Tiêu đề 10.THE S-BLOCK ELEMENTS - Explanations.pdf ✅

On moving down the second group the thermal stability of alkaline earth metal carbonates increases. Hence, MgCO3, being the carbonate of upper element, decomposes at lowest temperature. 55 (b) BeCl2 exists in polymeric form. 56 (b) Salts of calcium are used in the form of manure e.g., triple superphosphate of lime [Ca(H2PO4 )2H2O]. 57 (c) All the alkali halides except lithium fluoride are freely soluble in water. I2 (non-polar) is least soluble in water. Group IIA carbonates (BaCO3 ) are insoluble in water. PbI2 is sparingly soluble in cold water but quite soluble in hot water. KF (most polar) is most readily soluble in water. 59 (a) (i) As we go down in group, in group. I, ionisation potential decreases and dissociation (M − OH) bond becomes easier. (ii) The hydroxide which can give OH − ion most easily will have highest basicity. ∴ Ionisation energy of Cs is least among Li, Na, K, Cs ∴ CsOH furnishes OH − most easily. ∴ CsOH is most basic. 60 (b) Among the alkaline earth metals, the size of beryllium and magnesium metals is very small. Therefore, the electrons in these metals are bounded more strongly and are not excited by the energy of flame to higher energy states. Hence, these metals or their salts do not impart any colour to the flame. 61 (c) Anhydrous CaCl2 is used for fast drying of neutral gases. 62 (b) Solubilities of carbonates decrease down the group because lattice energy decrease is almost constant while decrease in hydration energy downs sharply, finally difference of hydration energy and lattice energy decrease thus solubility decreases. 63 (a) Alkali metals are strongest reducing agent among elements of Periodic Table. The reducing character decreases down the group. ∴ Li is strongest reducing agent among Li, Na, Mg and Ca. 64 (c) As we go down in the group, ionic character increases hence, melting point of halides should increase but NaCl has the highest melting point (800°C) due to its high lattice energy. 65 (b) Basic mercuric carbonate is abtained in this reaction. Na2CO3 + 2HgCl2 → HgCO3 .HgO + 2NaCl + Cl2 + CO2 66 (d) Electropositive character increases as we move down the group because of the increase in atomic size, atoms have more tendency to lose electrons. Hence, Cs is most electropositive element in alkali metals. 67 (b) Alkali metals have only one electron in their ultimate shell, hence they can easily donate electron and act as reductant e.g., Fe2O3 + 6Na → 2Fe + 2Na2O 68 (d) Na2S2O3 r 2Na + + S2O3 2− S2O3 2− + I2 ⟶ S4O6 2− + I − i. e. , 2Na2S2O3 + I2 ⟶ Na2S4O6 + 2NaI 69 (b) Ca(OH)2 + Cl2 → CaOCl2 + H2O bleaching powder 70 (d) Carnallite is an ore of potassium and magnesium i.e., KCl . MgCl2 . 6H2O. 71 (b) Ti and Cu transition metals show variable valency. Pb so variable valency due to inert pair effect, while barium shows fixed valency 72 (b) Bleaching powder is obtained by treating chlorine with slaked lime. Ca(OH)2 + Cl2 → CaOCl2 + H2O Slaked lime bleaching powder 74 (c) Lithium and magnesium shows diagonal relationship. Some points of similarity are