CBSE Class 10 Science HOTs Carbon And its Compounds Set 07

Question. Write the equation for the preparation of ethylene from ethyl alcohol.
Answer: \( \text{C}_2\text{H}_5\text{OH} \xrightarrow{\text{Conc. H}_2\text{SO}_4} \text{C}_2\text{H}_4 + \text{H}_2\text{O} \)

Question. State the general formula for a saturated hydrocarbon and give one example and structural formula of the same.
Answer: General formula for a saturated hydrocarbon (alkanes): \( \text{C}_n\text{H}_{2n+2} \).
Example of saturated hydrocarbons (alkanes): \( \text{CH}_4 \) (Methane).
Structural formula of \( \text{CH}_4 \) (Methane):

  H
  |
H-C-H
  |
  H

Question. Name a compound which will give acetylene gas when treated with water.
Answer: \( \text{CaC}_2 \) (calcium carbide)

Question. Define the term ‘catenation’.
Answer: It is the property of elements by virtue of which atoms of the element can link to each other to form chains or rings of different sizes.

Question. State the term for: – Compounds having the same general formula, and similar chemical properties.
Answer: Homologous series.

Question. Draw the structural formula of a compound with two carbon atoms in each of the following cases:
1. An alkane with a carbon to carbon single bond.
2. An alcohol containing two carbon atoms.
3. An unsaturated hydrocarbon with a carbon to carbon triple bond.
Answer:
1. An alkane with a carbon to carbon single bond (ethane):

  H   H
  |   |
H-C - C-H
  |   |
  H   H

2. An alcohol containing two carbon atoms (ethanol):

  H   H
  |   |
H-C - C-OH
  |   |
  H   H

3. An unsaturated hydrocarbon with a carbon to carbon triple bond (ethyne):

H - C ≡ C - H

Question. Ethane, Ethene, Ethanoic acid, Ethyne, Ethanol — From the compounds, name:
1. The compound with — OH and with — COOH,
2. Homologue of homologous series with general formula \( \text{C}_n\text{H}_{2n} \).
Answer:
1. Compound with — OH group: Ethanol (\( \text{C}_2\text{H}_5\text{OH} \))
2. Compound with — COOH group: Ethanoic acid (\( \text{CH}_3\text{COOH} \))
3. Homologue of homologous series with G.F. \( \text{C}_n\text{H}_{2n} \): Ethene (\( \text{C}_2\text{H}_4 \))

Question. Write the equations for the following laboratory preparations:
1. Ethane from Sodium propionate.
2. Ethene from Iodoethane.
3. Ethyne from Calcium carbide.
4. Methanol from Iodomethane.
Answer:
1. \( \text{C}_2\text{H}_5\text{COONa} + \text{NaOH} \rightarrow \text{C}_2\text{H}_6 + \text{Na}_2\text{CO}_3 \)
2. \( \text{C}_2\text{H}_5\text{I} + \text{alcoholic KOH} \rightarrow \text{C}_2\text{H}_4 + \text{KI} + \text{H}_2\text{O} \)
3. \( \text{CaC}_2 + 2\text{H}_2\text{O} \rightarrow \text{HC}\equiv\text{CH} + \text{Ca(OH)}_2 \)
4. \( \text{CH}_3\text{I} + \text{KOH (aq)} \rightarrow \text{CH}_3\text{OH} + \text{KI} \)

Question. Which one of the elements — Li, Be, B, C, O, F, Ne shows the property of catenation.
Answer: C (carbon).

Question. Write a balanced equation for:
1. Reaction of ethane and oxygen in presence of molybdenum oxide.
2. Preparation of \( \text{CH}_4 \) from anhydrous sodium ethanoate (sodium acetate).
3. Reaction of heating ethanol at 170° C in the presence of conc. \( \text{H}_2\text{SO}_4 \).
4. Preparation of carbon tetrachloride from methane.
Answer:
1. \( 2\text{C}_2\text{H}_6 + 2\text{O}_2 \xrightarrow{\text{MoO}} 2\text{CH}_3\text{CHO} + 2\text{H}_2\text{O} \)
2. \( \text{CH}_3\text{COONa} + \text{NaOH} \xrightarrow{\text{CaO}, \Delta} \text{CH}_4 + \text{Na}_2\text{CO}_3 \)
3. \( \text{C}_2\text{H}_5\text{OH} \xrightarrow{\text{Conc. H}_2\text{SO}_4, 170^\circ\text{C}} \text{C}_2\text{H}_4 + \text{H}_2\text{O} \)
4. \( \text{CH}_4 + 4\text{Cl}_2 \xrightarrow{\text{CuCl}_2, \Delta} \text{CCl}_4 + 4\text{HCl} \)

Question. Give the IUPAC name and the functional group for:
1. \( \text{CH}_3 - \text{CH}_2 - \text{CHO} \)
2. \( \text{H}_3\text{C} - \text{CH}_2 - \text{CH}_2 - \text{OH} \)
Answer:
1. IUPAC name: Propanal | Functional group: \( -\text{CHO} \) (Aldehydic group)
2. IUPAC name: Propan-1-ol | Functional group: \( -\text{OH} \) (Alcoholic group)

Question. Draw the structural formula of ethyne. How does the structure of alkynes differ from that of alkenes.
Answer: Structural formula of ethyne: \( \text{H}-\text{C}\equiv\text{C}-\text{H} \).
In alkynes there are triple covalent bonds (\( -\text{C}\equiv\text{C}- \)) but in alkenes there are double covalent bonds (\( \text{C}=\text{C} \)).

Question. Fill in the blanks with the correct words:
Alkenes are the_______ (analogous / homologous) series of_______ (saturated / unsaturated) hydrocarbons. They differ from alkanes due to the presence of_______ (double / single) bonds. Alkenes mainly undergo________ (addition / substitution) reactions.
Answer: Alkenes are the homologous series of unsaturated hydrocarbons. They differ from alkanes due to the presence of double bonds. Alkenes mainly undergo addition reactions.

Question. Draw the structural formulae of the two isomers of Butane. Give the correct IUPAC name of each.
Answer:
1. butane (n-butane):

  H   H   H   H
  |   |   |   |
H-C - C - C - C-H
  |   |   |   |
  H   H   H   H

2. 2-methylpropane (isobutane):

  H   H   H
  |   |   |
H-C - C - C-H
  |   |   |
  H   |   H
    H-C-H
      |
      H

Question. Give the IUPAC names of the compounds numbered (i) to (v).
1. \( \text{CH}_3-\text{C}\equiv\text{CH} \)
2. \( \text{CH}_3-\text{CH}_2-\text{CH(OH)}-\text{CH}_2-\text{CH}_3 \)
3. \( \text{CH}_3-\text{CH(CH}_3)-\text{CH}_3 \)
4. \( \text{CH}_3-\text{COOH} \)
5. \( \text{CH}_2\text{Cl}-\text{CH}_2\text{Cl} \)
Answer:
1. Propyne
2. Pentan-3-ol
3. 2-Methylpropane
4. Ethanoic acid
5. 1,2-Dichloroethane

Question. Copy and complete the table which relates to three homologous series of Hydrocarbons:

Answer:

Question. Name the type of reaction by which X (compound of C and Br) can be prepared from ethane.
Answer: By substitution reactions.

Question. The formation of 1, 2-dibromoethane from ethene and bromine is an example of :
(a) Substitution
(b) Dehydration
(c) Dehydrohalogenation
(d) Addition
Answer: (d) Addition

Question. Name the organic compound prepared by each of the following reactions:
1. \( \text{C}_2\text{H}_5\text{COONa} + \text{NaOH} \rightarrow \)
2. \( \text{CH}_3\text{I} + 2[\text{H}] \rightarrow \)
3. \( \text{C}_2\text{H}_5\text{Br} + \text{KOH (alcoholic soln.)} \rightarrow \)
4. \( \text{CaC}_2 + 2\text{H}_2\text{O} \rightarrow \)
Answer:
1. Ethane
2. Methane
3. Ethene
4. Acetylene (Ethyne)

Question. Write the equation for the following:
1. Calcium carbide and water
2. Ethene and water (steam)
3. Bromoethane and an aqueous solution of sodium hydroxide
Answer:
1. \( \text{CaC}_2 + 2\text{H}_2\text{O} \rightarrow \text{Ca(OH)}_2 + \text{C}_2\text{H}_2 \)
2. \( \text{C}_2\text{H}_4 + \text{H}_2\text{O} \rightarrow \text{C}_2\text{H}_5\text{OH} \)
3. \( \text{C}_2\text{H}_5\text{Br} + \text{NaOH(aq)} \rightarrow \text{C}_2\text{H}_5\text{OH} + \text{NaBr} \)

Question. Distinguish between the saturated hydrocarbon ethane and the unsaturated hydrocarbon ethene by drawing their structural formulae.
Answer:
Saturated hydrocarbon (ethane):

  H   H
  |   |
H-C - C-H
  |   |
  H   H
(Single bond)

Unsaturated hydrocarbon (ethene):

  H   H
  |   |
H-C = C-H
(Double bond)

Question. Which type of reaction i.e. addition or substitution is shown by ethane and ethene ?
Answer: ethane \(\rightarrow\) Substitution, ethene \(\rightarrow\) addition reaction

Question. Write the equation for the complete combustion of ethane.
Answer: \( 2\text{C}_2\text{H}_6 + 7\text{O}_2 \rightarrow 4\text{CO}_2 + 6\text{H}_2\text{O} + \Delta \)

Question. Name the alcohol, aldehyde and acid formed when ethane is oxidised.
Answer: Alcohol obtained from ethane is ethyl alcohol [\( \text{C}_2\text{H}_5\text{OH} \)]. The aldehyde obtained from ethane is acetaldehyde [\( \text{CH}_3\text{CHO} \)]. The acid obtained from ethane is acetic acid [\( \text{CH}_3\text{COOH} \)].

Question. Why is pure acetic acid known as glacial acetic acid ?
Answer: Pure acetic acid is known as glacial acetic acid because it freezes below 16.5°C to an icy mass (glacier).

Question. What type of compound is formed by the reaction between acetic acid and an alcohol ?
Answer: Ester is formed by the reaction between acid and an alcohol.
\( \text{CH}_3\text{COOH} + \text{C}_2\text{H}_5\text{OH} \xrightarrow{\text{Conc. H}_2\text{SO}_4} \text{CH}_3\text{COOC}_2\text{H}_5 + \text{H}_2\text{O} \) (Ethyl ethanoate)

Question. By what type of reaction could a compound containing C, H and Cl be obtained from ethyne ?
Answer: Addition reaction.
\( \text{CH}\equiv\text{CH} + \text{Cl}_2 \rightarrow \text{CHCl}=\text{CHCl} \xrightarrow{\text{Cl}_2} \text{CHCl}_2-\text{CHCl}_2 \) (1,1,2,2-tetrachloroethane)

Question. State the term for the reaction in which the hydrogen of an alkane is replaced by chlorine.
Answer: Substitution reaction.

Question. Which of the following statements is wrong about alkanes ?
(a) They are all saturated hydrocarbons.
(b) They can undergo addition as well as substitution reaction.
(c) They are almost non polar in nature.
(d) On complete combustion give out carbon dioxide and water.
Answer: (b) They can undergo addition as well as substitution reaction.

Question. Write balanced equation for : Acetic acid is warmed with ethanol in the presence of conc. \( \text{H}_2\text{SO}_4 \).
Answer: \( \text{CH}_3\text{COOH} + \text{C}_2\text{H}_5\text{OH} \xrightarrow{\text{Conc. H}_2\text{SO}_4} \text{CH}_3\text{COOC}_2\text{H}_5 + \text{H}_2\text{O} \)

Question. Find the odd one out in each case and explain your choice.
1. \( \text{C}_3\text{H}_8 \), \( \text{C}_5\text{H}_{10} \), \( \text{C}_2\text{H}_6 \), \( \text{CH}_4 \)
2. Formic acid, Nitric acid, Acetic acid, Propanoic acid.
Answer:
1. \( \text{C}_5\text{H}_{10} \) [All others are alkanes, this is an alkene]
2. Nitric acid [This is the only inorganic acid, rest all are organic acids]

Question. Identify the substance 'S' based on the information given below:
The reddish brown liquid 'S' is dissolved in water. When ethyne gas is passed through it, it turns colourless.
Answer: Bromine solution

Question. Fill in the blanks with the correct words from the brackets.
Generally ionic compounds exist in (i) _______________ (solid/liquid/gas) state. Melting and boiling points of covalent compounds are generally (ii) _______________ (low/high). The general formula for alkane is (iii) _______________ (\( \text{C}_n\text{H}_{2n} \) / \( \text{C}_n\text{H}_{2n-2} \) / \( \text{C}_n\text{H}_{2n+2} \)). For alkynes the general formula is (iv) _______________ (\( \text{C}_n\text{H}_{2n} \) / \( \text{C}_n\text{H}_{2n-2} \) / \( \text{C}_n\text{H}_{2n+2} \)).
Answer:
(i) solid
(ii) low
(iii) \( \text{C}_n\text{H}_{2n+2} \)
(iv) \( \text{C}_n\text{H}_{2n-2} \)

Question. Give chemical equation for the following:
1. The laboratory preparation of methane from sodium acetate.
2. The reaction of one mole of ethene with one mole of chlorine gas.
3. The preparation of ethyne from 1, 2 – dibromoethane.
Answer:
1. \( \text{CH}_3\text{COONa} + \text{NaOH} \rightarrow \text{CH}_4 + \text{Na}_2\text{CO}_3 \)
2. \( \text{CH}_2=\text{CH}_2 + \text{Cl}_2 \rightarrow \text{CH}_2\text{Cl}-\text{CH}_2\text{Cl} \)
3. \( \text{CH}_2\text{Br}-\text{CH}_2\text{Br} + 2\text{KOH(alc)} \xrightarrow{\Delta} \text{CH}\equiv\text{CH} + 2\text{KBr} + 2\text{H}_2\text{O} \)

Question. State how the following conversions can be carried out:
1. Ethyl chloride to Ethyl alcohol.
2. Ethyl chloride to Ethene.
3. Ethene to Ethyl alcohol.
4. Ethyl alcohol to Ethene.
Answer:
1. By treating ethyl chloride with aqueous KOH.
2. By heating ethyl chloride with alcoholic KOH.
3. By passing ethene into concentrated \( \text{H}_2\text{SO}_4 \) at 80°C and high pressure or by hydration of ethene.
4. By heating ethyl alcohol with concentrated \( \text{H}_2\text{SO}_4 \) at 170°C.

Question. Define isomerism. Give the IUPAC name of the isomer \( \text{C}_4\text{H}_{10} \) which has a branched chain.
Answer: Isomerism: Organic compounds having the same molecular formula but different structural formulae are called isomers and this property is known as isomerism. Example: n-pentane & isopentane.
The branched chain isomer of \( \text{C}_4\text{H}_{10} \) is 2-Methylpropane:

  H   H   H
  |   |   |
H-C - C - C-H
  |   |   |
  H   |   H
    H-C-H
      |
      H

Question. The organic compound, which gives a red precipitate with ammoniacal cuprous chloride and undergoes an addition reaction:
(a) Ethane
(b) Ethene
(c) Ethyne
(d) Ethanol
Answer: (c) Ethyne

Question. The organic compound which when mixed with ethyl alcohol [ethanol], makes it spurious:
(a) Methanol
(b) Methanoic acid
(c) Methanal
(d) Ethanoic acid
Answer: (a) Methanol

Question. Draw the structural formula of:
1. Ethanoic acid
2. But-2-yne
Answer:
1. Ethanoic acid:

  H   O
  |  //
H-C-C-OH
  |
  H

2. But-2-yne:

  H           H
  |           |
H-C-C ≡ C-C-H
  |           |
  H           H

Question. Compound 'X' is bubbled through bromine dissolved in \( \text{CCl}_4 \) and the product formed is \( \text{CH}_2\text{Br}-\text{CH}_2\text{Br} \).
1. Draw the structural formula of X and state what type of reaction X has undergone.
2. State your observation for the above reaction.
3. Name the compound formed when steam reacts with X in the presence of phosphoric acid.
4. What is the procedure for converting the product back to X ?
Answer:
1. Structural formula of X (Ethene):

H-C = C-H
  |   |
  H   H

The above reaction is called an addition reaction.
2. The reddish-brown colour of bromine fades (turns colourless).
3. Ethanol (\( \text{CH}_3\text{CH}_2\text{OH} \)) is formed.
\( \text{CH}_2=\text{CH}_2 + \text{H}_2\text{O} \xrightarrow{\text{Phosphoric acid}} \text{CH}_3-\text{CH}_2-\text{OH} \)
4. Ethanol can be converted back to ethene by dehydrating it with concentrated sulphuric acid at 170°C.

\( \text{C}_2\text{H}_5\text{OH} \xrightarrow[\text{300}^\circ\text{C}]{\text{Al}_2\text{O}_3} \text{C}_2\text{H}_4 + \text{H}_2\text{O} \)
Ethanol                         Ethene

Question. Name a gaseous hydrocarbon commonly used for welding purposes.
Answer: Acetylene

Question. Give reasons for the following –
1. almost 90% of all known compounds are organic in nature.
2. it is dangerous to burn methane in an insufficient supply of air.
Answer:
1. Because of the ability of carbon to catenate i.e., form straight chain, branched chains or ring-like compounds.
2. Because carbon monoxide is produced in an insufficient supply of air. This gas is extremely poisonous for human beings as it cuts off the oxygen supply by forming carboxy haemoglobin in the blood.

Question. The functional group present in acetic acid is:
(a) Ketonic \( \text{C} = \text{O} \)
(b) Hydroxyl -OH
(c) Aldehydic – CHO
(d) Carboxyl – COOH
Answer: (d) Carboxyl – COOH

Question. Unsaturated hydrocarbons undergo :
(a) a substitution reaction
(b) an oxidation reaction
(c) an addition reaction
(d) None of the options
Answer: (c) an addition reaction

Question. The number of \( \text{C}-\text{H} \) bonds in ethane molecule are:
(a) Four
(b) Six
(c) Eight
(d) Ten
Answer: (b) Six

Question. The catalyst used for conversion of ethene to ethane is commonly……… [nickel/iron/cobalt]
Answer: Nickel

Question. Acetaldehyde when oxidized with acidified potassium dichromate, forms ……… [ester/ethanol/acetic acid]
Answer: Acetic acid

Question. Ethanoic acid reacts with ethanol in presence of conc. \( \text{H}_2\text{SO}_4 \), so as to form a compound and water. The chemical reaction which takes place is called………… [dehydration/hydrogenation/esterification]
Answer: Esterification

Question. Write the balanced chemical equation for the reaction taking place between 1, 2 – dibromoethane and alcoholic potassium hydroxide.
Answer: \( \underset{\text{1, 2- dibromo ethane}}{\text{CH}_2(\text{Br})-\text{CH}_2(\text{Br})} + 2\text{KOH(alc.)} \rightarrow \text{CH} \equiv \text{CH (Acetylene)} + 2\text{KBr} + 2\text{H}_2\text{O} \)

Question. Write the balanced chemical equation when monochloro ethane is hydrolysed with aqueous KOH.
Answer: \( \underset{\text{Monochloro ethane}}{\text{CH}_3\text{CH}_2\text{Cl}} + \text{KOH(aq)} \rightarrow \underset{\text{Ethanol}}{\text{CH}_3\text{CH}_2\text{OH}} + \text{KCl} \)

Question. Write the balanced chemical equation when a mixture of sodalime and sodium acetate is heated.
Answer: \( \underset{\text{Sodium Ethanoate}}{\text{CH}_3\text{COONa}} + \text{NaOH} \xrightarrow{\text{CaO}} \text{Na}_2\text{CO}_3 + \text{CH}_4 \uparrow \ (\text{Methane}) \)

Question. Write the balanced chemical equation when ethanol under high pressure and low temperature is treated with acidified potassium dichromate.
Answer: \( \underset{\text{Ethanol}}{\text{CH}_3\text{CH}_2\text{OH}} \xrightarrow[\text{K}_2\text{Cr}_2\text{O}_7 / \text{H}_2\text{SO}_4]{2[\text{O}]} \underset{\text{Ethanoic acid}}{\text{CH}_3\text{COOH}} + \text{H}_2\text{O} \)

Question. Write the balanced chemical equation when water is added to calcium carbide.
Answer: \( \underset{\text{Calcium carbide}}{\text{CaC}_2} + 2\text{H}_2\text{O} \rightarrow \text{Ca(OH)}_2 + \text{CH} \equiv \text{CH} \ (\text{Acetylene}) \)

Question. Write the balanced chemical equation when ethanol reacts with sodium at room temperature.
Answer: \( \underset{\text{Ethanol}}{2\text{C}_2\text{H}_5\text{OH}} + 2\text{Na} \rightarrow \underset{\text{Sodium ethoxide}}{2\text{C}_2\text{H}_5\text{ONa}} + \text{H}_2 \uparrow \)