12th Standard Chemistry Supplementary 2021: Online Practice Test

Explanation. Colloidal particles scatter light, so the path of the beam becomes visible. This scattering is the Tyndall effect.

Explanation. Impure Zr is converted to volatile \(ZrI_4\), which is then decomposed on a hot filament to give pure Zr. This iodide decomposition method is the Van Arkel process.

Explanation. Cream is an emulsion (liquid in liquid), butter is a gel (liquid in solid), whipped cream is a foam (gas in liquid) and ink is a sol (solid in liquid).

Explanation. DNA contains the pyrimidines cytosine and thymine; uracil occurs only in RNA, while adenine and guanine are purines. (The paper prints "Thiamine", a misprint for thymine.)

Explanation. pH = 0 means \([H_3O^+] = 10^0 = 1\) M, a very high hydrogen ion concentration, so the solution is strongly acidic.

Explanation. Phenol forms a violet coloured iron-phenoxide complex with neutral \(FeCl_3\); this is the test for phenols.

Explanation. The chain has 1 + 4 + 1 = 6 carbon atoms with \(-NH_2\) groups on C-1 and C-6, so the name is hexane-1,6-diamine. Hexamethylene diamine is only the common name.

Explanation. 9650 C = 9650/96500 = 0.1 mol of electrons. Number of electrons = \(0.1 \times 6.022\times10^{23} = 6.022\times10^{22}\).

Explanation. In diamond each carbon is bonded tetrahedrally to four other carbons (\(sp^3\)). Fullerene, graphite and graphene contain \(sp^2\) carbons.

Explanation. Carbonylation of methanol with CO over a Rh/Ir complex catalyst (Monsanto process) gives acetic acid. The paper misprints the reactant as \(CH_3-CHO\); the intended reactant is methanol.

Explanation. In FeO some \(Fe^{2+}\) sites are vacant and the charge is balanced by \(Fe^{3+}\) ions, so the crystal has fewer metal ions (metal deficiency). ZnO shows metal excess.

Explanation. Hydration of acetylene with dil. \(H_2SO_4\)/\(HgSO_4\) gives acetaldehyde (X). Being an aldehyde with a \(CH_3CO-\) group it gives iodoform, Tollen's and Fehling tests; the Victor Meyer test is for alcohols, so X does not give it.

Explanation. Arrhenius equation: \(\log k = \log A - \frac{E_a}{2.303RT}\), so a plot of log k (or ln k) against 1/T is a straight line with negative slope. Only graph (b) shows this; (a) is a curve and (c) has a positive slope.

Explanation. Xenon forms fluorides and oxides because its outer electrons are loosely held. Neon is very small with a very high ionisation energy, so \(NeF_2\) is not formed.

Explanation. Six monodentate \(CN^-\) ligands are bonded to the central \(Fe^{2+}\) ion, so its coordination number is 6.