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Science Class- 10

Class 10 - Chapter 4: Carbon and its compounds

NCERTChapter 4Solution

Q1. Ethane, with the molecular formula C2H6 has

Answer: (b) 7 covalent bonds.

Ethane contains six C–H covalent bonds and one C–C covalent bond.

Total covalent bonds = 6 + 1 = 7.

Q2. Butanone is a four-carbon compound with the functional group

Answer: (c) Ketone.

Butanone contains the ketone functional group (>C=O).

Q3. While cooking, if the bottom of the vessel is getting blackened on the outside, it means that

Answer: (b) The fuel is not burning completely.

Incomplete combustion produces soot (carbon particles) which blackens the vessel.

Q4. Explain the nature of the covalent bond using the bond formation in CH3Cl.

A covalent bond is formed by the sharing of electrons between atoms.

In CH3Cl, carbon has four valence electrons and shares:

  • One electron each with three hydrogen atoms.
  • One electron with one chlorine atom.

Thus, carbon completes its octet, hydrogen attains a duplet and chlorine completes its octet by sharing electrons.

This sharing of electrons results in the formation of covalent bonds.

Q5(a). Draw the electron dot structure for ethanoic acid.

      O
      ||
H — C — C — O — H
    |     
    H

Structural formula: CH3COOH

Q5(b). Draw the electron dot structure for H2S.

H : S : H

Sulphur shares one electron with each hydrogen atom.

Q5(c). Draw the electron dot structure for propanone.

CH3 — C(=O) — CH3

Structural formula: CH3COCH3

Q5(d). Draw the electron dot structure for F2.

:F : F:

Each fluorine atom shares one electron to complete its octet.

Q6. What is a homologous series? Explain with an example.

A homologous series is a group of organic compounds having the same functional group and similar chemical properties.

Successive members differ by a –CH2 unit and have a molecular mass difference of 14 u.

Example:

Compound Molecular Formula
Methane CH4
Ethane C2H6
Propane C3H8

Q7. How can ethanol and ethanoic acid be differentiated on the basis of their physical and chemical properties?

Ethanol Ethanoic Acid
Has a pleasant smell. Has a pungent vinegar-like smell.
Does not change blue litmus. Turns blue litmus red.
Does not react with sodium carbonate. Reacts with sodium carbonate producing CO2.

Q8. Why does micelle formation take place when soap is added to water? Will a micelle be formed in ethanol also?

Soap molecules have:

  • A hydrophilic (water-loving) ionic end.
  • A hydrophobic (water-repelling) hydrocarbon tail.

In water, soap molecules arrange themselves into micelles with tails inward and ionic ends outward.

Micelles are not formed in ethanol because the hydrocarbon tail is soluble in ethanol.

Q9. Why are carbon and its compounds used as fuels for most applications?

Carbon compounds are used as fuels because:

  • They have high calorific value.
  • They burn easily.
  • They produce large amounts of heat.
  • Many burn with comparatively clean flames.

Q10. Explain the formation of scum when hard water is treated with soap.

Hard water contains calcium and magnesium salts.

These react with soap to form insoluble calcium and magnesium soaps called scum.

As a result, more soap is required for cleaning.

Q11. What change will you observe if you test soap with litmus paper (red and blue)?

Soap solution is basic in nature.

  • Red litmus turns blue.
  • Blue litmus remains blue.

Q12. What is hydrogenation? What is its industrial application?

Hydrogenation is the addition of hydrogen to unsaturated compounds in the presence of a catalyst such as nickel.

Example:

Vegetable Oil + H2 → Vanaspati Ghee

Industrial Application:

It is used in the manufacture of vanaspati ghee and margarine from vegetable oils.

Q13. Which of the following hydrocarbons undergo addition reactions: C2H6, C3H8, C3H6, C2H2 and CH4?

Addition reactions are shown by unsaturated hydrocarbons.

Therefore:

  • C3H6
  • C2H2

undergo addition reactions.

Q14. Give a test that can be used to differentiate between saturated and unsaturated hydrocarbons.

Bromine Water Test:

  • Unsaturated hydrocarbons decolourise bromine water.
  • Saturated hydrocarbons do not decolourise bromine water.

OR

Alkaline KMnO4 Test:

  • Unsaturated hydrocarbons decolourise pink potassium permanganate solution.
  • Saturated hydrocarbons do not.

Q15. Explain the mechanism of the cleaning action of soaps.

Soap molecules have a hydrophobic tail and a hydrophilic head.

The hydrophobic tail attaches to oily dirt while the hydrophilic head remains in water.

Many soap molecules surround the grease particle and form a micelle.

The dirt gets suspended in water and is removed during rinsing.