1. Why reversible reactions never complete?
Reversible reactions never complete because they reach a state of dynamic equilibrium where the rate of the forward reaction equals the rate of the reverse reaction. At this point, the concentrations of reactants and products remain constant, but both reactions continue to occur.
2. Define static equilibrium with an example.
Static equilibrium occurs when a reaction has stopped completely, and there is no further change in the concentrations of reactants and products. An example is the reaction between strong acids and strong bases that goes to completion, like HCl + NaOH → NaCl + H₂O.
3. Define functional group with an example.
A functional group is an atom or group of atoms that determines the chemical properties of an organic compound. For example, the hydroxyl group (-OH) is the functional group in alcohols, giving them their characteristic properties.
4. How are alkyl radicals formed? Give an example.
Alkyl radicals are formed by the removal of a hydrogen atom from an alkane molecule. For example, methane (CH₄) can lose a hydrogen atom to form the methyl radical (•CH₃).
5. Why are the melting and boiling points of organic compounds low?
Organic compounds generally have low melting and boiling points because they are mostly covalent compounds with weak intermolecular forces (van der Waals forces) between molecules. These weak forces require less energy to overcome compared to ionic or metallic bonds.
6. Why and how carbon completes its octet?
Carbon completes its octet to achieve a stable electronic configuration similar to noble gases. It does so by sharing four electrons with other atoms through covalent bonding, forming four covalent bonds.
7. Why are the alkanes called paraffins?
Alkanes are called paraffins because they have little reactivity (from Latin: parum affinis, meaning “little affinity”). They are saturated hydrocarbons with only single bonds and are relatively inert compared to other organic compounds.
8. Differentiate between saturated and unsaturated hydrocarbons.
Saturated hydrocarbons: Contain only single bonds between carbon atoms (alkanes). They are less reactive. General formula: CₙH₂ₙ₊₂.
Unsaturated hydrocarbons: Contain double or triple bonds between carbon atoms (alkenes and alkynes). They are more reactive. General formulas: CₙH₂ₙ (alkenes), CₙH₂ₙ₋₂ (alkynes).
9. Define conjugate acid and conjugate base. Give example.
Conjugate acid: Formed when a base gains a proton (H⁺).
Conjugate base: Formed when an acid loses a proton (H⁺).
Example: In the reaction NH₃ + H₂O ⇌ NH₄⁺ + OH⁻, NH₄⁺ is the conjugate acid of base NH₃, and OH⁻ is the conjugate base of acid H₂O.
10. Why BF₃ acts as Lewis acid?
BF₃ acts as a Lewis acid because it has an incomplete octet. The boron atom in BF₃ has only six electrons in its valence shell and can accept a pair of electrons from a Lewis base to complete its octet.
11. What are acidic and Basic radicals?
Acidic radicals: Negatively charged ions (anions) derived from acids. Example: Cl⁻ from HCl, SO₄²⁻ from H₂SO₄.
Basic radicals: Positively charged ions (cations) derived from bases. Example: Na⁺ from NaOH, Ca²⁺ from Ca(OH)₂.
12. Draw the structural formulae of glucose and fructose.
Glucose (C₆H₁₂O₆): An aldohexose with an aldehyde group.
Fructose (C₆H₁₂O₆): A ketohexose with a ketone group.
(Note: In an actual exam, you would draw the structural formulas showing the carbon chain and functional groups.)
13. What is meant by triglycerides? Write their general formula.
Triglycerides are esters derived from glycerol and three fatty acids. They are the main constituents of body fat in animals and vegetable fat.
General formula:
CH₂OCOR¹ | CHOCOR² | CH₂OCOR³
where R¹, R², and R³ are long hydrocarbon chains of fatty acids.
14. Why use of detergents is increasing day by day?
The use of detergents is increasing because:
- They work effectively in hard water (unlike soaps which form scum)
- They have better cleaning power
- They are available in various forms (powder, liquid, bars)
- They are often more convenient to use
15. Why are pesticides used?
Pesticides are used to:
- Protect crops from insects, fungi, and other pests
- Increase agricultural yield
- Prevent damage to stored food products
- Control disease-carrying vectors like mosquitoes
16. What do you mean by boiler scales? How are they removed?
Boiler scales are hard deposits (mainly calcium and magnesium salts) that form on the inner surfaces of boilers when hard water is heated.
They are removed by:
- Mechanical scraping
- Chemical cleaning with acids (like HCl)
- Using ion-exchange resins to soften water before use
17. Write down composition of dry air.
Dry air composition by volume:
- Nitrogen (N₂): 78.09%
- Oxygen (O₂): 20.95%
- Argon (Ar): 0.93%
- Carbon dioxide (CO₂): 0.04%
- Trace gases: Neon, Helium, Methane, Krypton, Hydrogen, etc.
18. How does acid rain increase the acidity of Soil?
Acid rain increases soil acidity by:
- Adding hydrogen ions (H⁺) to the soil
- Leaching away essential nutrients like calcium and magnesium
- Releasing aluminum ions which are toxic to plants
- Reducing soil pH, making it difficult for plants to absorb nutrients
19. Write names of any four primary air pollutants.
Four primary air pollutants:
- Sulfur dioxide (SO₂)
- Nitrogen oxides (NOₓ)
- Carbon monoxide (CO)
- Particulate matter (PM)
20. Write down the height of four regions of atmosphere form the level of earth.
The four main regions of the atmosphere and their approximate heights:
- Troposphere: 0-12 km (contains weather phenomena)
- Stratosphere: 12-50 km (contains ozone layer)
- Mesosphere: 50-85 km (meteors burn up here)
- Thermosphere: 85-600 km (auroras occur here)