3.Carbon and Its Compounds
Very Short Answer Type Questions for Class 10 CBSE - Carbon and Its Compounds, along with answers:
1.
Q: Name the gas evolved when ethanoic acid is added to sodium carbonate. How would you prove the presence of this gas?
A: The gas evolved is carbon dioxide (CO₂). It can be confirmed by passing it through lime water, which turns milky.
2.
Q: Which of the following will give brisk effervescence with sodium hydrogencarbonate and why?
CH₃COOH, CH₃CH₂OH
A: CH₃COOH (ethanoic acid) will give brisk effervescence because it reacts with NaHCO₃ to release CO₂ gas. Ethanol (CH₃CH₂OH) does not react with NaHCO₃.
3.
Q: Name the functional group present in an organic compound which gives brisk effervescence with NaHCO₃.
A: Carboxylic acid group (–COOH)
4.
Q: Name the hydrocarbon formed when ethanol is heated with conc. H₂SO₄ at 170°C. What is this reaction known as?
A: The hydrocarbon formed is ethene (C₂H₄). This reaction is called dehydration of ethanol.
5.
Q: Why does ethyne (acetylene) burn with a sooty flame?
A: Because ethyne is an unsaturated hydrocarbon with a higher carbon content, leading to incomplete combustion and formation of soot.
6.
Q: Name the product formed when hydrogen is added to ethene.
A: Ethane (C₂H₆)
7.
Q: Explain why ethene decolourises bromine water whereas ethane does not.
A: Ethene is unsaturated and adds bromine across the double bond, decolourising bromine water. Ethane is saturated and does not react.
8.
Q: Name two catalysts which can be used in the hydrogenation of unsaturated compounds.
A: Nickel (Ni) and Palladium (Pd)
9.
Q: State two disadvantages of incomplete combustion.
A:
- It produces carbon monoxide, a poisonous gas.
- It results in less energy and sooty flames.
10.
Q: What happens when sodium reacts with ethanol? (Give chemical equation)
A:
Sodium ethoxide and hydrogen gas are formed.
11.
Q: Describe one reaction of ethanol.
A: Ethanol reacts with acetic acid in the presence of concentrated H₂SO₄ to form an ester (ethyl ethanoate):
12.
Q: Name one liquid carbon compound used as an additive in petrol in some countries.
A: Ethanol
13.
Q: What are the raw materials required for making soap in a laboratory (or at home)?
A: Vegetable oil (or animal fat), sodium hydroxide (NaOH), and water
14.
Q: Would you be able to check whether water is hard by using a detergent? Why?
A: No, because detergents work well in hard water, unlike soap which forms scum.
15.
Q: Describe a test for carboxylic acids.
A: Add sodium bicarbonate (NaHCO₃). Brisk effervescence of CO₂ gas confirms a carboxylic acid.
16.
Q: Why is the conversion of ethanol into ethanoic acid an oxidation reaction?
A: Because oxygen is added during the conversion of ethanol to ethanoic acid.
17.
Q: Explain why alkanes are excellent fuels.
A: Alkanes undergo complete combustion producing a large amount of heat energy and no smoke.
18.
Q: Name one chemical compound which can be used to distinguish between ethanol and ethanoic acid.
A: Sodium bicarbonate (NaHCO₃) – only ethanoic acid gives effervescence.
19.
Q: Complete following equations:
(a) CH₃CH₂OH → (Conc. H₂SO₄, 170°C)
A:
(b) CH₃COOH + C₂H₅OH → (Conc. H₂SO₄)
A:
20.
Q: Complete and balance the following equations:
(a) CH₄ + O₂ →
A:
(b) CH₄ + Cl₂ → (Sunlight)
A:
21.
Q: Fill in the following blanks with suitable words:
(a) The process of burning of a hydrocarbon in the presence of air to give CO₂, H₂O, heat and light is known as combustion.
(b) The sodium salt of a long chain fatty acid is called soap.
(c) Detergent is better than soap for washing clothes when the water is hard.
(d) The organic acid present in vinegar is acetic acid (or ethanoic acid).
Short Answer Type Questions with Answers for Class 10 CBSE (Carbon and Its Compounds, Q.22–45):
22. Which of the following hydrocarbons will give substitution reactions and why?
Hydrocarbons:
C₃H₈, C₄H₆, C₅H₁₂, C₅H₁₀, C₃H₆, CH₄
Answer:
Hydrocarbons that are saturated (alkanes) undergo substitution reactions.
Hence, CH₄ (methane), C₃H₈ (propane), and C₅H₁₂ (pentane) will undergo substitution reactions because they are alkanes with single bonds only.
23. Which of the following will give addition reactions and why?
Hydrocarbons:
C₂H₄, C₃H₄, C₂H₆, C₄H₁₀, CH₄, C₃H₈
Answer:
Unsaturated hydrocarbons (alkenes and alkynes) undergo addition reactions.
Hence, C₂H₄ (ethene) and C₃H₄ (propyne) will give addition reactions because they contain double/triple bonds.
24. (a) Write the chemical equation of the reaction which takes place during the burning of ethanol in air.
(b) Why is ethanol used as a fuel?
(c) State two uses of ethanol (other than as a fuel).
Answer:
(a) C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O + heat
(b) Ethanol burns with a clean flame and releases a good amount of energy, making it a clean fuel.
(c)
- Used in hand sanitizers.
- Used as a solvent in medicines and perfumes.
25. (a) What happens when propanoic acid is warmed with methanol in presence of conc. H₂SO₄?
(b) What change will you observe if you test soap solution with red and blue litmus paper?
(c) What is denatured alcohol? Why is it needed?
Answer:
(a) Esterification occurs.
CH₃CH₂COOH + CH₃OH → CH₃CH₂COOCH₃ + H₂O
(b) Soap solution turns red litmus blue as it is basic. No change with blue litmus.
(c) Denatured alcohol is ethanol mixed with toxic substances to make it undrinkable. It prevents misuse for consumption.
26. (a) How would you test for an alcohol?
(b) Give the harmful effects of drinking alcohol.
(c) Why is methanol more dangerous than ethanol?
Answer:
(a) React with sodium: alcohol liberates hydrogen gas (effervescence).
(b) Liver damage, addiction, impaired judgment.
(c) Methanol is toxic and gets converted to formaldehyde in the body, which can cause blindness or death.
27. Convert the following: (a) Ethanol to ethene, (b) Propanol to propanoic acid. Name the process and write the equations.
Answer:
(a) Dehydration:
C₂H₅OH → C₂H₄ + H₂O (using conc. H₂SO₄ at 170°C)
(b) Oxidation:
CH₃CH₂CH₂OH + [O] → CH₃CH₂COOH (using acidified KMnO₄)
28. (a) Why adjust gas burner air holes when vessels get blackened?
(b) Why do synthetic detergents pollute water?
Answer:
(a) To allow complete combustion. Incomplete combustion produces carbon soot.
(b) Detergents are non-biodegradable and remain in water, harming aquatic life.
29. (a) Observation when KMnO₄ is added to warm ethanol?
(b) How to distinguish between alcohol and carboxylic acid?
Answer:
(a) Purple KMnO₄ gets decolorized. Ethanoic acid is formed:
C₂H₅OH + 2[O] → CH₃COOH + H₂O
(b) Add NaHCO₃: acid gives brisk effervescence; alcohol doesn’t.
30. Name functional group that can be hydrogenated. Explain with example and condition. One natural source?
Answer:
Alkenes (–C=C–) undergo hydrogenation.
Example: C₂H₄ + H₂ → C₂H₆ (with Ni catalyst at 200°C)
Change: liquid oil becomes solid fat.
Natural source: vegetable oils.
31. (a) Gas evolved when ethanol reacts with sodium?
(b) What is formed when carboxylic acid reacts with alcohol + conc. H₂SO₄?
(c) What is observed when ethanoic and HCl are tested with universal indicator?
Answer:
(a) Hydrogen gas (H₂)
(b) Ester (RCOOR') is formed
(c) Both turn the paper red (acidic), but HCl shows stronger acidity.
32. (a) What type of compound is CH₃COOH?
(b) What is oxidised to get CH₃COOH?
(c) State of CH₃COOH?
(d) One advantage of soaps over detergents?
Answer:
(a) Carboxylic acid
(b) Ethanol
(c) Liquid
(d) Soaps are biodegradable.
33. (a) Ethanol + Ethanoic acid + H₂SO₄ = ?
(b) What happens when ethanol is heated with conc. H₂SO₄ at 170°C?
Answer:
(a) Ester is formed: CH₃COOC₂H₅ (ethyl ethanoate)
(b) Dehydration to ethene:
C₂H₅OH → C₂H₄ + H₂O
34. (a) Ethanol + KMnO₄ → ?
(b) Which turn blue litmus red: HCHO, CH₃COOH, CH₃OH, C₂H₅OH, HCOOH, CH₃CHO? Why?
Answer:
(a) CH₃COOH is formed
(b) CH₃COOH and HCOOH – because they are carboxylic acids (acidic).
35. (a) Preparation of soap in lab?
(b) Why is NaCl added?
(c) Why not use soap in hard water?
Answer:
(a) Boil fat/oil with NaOH → soap + glycerol (saponification)
(b) To precipitate soap
(c) Soap forms scum with hard water (Ca²⁺/Mg²⁺).
36. (a) Methane burns in air? Equation?
(b) Ethanoic acid + Na₂CO₃ = ?
(c) Test between butter and oil?
Answer:
(a) CH₄ + 2O₂ → CO₂ + 2H₂O
(b) CH₃COOH + Na₂CO₃ → CH₃COONa + CO₂ + H₂O
(c) Bromine water test: oil decolorizes it, butter doesn’t (unsaturation test).
37. (a) Reaction for saturated hydrocarbon?
(b) What is oxidising agent? Examples?
(c) One reaction of carboxylic acid?
Answer:
(a) Substitution: CH₄ + Cl₂ → CH₃Cl + HCl
(b) Substances that add oxygen/remove H; KMnO₄, K₂Cr₂O₇
(c) CH₃COOH + NaOH → CH₃COONa + H₂O
38. (a) Examples of hydrocarbons:
Single bond: CH₄; Double bond: C₂H₄
Property: Alkanes—substitution; Alkenes—addition
(b) Detergent: Cleaning agent made from petrochemicals; Example: Sodium lauryl sulfate
(c) Detergents work in hard water.
39. (a) CH₃COOH + NaHCO₃ = ?
(b) Why are carbon compounds used as fuels?
(c) Better for hard water: soap or detergent?
Answer:
(a) CH₃COOH + NaHCO₃ → CH₃COONa + CO₂ + H₂O
(b) They burn easily and release high energy.
(c) Detergents, as they don’t form scum.
40. (a) What is substitution reaction? Example?
(b) How is soap made? Word equation?
Answer:
(a) Replacement of an atom; CH₄ + Cl₂ → CH₃Cl + HCl
(b) Fat/oil + NaOH → soap + glycerol
41. (a) Ethanoic acid from ethanol? Equation?
(b) Chemical test to distinguish ethanol & ethanoic acid?
(c) Why does scum form in hard water?
Answer:
(a) C₂H₅OH + [O] → CH₃COOH
(b) Add NaHCO₃: CO₂ from acid
(c) Ca²⁺/Mg²⁺ react with soap to form scum.
42. (a) Methane + chlorine? Equation?
(b) What is hydrogenation? Use?
(c) Two differences: soap vs detergent?
Answer:
(a) CH₄ + Cl₂ → CH₃Cl + HCl
(b) Addition of H₂ to unsaturated fats using Ni catalyst; makes vanaspati ghee
(c) Soaps: natural, not work in hard water; Detergents: synthetic, work in hard water
43. (a) CH₃COOH + NaOH = ?
(b) Vegetable oil + H₂ → ? Catalyst?
(c) Advantage & disadvantage of detergents?
Answer:
(a) CH₃COOH + NaOH → CH₃COONa + H₂O
(b) Solid fat (ghee); Ni catalyst
(c) Work in hard water; non-biodegradable
44. (a) X = CH₃COOH (acid, effervescence with NaHCO₃)
(b) Ethyne + air is explosive; with O₂ gives controlled flame
(c) Unsaturated hydrocarbon: Addition reaction
Example: C₂H₄ + H₂ → C₂H₆
45. (a) What is addition reaction? Example?
(b) What is added to groundnut oil?
(c) Which is healthier: butter or vegetable oil?
Answer:
(a) Reaction where atoms add across double/triple bonds.
C₂H₄ + H₂ → C₂H₆
(b) Hydrogen gas
(c) Vegetable oil—unsaturated fats are healthier.
Here are the Long Answer Type Questions with detailed answers for Class 10 CBSE - Chapter: Carbon and Its Compounds:
46. (a)
Question: When ethanoic acid reacts with sodium hydrogencarbonate, then a salt X is formed and a gas Y is evolved.
(i) Name the salt X and the gas Y.
(ii) Describe an activity with the help of a labelled diagram to prove the identity of gas Y.
(iii) Write the chemical equation of the reaction.
Answer:
(i)
- Salt X: Sodium ethanoate (CH₃COONa)
- Gas Y: Carbon dioxide (CO₂)
(ii)
Activity to identify CO₂ gas:
Materials Required:
- Test tube
- Delivery tube
- Lime water
- Sodium hydrogencarbonate
- Ethanoic acid
Procedure:
- Take a test tube and add a small amount of sodium hydrogencarbonate to it.
- Add ethanoic acid slowly to the test tube.
- Immediately fit the test tube with a cork and delivery tube that passes the gas into another test tube containing lime water.
Observation:
Effervescence is observed due to the release of CO₂ gas. The lime water turns milky, confirming the presence of CO₂.
Diagram:
[Ethanoic Acid + NaHCO₃] —> [CO₂] —> [Lime Water] → Milky
(iii)
Chemical Equation:
CH_3COOH + NaHCO_3 \rightarrow CH_3COONa + CO_2 + H_2O
(b)
Give any two uses of ethanoic acid:
- Used in the preparation of vinegar (5-8% solution in water).
- Used as a reagent in chemical industries for making esters, plastics, and dyes.
47. (a)
Question: Esters are sweet-smelling substances and are used in making perfumes.
(i) Describe an activity to prepare an ester with a labelled diagram.
(ii) Write the chemical equation.
(iii) Name all the substances involved.
Answer:
(i)
Activity to Prepare an Ester (Esterification):
Materials Required:
- Test tube
- Alcohol (e.g. ethanol)
- Carboxylic acid (e.g. ethanoic acid)
- Concentrated sulfuric acid (as catalyst)
- Water bath
Procedure:
- In a test tube, mix 1 mL ethanol and 1 mL ethanoic acid.
- Add a few drops of concentrated H₂SO₄.
- Place the test tube in a hot water bath for about 5 minutes.
- Smell the contents carefully after cooling.
Observation:
A sweet fruity smell is produced, indicating the formation of an ester.
Diagram:
(ii)
Chemical Equation:
(iii)
- Reactants: Ethanoic acid (CH₃COOH), Ethanol (C₂H₅OH)
- Catalyst: Concentrated sulfuric acid (H₂SO₄)
- Product: Ethyl ethanoate (ester) and water
(b)
Two uses of esters:
- Used in perfumes and flavouring agents due to their pleasant odour.
- Used in making artificial flavours and cosmetics.
48. (a)
Question: Name the reaction used to convert vegetable oils into fats. Explain it with a chemical equation.
Answer:
- Name of the reaction: Hydrogenation
- It is an addition reaction where hydrogen is added to unsaturated hydrocarbons in the presence of a nickel catalyst at high temperature to form saturated hydrocarbons.
Chemical Equation:
Explanation:
The double bonds (C=C) in unsaturated oils are converted to single bonds (C−C) by the addition of hydrogen, turning the oil into solid fat.
(b)
What is saponification? Write the chemical equation and name all substances involved.
Answer:
- Saponification is the process of making soap by hydrolysing esters (fats or oils) with alkali (NaOH or KOH).
Chemical Equation:
Substances Involved:
- Reactants: Fat/Oil (Ester), Sodium hydroxide (NaOH)
- Products: Soap, Glycerol (a by-product)
(c)
Why does micelle formation occur when soap is added to water? Will it form in ethanol?
Answer:
-
Micelle formation occurs because soap molecules have two ends:
- Hydrophobic (non-polar tail): repelled by water, attracted to oil/grease
- Hydrophilic (polar head): attracted to water
-
In water, the hydrophobic tails embed into grease, and hydrophilic heads remain in water forming micelles, which can be rinsed away.
-
Micelles do not form in ethanol because ethanol is not polar enough to allow the segregation of hydrophobic and hydrophilic ends.
49. (a)
Question: What is a soap? Name one soap.
Answer:
- A soap is a sodium or potassium salt of long-chain fatty acids.
- Example: Sodium stearate (C₁₇H₃₅COONa)
(b)
Describe the structure of a soap molecule with a diagram.
Answer:
- Soap molecule has two ends:
- Hydrophobic tail (long hydrocarbon chain) – repels water, dissolves in grease
- Hydrophilic head (carboxylate group -COO⁻) – attracts water
Diagram:
Hydrophobic Tail Hydrophilic Head
↓ ↓
CH₃–(CH₂)₁₆–COO⁻ ← Na
(c)
Explain the cleansing action of soap with diagrams.
Answer:
- Soap molecules surround the grease/oil particle with their hydrophobic tails pointing inward and hydrophilic heads pointing outward.
- They form a micelle around the dirt.
- These micelles get suspended in water and are washed away.
Diagrams:
1. Grease + Soap Molecules → Micelle Formation:
Micelle:
[COO⁻ COO⁻]
\ /
\___/ ← Grease trapped inside hydrophobic tails
/ \
[COO⁻ COO⁻]
2. Soap removes dirt with water:
- Micelle is lifted and rinsed off with water, cleaning the surface.
Multiple Choice Questions (MCQs) with correct answers and detailed explanations for each:
50. While cooking, if the bottom of the utensil is getting blackened on the outside, it means that:
✅ (b) the fuel is not burning completely.
Explanation:
Incomplete combustion of fuel produces soot (carbon particles), which blackens the utensil. Complete combustion produces only carbon dioxide and water.
51. When ethanol is heated with alkaline potassium permanganate solution, it gets converted into ethanoic acid. In this reaction, alkaline potassium permanganate acts as:
✅ (b) oxidising agent
Explanation:
Alkaline KMnO₄ provides oxygen to oxidise ethanol (CH₃CH₂OH) into ethanoic acid (CH₃COOH). Hence, it acts as an oxidising agent.
52. When ethanol is heated with concentrated sulphuric acid at 170°C, it gets converted into ethene. In this reaction, concentrated sulphuric acid acts as:
✅ (c) dehydrating agent
Explanation:
H₂SO₄ removes a water molecule from ethanol to form ethene (C₂H₄), an elimination reaction.
53. When a vegetable oil is treated with hydrogen in the presence of nickel (or palladium) catalyst, it forms a fat. This is an example of:
✅ (d) addition reaction
Explanation:
Unsaturated hydrocarbons (in vegetable oil) undergo addition of hydrogen (hydrogenation) to become saturated fats.
54. The soap molecule has a:
✅ (a) hydrophilic head and a hydrophobic tail
Explanation:
The hydrophilic (water-attracting) head is ionic, and the hydrophobic (water-repelling) tail is hydrocarbon-based. This helps in cleansing action.
55. Chlorine reacts with saturated hydrocarbons at room temperature in the:
✅ (b) presence of sunlight
Explanation:
Substitution reactions between chlorine and saturated hydrocarbons require UV light (from sunlight) to proceed.
56. In a soap micelle, the soap molecules are arranged radially with:
✅ (b) hydrocarbon ends directed towards the centre and ionic ends directed outwards
Explanation:
Micelles trap oil/dirt in the centre (hydrophobic tails), while the hydrophilic heads face outward into water.
57. When ethanol reacts with sodium metal, it forms two products. These products are:
✅ (d) sodium ethoxide and hydrogen
Explanation:
Sodium ethoxide and hydrogen gas are produced.
58. Vinegar is a solution of about:
✅ (b) 5 to 8 per cent ethanoic acid in water
Explanation:
Vinegar is a dilute solution of acetic acid (CH₃COOH) in water, commonly used in cooking and preservation.
59. One of the following substances is not added to make denatured alcohol. This is:
✅ (c) chloroform
Explanation:
Methyl alcohol, copper sulphate, and pyridine are common denaturants. Chloroform is not used for denaturing.
60. One of the following organic compounds cannot decolourise the red-brown colour of bromine water. This compound is:
✅ (c) C6H14
Explanation:
C₆H₁₄ is a saturated hydrocarbon (alkane). Only unsaturated hydrocarbons (alkenes/alkynes) decolourise bromine water.
61. The substance which can produce brisk effervescence with baking soda solution is:
✅ (c) vinegar
Explanation:
Vinegar (ethanoic acid) reacts with baking soda (NaHCO₃) to release CO₂ gas, producing brisk effervescence.
62. The chemical which is not required for the preparation of soap in the laboratory is:
✅ (b) baking soda
Explanation:
Soap is prepared using vegetable oil + caustic soda (NaOH). Baking soda (NaHCO₃) is not used.
63. Which of the following can damage optic nerve leading to blindness, if taken internally?
✅ (d) CH₂OH (methanol)
Explanation:
Methanol (CH₃OH) is highly toxic. Even small amounts can cause blindness or death by damaging the optic nerve.
64. The usual disease caused by the excessive drinking of alcohol over a long period of time is:
✅ (c) cirrhosis
Explanation:
Cirrhosis is liver damage due to long-term alcohol abuse. Liver tissue is replaced by scar tissue.
65. Which of the following molecular formula corresponds to ethyl butanoate ester?
✅ (c) C7H14O2
Explanation:
Ethyl butanoate = Ethyl group (C₂H₅) + Butanoic acid (C₄H₇COO) → Total:
C₂H₅–COOC₃H₇ = C₇H₁₄O₂
Class 10 CBSE HOTS/Case-Based Questions with Answers based on the topic Carbon and its Compounds (Q66–73):
66.
Question:
A neutral organic compound X of molecular formula C₂H₆O on oxidation with acidified potassium dichromate gives an acidic compound Y. Compound X reacts with Y on warming in the presence of conc. H₂SO₄ to give a sweet smelling substance Z.
What are X, Y, and Z?
Answer:
- X is ethanol (C₂H₅OH)
- Y is ethanoic acid (CH₃COOH)
- Z is ethyl ethanoate (CH₃COOC₂H₅) (an ester with fruity smell)
67.
Question:
Consider the following organic compounds:
HCHO, C₂H₅OH, C₂H₆, CH₃COOH, C₂H₅Cl
Choose two compounds which can react in the presence of conc. H₂SO₄ to form an ester.
Give the name and formula of the ester formed.
Answer:
- C₂H₅OH (ethanol) and CH₃COOH (ethanoic acid) react to form the ester.
- Ester formed: Ethyl ethanoate (CH₃COOC₂H₅)
68.
Question:
A neutral organic compound is warmed with some ethanoic acid and a little conc. H₂SO₄. Vapours having a fruity (sweet) smell are evolved.
What type of functional group is present in the organic compound?
Answer:
- The organic compound contains the alcohol (-OH) functional group.
69.
Question:
The structural formula of an ester is:
H H H
| | |
H–C–C–O
| |
H H
Write the formula of the acid and alcohol from which it is formed.
Answer:
This is ethyl methanoate (HCOOC₂H₅)
- Acid: Methanoic acid (HCOOH)
- Alcohol: Ethanol (C₂H₅OH)
70.
Question:
Consider the following organic compounds:
CH₃OH, C₂H₅OH, CH₃COCH₃, CH₃COOH, C₂H₅COOH, C₄H₉COOC₂H₅, CH₄, C₂H₆, CH₃CHO, HCHO
(a) Which compound is most likely to be sweet-smelling?
(b) Which compound on treatment with conc. H₂SO₄ at 170°C forms an alkene?
(c) Which compound on repeated chlorination forms chloroform?
(d) Which compound is added to alcohol to denature it?
(e) Which compound is a constituent of vinegar?
(f) Which compound is used to sterilise wounds and syringes?
Answer:
(a) C₄H₉COOC₂H₅ – an ester (sweet-smelling)
(b) C₂H₅OH – forms ethene (C₂H₄)
(c) CH₄ – forms chloroform (CHCl₃) on chlorination
(d) CH₃OH – methanol (toxic, added to denature alcohol)
(e) CH₃COOH – ethanoic acid (main constituent of vinegar)
(f) HCHO – formaldehyde (used in sterilisation)
71.
Question:
An organic acid X is a liquid, which often freezes during winter in cold countries. Its molecular formula is C₂H₄O₂. On warming it with methanol in the presence of conc. H₂SO₄, compound Y with a sweet smell is formed.
(a) Identify X and Y. Also write their formulae showing the functional groups present.
(b) Write a chemical equation for the reaction involved.
Answer:
(a)
- X: Ethanoic acid (CH₃COOH) – Carboxylic acid group (-COOH)
- Y: Methyl ethanoate (CH₃COOCH₃) – Ester group (-COOR)
(b)
CH₃COOH + CH₃OH → CH₃COOCH₃ + H₂O
(In presence of conc. H₂SO₄)
72.
Question:
An organic compound A (C₃H₈O) is a liquid at room temperature. It reacts with sodium metal to evolve a gas which burns with a pop sound. On heating A with conc. H₂SO₄ at 170°C, it forms compound B which decolourises bromine water. B adds one molecule of hydrogen in the presence of Ni catalyst to form compound C which gives substitution reactions with chlorine.
(a) What is compound A?
(b) What is compound B?
(c) What type of reaction occurs when A is converted into B?
(d) What is compound C?
(e) What type of reaction takes place when B is converted into C?
Answer:
(a) Propanol (C₃H₇OH)
(b) Propene (C₃H₆)
(c) Dehydration (Elimination reaction)
(d) Propane (C₃H₈)
(e) Addition reaction
73.
Question:
An organic compound A (C₂H₄O₂) reacts with Na metal to form compound B and evolves a gas which burns with a pop sound. A on treatment with alcohol C in the presence of conc. H₂SO₄ forms a sweet-smelling compound D (C₃H₆O₂). Compound D on treatment with NaOH gives back B and C.
Identify A, B, C and D.
Answer:
- A: Ethanoic acid (CH₃COOH)
- B: Sodium ethanoate (CH₃COONa)
- C: Ethanol (C₂H₅OH)
- d: Ethyl ethanoate (CH₃COOC₂H₅)
Assertion-Reason based questions with solutions and explanations for Class 10 CBSE chapter Carbon and Its Compounds:
1.
Assertion (A): Carbon element forms a very large number of carbon compounds (or organic compounds).
Reason (R): The two characteristic properties of carbon element which lead to the formation of a very large number of carbon compounds (or organic compounds) are:
(i) Catenation (self-linking), and
(ii) Tetravalency (four valency).
Answer: (a) Both A and R are true and R is the correct explanation of the assertion.
Explanation:
Carbon can form strong covalent bonds with other carbon atoms (catenation) and has four valence electrons (tetravalency), allowing it to form a wide variety of stable compounds. These two reasons directly explain why carbon forms so many compounds.
2.
Assertion (A): A homologous series is a group of organic compounds having similar structure and similar chemical properties in which the successive compounds differ by a CH₂ group.
Reason (R): The organic compounds having same molecular formula but different structures are known as isomers.
Answer: (b) Both A and R are true but R is not the correct explanation of the assertion.
Explanation:
The assertion correctly defines a homologous series. The reason is also a true statement about isomerism, but it is not the explanation for what a homologous series is.
3.
Assertion (A): When ethanoic acid is warmed with ethanol in the presence of a few drops of concentrated sulphuric acid, a sweet smelling ester called ethyl ethanoate is formed.
Reason (R): The animal fats (like butter and desi ghee) are unsaturated fats containing unsaturated fatty acids which are said to be good for health (even if taken in large amounts).
Answer: (c) A is true but R is false.
Explanation:
The assertion is correct — this is a classic esterification reaction. However, the reason is incorrect and unrelated. Animal fats are saturated, not unsaturated, and taking large amounts is not healthy.
4.
Assertion (A): A mixture of acetylene and air is used for welding because burning of acetylene in air produces a blue flame (due to complete combustion) which is hot enough to melt metals for welding.
Reason (R): Iodine tincture is an antiseptic solution. It is a solution of iodine in ethanol. Iodine is the real germ killer. Ethanol acts as a solvent to dissolve iodine.
Answer: (c) A is true but R is false.
Explanation:
Assertion is true – acetylene burns with a hot blue flame suitable for welding.
Reason is true as a fact, but it is completely unrelated to the assertion.
5.
Assertion (A): Graphite is an allotrope of carbon (which is a non-metal). Though most non-metals are non-conductors of electricity, graphite is a good conductor of electricity.
Reason (R): A carbon atom has 4 valence electrons. In graphite, each carbon forms 3 covalent bonds. The 4th electron is free and moves between layers, conducting electricity.
Answer: (a) Both A and R are true and R is the correct explanation of the assertion.
Explanation:
Graphite conducts electricity because of the presence of delocalized electrons. The reason explains this correctly by pointing out the bonding and free electron.
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