Which of the following would support the conclusion that a solid sample is a mixture?
A mixture typically has a melting range rather than a sharp melting point, as different components melt at slightly different temperatures. A range of 300°C to 309°C indicates a mixture.
A volatile liquid compound has a C:H:O ratio of 3:6:3. 0.127 g of the liquid on evaporation at s.t.p gave 32 cm³ of vapour. The molecular formula of the liquid is [G.M.V = 22.4 dm³]
Moles of vapour = 0.032/22.4 = 0.00143 mol. Molar mass = 0.127/0.00143 ≈ 89 g/mol. The empirical formula from C:H:O = 3:6:3 is CH₂O (molar mass = 30 g/mol). The molecular formula is (CH₂O)₃ = C₃H₆O₃ (molar mass = 90 g/mol), which is close to 89 g/mol.
Which of the following properties can be used to distinguish between two liquids with different boiling points?
Liquids with different boiling points will have different vapour pressures at a given temperature; the liquid with the lower boiling point will have a higher vapour pressure.
20.00 cm³ of a solution containing 0.53 g of anhydrous Na₂CO₃ in 100 cm³ requires 25.00 cm³ of H₂SO₄ for complete neutralization. The concentration of the acid in moles per dm³ is
Moles of Na₂CO₃ = (0.53/106) × (20/100) = 0.001 mol. Na₂CO₃ + H₂SO₄ → Na₂SO₄ + H₂O + CO₂. Moles of H₂SO₄ = 0.001 mol. Concentration of H₂SO₄ = 0.001/(25/1000) = 0.05 mol/dm³.
The minimum volume of oxygen required for the complete combustion of a mixture of 10 cm³ of CO and 15 cm³ of H₂ is
CO + ½O₂ → CO₂ (10 cm³ CO needs 5 cm³ O₂). H₂ + ½O₂ → H₂O (15 cm³ H₂ needs 7.5 cm³ O₂). Total O₂ = 5 + 7.5 = 12.5 cm³.
What is the partial pressure of hydrogen gas collected over water at standard atmospheric pressure and 25°C if the saturation vapour pressure of water is 23 mmHg at that temperature?
Standard atmospheric pressure = 760 mmHg. Partial pressure of H₂ = 760 - 23 = 737 mmHg.
The atomic radii of Li, Na, and K are 1.33Å, 1.54Å, and 1.96Å respectively. Which of the following explains this variation in atomic radii?
Li, Na, and K are in Group 1. As you go down the group, the number of electron shells increases, leading to larger atomic radii.
Which gas law describes the behavior of a gas when its pressure is inversely proportional to its volume at constant temperature?
Boyle’s Law states that P ∝ 1/V at constant temperature, meaning the product PV is constant for an ideal gas.
Elements X and Y have electronic configurations 1s²2s²2p⁶3s² and 1s²2s²2p⁶3s²3p⁵ respectively. When they combine, the formula of the compound formed is
X (1s²2s²2p⁶3s²) is magnesium (Mg), and Y (1s²2s²2p⁶3s²3p⁵) is chlorine (Cl). Mg²⁺ and Cl⁻ form MgCl₂, which is XY₂.
The atomic number of caesium is 55 and its atomic mass is 133. The nucleus of caesium atom therefore contains
Atomic number = 55 (protons), mass number = 133. Neutrons = 133 - 55 = 78. The nucleus contains 55 protons and 78 neutrons.
Four elements P, Q, R, and S have atomic numbers of 4, 10, 16, and 17 respectively. Which of these elements is a noble gas?
Element Q with atomic number 10 is neon, a noble gas.
How many valence electrons are contained in the element ₁₅P³⁻?
Phosphorus (P, atomic number 15) has 5 valence electrons (3s²3p³). P³⁻ gains 3 electrons, giving it 8 valence electrons (like argon).
If 1 dm³ of a saturated solution of HCl is cooled from 80°C to 20°C, the solubility of HCl decreases from 80 g/dm³ to 65 g/dm³. The mass of crystals deposited will be
Solubility drops from 80 g/dm³ to 65 g/dm³, so the mass deposited = 80 - 65 = 15 g per dm³.
Using 50 cm³ of 1 M potassium hydroxide and 100 cm³ of 1 M tetraoxosulphate(VI) acid, calculate the volume of acid in cm³ required to produce the maximum amount of potassium tetraoxosulphate(VI)
KOH + H₂SO₄ → KHSO₄ + H₂O (1:1 ratio). Moles of KOH = 1 × 0.05 = 0.05 mol, moles of H₂SO₄ = 1 × 0.1 = 0.1 mol. The limiting reagent is KOH, so 0.05 mol of H₂SO₄ is needed, which is 50 cm³.
A solution of calcium bromide contains 20 g dm⁻³. What is the molarity of the solution with respect to calcium bromide and bromide ions? [Molar mass of CaBr₂ = 200 g/mol]
Molarity of CaBr₂ = 20/200 = 0.1 mol/dm³. Each CaBr₂ dissociates into 1 Ca²⁺ and 2 Br⁻, so [Br⁻] = 2 × 0.1 = 0.2 mol/dm³.
The substance ZnO dissolves in sodium hydroxide solution and mineral acid solution to give soluble products in each case. ZnO is therefore referred to as
ZnO dissolves in both acids and bases, forming soluble salts, which is characteristic of an amphoteric oxide.
An acid and its conjugate base
A conjugate acid-base pair differs by one proton (H⁺). For example, HCl and Cl⁻ are a conjugate pair.
The same current is passed for the same length of time through solutions of AgNO₃ and CuSO₄. How much silver will be deposited if 1 g of copper is deposited? [Molar mass of Cu = 63.5 g/mol, Ag = 108 g/mol]
Moles of Cu = 1/63.5 = 0.0157 mol (Cu²⁺ + 2e⁻ → Cu). Moles of Ag = 2 × 0.0157 = 0.0314 mol (Ag⁺ + e⁻ → Ag). Mass of Ag = 0.0314 × 108 = 3.4 g.
Which substance is typically used to test for the presence of carbon dioxide in the laboratory?
Lime water (Ca(OH)₂) turns milky when carbon dioxide is passed through it due to the formation of calcium carbonate: Ca(OH)₂ + CO₂ → CaCO₃ + H₂O.
The gaseous pollutant sulphur(IV) oxide is most likely to be detected in fairly reasonable quantities in the
Smelting of copper often involves sulfide ores (e.g., Cu₂S), which release SO₂ when roasted: 2Cu₂S + 3O₂ → 2Cu₂O + 2SO₂.
Calcium hydroxide is added in the treatment of town water supply to
Calcium hydroxide (lime) is added to water to raise the pH and facilitate the coagulation of organic particles, aiding in their removal during water treatment.
What is discharged at the cathode during the electrolysis of concentrated sodium chloride solution with carbon electrodes?
In concentrated NaCl solution, water is reduced at the cathode: 2H₂O + 2e⁻ → H₂ + 2OH⁻, producing hydrogen gas.
Which of the following reactions involves the formation of a gas?
Fe + H₂SO₄ produces H₂ gas, and CaCO₃ + 2HCl produces CO₂ gas. Both reactions involve gas formation.
Bleaching powder, CaOCl₂·H₂O, deteriorates on exposure to air because
Bleaching powder reacts with CO₂ in the air: CaOCl₂ + CO₂ → CaCO₃ + Cl₂, losing its bleaching ability as chlorine is displaced.
The product of the thermal decomposition of ammonium trioxonitrate(V) are
NH₄NO₃ decomposes as: NH₄NO₃ → N₂O + 2H₂O.
The scale of a chemical balance is made of iron plate and coated with copper electrolytically because
Copper is less reactive and less susceptible to corrosion than iron, making it a suitable coating to protect the iron scale.
A metal is extracted by the electrolysis of its molten chloride and it displaces lead from lead(II) trioxonitrate(V) solution. The metal is
Sodium is extracted by electrolysis of its molten chloride (NaCl) and can displace lead from Pb(NO₃)₂ due to its high reactivity.
Mortar is NOT used for underwater construction because
Mortar sets by hydration, but underwater, the loss of water needed for hardening is hindered, and it may not set properly.
Which of the following is NOT involved in the extraction of metals from their ores?
Metal extraction typically involves reduction (e.g., with carbon, aluminium, or electrolysis). Oxidation is not a standard method for extracting metals from ores.
Which of the following compounds is an isomer of the compound CH₃CH₂CH₃?
CH₃CH₂CH₃ (propane, C₃H₈) has an isomer CH₃CH(CH₃)CH₃ (2-methylpropane), which has the same molecular formula but a different structure.
What is the gas responsible for most of the fatal explosions in coal mines?
Methane (CH₄) is the primary gas responsible for coal mine explosions due to its flammability and accumulation in mines.
The IUPAC name for CH₃CH₂COOH is
CH₃CH₂COOH has three carbons, with the carboxyl group (-COOH) as the functional group. The IUPAC name is propanoic acid.
When excess chlorine is mixed with ethene at room temperature, the product is
Ethene (C₂H₄) reacts with Cl₂ to form 1,2-dichloroethane (ClCH₂CH₂Cl) via addition across the double bond: C₂H₄ + Cl₂ → ClCH₂CH₂Cl.
Vulcanization of rubber is enhanced by which of the following?
Vulcanization involves heating rubber with sulphur, which forms cross-links between polymer chains, making the rubber stronger and more elastic.
The reaction between ethanoic acid and sodium hydroxide is an example of
Ethanoic acid (CH₃COOH) reacts with sodium hydroxide (NaOH) to form sodium ethanoate and water: CH₃COOH + NaOH → CH₃COONa + H₂O, which is a neutralization reaction.
The bond which joins two ethanoic acid molecules in the liquid state is
Ethanoic acid molecules form dimers in the liquid state through hydrogen bonding between the -OH group of one molecule and the C=O group of another.
The alkaline hydrolysis of fats and oils produces soap by the reaction of
Fats and oils are esters of glycerol (propane-1,2,3-triol) and fatty acids. Hydrolysis with a base (saponification) produces glycerol and soap.
Which of the following is NOT a monomer?
Starch is a polymer made of glucose monomers. Vinyl chloride, ethene, and propene are monomers used to form polymers like PVC and polyethene.
Three liquids X, Y, and Z containing only hydrogen and carbon were burnt on a spoon. X and Y burnt with sooty flames while Z did not. Y is able to discharge the colour of bromine water whereas X and Z cannot. Which of the liquids would be aromatic in nature?
X burns with a sooty flame (indicating unsaturation or aromaticity) but does not decolorize bromine water (ruling out alkenes), suggesting X is aromatic (e.g., benzene). Y decolorizes bromine water, indicating it’s an alkene, and Z is likely a saturated hydrocarbon (alkane).
Which of the following factors favors the formation of hydrogen in the reaction CO(g) + H₂O(g) ⇌ CO₂(g) + H₂(g), ΔH = -41000 J? I High pressure II Low pressure III High temperature IV Use of excess steam
The reaction has the same number of moles on both sides, so pressure has no effect. ΔH is negative (exothermic), so high temperature favors the reverse reaction (producing H₂). Excess steam shifts the equilibrium to the right (Le Chatelier’s principle).
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