2021 JAMB CHEMISTRY PAST QUESTIONS AND ANSWERS

Isobutyl bromide is the correct name for this compound. The structure shows a branched four-carbon chain with a bromine atom. The “iso” prefix indicates the methyl branch on the second carbon. The compound has a butyl group with a bromine substitution.

Zymase is the specific enzyme responsible for converting glucose to ethanol during fermentation. This enzyme is found in yeast cells and catalyzes the conversion of glucose to ethanol and carbon dioxide. Other options are enzymes with different functions: maltase breaks down maltose, diastase converts starch to maltose, and invertase breaks down sucrose.

Einstein proposed the mass-energy equivalence through his famous equation $E = mc^2$, which demonstrates that mass and energy are interchangeable. This revolutionary concept showed that matter could be converted into energy and vice versa. Other scientists listed made different contributions: Boyle (gas laws), Lavoisier (conservation of mass), and Avogadro (molecular theory).

Propyne (methyl acetylene) is the IUPAC name for this compound. It contains a triple bond between carbons and has three carbons in total. The compound shows an alkyne functional group with a methyl substituent. Acetylene refers to ethyne ($HC≡CH$), while butanol and decanoic acid are completely different compounds.

Copper(II) carbonate is the correct name as copper forms a +2 oxidation state in this carbonate compound. The carbonate ion ($CO_3^{2-}$) combines with $Cu^{2+}$ to form a neutral compound. Copper(I) and Copper(III) are incorrect oxidation states for this compound.

Potassium dichromate-sulfuric acid solution turns from orange to green when it reacts with alcohol in breath. This color change serves as an indicator of alcohol consumption. The other options don’t react specifically with alcohol in breath samples.

Mercury is a pure element (symbol Hg), not a mixture. All other options are mixtures: air (mixture of gases), milk (mixture of water, fats, proteins), and cement (mixture of calcium compounds and other materials).

Bromine is the only non-metal that exists as a liquid at room temperature ($20°C$). Chlorine is a gas, phosphorus is a solid, and helium is a gas at room temperature and standard pressure.

Only cooking and digestion of food involve chemical changes where new substances are formed. Freezing water and heating water are physical changes as they only change the state of matter without forming new substances.

The atomic mass of nitrogen is 14 atomic mass units (amu). This represents the weighted average of all naturally occurring isotopes of nitrogen, with nitrogen-14 being the most abundant isotope.

Carbon dioxide ($CO_2$) is the primary greenhouse gas responsible for global warming. It traps heat in the atmosphere and increases global temperatures. Other gases listed ($O_2$, $N_2$, He) are not greenhouse gases.

Kerosene is a hydrocarbon fuel composed only of carbon and hydrogen atoms. All other options contain oxygen: soil (metal oxides), glass (silicon dioxide), and cement (calcium compounds with oxygen).

Sublimation is the direct conversion of a solid to gas without passing through the liquid state. This process occurs in substances like camphor, naphthalene, and dry ice ($CO_2$). The other options describe different physical phenomena.

The maximum number of electrons in the N shell (n=4) is 32, calculated using the formula $2n^2$ where n is the principal quantum number. For N shell, n=4, so maximum electrons = $2(4)^2 = 32$.

James Chadwick discovered neutrons in 1932 through experiments with beryllium radiation. The other scientists made different discoveries: Rutherford (proton), Thompson (electron), and Dalton (atomic theory).

All listed options are forms of calcium carbonate ($CaCO_3$). Limestone, marble, chalk, and egg shells all contain $CaCO_3$ as their primary component, though they differ in their physical structure and purity.

Surface tension reduction is the principle behind soap’s cleaning action. Soap molecules reduce water’s surface tension, allowing it to better wet surfaces and remove dirt. Other options don’t explain soap’s cleaning mechanism.

Fluorine’s high electronegativity makes it extremely reactive. This property causes fluorine to strongly attract electrons from other atoms, making it the most electronegative element and highly reactive.

The mass number is the sum of protons and neutrons in the nucleus. This number determines the isotope of an element and is always a whole number, not a fraction or related to atomic weight.

One mole (Avogadro’s number) of helium atoms has a mass of 4.00 grams, which is its atomic mass in grams. This follows from the definition of a mole and atomic mass units.

To find moles, divide mass by molar mass. For $CO_2$: $\frac{220g}{44g/mol} = 5$ moles. ($CO_2$ molar mass = 44 g/mol)

DNA molecules contain genetic information that controls inherited traits. While RNA, nucleotides, and enzymes play roles in gene expression, DNA is the primary molecule responsible for inheritance.

Argon (Ar) makes up about 0.93% of Earth’s atmosphere, making it the most abundant noble gas. The other noble gases (He, Ne, Xe) are present in much smaller quantities.

Thermal capacity is the amount of heat energy required to raise the temperature of an object by one Kelvin (K) or one degree Celsius (°C). This is a specific property of the material.

A hydrogen atom’s nucleus contains only one proton. The most common isotope of hydrogen (protium) has no neutrons, and electrons orbit the nucleus rather than being part of it.

Iron (Fe) can displace copper from copper sulfate solution due to its higher reactivity. This is a single displacement reaction where Fe replaces Cu in $CuSO_4$ solution.

The nucleus contains protons and neutrons. Electrons orbit the nucleus in electron shells but are not part of the nucleus itself. This is fundamental to atomic structure.

Concentration = $\frac{mass\space of\space solute}{total\space mass} × 100$ = $\frac{20g}{20g + 180g} × 100$ = $\frac{20}{200} × 100$ = 10%

Copper has natural antibacterial properties due to its ability to release ions that disrupt bacterial cell membranes. This property makes it useful in medical and hygiene applications.

Element 35 (Br) would resemble element 17 (Cl) as they are in the same group (halogens) and have similar electron configurations and chemical properties.

Reduction involves gain of electrons. This process occurs simultaneously with oxidation in redox reactions. The other options describe different chemical processes.

Redox reactions involve simultaneous oxidation (loss of electrons) and reduction (gain of electrons). These reactions are fundamental to many chemical processes including electrolysis and battery operation.

An oxide is a binary compound where oxygen combines with another element. The term specifically refers to compounds containing only oxygen and one other element.

Metallurgy is the comprehensive process of extracting metals from their ores and refining them for use. This includes various steps from mining to purification and processing.

Hydrocarbons are compounds containing only carbon and hydrogen atoms. These form the basis of organic chemistry and include alkanes, alkenes, alkynes, and aromatic compounds.

The exploration of metals is not a property of monosaccharides. The other options describe actual physical properties of monosaccharides including their solubility and behavior when heated.

Tropospheric pollutants are classified as gaseous (like $CO_2$, $SO_2$) and particulate (dust, smoke) based on their physical state. This classification helps in understanding their effects and control measures.

Ionization enthalpy is the energy required to remove an electron from a gaseous atom or ion in its ground state. This is a fundamental property that helps understand atomic structure and reactivity.

Actinoids are the fourteen elements following actinium, with atomic numbers 90-103. These elements are part of the f-block and share similar electronic configurations.

Hydrolysis is the reaction between salt and water that produces an acid or base. This process explains why some salt solutions are not neutral and is important in understanding buffer solutions.