses will not for precipitate with calcium and magnesium present in hard water. On the other hand soaps will form precipitate with calcium and magnesium ions present in the hard water.
35. Name the
functional groups present in the following compounds
(a) $CH_3 COCH_2 CH_2 CH_2 CH_3$
(b) $CH_3 CH_2 CH_2 {C O O H}$
(c) $CH_3 CH_2 CH_2 CH_2 CHO$
(d) $CH_3 CH_2 OH$
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Answer
a) Ketone
b) Carboxylic acid
c) Aldehyde
d) Alcohol
36. How is ethene prepared from ethanol? Give the reaction involved in it.
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Answer
Ethanol is heated at 443k along with excess Sulphuric acid to obtain Ethene.
$\underset{\text{(ethanol)}}{CH 3-CH _2OH} \xrightarrow{{(H_2SO_4)}} \underset{\text{(ethene)}}{CH _2=CH _2+H _2O}$
37. Intake of small quantity of methanol can be lethal. Comment.
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Answer
Methanol gets converted to Methanal and liver and kills all the cells. Methanol also affect the optic nerves and causes blindness. Hence intake of small quantity of methanol can be lethal.
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.
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Answer
When ethanol reacts with sodium it gives Sodium ethoxide with the liberation of Hydrogen gas.
$2 CH_3-CH_2-OH+2 Na \longrightarrow 2 CH_3-CH_2-ONa+H_2$
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.
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Answer
Sulphuric acid acts as a catalyst and a dehydrating agent in the formation of ethene.
$ \underset{\text{ Ethyl alcohol }}{\underset{443 K}{CH_3 CH_2 OH} } \xrightarrow{\text{ Conc. } H_2 SO_4} \underset{\text{ Ethene }}{CH _2=CH_2}+ \underset{\text{Water}}{H_2 O} $
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) oxgygen (Group 16 of Periodic Table)
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Answer
a) $CCl_4$ - Carbon Tetra chloride
b) Carbon-di-oxide- $CO_2$
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
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Answer
a) KLM- 2,8,7
(b)
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.
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Answer
Catenation is shown by both Silicon and Carbon. Silicon bonds are less stable and reactive whereas bonds formed by Carbon bonds are very strong hence carbon shows better catenation than Silicon.
43. Unsaturated hydrocarbons contain multiple bonds between the two $C$-atoms and show addition reactions. Give the test to distinguish ethane from ethene.
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Answer
Saturated Hydrocarbons burns with clean flame and produce no soot where as non-saturated Hydrocarbons burns with yellow flame and produces lot of soot. Ethane is saturated hydrocarbon and it burns with clean flame with no soot. Ethene is unsaturated hence it burns with yellow flame producing lot of soot.
44. Match the reactions given in Column (A) with the names given in column (B).
| Column A | Column B |
|---|---|
| (a) $CH _3 OH+CH _3 COOH CH _3 COOCH_3+H _2 O$ | (i) Addition reaction |
| (b) $CH _2=CH _2+H _2 CH _3-CH _3$ | (ii) Substitution reaction |
| (c) $CH _4+Cl _2 \xrightarrow{\text{Sunlight}} CH _3 Cl+HCl$ | (iii) Neutralisation reaction |
| (d) $CH _3 COOH+NaOH CH_3COONa+H _2 O$ | (iv) Esterification reaction |
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Answer
| Column A | Column B |
|---|---|
| (a) $CH _3 OH+CH _3 COOH CH _3 COOCH_3+H _2 O$ | (iv) Esterification reaction |
| $(b) CH _2=CH _2+H _2 CH _3-CH _3$ | (i) Addition reaction |
| $($ c) $CH _4+Cl _2 \xrightarrow{\text{ Sunlight } } CH _3 Cl+HCl$ | (ii) Substitution reaction |
| (d) $CH _3 COOH+NaOH CH_3COONa+H _2 O$ | (iii) Neutralisation reaction |
45. Write the structural formulae of all the isomers of hexane.
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Answer
46. What is the role of metal or reagents written on arrows in the given chemical reactions?
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Answer
(a)
(b) $CH_3 COOH+CH_3 CH_2 OH \xrightarrow{\text{ Conc. } H_2 SO_4} CH_3 COOC_2 H_5+H_2 O$
(c) $CH_3 CH_2 OH \xrightarrow[\text{ Heat }]{\text{ Alk. } KMnO_4} CH_3 COOH$
47. A salt $X$ is formed and a gas is evolved when ethanoic acid reacts with sodium hydrogencarbonate. Name the salt $X$ and the gas evolved. Describe an activity and draw the diagram of the apparatus to prove that the evolved gas is the one which you have named. Also, write chemical equation of the reaction involved.
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Answer
When ethanoic acid reacts with Sodium Hydrogen Carbonate with production of Sodium Ethanoate and producing Carbon-di-oxide gas.
$CH_3 COOH+NaHCO_3 \longrightarrow CH_3 COONA+H_2 O+CO_2$
Here salt X is Sodium Ethanoate and gas eveolved is Carbon-di-oxide.
Activity
- Set up the experiment as shown in figure.
- Take a spoon full of Sodium Hydrogen Carbonate in a test-tube and add $2 ml$ of dilute ethanoic acid.
- Brisk effervescence occur in testtube.
- Pass the produce gas into lime water
- Lime water turn milky confirming the evolution of $CO_2$
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.
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Answer
a) Compounds of Carbon and hydrogen are called as Hydrocarbons. Ex: Ethane, Methane
b) All the bond in saturated Hydrocarbons are single bonds whereas bonds in the unsaturated Hydrocarbons are either double or triple bonds.
Saturated Hydrocarbon Ex: Ethane, Methane
Unsaturated Hydrocarbons-Ethyne, Ethene
c) Functional groups are set of atoms joined in a specific manner which are responsible for characteristic chemical property of the compound.Ex: CHO-Aldehyde, OH-Hydroxyl, COOH- Carboxylic acid.
49. Name the reaction which is commonly used in the conversion of vegetable oils to fats. Explain the reaction involved in detail.
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Answer
Addition reaction is involved in the conversion of oils into fats. This process is known as Hydrogenation. Here Unsaturated vegetable are converted to saturated fats which have saturated carbons.
Nickel is used as a catalyst in the hydrogenation process and the reaction is given below
50. (a) Write the formula and draw electron dot structure of carbon tetrachloride.
(b) What is saponification? Write the reaction involved in this process.
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Answer
a) Carbon tetra chloride- $CCl_4$
b) The reaction of an ester in the presence of base to give sodium salt of carboxylic acid and alcohol is known as saponification and it is used in the preparation of soap.
$ CH_3 COOC_2 H_5+NaOH \longrigharrow CH_3 COONa+C_2 H_5 OH $
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.
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Answer
In a test- tube take $1 ml$ ethanol and $1 ml$ glacial acetic acid and add few drops of concentrated $H_2 SO_4$. Warm the testtube for 5 minutes over a waterbath. Transfer the content in a beaker. Sweet smell confirms the formation of Ester.
${CH}_3 {COOH}+{CH}_3 {CH}_2 {OH} \xrightarrow{\text { Conc. } {H}_2 {SO}_4} {CH}_3 {CH}_2 {COOCH}_2 {CH}_3+{H}_2 {O}$
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, $C3H6O2$ ). 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.
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Answer
1) Compound $C$ is Ethanoic acid[Acetic acid]
It reacts with sodium metal to form a compound called R . R is Sodium Ethanoate.
$2 CH _3 COOH+2 Na \longrightarrow 2 CH _3 COONa+H _2$
2) $CH _3 COOH+C _2 H 5 OH \xrightarrow{\text{ conc, } H _2 SO _4} CH _3 COOC _2 H _5+H _20$
so compound S is Ester or Ethyl ethanoate and compound A is Ethanol
3) $CH _3 COOC _2 H _5+NaOH \longrightarrow CH _3 COONa+C _2 H _5 OH$.
so compound $R$ is again Sodium Ethanoate.
So compound C is Ethanoic acid
A is Ethanol
$S$ is EsterR is sodium Ethanoate.
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?
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Answer
a) Calcium Hydroxide solution would become milky
b) Reaction in Tube $A$
$CH_3 COOH+NAHCO_3 \longrightarrow CH_3 COONA+CO_2+H_2 O$
Reaction in tube B
$Ca(OH)_2+CO_2 \longrightarrow CaCO_3+H_2 O$
c) Ethanol will not react with Sodium Hydrgen carbonate. Hence same change will not be observed.
d) In a beaker take distilled water and mix Calcium carbonate powder and mix thoroughly. Allow the solution to settle and decant the clear solution to obtain the lime water.
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.
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Answer
a) Ethene is formed when ethanol is heated at $443 K$ with excess of concentrated sulphuric acid.
${CH_3CH_2OH} \xrightarrow{{Conc. H_2SO_4}} {CH_2=CH + H_2O}$
b) Propanol is treated with alkaline Potassium permanganate or acidified Potassium-di-chromate to obtain propanoic acid.
$CH_3 CH_2 CH_2 OH\xrightarrow{ \text{Alk } {KMnO} / \text{acidified } K _2 Cr _2 O_7 } CH_3 CH_2 COOH$
55. Draw the possible isomers of the compound with molecular formula $C _3H _6O$ and also give their electron dot structures.
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Answer
(ii) Electron dot structure of propanal.
Electron dot structure of propanone
(i) The two possible isomers of the compound with molecular formula $C_2 H_6 O$ are :
(ii) Electron dot structure of propanal.
Electron dot structure of propanone
56. Explain the given reactions with the examples
(a) Hydrogenation reaction
(b) Oxidation reaction
(c) Substitution reaction
(d) Saponification reaction
(e) Combustion reaction
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Answer
(a) Hydrogenation reaction:
In hydrogenation reaction is defined as a reaction in which the addition of hydrogen takes place in the presence of a catalyst. Example of hydrogenation reaction:
$\underset{\text { (Ethene) }}{{CH}_2={CH}_2({~g})}+\underset{\text { (Hydrogen) }}{{H}_2({~g})} \rightarrow \underset{\text { (Ethane) }}{{CH}_3-{CH}_3({~g})}$
In the above reaction, hydrogen is added to the Ethene molecule, and it gets converted to ethane by breaking a double bond.
(b) Oxidation reaction:
Oxidation reaction can be defined as the addition of oxygen to a compound, loss of electrons, and removal of hydrogen.
1. Example of addition of oxygen :
$$ \underset{\text{Magnesium}}{2 {Mg}({s})}+\underset{\text{Oxygen}}{{O}_2({~g})} \rightarrow 2 \underset{\text{Magnesium oxide}}{{MgO}({s})} $$
The addition of oxygen to Magnesium forms Magnesium oxide.
2. Example of loss of electrons:
$$ \underset{\text{Zinc}}{{Zn}({s})}+\underset{\text { Copper sulphate }}{{CuSO}_4({aq})} \rightarrow \underset{\text { Zinc sulphate }}{{ZnSO}_4({aq})}+\underset{\text{Copper}}{{Cu}({s})} $$
In the above reaction, zinc loses electrons to form Zinc sulphate.
The oxidation state of Zinc is changed from ${O}$ to +2 .
3. Example of removal of hydrogen:
$$ \underset{\text { Hydrogen sulphide }}{2 {H}_2 {~S}({~g})}+ \underset{\text { Oxygen }}{3 {O}_2({~g})} \rightarrow \underset{\text { Water }}{2 {H}_2 {O}({aq})}+ \underset{\text { Sulphur dioxide }}{2 {SO}_2({~g}) } $$
Hydrogen sulphide gas reacts with oxygen to form water and Sulphur dioxide. In the above reaction, hydrogen is removed from Hydrogen sulphide to give sulphur dioxide.
(c) Substitution reaction:
In this reaction, one functional group in a chemical compound is replaced by another functional group
Example:
$ \underset{\text{Methane}}{{CH}_4({~g})}+\underset{\text{Chlorine}}{{Cl}_2({~g})} \rightarrow \underset{\text{Methyl chloride}}{{CH}_3 {Cl} {(g)}} +\underset{\text{Hydrogen chloride}}{{HCl} {(g)}} $
In the above reaction hydrogen is substituted by chlorine.
(d) Saponification reaction:
Saponification is the process of converting ester into alcohol and soap by the action of alkali.
In saponification reaction hydrolysis of an ester takes place with a base to give alcohol and sodium or potassium salt of carboxylic acid.
Example:
$$ \underset{\text{Ethyl ethanoate}}{{CH}_3 {COOC}_2 {H}_5({l})}+\underset{\text{sodium hydroxide}}{{NaOH}({l})} \rightarrow \underset{\text{Ethanol}}{{C}_2 {H}_5 {OH}({l})}+\underset{\text{Sodium ethanoate}}{{CH}_3 {COONa}({s})} $$
In the above reaction, ester reacts with a base to form alcohol and salt of carboxylic acid.
(e) Combustion reaction:
In combustion reaction substance reacts with oxygen, to form carbon dioxide and water. It is an exothermic reaction.
Example: $$ \underset{\text{Methane}}{{CH}_4({~g})}+\underset{\text{oxygen}}{2 {O}_2({~g})} \rightarrow \underset{\text{water}}{2 {H}_2 {O}({l})}+\underset{\text{carbon dioxide}}{{CO}_2({~g})} $$
In the above reaction combustion of methane takes place in the presence of oxygen to form carbon dioxide and water.
Hence,
(a)Hydrogenation reaction: It involves the addition of hydrogen.
(b) Oxidation reaction: It involves the addition of oxygen.
(c) Substitution reaction: It involves the substitution of one functional group over another.
(d) Saponification reaction: It involves the formation of soap.
(e) Combustion reaction: It involves a reaction with oxygen releasing energy in the form of heat and light.
57. An organic compound $A$ on heating with concentrated $H _2 SO _4$ 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 $H _2 O$. Identify the compounds $A, B$ and $C$ and write the chemical equations of the reactions involved.
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Answer
Compound $A$ is Ethanol
Compound $A=CH_3 CH_2 OH$
$CH_3 CH_2 OH \xrightarrow{ {conc. H_2 SO_4}} CH_2-CH_2+H_2 O$
Compound B is Ethane
Compound $B=CH_2=CH_2$
$CH_2=CH_2 \xrightarrow{Ni} C_2 H_6$
Compound $C=CH _3-CH _3$
$2 C_2 H_6+7 O_2 \longrightarrow 4 CO_2+6 H_2 O$
