JAMB Chemistry 2001
Questions & Answers

One might erroneously pick fixed shape and volume, which describes solids rather than fluids. Because there are large spaces between particles, gases are highly compressible. Common mistake: Confusing the particulate spacing of gases with that of solids.

A student might mistakenly select a pure substance like common salt or washing soda, assuming all white crystalline solids are compounds. Blood is classified as a mixture because it is composed of plasma, cells, and other diverse components. Common mistake: Failing to distinguish between a chemical compound and a biological suspension or mixture.

A student might miscalculate by omitting the subscript multiplier for nitrogen or using an incorrect total molar mass. By determining the molar mass of Ca(NO3)2 as 164 and calculating the mass percentage of the two nitrogen atoms, the resulting value is (2 multiplied by 14) divided by 164 multiplied by 100, which equals 17.1%. Common mistake: Forgetting to multiply the atomic mass of nitrogen by two to account for the formula's subscripts.

A student might mistakenly think the cold bottle transfers heat into the surrounding air or that the milk loses heat internally. Water vapour condenses on the cold surface because it loses some of its energy to the cold bottle. Common mistake: Misinterpreting the direction of heat transfer during condensation.

A student might mistakenly select half the original volume or four times the volume by misapplying Boyle's law proportions. According to Boyle's law, pressure and volume are inversely proportional; thus, reducing the pressure to half at constant temperature doubles the volume to 2V cm3. Common mistake: Inverting the relationship between pressure and volume.

One might mistakenly attribute the trend to a decrease in nuclear charge or screening effects. Moving across a period, the nuclear charge increases, which pulls electrons closer and makes them harder to remove, leading to higher ionization energy. Common mistake: Confusing periodic trends in atomic radius with ionization energy mechanisms.

A student might guess none or two by misinterpreting electron configuration filling rules. Nitrogen has the electron configuration 1s2 2s2 2p3, meaning its 2p sub-level contains three unpaired electrons. Common mistake: Miscounting electrons in sub-level orbitals.

One might incorrectly believe noble gases are stable because they belong to group zero or are volatile. Their chemical stability is directly due to having complete duplet or octet electron configurations. Common mistake: Associating group location with chemical reactivity rather than valence shell configuration.

A student might mistakenly choose 18 or 32 by applying the formula to higher principal energy levels. The L shell corresponds to the second principal shell (n=2), and using the 2n2 rule yields a maximum capacity of 2 times 2 squared, which equals 8 electrons. Common mistake: Miscalculating shell electron capacities using the principal quantum number.

A student might mistakenly select atomic number or chemical properties, forgetting that elements in a group share similar chemical traits rather than elements in a period. Elements in the same period share the same number of electron shells. Common mistake: Confusing periodic table groups with periods regarding property similarities.

One might incorrectly identify the process as alpha decay or nuclear fission due to the presence of helium or neutrons. The combination of deuterium and tritium to form helium and energy illustrates nuclear fusion. Common mistake: Confusing the joining of light nuclei in fusion with the splitting of heavy nuclei in fission.

A student might mistakenly select neon or argon, which are common noble gases used in general lighting. Krypton emits a specialized light with a high power of fog penetration, making it ideal for aerodrome beacons. Common mistake: Confusing general noble gas applications with specialized aviation lighting.

A student might mistakenly choose boiling or filtration, which only remove temporary hardness or suspended particles. Caustic soda removes permanent hardness from water by precipitation. Common mistake: Confusing the treatment methods for temporary versus permanent water hardness.

One might mistakenly select efflorescent or amphoteric, confusing water-losing compounds with moisture-absorbing ones. Substances employed as drying agents are usually hygroscopic because they absorb moisture from their surroundings. Common mistake: Confusing hygroscopic moisture absorbers with efflorescent compounds.

A student might mistakenly divide by the wrong solvent volume or miscalculate the molar mass of copper (II) sulphate. With a molar mass of 160 for CuSO4, 40g yields 0.25 moles, which when dissolved in 0.1 dm3 of water gives a solubility of 2.5 mol dm-3. Common mistake: Failing to convert the mass of water from grams to cubic decimeters for concentration calculations.

One might mistakenly choose kerosene or turpentine, which are typically used for oily or grease stains. Coffee stains are best removed using an ammonia solution. Common mistake: Using petroleum solvents on water-soluble organic stains like coffee.

A student might mistakenly assume it causes lung cancer or directly injures the nervous system. Carbon (IV) oxide is dangerous because it competes with oxygen in the blood, reducing oxygen availability. Common mistake: Confusing asphyxiation mechanisms with direct cellular toxicity.

One might mistakenly choose trioxonitrate (V) or boric acid, which lack the specific iron-dissolving properties needed. Hydrochloric acid is the correct acid used to dissolve rust, which is iron oxide. Common mistake: Choosing weak acids for mineral deposit and corrosion removal.

A student might mistakenly use an incorrect stoichiometric ratio or miscalculate the moles of sodium hydroxide. Since 25 cm3 of 0.1 mol dm-3 NaOH contains 0.0025 moles, and the reaction requires a 2:1 ratio, the required volume of 0.5 mol dm-3 H2SO4 is 2.5 cm3. Common mistake: Forgetting the stoichiometric mole ratio from the balanced neutralization equation.

A student might mistakenly choose pink or red, which are the indicator's colors in acidic environments. Methyl orange turns yellow in an alkaline medium when the pH exceeds 4.4. Common mistake: Confusing acid-base indicator color changes.