This 2024 chemistry evaluation emphasizes organic compound nomenclature, gas laws, and solution chemistry calculations. Across the provided questions, you will frequently encounter topics involving hydrocarbons and functional group transformations, gas behavior laws and diffusion rates, and acid-base titrations alongside pH determinations. A successful study strategy involves reading the detailed solution explanations for each calculation to fully master the core formulas.
Topics in this paper
What is the IUPAC name of the compound with the formula (CH₃)₃CCH₂CH₃?
A student might mistakenly select 2,5-dimethyl or a different carbon chain length due to numbering from the wrong end. (CH₃)₃CCH₂CH₃ is a five-carbon chain (pentane) with two methyl groups on the second carbon. The longest chain is pentane, and the substituents are named as 2,2-dimethylpentane, following IUPAC rules for the lowest possible numbers. Common mistake: failing to locate the longest continuous carbon chain properly.
The reaction of an alcohol with an alkanoic acid in the presence of concentrated H₂SO₄ will produce an
One might mistakenly choose an alkene or alkanol by confusing esterification with dehydration or hydration reactions. An alcohol (ROH) reacts with an alkanoic acid (R'COOH) in the presence of H₂SO₄ (catalyst) to form an ester (alkanoate, R'COOR) and water via esterification: ROH + R'COOH → R'COOR + H₂O. Common mistake: mistaking the acid-catalysed combination of organic acids and alcohols for simple dehydration.
The final product of the reaction of ethyne with hydrogen in the presence of a palladium catalyst is
A student could mistakenly select an alkene like ethene if they assume hydrogenation stops halfway. Ethyne (C₂H₂) undergoes complete hydrogenation with H₂ in the presence of a palladium catalyst: C₂H₂ + 2H₂ → C₂H₆ (ethane, CH₃—CH₃), a fully saturated alkane. The triple bond is entirely reduced when excess hydrogen is applied with a palladium catalyst. Common mistake: stopping the reduction at the double-bond stage when complete hydrogenation occurs.
How many structural isomers can be drawn for the non-cyclic alkane with the molecular formula C₅H₁₂?
One might mistakenly select 2 or 4 isomers by either missing the branched structures or overcounting stereoisomers. C₅H₁₂ (pentane) has three structural isomers: n-pentane (straight chain), 2-methylbutane (isopentane), and 2,2-dimethylpropane (neopentane). These represent all unique connectivity patterns available for a five-carbon alkane. Common mistake: missing the neopentane branched configuration.
Synthetic detergents are preferred over soap for laundry in hard water because
A student might mistakenly believe that detergents lack hydrocarbon chains or that soap salts are soluble. Hard water contains Ca²⁺ and Mg²⁺ ions, which form insoluble salts with soap (e.g., calcium stearate), reducing its effectiveness. Detergents form soluble salts with these ions, maintaining cleaning efficiency. Common mistake: thinking traditional soaps perform equally well in hard water conditions.
The synthetic rubber obtained by the polymerization of chlorobutadiene in the presence of sodium is called
One might mistakenly choose teflon, polythene, or isoprene by confusing different polymer classes. Chlorobutadiene (2-chlorobuta-1,3-diene) polymerizes to form neoprene, a synthetic rubber used in applications like wetsuits due to its durability. The polymerization of this specific halodiene yields neoprene rubber. Common mistake: confusing chloroprene polymers with natural rubber isoprene units.
25 cm³ of 0.02 M KOH neutralized 0.03 g of a monobasic acid. The molecular mass of the acid is
A student might miscalculate the stoichiometry or confuse the acid basicity, leading to alternative numerical values. Moles of KOH = 0.02 × (25/1000) = 0.0005 mol. For a monobasic acid (HA), moles of acid = moles of KOH = 0.0005 mol. Mass of acid = 0.03 g. Molecular mass = 0.03 / 0.0005 = 60 g mol⁻¹. The closest option is 75 g mol⁻¹, suggesting a possible error in the provided options. Common mistake: arithmetic errors when converting volume units from cubic centimeters to liters.
When Fehling’s solution is added to two isomeric carbonyl compounds X and Y with the molecular formula C₅H₁₀O, compound X gives a red precipitate while Y does not react. It can be inferred that X is
One might mistakenly select a ketone or an alkane by misunderstanding how Tollens or Fehling's reagents identify functional groups. Fehling’s solution detects aldehydes, forming a red Cu₂O precipitate. Compound X (C₅H₁₀O) is an aldehyde, CH₃CH₂CH₂CH₂CHO (pentanal). Compound B is a ketone (pentan-2-one), C is an alkane, and D is also an aldehyde but not the primary choice. Common mistake: failing to distinguish between reducing aldehydes and non-reducing ketones.
Which of the following compounds contains only sp³ hybridized carbon atoms?
A student could mistakenly choose ethene, benzene, or ethyne, overlooking multiple bonds and their respective orbital states. Ethane (C₂H₆) has carbon atoms with four single bonds (sp³ hybridized). Ethene (C₂H₄, sp²), benzene (C₆H₆, sp²), and ethyne (C₂H₂, sp) have carbons with double or triple bonds, indicating different hybridizations. Common mistake: ignoring the presence of pi bonds when determining carbon hybridization.
The oxidation of which of the following alcohols will produce a ketone?
One might mistakenly select a primary or tertiary alcohol, forgetting that they yield aldehydes/carboxylic acids or resist oxidation. Secondary alcohols oxidize to ketones. Pentan-2-ol (CH₃CH(OH)CH₂CH₂CH₃) is a secondary alcohol, forming pentan-2-one (CH₃COCH₂CH₂CH₃). Option A is tertiary (no ketone), B and C are primary (form aldehydes/acids). Common mistake: confusing the oxidation products of primary versus secondary hydroxyl groups.
The addition of water to calcium oxide leads to
Options like a physical change or the formation of a mixture might be selected by mistaking hydration for simple mixing. The process involves mixing water with calcium oxide, also known as the slaking of lime, which yields calcium hydroxide. Because a brand new chemical substance is created through this reaction, it represents a permanent chemical change rather than a physical one. Common mistake: confusing the production of a new compound with a physical phase mixture.
A mixture of iron and sulphur can be separated by dissolving the mixture in
Students might incorrectly try steam, benzene, or sodium hydroxide thinking they selectively dissolve the solid. Iron reacts with dilute hydrochloric acid to produce iron(II) chloride and hydrogen gas, whereas sulphur does not react. By applying filtration, the insoluble sulphur remains trapped while the iron solution passes through to achieve separation. Common mistake: selecting unreactive solvents that fail to dissolve or react with either component.
A given amount of gas occupies 10.0 dm³ at 4 atm and 273°C. The number of moles of the gas present is [Molar volume of a gas at s.t.p = 22.4 dm³, R = 0.0821 dm³ atm K⁻¹ mol⁻¹]
Some candidates might pick alternative values from poor temperature conversion or arithmetic errors. Applying the ideal gas law equation, pressure is 4 atm, volume is 10.0 dm³, and temperature must be converted to Kelvin by adding 273 to 273°C to obtain 546 K. Dividing pressure times volume by the product of the gas constant 0.0821 and temperature yields approximately 0.89 mol. Common mistake: forgetting to convert Celsius to Kelvin before using the ideal gas equation.
If sulphur dioxide and methane are released simultaneously at the opposite ends of a narrow tube, the rates of diffusion R_SO₂ and R_CH₄ will be in the ratio
Distractors like 1:4 or 2:1 are easily chosen by inverting molar masses or misapplying Graham's law. According to Graham's law, the diffusion rate ratio is inversely proportional to the square root of their molar masses. Calculating the molar masses gives 64 for sulphur dioxide and 16 for methane, leading to the square root of 16 over 64, which simplifies to 1 in 2. Common mistake: placing the wrong molar mass in the numerator of the diffusion ratio.
30 cm³ of hydrogen was collected over water at 27°C and 780 mm Hg. If the vapour pressure of water at this temperature is 80 mm Hg, calculate the volume of the gas at 760 mm Hg and 70°C.
Options like 25.2 cm³ or 27.5 cm³ are typically chosen by omitting vapor pressure adjustments. The pressure of dry hydrogen is found by subtracting the water vapor pressure of 80 mm Hg from the total 780 mm Hg to yield 700 mm Hg. Using the combined gas law with initial conditions of 700 mm Hg, 30 cm³, and 300 K alongside final conditions of 760 mm Hg and 343 K computes to about 28.4 cm³. Common mistake: failing to subtract aqueous tension from the total pressure.
A given amount of gas occupies 10.0 dm³ at 4 atm and 277°C. The number of moles of the gas present is [R = 0.0821 dm³ atm K⁻¹ mol⁻¹]
Miscalculations involving the temperature or decimal placement often lead students to choose 0.089 mol or 2.70 mol. By utilizing the ideal gas law formula, insert 4 atm for pressure, 10.0 dm³ for volume, and 550 K derived from 277 plus 273 for absolute temperature. Multiplying pressure and volume and then dividing by the product of the gas constant 0.0821 and 550 yields approximately 0.89 mol. Common mistake: incorrect addition when converting Celsius to Kelvin.
32 g of anhydrous copper(II) tetraoxosulphate(IV) dissolved in 1 dm³ of water generated 130 kJ mol⁻¹ of heat. The heat of solution is
Distractors such as 65 or 260 kJ mol⁻¹ arise from dividing or multiplying by the incorrect stoichiometric mole fraction. The molar mass of anhydrous copper(II) tetraoxosulphate(IV) is calculated as 159.5 g per mole, meaning 32 g gives roughly 0.2 moles. Since the heat of solution is already defined per mole as 130 kJ mol⁻¹ directly in the setup, the value remains unchanged. Common mistake: recalculating the per-mole enthalpy value using mass ratios unnecessarily.
Excess phosphorus was burnt in a gas jar, and the residual gas was passed over concentrated KOH solution. The gases collected are
Students may mistakenly select oxygen or nitrogen alone by overlooking the components of air trapped inside the jar. Air consists of nitrogen, oxygen, and rare gases, but burning excess phosphorus consumes all the oxygen and turns it into phosphorus pentoxide, which is completely absorbed by the potassium hydroxide. This leaves behind only unreactive nitrogen and rare gases. Common mistake: forgetting that air is a mixture containing unreactive noble gases alongside nitrogen.
Potassium tetraoxomanganate(VII) is often added to impure water to
Options like reducing inorganic impurities or removing hardness are commonly guessed due to a general view of water treatment chemicals. Potassium tetraoxomanganate(VII) acts as a powerful oxidizing agent capable of destroying harmful bacteria and algae during purification. Common mistake: confusing oxidizing disinfectants with water softeners that target mineral ions.
The soil in a battery manufacturing factory is likely to contain a high concentration of
Students might incorrectly guess calcium or aluminum salts by associating general industrial waste with common geological minerals. Manufacturing lead-acid batteries involves heavy use of lead compounds, meaning contaminated soil surrounding such factories will naturally show a high concentration of lead ions. Common mistake: associating factory pollutants with general hardness minerals instead of the specific heavy metal manufactured.
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