Chemistry 2018 Jamb Examination

Ammonia is a basic gas and reacts with acids to form salts. Among the listed drying agents, concentrated tetraoxosulphate (VI) acid (H₂SO₄) is the only one that can chemically react with ammonia to remove it effectively by forming ammonium sulphate. Phosphorus(V) oxide, calcium chloride, and calcium oxide only remove moisture but not basic gases like ammonia.

When aluminium comes into contact with trioxonitrate (V) acid, a thin layer of aluminium oxide (Al₂O₃) forms on its surface. This oxide film is insoluble and prevents further reaction between the metal and the acid. The formation of this protective layer makes aluminium passive to both dilute and concentrated nitric acid.

Tap water undergoes treatment processes before distribution, which often include filtration and softening, removing calcium and magnesium ions. These minerals contribute to "hardness" in water. While the exact composition of tap water can vary depending on the source and treatment methods, it generally has a lower concentration of Ca²⁺ and Mg²⁺ compared to other natural water sources. 

The conductivity of an acid solution is determined by both the number of ions (which indicates how much the acid ionises) and the mobility of these ions in solution. A strong acid ionises completely and has more mobile ions, leading to higher conductivity. Hence, both factors — the amount of ions and their mobility — govern the solution’s electrical conductivity.

A metal can displace hydrogen from water or steam only if it is above hydrogen in the electrochemical series. Sodium, magnesium, and iron are all above hydrogen and can therefore react with water or steam. Copper, however, is below hydrogen in the series and cannot displace hydrogen from either water or steam.

P (6 electrons) is oxygen, Q (11 electrons) is sodium, R (15 electrons) is phosphorus, and S (17 electrons) is chlorine. Sodium (Q) is a metal that loses one electron to form Na⁺, while chlorine (S) is a non-metal that gains one electron to form Cl⁻. Thus, they form an electrovalent (ionic) bond NaCl. Hence, Q will form an electrovalent bond with S.

At the anode during the electrolysis of CuSO₄ with platinum electrodes, oxygen gas is evolved due to the oxidation of water. The reaction produces hydrogen ions, making the solution acidic. Hence, litmus in the anode compartment turns red. The reaction is:\[2H₂O \rightarrow O₂ + 4H⁺ + 4e⁻\]

Toluene (C₆H₅CH₃) can be nitrated to form trinitrotoluene (TNT), which is a well-known explosive compound. The nitration process involves treating toluene with a mixture of concentrated nitric acid and sulphuric acid to introduce nitro groups into the aromatic ring. Hence, toluene is the benzene derivative used in making explosives.

In electrovalent (ionic) bonding, a metal atom loses one or more electrons to form a positively charged ion (cation). This loss of electrons increases its oxidation number. For example, sodium (0 oxidation state) loses one electron to form Na⁺ with an oxidation number of +1. Thus, the oxidation number of the participating metal always increases.

When a metal atom loses electrons to form a cation, the resulting ionic radius becomes smaller than its atomic radius. This happens because the loss of electrons reduces electron-electron repulsion in the outer shells, allowing the nucleus to pull the remaining electrons closer. Hence, the ionic radius of metals is less than their atomic radius.