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CHEMISTRY OBJ
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(1ai)
(i) Rhombic sulfur
(ii) Monoclinic sulfur
(1aii)
(i) Production of sulphuric acid for industrial processes.
(ii) Manufacturing vulcanized rubber for tires and other products.
(1aiii)
Allotropy is the existence of an element in two or more different physical forms in the same state, each having distinct properties.
(1aiv)
(i) It is a colorless, odorless gas.
(ii) It is slightly less dense than air.
(1bi)
Molar mass of H₂SO₄ = 2(1) + 32 + 4(16) = 98 g/mol
Moles = 0.0650
Mass = moles x molar mass
= 0.0650 x 98
= 6.37g
(1bii)
A physical change is a transformation in which a substance changes its state (solid, liquid, gas) without altering its chemical composition.
(1ci)
ELECTROVALENT (IONIC):
(i) Formed by transfer of electrons
(ii) Typically have high melting and boiling points
COVALENT:
(i) Formed by sharing of electrons
(ii) Typically have low melting and boiling points
(1cii)
I. Ammonium ion (NH₄⁺): Tetrahedral
II. Water molecule (H₂O): Bent or V-shaped
(1di)
(i) Availability of raw materials.
(ii) Proximity to water supply.
(iii) Accessibility to transportation networks.
(1dii)
(i) Magnetic separation (for iron filings)
(ii) Sublimation (for ammonium chloride)
(iii) Filtration (for sand)
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(2ai)
Equation: Zn(s) + 2AgNO₃(aq) —> Zn(NO₃)₂(aq) + 2Ag(s)
(2aii)
I. Reduced: Silver ions (Ag⁺) are reduced to metallic silver (Ag(s))
II. Oxidized: Zinc (Zn(s)) is oxidized to zinc ions (Zn²⁺)
(2bi)
Initial conditions: V₁ = 200cm³, T₁ = 25°C + 273 = 298K, P₁ = 700mmHg
Final conditions: V₂ = 350cm³, T₂ = 70°C + 273 = 343K
Using the ideal gas law: P₁V₁/T₁ = P₂V₂/T₂
(700*200)/298 = (P₂ *350)/343
P₂ = (700*200 *343)/(298*350)
P₂ = 460.4mmHg
(2bii)
(i) They form salts when they react with metals.
(ii) They act as strong oxidizing agents.
(iii) They react with hydrogen to form hydrogen halides.
(2ci)
(i) Monosaccharide: Glucose
(ii) Disaccharide: Sucrose
(2cii)
(i) Impaired judgment and decision-making.
(ii) Health problems such as liver damage and respiratory issues.
(iii) Dependency and addiction leading to withdrawal symptoms.
(2di)
(i) It is a silvery-white metal.
(ii) It has a low density and is lightweight.
(2dii)
(i) It exists as diatomic molecules
(ii) Form compounds with other elements
(2diii)
(i) Nitrogen
(ii) Oxygen
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(3)
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(6ai)
I – Sulphur dioxide (SO₂) and sulphur trioxide (SO₃)
II – Carbon monoxide (CO), unburnt hydrocarbons, and particulate matter (soot)
(6aii)
Efflorescence is the phenomenon where a hydrated salt loses its water of crystallization when exposed to air, forming a powdery surface.
(6aiii)
Fe + 2HCL —> FeCL₂ + H₂
(6aiv)
(i) Electroplating (coating the metal surface with another metal, such as chromium or nickel).
(ii) Using sacrificial anodes (attaching a more reactive metal like zinc to corrode instead of the iron).
(iii) Storing metals in a dry or controlled environment to prevent exposure to moisture and oxygen.
(6bi)
Number of moles in 5.0×10²⁰ atoms of magnesium
Moles = Number of atoms / Avogadro’s number
Moles = 5.10 × 10²⁰ / 6.02 × 10²³
Moles = 8.31 × 10-⁴
(6bii)
Petroleum gasses –> Petrol –> Ligroin –> Kerosene
(6biii)
Octane rating measures the fuel’s ability to resist knocking during combustion in an engine. Higher ratings indicate better performance.
(6biv)
Variation of electron affinity across a period, electron affinity generally increases across a period due to an increase in nuclear charge, which attracts electrons more strongly.
(6ci)
Na₂CO₃ – 7H₂O
Molar mass of Na₂CO₃ – 7H₂O =
(23×2) + 12 + (16 × 3) + 7 [(2×1) + 16] =
286g/mol
Mass of oxygen
(3×16) + (7×16) = 112 + 16
= 128g
(6cii)
(6ciii)
Ammonia gas turns moist red litmus paper blue due to its basic nature.
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