List of top Chemistry Questions asked in CBSE CLASS XII

Calculate the cell voltage of the voltaic cell which is set up by joining the following half-cells at 25°C:
Al/Al³⁺ (0.002 M) and Ni/Ni²⁺ (0.002 M)
Given: $ E^\circ_{\text{Ni}^{2+}/\text{Ni}} = -0.25 \, \text{V} $
$ E^\circ_{\text{Al}^{3+}/\text{Al}} = -1.66 \, \text{V} $
$ \log 5 = 0.6990 $

An aromatic compound ‘A’ with molecular formula C₈H₈O gives positive 2,4-DNP test. It gives yellow precipitate of compound ‘B’ on treatment with sodium hypoiodite. Compound ‘A’ does not react with Tollen’s or Fehling’s reagent; on drastic oxidation with KMnO₄ it forms a carboxylic acid ‘C’. Elucidate the structures of A, B, and C. Also give their IUPAC names.

Arrange the following compounds as asked:
(a) In decreasing order of pK_b values
C₂H₅NH₂, (C₂H₅)₂NH, C₆H₅NHCH₃, C₆H₅NH₂
(b) In increasing order of boiling point
C₂H₅OH, C₂H₅NH₂, (CH₃)₂NH
(c) In increasing order of solubility in water
C₆H₅NH₂, (C₂H₅)₂NH, C₂H₅NH₂

Give explanation for each of the following observations:

(a) With the same d-orbital configuration (d⁴), Mn³⁺ ion is an oxidizing agent whereas Cr²⁺ ion is a reducing agent.

(b) Actinoid contraction is greater from element to element than that among lanthanoids.

(c) Transition metals form a large number of interstitial compounds with H, B, C, and N.

For the reaction:
2H$_2$O$_2$ $\xrightarrow{I^-}$ 2H$_2$O + O$_2$
Given mechanism:
(I) H$_2$O$_2$ + I$^-$ → H$_2$O + IO$^-$ (slow)
(II) H$_2$O$_2$ + IO$^-$ → H$_2$O + I$^-$ + O$_2$ (fast)
(1) Write rate law for the reaction.
(2) Write the overall order and molecularity of the reaction.

The reaction between A₂ (g) and B₂ (g) was carried out in a sealed isothermal container. The rate law for the reaction was found to be:

Rate = $ k[\text{A}_2][\text{B}_2] $

If 1 mole of A₂ (g) was added to the reaction chamber and the temperature was kept constant, then predict the change in rate of the reaction and the rate constant.

Name and define the cell which was used for providing electric power in the Apollo space programme. Also write its one advantage.

Identify and draw the main products formed in the following chemical reactions:

A compound ‘A’ with molecular formula C₄H₈O gives positive 2,4-DNP test. It gives yellow precipitate of compound ‘B’ on treatment with sodium hydrogen sulphite. Compound ‘A’ does not react with Tollen’s or Fehling’s reagent; on oxidation with KMnO₄, it forms carboxylic acid ‘C’. Elucidate the structures of ‘A’, ‘B’ and ‘C’. Also give their IUPAC names.

Which of the following properties of transition metals enables them to behave as catalysts?

Out of Ti³⁺, Cr³⁺, Fe²⁺ and Ni²⁺ ions, the one which is the most stable ion in aqueous solution is:

Name the type of isomerism exhibited and draw isomers:

(I) [Co(NH₃)₆][Cr(CN)₆]

(II) [Co(en)₃]³⁺

(III) [Co(NH₃)₃(NO₂)₃]

Account for the following:
(i) Allyl chloride is hydrolysed more readily than n-propyl chloride.(ii) Isocyanides are formed when alkyl halides are treated with silver cyanide.
(iii) Methyl chloride reacts faster with OH– ion in SN2 reaction than ethyl chloride.

Give the IUPAC name of t-butyl methyl ether.

Calculate the cell voltage of the voltaic cell which is set up by joining the following half-cells at 25°C:
Al/Al³⁺ (0.001 M) and Ni/Ni²⁺ (0.001 M)
Given: $ E^\circ_{\text{Ni}^{2+}/\text{Ni}} = -0.25 \, \text{V}, \, E^\circ_{\text{Al}^{3+}/\text{Al}} = -1.66 \, \text{V} $

Hofmann Bromamide degradation reaction is given by:

Give explanation for each of the following observations:

(a) Mn³⁺ is an oxidizing agent, whereas Cr²⁺ is a reducing agent (both d⁴ configuration).

(b) Actinoid contraction is greater than lanthanoid contraction.

(c) Transition metals form interstitial compounds with H, B, C, N.

Complete the following reactions by writing the structural formulae of ‘A’ and ‘B’:

(i) $ \text{CH}_3\text{CH} = \text{CH}_2 $
$ \xrightarrow{\text{HBr, Peroxide}} $ ‘A’ $ \xrightarrow{\text{aq. KOH}} $ ‘B’

(ii) $ \text{CH}_3\text{CH}_2\text{CH(Cl)CH}_3 $
$ \xrightarrow{\text{alc. KOH}, \Delta} $ ‘A’ $ \xrightarrow{\text{HBr}} $ ‘B’

(iii) ‘A’ $ \xrightarrow{\text{Mg}} $ $ \text{CH}_3\text{CH}_2\text{CH}_2\text{MgCl} $ $ \xrightarrow{\text{H}_2\text{O, H}^+} $ ‘B’ (Main product)

Can sodium methoxide and t-butyl bromide be used for the preparation of t-butyl methyl ether? Give suitable reason. Justify your answer by suggesting the appropriate starting material if required for the preparation of t-butyl methyl ether.

Arrange the following compounds as asked:
(a) In increasing order of pK_b values: $ \text{C}_2\text{H}_5\text{NH}_2 $, $ (\text{C}_2\text{H}_5)_2\text{NH} $, $ \text{C}_6\text{H}_5\text{NHCH}_3 $, $ \text{C}_6\text{H}_5\text{NH}_2 $
(b) In decreasing order of boiling point: $ \text{C}_2\text{H}_5\text{OH} $, $ \text{C}_2\text{H}_5\text{NH}_2 $, $ (\text{CH}_3)_2\text{NH} $
(c) In decreasing order of solubility in water: $ \text{C}_6\text{H}_5\text{NH}_2 $, $ (\text{C}_2\text{H}_5)_2\text{NH} $, $ \text{C}_2\text{H}_5\text{NH}_2 $

Name the type of isomerism exhibited by the following compounds. Also, draw their corresponding isomers.

(I) $ [\text{Co(NH}_3\text{)}_6][\text{Cr(CN)}_6] $

(II) $ [\text{Co(en)}_3]^{3+} $

(III) $ [\text{Co(NH}_3\text{)}_3(\text{NO}_2)_3] $

Out of Ti³⁺, Cr³⁺, Mn²⁺ and Ni²⁺ ions, the one which has the highest magnetic moment is:

Differentiate between weak field and strong field ligands. How does the strength of the ligand influence the spin of the complex?

Using Crystal Field theory, write the number of unpaired electrons in octahedral complexes of Fe³⁺ in the presence of:
(I) Strong field ligand
(II) Weak field ligand
Atomic number: Fe = 26

The initial concentration of N$_2$O$_5$ in the first-order reaction:
\[ \text{N}_2\text{O}_5 (\text{g}) \rightarrow 2 \text{NO}_2 (\text{g}) + \frac{1}{2} \text{O}_2 (\text{g}) \] was $ 1.2 \times 10^{-2} $ mol L$^{-1}$. The concentration of N$_2$O$_5$ after 60 minutes was $ 0.2 \times 10^{-2} $ mol L$^{-1}$. Calculate the rate constant of the reaction at 318 K.
$[ \log 6 = 0.778 ]$