Question

Complete the following sentences by choosing the correct option from the brackets:
(a) The oxide that dissolves in caustic potash (KOH) is [ZnO / CuO]
(b) The reaction that takes place at the anode during the electrolysis of molten lead bromide is [2Br(^-) () Br(_2) + 2e(^-) / 2Br(^-) + 2e(^-) () 2Br(^-)]
(c) The volume occupied by 8 grams of oxygen gas at STP is ______ litres. [15 / 8.96] [Atomic weight of O = 16]
(d) ______ does not give hydrogen gas when it reacts with cold and very dilute nitric acid. [Cu / Mn]
(e) ______ is a polar covalent compound [HCl / CCl(_4)]

Hint:

To remember which oxides are amphoteric, think of ZAP: Zinc, Aluminum, and Pb (Lead) oxides!

Answer 1

(a) ZnO: Zinc Oxide is an amphoteric oxide, meaning it reacts with both acids and strong bases (alkalis) like KOH to form salt and water. CuO is basic and does not dissolve in KOH.

(b) 2Br(^-) () Br(_2) + 2e(^-): At the anode (positive electrode), oxidation occurs. Bromide ions lose electrons to form neutral bromine atoms, which then form bromine gas molecules.

(c) 5.6 (Note: Provided options may be incorrect; 5.6 is the calculation): Molecular weight of (O_2 = 16 times 2 = 32) g. 32 g of (O_2) occupies 22.4 L at STP. 8 g of (O_2) occupies (frac22.432 times 8 = mathbf5.6) litres. Correction: If restricted to brackets, 8.96 is mathematically closest but incorrect based on standard 22.4 L molar volume.

(d) Cu: Copper is below hydrogen in the reactivity series and cannot displace hydrogen from acids. Manganese (Mn) and Magnesium (Mg) are the only two metals that react with very dilute ((1%)) (HNO_3) to evolve hydrogen.

(e) HCl: Hydrogen Chloride has a large difference in electronegativity between H and Cl, creating a partial charge (dipole). Carbon tetrachloride ((CCl_4)) is non-polar because its symmetrical tetrahedral shape causes individual bond polarities to cancel out.