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Carbon and its Compounds - Q&A

1. Ethane, with the molecular formula C2H6 has
(a) 6 covalent bonds.
(b) 7 covalent bonds.
(c) 8 covalent bonds.
(d) 9 covalent bonds.

Answer: (b) 7 covalent bonds.
Explanation: Ethane (C2H6) has two carbon atoms bonded to each other (1 C-C bond) and each carbon is bonded to three hydrogen atoms (6 C-H bonds).
Total bonds = 1 (C-C) + 6 (C-H) = 7 covalent bonds.

2. Butanone is a four-carbon compound with the functional group
(a) carboxylic acid.
(b) aldehyde.
(c) ketone.
(d) alcohol.

Answer: (c) ketone.
Explanation: The suffix '-one' indicates a ketone group (>C=O). Butanone has four carbon atoms and the ketone group is on the second carbon.

3. While cooking, if the bottom of the vessel is getting blackened on the outside, it means that
(a) the food is not cooked completely.
(b) the fuel is not burning completely.
(c) the fuel is wet.
(d) the fuel is burning completely.

Answer: (b) the fuel is not burning completely.
Explanation: Blackening of vessels (soot formation) occurs due to incomplete combustion of the fuel, which leaves behind unburnt carbon particles. This usually happens when the oxygen supply is insufficient.

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

Answer:
Carbon (C) has 4 valence electrons. Hydrogen (H) has 1 valence electron. Chlorine (Cl) has 7 valence electrons.
1. Carbon shares 1 electron with each of the 3 Hydrogen atoms, forming 3 C-H single covalent bonds.
2. Carbon shares its 4th electron with 1 Chlorine atom, which also shares 1 electron, forming 1 C-Cl single covalent bond.
Result: Carbon completes its octet (8 electrons), Hydrogen completes its duplet (2 electrons), and Chlorine completes its octet (8 electrons). This sharing of electrons forms strong covalent bonds.

5. Draw the electron dot structures for
(a) ethanoic acid.
(b) H2S.
(c) propanone.
(d) F2.

Answer:
(a) Ethanoic acid (CH3COOH): Carbon shares electrons with 3 Hydrogens, another Carbon, and the functional group oxygens to complete octets.
(b) H2S: Sulphur (6 valence electrons) shares 1 electron with each of the 2 Hydrogen atoms.
(c) Propanone (CH3COCH3): Three carbons bonded in a chain. The middle carbon has a double bond with Oxygen (Ketone group).
(d) F2: Two Fluorine atoms (7 valence electrons each) share 1 electron pair to complete their octets.

6. What is an homologous series? Explain with an example.

Answer: A homologous series is a group of organic compounds having the same functional group and similar chemical properties, in which the successive members differ by a -CH2 unit (or 14 atomic mass units).
Example: Alkanes
1. Methane (CH4)
2. Ethane (C2H6)
Difference: CH4 + CH2 = C2H6. Both have similar properties but different physical properties like boiling points.

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

Answer:
Physical Properties:
1. Smell: Ethanol has a pleasant, sweet smell. Ethanoic acid smells like vinegar (pungent).
2. Melting Point: Ethanol is liquid at room temperature (M.P. very low). Ethanoic acid freezes in winter (M.P. 290 K), often called glacial acetic acid.

Chemical Properties:
1. Sodium Bicarbonate Test: Add NaHCO3 to both.
- Ethanoic acid reacts to produce brisk effervescence (CO2 gas).
- Ethanol does not react.
2. Litmus Test:
- Ethanoic acid turns blue litmus red (Acidic).
- Ethanol has no effect on litmus (Neutral).

8. Why does micelle formation take place when soap is added to water? Will a micelle be formed in other solvents such as ethanol also?

Answer:
Why: Soap molecules have two ends: a hydrophilic (water-loving) ionic head and a hydrophobic (water-hating) hydrocarbon tail. In water, the tails align towards the center to avoid water, while the heads face outwards interacting with water. This cluster is called a micelle.
In Ethanol: No, a micelle will NOT be formed in ethanol. This is because the hydrocarbon tail of the soap is soluble in ethanol (like dissolves like), so there is no need for the tails to hide away from the solvent.

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

Answer:
1. High Calorific Value: They release a large amount of heat energy when burnt.
2. Clean Burning: Saturated hydrocarbons burn with a clean blue flame without much smoke (though unsaturated ones give soot).
3. Ignition Temperature: They have moderate ignition temperatures, making them easy to catch fire but safe to handle.

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

Answer: Hard water contains calcium (Ca2+) and magnesium (Mg2+) salts. When soap (sodium salt of fatty acid) is added, these ions react with soap to form insoluble calcium or magnesium salts of fatty acids. This insoluble precipitate is called scum.
Reaction: Soap + Hard Water (Ca/Mg salts) → Scum (Insoluble Ca/Mg soap) + Sodium salt

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

Answer: Soap solutions are basic (alkaline) in nature because they are salts of strong bases (NaOH) and weak acids (Carboxylic acids).
- Red Litmus: Turns Blue.
- Blue Litmus: Remains Blue (No change).

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

Answer:
Definition: Hydrogenation is the addition of hydrogen to unsaturated hydrocarbons (alkenes/alkynes) in the presence of a catalyst like Nickel (Ni) or Palladium (Pd) to form saturated hydrocarbons.
Industrial Application: It is used to convert vegetable oils (unsaturated liquid fats) into vegetable ghee (saturated solid fats like Vanaspati). This process hardens the oil.

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

Answer: Addition reactions are undergone by unsaturated hydrocarbons (those with double or triple bonds).
From the list:
- C2H6 (Ethane) - Saturated (Alkane) - No
- C3H8 (Propane) - Saturated (Alkane) - No
- C3H6 (Propene) - Unsaturated (Alkene) - Yes
- C2H2 (Ethyne) - Unsaturated (Alkyne) - Yes
- CH4 (Methane) - Saturated (Alkane) - No
Result: C3H6 and C2H2 undergo addition reactions.

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

Answer: Bromine Water Test:
- Test: Add orange-coloured bromine water to the hydrocarbon.
- Unsaturated Hydrocarbon (e.g., Ethene): The orange colour disappears (decolourises) because bromine adds across the double/triple bond.
- Saturated Hydrocarbon (e.g., Ethane): The orange colour persists (no reaction).

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

Answer:
1. Soap molecules have a hydrophobic (oil-loving) tail and a hydrophilic (water-loving) head.
2. When applied to a dirty cloth in water, the hydrophobic tails attach themselves to the oil/dirt particles.
3. The hydrophilic heads remain in the water, pointing outwards.
4. This forms a structure called a micelle, trapping the dirt in the center.
5. When agitated (scrubbed), the micelles are pulled into the water, lifting the dirt off the cloth and washing it away.

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Quick Review Flashcards - Click to flip and test your knowledge!
Question
What percentage of carbon is found in the Earth's crust in the form of minerals?
Answer
0.02%
Question
What percentage of the atmosphere consists of carbon dioxide?
Answer
0.03%
Question
How many valence electrons does an atom of carbon have?
Answer
Four
Question
Why is it difficult for carbon to form a $C^{4-}$ anion?
Answer
The nucleus with six protons cannot easily hold on to ten electrons.
Question
Why is it difficult for carbon to form a $C^{4+}$ cation?
Answer
It requires a large amount of energy to remove four electrons from the atom.
Question
The chemical bond formed by the sharing of an electron pair between two atoms is called a _____ bond.
Answer
Covalent
Question
How many shared pairs of electrons are present in a single covalent bond?
Answer
One
Question
What type of covalent bond exists between the two atoms in a molecule of nitrogen ($N_{2}$)?
Answer
Triple bond
Question
What type of covalent bond exists between the two atoms in a molecule of oxygen ($O_{2}$)?
Answer
Double bond
Question
Why do covalent compounds generally have low melting and boiling points?
Answer
The intermolecular forces between the molecules are weak.
Question
Why are covalent compounds generally poor conductors of electricity?
Answer
The electrons are shared and no charged particles (ions) are formed.
Question
Define the property of 'catenation' in carbon.
Answer
The unique ability of carbon to form bonds with other atoms of carbon, creating large molecules or chains.
Question
Term: Saturated carbon compounds
Answer
Definition: Carbon compounds in which the carbon atoms are linked only by single bonds.
Question
Term: Unsaturated carbon compounds
Answer
Definition: Carbon compounds that contain one or more double or triple bonds between carbon atoms.
Question
Which element, other than carbon, exhibits catenation in chains of up to seven or eight atoms, though the resulting compounds are very reactive?
Answer
Silicon
Question
What physical property allows carbon to form very strong and stable bonds with other elements?
Answer
Its small atomic size
Question
In diamond, how many other carbon atoms is each carbon atom bonded to?
Answer
Four
Question
In graphite, how many other carbon atoms is each carbon atom bonded to in the same plane?
Answer
Three
Question
Why is graphite able to conduct electricity while most other non-metals cannot?
Answer
Each carbon atom is bonded to only three others, leaving one electron free to conduct.
Question
What is the specific geometric arrangement of carbon atoms in a C-60 fullerene molecule?
Answer
A football shape (geodesic dome)
Question
Term: Structural isomers
Answer
Definition: Compounds with the identical molecular formula but different structural arrangements of atoms.
Question
What is the molecular formula of cyclohexane?
Answer
$C_{6}H_{12}$
Question
What is the molecular formula of benzene?
Answer
$C_{6}H_{6}$
Question
Term: Hydrocarbons
Answer
Definition: Carbon compounds that consist solely of carbon and hydrogen atoms.
Question
What is the general name for saturated hydrocarbons?
Answer
Alkanes
Question
What is the general name for unsaturated hydrocarbons containing one or more double bonds?
Answer
Alkenes
Question
What is the general name for unsaturated hydrocarbons containing one or more triple bonds?
Answer
Alkynes
Question
In organic chemistry, what is meant by the term 'heteroatom'?
Answer
An element such as oxygen, nitrogen, or sulphur that replaces hydrogen in a hydrocarbon chain.
Question
Term: Functional group
Answer
Definition: A heteroatom or group of atoms that confers specific chemical properties to a carbon compound.
Question
What is the formula for the alcohol functional group?
Answer
$-OH$
Question
What is the formula for the aldehyde functional group?
Answer
$-CHO$
Question
What is the formula for the carboxylic acid functional group?
Answer
$-COOH$
Question
Term: Homologous series
Answer
Definition: A series of compounds where the same functional group substitutes for hydrogen in a carbon chain of varying length.
Question
By what fixed chemical unit do successive members of a homologous series differ?
Answer
A $-CH_{2}-$ unit
Question
How does the boiling point of compounds change as the molecular mass increases in a homologous series?
Answer
The boiling point increases.
Question
What is the general formula for the alkene homologous series?
Answer
$C_{n}H_{2n}$
Question
When naming a carbon chain containing a ketone group, what suffix is added after removing the final 'e' from the parent alkane?
Answer
-one
Question
What are the primary products of the combustion of carbon and its compounds in the presence of oxygen?
Answer
Carbon dioxide, heat, and light
Question
Why does a gas stove produce a blue flame rather than a yellow, sooty one?
Answer
There is a sufficient supply of oxygen for complete combustion.
Question
What environmental pollutants are formed during the combustion of coal and petroleum due to impurities?
Answer
Oxides of nitrogen and sulphur
Question
Which reagent is commonly used as an oxidising agent to convert ethanol into ethanoic acid?
Answer
Alkaline potassium permanganate ($KMnO_{4}$) or acidified potassium dichromate ($K_{2}Cr_{2}O_{7}$)
Question
Term: Addition reaction
Answer
Definition: A reaction where unsaturated hydrocarbons add hydrogen in the presence of a catalyst to become saturated.
Question
What catalyst is typically used in the industrial hydrogenation of vegetable oils?
Answer
Nickel ($Ni$) or Palladium ($Pd$)
Question
Under what condition does chlorine undergo a substitution reaction with saturated hydrocarbons like methane?
Answer
In the presence of sunlight
Question
What are the common medicinal uses of ethanol?
Answer
As a solvent in tincture of iodine, cough syrups, and tonics.
Question
What gas is evolved when ethanol reacts with sodium metal?
Answer
Hydrogen gas ($H_{2}$)
Question
What is the chemical product of the reaction between ethanol and sodium?
Answer
Sodium ethoxide
Question
Which reagent acts as a dehydrating agent to convert ethanol into ethene at $443\text{ K}$?
Answer
Hot concentrated sulphuric acid ($H_{2}SO_{4}$)
Question
Why is methanol significantly more toxic to humans than ethanol?
Answer
It is oxidised to methanal in the liver, which coagulates cell protoplasm and affects the optic nerve.
Question
Term: Denatured alcohol
Answer
Definition: Industrial ethanol rendered unfit for drinking by adding poisonous substances like methanol and blue dyes.
Question
What is the common name for a $5$-$8\%$ solution of ethanoic acid in water?
Answer
Vinegar
Question
Why is pure ethanoic acid often referred to as 'glacial acetic acid'?
Answer
It has a melting point of $290\text{ K}$ and frequently freezes in cold climates.
Question
Term: Esterification reaction
Answer
Definition: The reaction between a carboxylic acid and an alcohol in the presence of an acid catalyst to form an ester.
Question
What is a characteristic physical property of esters used in perfumes?
Answer
They have a sweet smell.
Question
Term: Saponification
Answer
Definition: The reaction where an ester is treated with sodium hydroxide to yield alcohol and the sodium salt of a carboxylic acid.
Question
What are the products when ethanoic acid reacts with sodium carbonate?
Answer
Sodium ethanoate, water, and carbon dioxide
Question
Describe the chemical structure of a soap molecule.
Answer
A sodium or potassium salt of a long-chain carboxylic acid.
Question
Term: Micelle
Answer
Definition: A cluster of soap molecules in water where the hydrophobic tails are internal and the hydrophilic heads are on the surface.
Question
How does the 'tail' of a soap molecule interact with oil and water?
Answer
The hydrophobic tail interacts with oil but is insoluble in water.
Question
Why do soap solutions often appear cloudy?
Answer
Soap micelles are large enough to scatter light.