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(1ai)
Hygroscopy refers to the ability of a substance to absorb moisture from the air without dissolving in it.
(1aii)
calcium chloride (CaCl₂).
(1b)
Ammonium sulfate.
(1c)
(i) Ionic bond
(ii) Dative bond
(iii) Covalent bond
(1d)
(i) C₂H₆(g)+O₂(g) —> 4CO₂(g) + 6H₂O(g)
(ii) CaC₂(s) + H₂O (l) —> Ca(OH)₂(aq) + C₂H₂(g)
(1e)
(i) Variable oxidation states: Transition metals can exhibit more than one oxidation state in their compounds.
(ii) Formation of colored compounds: Transition metals often form compounds that are vividly colored due to d-electron transitions.
(1g)
Dalton’s law of partial pressures states that the total pressure exerted by a mixture of non-reacting gases is equal to the sum of the partial pressures of the individual gases in the mixture.
(1h)
(i) Non-toxicity: Aluminium is non-toxic and does not react with food substances.
(ii) Corrosion resistance: Aluminium forms a protective oxide layer that resists corrosion.
(1i)
(i) Colliding particles must have sufficient energy to overcome the activation energy barrier.
(ii) Collisions must occur with the correct orientation to allow bond-breaking and bond-forming. If either of these conditions is not met, the reaction does not occur despite a collision.
(1j)
(i) A primary standard is a substance of known and high purity that is stable, non-hygroscopic, and can be used to prepare a solution of precise concentration.
(ii)
Sodium hydroxide is hygroscopic, meaning it absorbs moisture from the air, making it difficult to weigh accurately.
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(2a)
TABULATE
=REACTION=
(i) HCl + KMnO₄
(ii) NH₄Cl + Ca(OH)₂
(iii) Cu + HNO₃
=COLOR OF GAS PRODUCED=
(i) Greenish-yellow
(ii) Colourless
(iii) Brown
=SMELL OF GAS PRODUCED=
(i) Pungent
(ii) Pungent
(iii) Sharp, choking
=EFFECT OF GAS ON DAMP RED LITMUS=
(i) Turns blue
(ii) Turns blue
(iii) No effect
(2bi)
I. Neutral:
Formula: CO (Carbon monoxide)
II. Acidic:
Formula: SO₃ (Sulfur trioxide)
III. Basic:
Formula: Na₂O (Sodium oxide)
IV. Amphoteric:
Formula: Al₂O₃ (Aluminum oxide)
(2bii)
I. Making jewellery: High refractive index, giving diamond its brilliance.
II. Cutting and drilling: Extremely hard due to its strong covalent bonds in a tetrahedral structure.
(2ci)
(i) Potassium chlorate (KClO₃)
(ii) Potassium nitrate (KNO₃)
(2cii)
(i) For KClO₃: 2KClO₃(s) –> 2KCl(s) + 3O₂(g)
(ii) For KNO₃: 2KNO₃(s) —> 2KNO₂(s) + O₂(g)
(2d)
CBr₄ (carbon tetrabromide) has larger bromine atoms compared to chlorine in CCl₄, resulting in stronger London dispersion forces (van der Waals forces) in CBr₄. These stronger intermolecular forces require more energy to overcome, leading to a higher boiling point for CBr₄ compared to CCl₄.
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(4ai)
The industrial preparation of ammonia is typically done through the Haber-Bosch process. This process involves the reaction between nitrogen and hydrogen gases at high temperature and pressure, with the use of a metal catalyst to increase the rate of the reaction.
(4aii)
Removing the ammonia from the reaction mixture as it is formed to shift the equilibrium towards the products.
(4aiii)
(i)Explosive manufacturing
(ii) Wastewater treatment
(4bi)
(i) Screening
(ii) Coagulation and flocculation
(iii) Sedimentation
(iv) Filtration
(v) Disinfection
(4bii)
(i) Screening: Removes large debris and particles from the water.
(ii) Coagulation and flocculation: Causes small particles to clump together, making them easier to remove.
(iii) Sedimentation: Allows the clumped particles to settle out of the water.
(iv) Filtration: Removes any remaining small particles and contaminants from the water.
(v) Disinfection: Kills any remaining microorganisms in the water, making it safe for consumption.
(4c)
A laboratory test for hydrogen chloride gas can be done by passing the gas through water, which will form a solution of hydrochloric acid. The presence of hydrogen chloride gas can be detected by the formation of white fumes when a glass rod dipped in ammonia solution is brought near the test solution. The intensity of the white fumes can be used to estimate the concentration of the hydrogen chloride gas.
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(5ai)
Allotropy is the existence of an element in two or more different forms (allotropes) in the same physical state, with each form having distinct atomic arrangements and properties. Examples include diamond and graphite for carbon.
(5aii)
(I) Carbon – Diamond or Graphite
(II) Sulphur – Rhombic sulphur or Monoclinic sulphur
(5bi)
The CO₂ gas is impure because it contains other gaseous impurities such as water vapor and traces of unreacted hydrochloric acid vapor.
(5bii)
concentrated sulphuric acid
(5ci)
(i) Add freshly prepared iron(II) sulphate solution to the test sample.
(ii) Carefully add concentrated sulphuric acid down the side of the test tube.
(iii) A brown ring forms at the junction of the two liquids, indicating the presence of nitrate ions (NO₃⁻).
(5cii)
(i) Dissolve calcium chloride in water to form a calcium chloride solution.
(ii) Add a solution of sodium carbonate (or sodium trioxocarbonate (IV)) to the calcium chloride solution.
(iii) A white precipitate of calcium trioxocarbonate (IV) forms.
(iv) Filter the mixture to collect the precipitate.
(v) Wash the precipitate with distilled water and allow it to dry.
(5di)
(i) Both are made up of carbon atoms.
(ii) Both have covalent bonds between the carbon atoms.
(5dii)
Diamond has a tetrahedral structure, where each carbon atom is bonded to four other carbon atoms. In contrast, graphite has a layered structure, with each carbon atom bonded to three others in hexagonal sheets
(5diii)
Diamond is hard because of its 3D tetrahedral network where all carbon atoms are covalently bonded, forming a rigid structure WHILE Graphite is soft because its layers are held together by weak van der Waals forces, allowing them to slide over each other easily.
(5e)
Hydrogen chloride is soluble in water because it ionizes completely to form hydrogen ions (H⁺) and chloride ions (Cl⁻) when dissolved. This interaction is due to the high polarity of water molecules, which attract and stabilize the H⁺ and Cl⁻ ions.
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