Which of the following species determines the chemical properties of an atom?
The chemical properties of an atom are determined by the electrons, particularly those in the valence shell, as they participate in bonding and reactions.
The following glasswares are used to measure the volume of liquids except
A test tube is not designed for precise volume measurement; it is used for holding or heating small amounts of substances. The others are volumetric apparatus.
Pauli exclusion principle is related to
The Pauli exclusion principle states that no two electrons in an atom can have the same set of four quantum numbers, describing their unique states.
The species with no electron in the 3d-orbital is
Sc (atomic number 21) loses 3 electrons to form Sc³⁺ with configuration [Ar], having no electrons in the 3d orbital. The other species have electrons in 3d.
The separation of oxygen from nitrogen by fractional distillation of air is possible because
Fractional distillation separates gases based on differences in boiling points: nitrogen boils at -196°C and oxygen at -183°C.
The purity of a solid sample can best be determined by its
A pure solid has a sharp melting point; impurities cause the melting range to broaden and lower the temperature.
The mass of one mole of (NH₄)₂CO₃ is [O=16.0, N=14.0, C=12.0, H=1.0]
Molar mass = (2×14) + (8×1) + 12 + (3×16) = 28 + 8 + 12 + 48 = 96 g/mol.
Atomic orbital is
In quantum mechanics, an atomic orbital is a probability region where an electron is likely to be found, not a fixed path.
The property of elements which increases down a group of the Periodic Table is
Ionic radius increases down a group due to additional electron shells, while electronegativity, electron affinity, and ionization energy decrease.
The reason for the decrease in the atomic size of elements across a period is that
Across a period, protons increase, enhancing nuclear charge, which pulls electrons closer despite the same shell.
The oxidation number of nitrogen in Pb(NO₃)₂ is
In NO₃⁻, oxygen is -2 (3×-2 = -6), so N is +5 to make the ion -1.
Which of the following arrangements indicates the correct decreasing order of ionization energy of period 3 elements?
Ionization energy generally increases across a period: Cl > P > Al > Na (noting the anomaly at Al due to p-subshell).
Which of the following metals has the strongest metallic bond?
Al has three valence electrons for delocalization and smaller size than Mg, K, Na, leading to stronger metallic bonding.
Which of the following substances does not have van der Waals' forces?
Copper has metallic bonding; the others have van der Waals' forces (Neon: atomic, Graphite and Iodine: intermolecular).
The oxidation number of X in XF₄ is
Each F is -1, so 4F = -4; X must be +4 for neutrality.
The ionization energy is affected by the following factors except
Ionization energy concerns isolated atoms; attracting shared electrons relates to electronegativity in molecules.
Which of the following statements is correct?
Ionic compounds dissociate into free ions in aqueous solution, allowing conduction; the others are incorrect.
The bond angle in tetrahedral molecules such as tetrachloromethane is
Tetrahedral geometry from sp³ hybridization results in bond angles of approximately 109.5°.
The properties of a good primary standard include the following except
Primary standards should have high molar mass to minimize errors from impurities or hygroscopicity; low molar mass is not preferred.
The use of diamond in abrasives is due to its
Diamond's extreme hardness from strong covalent bonds in a tetrahedral structure makes it ideal for abrasives.
Which of the following statements about endothermic reaction is correct?
Endothermic reactions absorb heat from the surroundings to proceed, increasing the system's energy.
A 0.1 moldm⁻³ solution of sodium hydroxide was diluted with distilled water to 0.001 moldm⁻³. What is the dilution factor?
Dilution factor = initial concentration / final concentration = 0.1 / 0.001 = 100.
Graphite and diamond are similar in that they
Both allotropes of carbon combust to form CO₂; graphite conducts electricity, but diamond does not, and they have different densities and structures.
In a saturated solution at a given temperature, the undissolved solute are in equilibrium with
Dynamic equilibrium exists between undissolved solute and dissolved solute ions/molecules in a saturated solution.
The number of atoms present in 2.5 moles of a triatomic gas is equivalent to [1 mole = 6.0 × 10²³]
Number of molecules = 2.5 × 6.0 × 10²³ = 1.5 × 10²⁴; atoms = 3 × 1.5 × 10²⁴ = 4.5 × 10²⁴. (Option C fixed for accuracy.)
When magnesium reacts with oxygen, heat is
2Mg + O₂ → 2MgO is exothermic, releasing heat as bonds form in the product.
Which of the following gases is not acidic?
CO is neutral and does not form acidic solutions with water; the others do (NO₂ → HNO₃/HNO₂, SO₂ → H₂SO₃, CO₂ → H₂CO₃).
A hydrocarbon contained 14.3% hydrogen. The empirical formula of the hydrocarbon would be [C=12, H=1]
%C = 85.7; moles C = 85.7/12 = 7.14, H = 14.3/1 = 14.3; ratio C:H = 1:2, so CH₂.
Which of the following statements is not a chemical property of an acid?
Bases, not acids, evolve NH₃ when heated with ammonium salts; the other reactions are typical acid properties.
Halogens generally react with metals to form
Halogens react with metals to form ionic halide salts, e.g., NaCl.
Potassium chloride solid does not conduct electricity because
In solid KCl, ions are held in a fixed lattice by strong electrostatic forces, preventing movement needed for conduction.
When water was added to a white anhydrous substance X, the colour changed to blue, X is
Anhydrous CuSO₄ is white and forms blue CuSO₄·5H₂O upon hydration; the others do not change to blue.
Solubility curve can be applied in the determination of the
Solubility curves show how solubility changes with temperature, allowing calculation of crystals formed upon cooling.
If 0.2 g of a salt is required to saturate 200 cm³ of water at room temperature, What is the solubility of the salt?
Solubility = mass / volume = 0.2 g / 0.2 dm³ (200 cm³ = 0.2 dm³) = 1.0 g dm⁻³.
The property of a chemical reaction that is affected by a catalyst is the
A catalyst lowers the activation energy, speeding up the reaction without affecting ΔH, ΔG, or equilibrium position.
Soluble salts can be prepared by the following methods except
Double decomposition is typically used to prepare insoluble salts via precipitation; the others directly yield soluble salts.
Chemical reaction occurs when the colliding reactants have energy that is
Reactants must have energy exceeding the activation energy for successful collisions leading to products.
The common features of reactions at the anode is that
The anode is the site of oxidation, where species lose electrons; reduction occurs at the cathode.
Consider the following reaction: 2NO(g) + O₂(g) → 2NO₂. What is the change in the oxidation number of nitrogen?
In NO, N is +2; in NO₂, N is +4 (O₂ is -4, so N +4).
Which of the following characterize members of the same homologous series?
Homologous series members differ by -CH₂- in formula, with gradual physical property changes and similar chemical properties due to the same functional group.
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