What is allotropy?
Allotropy refers to the existence of an element in different forms in the same physical state. The different forms are called allotropes.
What are the main allotropes of carbon?
Diamond, graphite (crystalline), and charcoal (amorphous).
Describe the structure and bonding in a diamond.
Each carbon atom is covalently bonded to four other carbon atoms in a tetrahedral arrangement, forming a giant 3D structure.
What are the key physical properties of a diamond?
Hard, colourless, transparent with a high refractive index, forms octahedral crystals, density: 3.5 g/cm³, melting point: 3600°C, does not conduct electricity.
What are the main uses of diamonds?
Used in jewellery due to its sparkle and luster; employed in cutting glass, drilling rocks, boring holes, engine bearings, and abrasives.
Describe the structure and bonding in graphite.
Each carbon atom bonds with three others to form flat hexagonal layers. These layers are held together by weak van der Waals forces.
Why is graphite a good conductor of electricity?
One valence electron per carbon atom remains unbonded and is free to move, allowing electrical conductivity.
What are the key physical properties of graphite?
Forms soft, black, opaque hexagonal crystals, density: 2.3 g/cm³, melting point: ~3500°C, good conductor of heat and electricity.
What are the main uses of graphite?
Used as a lubricant, serves as electrodes, mixed with clay to make pencil leads, used to manufacture crucibles, and employed in nuclear reactors.
Compare the transparency of diamond and graphite.
Diamond is transparent and sparkles when polished, while graphite is opaque with a metallic luster.
Compare the electrical conductivity of diamond and graphite.
Diamond is a poor conductor of electricity, while graphite is a good conductor.
Compare the hardness of diamond and graphite.
Diamond is the hardest known substance, while graphite is very soft.
What is the product of carbon combustion in limited air?
Carbon monoxide (CO). 2C(s) + O₂(g) → 2CO(g)
What is the product of carbon combustion in excess air?
Carbon dioxide (CO₂). C(s) + O₂(g) → CO₂(g)
How does carbon act as a reducing agent?
It reduces metal oxides to their metals, e.g., Fe₂O₃ + 3C → 2Fe + 3CO.
How does carbon react with concentrated trioxonitrate(V) acid?
4HNO₃ + C → CO₂ + 4NO₂ + 2H₂O.
What is coal?
A naturally occurring black or brownish-black sedimentary rock formed from plant remains, composed mainly of carbon.
List the types of coal in order of increasing carbon content.
Peat, Lignite, Bituminous Coal, Anthracite.
What is anthracite?
The highest grade of coal; hard, glossy, and burns cleanly with high energy output.
What is destructive distillation of coal?
The process of heating coal in the absence of air to break it down into useful products like coke, coal tar, ammoniacal liquor, and coal gas.
What is coke and what is it used for?
A solid residue rich in carbon from destructive distillation, used as a fuel and in steel manufacturing.
What is coal tar?
A thick, black liquid from destructive distillation, containing aromatic hydrocarbons used to make dyes, explosives, and drugs.
What is ammoniacal liquor?
A solution of ammonia in water from destructive distillation, used in fertilizers.
What is coal gas?
A mixture of gases from destructive distillation, like hydrogen, methane, and carbon monoxide, used as a fuel.
What is a major environmental effect of burning coal?
It releases CO₂, a greenhouse gas contributing to climate change.
How can burning coal lead to acid rain?
Coal combustion may release sulfur dioxide (SO₂), which reacts with water in the atmosphere to form acid rain.
What is synthetic gas (water gas)?
A mixture of carbon monoxide (CO) and hydrogen (H₂).
How is synthetic gas produced?
By passing natural gas (methane) over steam in the presence of a nickel catalyst at about 900°C.
What is the chemical equation for producing synthetic gas from methane and steam?
CH₄(g) + H₂O(g) → CO(g) + 3H₂(g).
Which metallic trioxocarbonates are soluble in water?
Those of sodium (Na), potassium (K), and ammonium (NH₄).
How are insoluble trioxocarbonates prepared?
Using the double decomposition method, e.g., Na₂CO₃(aq) + CuSO₄(aq) → CuCO₃(s) + Na₂SO₄(aq).
What happens when most trioxocarbonates are heated?
They decompose to release CO₂ gas, e.g., ZnCO₃(s) → ZnO(s) + CO₂(g).
Which trioxocarbonates are stable to heat?
Sodium carbonate (Na₂CO₃) and potassium carbonate (K₂CO₃).
What is the general reaction of trioxocarbonates with acids?
They produce a salt, water, and carbon dioxide gas. ZnCO₃(s) + 2HCl(aq) → ZnCl₂(aq) + H₂O(l) + CO₂(g).
What is trioxocarbonate(IV) acid (carbonic acid)?
A very weak, dibasic acid (H₂CO₃) formed when CO₂ dissolves in water, which is unstable and cannot be isolated.
What are the uses of sodium carbonate (Na₂CO₃)?
Water softening, soap and glass making, and as a base in titrations.
What are the uses of calcium carbonate (CaCO₃)?
Production of cement, glass, and lime, and in agriculture to reduce soil acidity (liming).
How do you perform a dry chemical test for carbonates?
Add dilute HCl to the solid sample. Effervescence of a colorless, odorless gas (CO₂) that turns limewater milky confirms its presence.
How do you perform a wet chemical test for carbonates?
Add barium chloride solution to the salt's solution. A white precipitate of barium trioxocarbonate (BaCO₃) forms.
What is the equation for the wet test of carbonates with barium chloride?
CO₃²⁻(aq) + BaCl₂(aq) → BaCO₃(s) + 2Cl⁻(aq).
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