Chemistry 2018 Jamb Examination

Concentrated sulphuric acid acts as a strong dehydrating agent but also as an acid. It reacts with basic gases such as ammonia (NH₃) to form ammonium sulphate \((NH_4)_2SO_4\).
Therefore, ammonia cannot be dried using concentrated sulphuric acid because it reacts chemically with it.
Other gases like hydrogen chloride (HCl), chlorine (Cl₂), and sulphur dioxide (SO₂) can be safely dried by the acid without chemical reaction.

Each successive member of the alkane homologous series differs from the previous one by a \(CH_2\) group. This means that as you move from methane \((CH_4)\) to ethane \((C_2H_6)\), and so on, the molecular formula increases by one carbon and two hydrogens each time.
Thus, the difference between consecutive alkanes is a methylene group (\(CH_2\)).

In the correct electrochemical (activity) series, metals are arranged in decreasing order of reactivity. Magnesium (Mg) is more reactive than aluminium (Al).
In the given sequence, aluminium appears before magnesium, which is incorrect. By interchanging Al and Mg, the series becomes correctly ordered from most to least reactive.
Therefore, the correct adjustment is interchanging Al and Mg.

According to the kinetic theory of gases, gas molecules move randomly in straight lines between collisions. This motion indicates that there are no attractive or repulsive forces acting between them, and collisions are perfectly elastic.
Perfectly elastic collisions mean that kinetic energy is conserved during collisions, and molecules change direction only when they collide with each other or the container walls.

The solubility of a gas in a liquid depends on several factors. It is influenced by the nature of both the solvent and solute (since chemical interactions matter), temperature (since solubility generally decreases with increasing temperature), and pressure (by Henry’s law, solubility increases with pressure).
Hence, all four factors — I, II, III, and IV — affect gas solubility.

In the periodic table, elements are arranged in periods (rows) and groups (columns). Across a period, the number of valence electrons increases progressively from left to right, while the number of shells remains the same.
Therefore, the correct statement is that the valence electrons of elements in the same period increase progressively across the period.

The modern periodic table is arranged according to increasing atomic numbers, not atomic weights. This arrangement resolves anomalies that were present in Mendeleev’s version which was based on atomic weights.
Moseley’s work established that atomic number, representing the number of protons in an atom, is the fundamental property determining an element’s position in the periodic table.

Using the dilution formula M₁V₁ = M₂V₂: M₁ = 2.2 M, V₁ = 1 L, V₂ = 1 + 10 = 11 L\[M_2 = \dfrac{M_1V_1}{V_2} = \dfrac{2.2 \times 1}{11} = 0.2M\]The resulting solution has a concentration of 0.2M.

On heating ammonium chloride \((NH_4Cl)\), it decomposes into ammonia \((NH_3)\) and hydrogen chloride \((HCl)\):\[NH_4Cl(s) \rightarrow NH_3(g) + HCl(g)\]Ammonia is basic and turns red litmus paper blue, while hydrogen chloride is acidic and turns blue litmus paper red.
Since the HCl gas diffuses faster initially due to its lower molecular mass, the damp neutral litmus paper first turns red.

When fats (esters of glycerol and long-chain fatty acids) are boiled with aqueous sodium hydroxide, they undergo a reaction that produces glycerol and sodium salts of fatty acids (soap).
This process is known as saponification.
It is the reverse of esterification and is a form of alkaline hydrolysis.