List of top Chemistry Questions asked in CBSE CLASS XII

Calculate emf of the given cell: Mg(s) $\mid$ Mg$^{2+}$(0.1 M) $\parallel$ Cu$^{2+}$(1.0 × 10$^{-3}$ M) $\mid$ Cu(s)
Given:
$E^\circ_{\text{Cu}^{2+}/\text{Cu}} = +0.34$ V, \quad $E^\circ_{\text{Mg}^{2+}/\text{Mg}} = -2.37$ V
(log 100 = 2)
State Kohlrausch’s law of independent migration of ions.
How much electricity in terms of Faraday is required to produce 40 g of Al from molten Al$_2$O$_3$? (Given: Atomic mass of Al = 27 u)
Calculate log \(K_c\) for the following reaction at 298 K: Zn(s) + Cu$^{2+}$(aq) $\rightleftharpoons$ Zn$^{2+}$(aq) + Cu(s)
Given:
$E^\circ_{\text{Zn}^{2+}/\text{Zn}} = -0.76 \, \text{V}$, \quad $E^\circ_{\text{Cu}^{2+}/\text{Cu}} = +0.34 \, \text{V}$
The chemistry of the actinoids is more complex as compared to the lanthanoids. Why?

Why is E for Mn3+/Mn2+ redox couple more positive?

What are reducing sugars?
Sucrose is dextrorotatory but the mixture obtained after hydrolysis is laevorotatory. Why?
A cell and its emf is given below:
Pt (s) $\mid$ H$_2$(g, 1 bar) $\mid$ H$^+$(aq, 1 M) $\parallel$ Cu$^{2+}$(aq, 1 M) $\mid$ Cu (s)
emf of the cell = +0.34 V
Write the reduction half-reaction at cathode.
How is standard Gibbs energy for a reaction related to equilibrium constant?
The boiling point of solution increases when 1 mol of NaCl is added to 1 litre of water while addition of 1 mol of methanol to one litre of water decreases its boiling point. Explain the above observations.
Define Enantiomers.
Why is chloroform stored in dark coloured air tight bottles?
Why do tertiary alkyl halides undergo S\textsubscript{N1 reaction at a faster rate?
Write the major alkene that would be formed by dehydrohalogenation of 2-Bromopentane.

Which would undergo SN2 reaction at a faster rate and why?
Given compounds:

Compound A: CH3–CH2–Br

Compound B:

CH3
|
CH3–C–Br
|
CH3
Why are iron pipes usually coated with zinc?
Why does mercury cell give a constant voltage throughout its life?

Why is \( pK_a \) of ClCH2COOH lower than the \( pK_a \) of CH3COOH?

Write the chemical equation for Hell-Volhard-Zelinsky reaction.
Write the mathematical relation between rate constant and half-life period of a zero order reaction.
Define Pseudo first order reaction with an example.
Give reasons for the following: (a) Reduction with iron scrap and HCl is preferred for the preparation of amines from nitro compounds.
(b) Lower aliphatic amines are soluble in water.
(c) Pyridine is used in the acylation reaction of amines.
(d) Although amino group is o- and p-directing in aromatic electrophilic substitution reactions, aniline on nitration gives a substantial amount of m-nitroaniline.
Write the chemical equation for the following: (a) Hydration of propene in presence of an acid
(b) Reaction between Ethyl bromide and C2H5ONa
(c) Reaction between Dimethyl ether and Hydrogen iodide
Using valence bond theory, predict: (a) Hybridisation of central metal atom of the complex \([Co(NH_3)_6]^{3+}\)
(b) Its shape and magnetic behaviour
(c) Whether it is a high spin or a low spin complex
[Atomic number: $CO$ = 27]