12th Standard Chemistry March 2024: Online Practice Test

Explanation. Monoclinic sulphur crystallises with unequal axes a ≠ b ≠ c and angles α = γ = 90°, β ≠ 90°, which are exactly the parameters of the monoclinic system. So both statements are true and the reason explains why it is classed as monoclinic.

Explanation. The complex ion is anionic, so the metal name ends in -ate (aluminate). Three oxalate ligands give 'trioxalato', and x + 3(−2) = −3 gives Al in the +3 state: potassium trioxalato aluminate (III).

Explanation. Down group 17 the H–X bond becomes longer and weaker, so HI releases H⁺ most easily. HI is the strongest acid among the hydrogen halides.

Explanation. Fullerene, graphite and graphene have sp² hybridised carbon atoms. Dry ice is solid CO₂, where carbon (O=C=O) is sp hybridised.

Explanation. RNA contains the purines adenine and guanine and the pyrimidines cytosine and uracil. Thymine occurs in DNA, not RNA.

Explanation. Aspirin is obtained by acetylating the –OH group of salicylic acid with acetic anhydride, so it is acetyl salicylic acid (2-acetoxybenzoic acid).

Explanation. In acid medium \(MnO_4^-\) is reduced to \(Mn^{2+}\) and oxalic acid is oxidised: \(5C_2O_4^{2-} + 2MnO_4^- + 16H^+ \rightarrow 2Mn^{2+} + 10CO_2 + 8H_2O\). The product is carbon dioxide.

Explanation. Aniline undergoes N-acetylation: \(C_6H_5NH_2 + (CH_3CO)_2O \rightarrow C_6H_5NHCOCH_3 + CH_3COOH\). The product is acetanilide.

Explanation. NaCl is a salt of a strong acid (HCl) and a strong base (NaOH), so neither ion reacts with water. The other salts contain a weak acid anion or a weak base cation and are hydrolysed.

Explanation. Primary cells cannot be recharged: the Leclanche cell and the mercury cell. The Ni-Cd cell and the lead storage battery are rechargeable secondary cells.

Explanation. The nucleophile \(CN^-\) attacks the electrophilic carbonyl carbon of acetone and the product adds \(H^+\) on oxygen, giving acetone cyanohydrin. This is nucleophilic addition.

Explanation. The unit of rate constant is \((mol\ L^{-1})^{1-n}\ s^{-1}\). A unit of \(s^{-1}\) means 1 − n = 0, so n = 1: first order.

Explanation. In electrolytic refining the impure metal is made the anode and a thin strip of pure metal the cathode. Copper dissolves from the impure anode and deposits as pure copper on the cathode.

Explanation. In the Haber process, \(Al_2O_3\) acts as a promoter and increases the activity of the iron catalyst. \(H_2S\) and \(As_2O_3\) are catalyst poisons.

Explanation. Pyridinium chlorochromate (PCC) is a mild oxidising agent that converts a primary alcohol only to the aldehyde. Acidified dichromate or KMnO₄ oxidise it further to the carboxylic acid.