📘 Carbon and its Compounds — Answers
⸻
✅ Q1.
Ethane C_2H_6 has:
🎯 Between 2 carbons → 1 bond
🎯 Each carbon has 3 H atoms → 6 bonds
Total: 1 + 6 = 7 covalent bonds.
Answer: (b) 7 covalent bonds
⸻
✅ Q2.
Butanone → C_4H_8O
Functional group: >C=O (carbonyl) in middle of chain → ketone.
Answer: (c) ketone
⸻
✅ Q3.
Bottom of vessel blackens → fuel is producing soot (incomplete combustion).
Answer: (b) the fuel is not burning completely
⸻
✅ Q4.
Covalent bond in CH_3Cl:
• Carbon shares 4 electrons → 3 with H & 1 with Cl.
• Cl shares 1 electron with C.
• Covalent bonds form because both share electrons without forming ions.
⸻
✅ Q5.
Electron dot structures:
(a) Ethanoic acid (CH_3COOH):
H
|
H—C—C=O
| \
H OH
(b) H_2S:
H—S—H
(c) Propanone (CH_3COCH_3):
H O H
| || |
H—C—C—C—H
| |
H H
(d) F_2:
F—F
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✅ Q6.
Homologous series:
A series of compounds where each successive member differs by -CH_2- group.
e.g., Alkanes: CH_4, C_2H_6, C_3H_8, …
⸻
✅ Q7.
Ethanol vs Ethanoic acid:
Property Ethanol Ethanoic Acid
Smell pleasant sour, pungent
Litmus neutral turns blue → red
Reaction with NaHCO₃ No reaction CO₂ gas evolves
Taste mild sour
⸻
✅ Q8.
Micelle formation:
Soap molecules have hydrophobic tail & hydrophilic head. In water, tails cluster inwards trapping oil, heads face water → micelle.
In ethanol: No micelles form, because ethanol is non-polar & dissolves both oil & soap.
⸻
✅ Q9.
Why use carbon compounds as fuels?
Because they release a lot of heat on combustion & are easily available, e.g., petrol, diesel.
⸻
✅ Q10.
Scum formation:
In hard water, Ca^{2+}/Mg^{2+} ions react with soap → insoluble salts (scum), which reduces cleaning.
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✅ Q11.
Soap & litmus:
Soap is basic:
• Red litmus → blue
• Blue litmus → no change
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✅ Q12.
Hydrogenation:
Adding hydrogen to unsaturated hydrocarbons (alkenes) in presence of catalyst (Ni/Pt) → saturated hydrocarbons.
Industrial use: Making vegetable oils into solid fats (margarine).
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✅ Q13.
Which undergo addition reactions?
Unsaturated hydrocarbons (double/triple bonds):
🎯 C_3H_6 (propene), C_2H_2 (ethyne)
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✅ Q14.
Test to differentiate:
Add bromine water →
• Unsaturated: decolourises bromine water (addition reaction)
• Saturated: no effect.
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✅ Q15.
Cleaning action of soap:
• Soap has hydrophobic tail & hydrophilic head.
• Tails attach to grease/dirt, heads remain in water.
• Agitation breaks grease into tiny droplets (micelles) which get washed away.
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