What is the percentage by mass of oxygen in potassium carbonate (K₂CO₃)? [K = 39, C = 12, O = 16]
Molar mass of K₂CO₃ = (2×39) + 12 + (3×16) = 138 g/mol. Mass of oxygen = 3×16 = 48 g. Percentage = (48/138) × 100 ≈ 34.8%.
Which of the following processes involves the absorption of heat?
Evaporation is endothermic, requiring heat to break intermolecular forces in water.
The technique used to separate pigments in a mixture of inks is
Chromatography separates pigments based on their differing affinities for a stationary phase.
A compound contains 52.2% carbon, 13.0% hydrogen, and 34.8% oxygen by mass. What is its empirical formula? [C = 12, H = 1, O = 16]
Assume 100 g: C = 52.2/12 = 4.35 mol, H = 13.0/1 = 13.0 mol, O = 34.8/16 = 2.175 mol. Divide by 2.175: C:H:O ≈ 2:6:1. Empirical formula = C₂H₆O.
A gas occupies 500 cm³ at 37°C and 1 atm. What is its volume at 0°C and 1 atm?
Using Charles’ law (V₁/T₁ = V₂/T₂) at constant pressure, T₁ = 310 K, T₂ = 273 K. V₂ = (500 × 273)/310 ≈ 462 cm³.
Which element in period 3 forms an amphoteric oxide?
Aluminium oxide (Al₂O₃) reacts with both acids and bases, making it amphoteric.
The oxidation number of nitrogen in NH₄NO₃ is
NH₄NO₃ contains NH₄⁺ and NO₃⁻. For NH₄⁺: N + 4(+1) = +1 → N = -3. For NO₃⁻: N + 3(-2) = -1 → N = +5.
The bond between carbon and oxygen in CO₂ is
CO₂ has double covalent bonds between carbon and each oxygen atom.
The molecular geometry of ammonia (NH₃) is
NH₃ has three bonding pairs and one lone pair, resulting in a trigonal pyramidal shape.
Which of the following is a property of transition metals?
Transition metals have variable oxidation states due to d-orbital electrons.
The emission of a beta particle from a nucleus results in
Beta decay (β⁻) converts a neutron to a proton, increasing the atomic number by 1.
What is the molarity of a solution containing 4 g of NaOH in 250 cm³ of solution? [Na = 23, O = 16, H = 1]
Molar mass of NaOH = 40 g/mol. Moles = 4/40 = 0.1 mol. Volume = 0.25 dm³. Molarity = 0.1/0.25 = 0.4 mol dm⁻³.
The raw material used in the Ostwald process for nitric acid production is
The Ostwald process oxidizes ammonia (NH₃) to produce nitric acid (HNO₃).
The pH of a 0.001 mol dm⁻³ solution of HCl is
HCl is a strong acid, [H⁺] = 0.001 M. pH = -log(0.001) = 3.
In the reaction 2H₂S + SO₂ → 3S + 2H₂O, the oxidizing agent is
Oxidation: H₂S (S = -2) to S (S = 0). Reduction: SO₂ (S = +4) to S (S = 0). SO₂ is reduced, so it is the oxidizing agent.
The catalyst used in the hydrogenation of alkenes is
Nickel catalyzes the addition of hydrogen to alkenes, forming alkanes.
Which of the following pollutants is primarily responsible for acid rain?
Sulfur dioxide (SO₂) forms sulfuric acid in the atmosphere, causing acid rain.
The IUPAC name of CH₃CH(CH₃)CH₂OH is
The longest chain is 3 carbons (propane) with -OH on carbon 1 and a methyl group on carbon 2, named 2-methylpropan-1-ol.
Which of the following is a ketone?
CH₃COCH₃ (propanone) is a ketone with the R₁COR₂ structure.
The reaction of an alkene with hydrogen gas in the presence of a catalyst is called
Alkenes undergo addition reactions with H₂ to form alkanes.
Which of the following is a secondary amine?
(CH₃)₂NH (dimethylamine) is a secondary amine with two alkyl groups.
The fractional distillation of crude oil produces
Crude oil yields gases (LPG), liquids (petrol), and solids (bitumen).
The functional group in an alkanoic acid is
Alkanoic acids (carboxylic acids) have the -COOH functional group.
Which of the following is used to soften hard water?
Sodium carbonate (Na₂CO₃) precipitates Ca²⁺ and Mg²⁺ ions to soften water.
The molecular formula of the third member of the alkyne homologous series is
Alkynes follow CₙH₂ₙ₋₂. The series is C₂H₂ (n=2), C₃H₄ (n=3), C₄H₆ (n=4). The third member is C₄H₆.
The product of the reaction between ethanoic acid and methanol is
CH₃COOH + CH₃OH → CH₃COOCH₃ (methyl ethanoate) + H₂O.
Which metal is extracted from bauxite?
Bauxite (Al₂O₃·nH₂O) is the primary ore for aluminium.
The type of isomerism exhibited by CH₃CH₂CHClCH₃ is
2-Chlorobutane (CH₃CH₂CHClCH₃) has a chiral carbon with four different groups (H, Cl, CH₃, C₂H₅), exhibiting optical isomerism.
The compound responsible for the temporary hardness of water is
Calcium hydrogen carbonate (Ca(HCO₃)₂) causes temporary hardness, removable by boiling.
The gas used in welding is
Ethyne (acetylene) produces a high-temperature flame for welding.
The electrolyte used in the lead-acid battery is
Dilute sulfuric acid (H₂SO₄) is the electrolyte in lead-acid batteries.
Which of the following is a natural polymer?
Starch is a natural polysaccharide polymer, unlike synthetic polymers.
The test for an aldehyde involves the use of
Aldehydes reduce Fehling’s solution, forming a red Cu₂O precipitate.
The major product of the saponification of an ester is
Saponification produces a soap (sodium salt of a fatty acid) and an alcohol.
Which of the following is an efflorescent substance?
Na₂CO₃·10H₂O loses water to the atmosphere, making it efflorescent.
The rate of a reaction is doubled when the temperature increases by 10°C. This is due to
Higher temperature increases molecular collisions, doubling the reaction rate.
The allotrope of sulfur used in vulcanizing rubber is
Rhombic sulfur is used to cross-link rubber during vulcanization.
During the electrolysis of dilute H₂SO₄ using platinum electrodes, the gas produced at the anode is
At the anode, water is oxidized: 2H₂O → O₂ + 4H⁺ + 4e⁻, producing oxygen.
The compound formed when propene reacts with HBr is
Propene (CH₃CH=CH₂) with HBr follows Markovnikov’s rule, forming 2-bromopropane (CH₃CHBrCH₃).
The industrial process used to produce ethanol from ethene is
Hydration of ethene (C₂H₄) with steam and a catalyst produces ethanol (C₂H₅OH).
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