2010 JAMB CHEMISTRY PAST QUESTIONS AND ANSWERS

$$\text{When a cold bottle is taken out, the temperature of the milk drops as it loses heat into the surroundings, causing water vapour in the air to condense into droplets. This is related to the saturated vapour pressure and temperature changes.}$$

$$\text{A mixture consists of two or more substances physically combined. Common salt is a pure compound, while blood, sand, and washing soda are mixtures. Blood is a heterogeneous mixture containing various components.}$$

$$\text{First, determine the molar mass of Ca(NO}_3)_2: Ca = 40, N = 14 \times 2 = 28, O = 16 \times 6 = 96. Total = 40 + 28 + 96 = 164. Percentage of N = \frac{28}{164} \times 100 = 17.07\% \approx 17.1\%.}$$

$$\text{Condensation occurs when warm moist air comes into contact with a cold surface, leading to water vapour turning into liquid droplets. This is because the saturated vapour pressure decreases with temperature drop.}$$

$$\text{According to Boyle’s Law, } P_1V_1 = P_2V_2. \text{ If } P_2 = \frac{P_1}{2}, \text{ then } V_2 = 2V. \text{ Therefore, the new volume is double the original volume.}$$

$$\text{First ionization energy increases across a period due to an increase in nuclear charge, which attracts electrons more strongly, and a decrease in the atomic radius. This makes it harder to remove an electron.}$$

$$\text{Nitrogen has an electronic configuration of } 1s^2 2s^2 2p^3. \text{ In the } 2p^3 \text{ sublevel, there are three unpaired electrons.}$$

$$\text{Noble gases have complete outer electron shells, achieving duplet or octet electron configurations, which makes them chemically inert and stable.}$$

$$\text{The L shell corresponds to the n=2 energy level, which can hold a maximum of 8 electrons.}$$

$$\text{Elements in the same period have the same number of electron shells.}$$

$$\text{This reaction represents nuclear fusion, where lighter nuclei combine to form a heavier nucleus, releasing energy in the process.}$$

$$\text{Krypton is commonly used in aerodrome beacons due to its high penetration power through fog, making it ideal for visibility in low-visibility conditions.}$$

$$\text{Permanent hardness, caused by calcium and magnesium ions, can be removed by adding substances like caustic soda or using ion-exchange resins. Boiling is ineffective.}$$

$$\text{Drying agents, or desiccants, are typically hygroscopic substances, which absorb moisture. Examples include silica gel and calcium chloride.}$$

$$\text{Solubility calculation: Molar mass of CuSO}_4 = 64 + 32 + (16 \times 4) = 160. \text{ Solubility} = \frac{40}{160 \times 0.1} = 2.5 \, \text{mol dm}^{-3}.}$$

$$\text{A solution of borax in water is effective for removing coffee stains due to its basic properties, which dissolve organic stains.}$$

$$\text{Carbon monoxide (CO) competes with oxygen for binding sites on hemoglobin, leading to potential suffocation. This toxic gas binds more strongly to hemoglobin than oxygen.}$$

$$\text{Hydrochloric acid (HCl) is often used to remove rust (iron oxide) from metal surfaces, as it reacts with the oxide to form soluble iron chloride.}$$

$$\text{Using the equation } \text{molarity } \times \text{ volume for neutralization, the volume of H}_2\text{SO}_4 needed is 2.5 \, \text{cm}^3.}$$

$$\text{Methyl orange turns yellow in an alkaline medium and red in acidic solutions. This color change is widely used as a pH indicator.}$$

$$\text{CaSO}_4 \text{ is slightly soluble in water, unlike Na}_2\text{CO}_3 \text{ and other highly soluble salts. AgCl and PbCl}_2 \text{ are sparingly soluble in cold water.}$$

$$\text{In this reaction, PH}_3 \text{ is oxidized to H}_3\text{PO}_3, \text{ thus it acts as the reducing agent. Oxidation and reduction are important in identifying electron transfer reactions.}$$

$$\text{According to IUPAC naming, LiAlH}_4 \text{ is called lithium tetrahydridoaluminate (III), as it contains Li and an Al-H bond structure.}$$

$$\text{Zinc coating, known as galvanization, protects iron by providing a sacrificial layer that corrodes before the iron.}$$

$$\text{Using Faraday’s law, the quantity deposited } = \frac{It}{nF}. \text{ Substituting values gives } 1.8 \, \text{g.}$$

$$\text{Thermal dissociation of ammonium chloride increases entropy, as solid decomposes into gases, increasing disorder.}$$

$$\text{An exothermic reaction with increased disorder results in a large decrease in free energy, favoring spontaneity.}$$

$$\text{MnO}_2 \text{ lowers the activation energy for decomposition of KClO}_3, \text{ thus reducing the required heat.}$$

$$\text{The graph illustrates the effect of surface area on the rate of reaction, as a larger surface area speeds up reactions by exposing more reactant particles to collisions.}$$

$$\text{Increasing the temperature shifts the equilibrium towards the reactants in an exothermic reaction, thereby decreasing the equilibrium constant.}$$

$$\text{The brown ring test is specific for detecting nitrate (NO}^-_3\text{) ions, which form a brown complex with Fe}^{2+} \text{ in acidic conditions.}$$

$$\text{Nitric oxide (NO) is produced during reactions involving nitrogen oxides, particularly when oxygen is limited, forming colorless NO gas.}$$

$$\text{HNO}_3 \text{ is commonly used in liquid rocket fuels due to its oxidizing properties, aiding in combustion.}$$

$$\text{Asbestos in chemical setups absorbs impurities or moisture, making it useful for drying or purifying gases.}$$

$$\text{Tin is a common component in both bronze and solder, enhancing durability and reducing melting points.}$$

$$\text{Rust forms as hydrated iron (III) oxide, resulting from oxidation in the presence of moisture.}$$

$$\text{Calcium ions (Ca}^{2+}\text{) produce an orange-red flame color, often used as a confirmatory test.}$$

$$\text{Stainless steel, resistant to corrosion, is commonly used in coins, medals, and durable tools.}$$

$$\text{Residues are often used to coat pipes or as raw material for further cracking to produce useful hydrocarbons.}$$

$$\text{Following IUPAC rules, the name for a structure with an eight-carbon chain with a propyl group at the third position is 3-propylheptane.}$$

$$\text{Ethyne (acetylene) is used in miners’ lamps as it produces a bright flame upon combustion, helpful in dark areas.}$$

$$\text{Acetic acid (CH}_3\text{COOH), due to its polar nature and hydrogen bonding, is highly soluble in water.}$$

$$\text{Cyclohexane is formed by hydrogenating benzene in the presence of a nickel catalyst, fully saturating the benzene ring.}$$

$$\text{Ethene (ethylene) is commonly used to accelerate fruit ripening by promoting ripening hormones.}$$

$$\text{In the presence of UV light, methane reacts with chlorine, resulting in the formation of tetrachloromethane (carbon tetrachloride) after a substitution reaction.}$$

$$\text{The boiling points increase as follows: C}_4\text{H}_{10} < C}_3\text{H}_7\text{OH} < C}_7\text{H}_{16}, \text{ based on molecular size and intermolecular forces.}$$

$$\text{Alkanes serve primarily as fuels in both domestic and industrial settings due to their combustibility.}$$

$$\text{Trichloromethane and tetrachloromethane are common in dry-cleaning for their ability to dissolve organic stains.}$$

$$\text{Alkanes do not decolorize bromine water, distinguishing them from unsaturated hydrocarbons like alkenes.}$$

$$\text{Chloroform (CHCl}_3\text{) is used in anesthesia for its depressant effects on the central nervous system.}$$