List of top Chemistry Questions asked in CBSE CLASS XII

The correct order of reactivity of alcohols with Lucas reagent is :

Which of the following statements is true about a galvanic cell consisting of Cu and \( \mathrm{H_2} \) electrodes ?

[Given : \( E^{o}_{\mathrm{Cu^{2+}/Cu}} = +0.34\ \mathrm{V},\ E^{o}_{\mathrm{H^{+}/H_2,\ Pt}} = 0.00\ \mathrm{V} \)]

According to Alfred Werner, the secondary valence(s) of the central metal atom/ion in a complex :

Identify the incorrect statement from the given statements.

The relationship between \( E^{o}_{(cell)} \) and \( \Delta_rG^{\ominus} \) is :

(i) (I) Explain why \( \mathrm{[Fe(CN)_6]^{3-}} \) is an inner orbital complex, whereas \( \mathrm{[FeF_6]^{3-}} \) is an outer orbital complex.

[Atomic number : Fe = 26]

(II) Write the formula of the given complex :

Hexaamminenickel (II) chloride

(ii) A solution of \( \mathrm{[Ni(H_2O)_6]^{2+}} \) is green in colour while a solution of \( \mathrm{[Ni(CN)_4]^{2-}} \) is colourless. Explain.

[Atomic number : Ni = 28]

(i) Complete the following equations :

(I) \( \mathrm{CH_3NH_2 + C_6H_5COCl} \longrightarrow \)

(II) \( \mathrm{C_6H_5NH_2} \) + 3 \( \mathrm{Br_2} \) \( \xrightarrow{\mathrm{H_2O}} \)

(III) \( \mathrm{C_6H_5CONH_2} \) \( \xrightarrow{\mathrm{NaOBr}} \)

(ii) (I) Explain the carbylamine reaction.

(II) Why can aromatic primary amines not be prepared by the Gabriel phthalimide synthesis ?

(i) (I) The \( \mathrm{pK_b} \) value of aniline is higher than that of methylamine. Explain why.

(II) Arrange the following compounds in decreasing order of their basic strength in the gaseous phase :

\( \mathrm{NH_3,\ (C_2H_5)_2NH,\ (C_2H_5)_3N,\ C_2H_5NH_2} \)

(III) What is Hinsberg's reagent ? Mention its one use.

(ii) How will you convert the following :

(I) Nitrobenzene to Benzenediazonium chloride ?

(II) Iodomethane to Ethanamine ?

(i) (I) Write IUPAC name of the given complexes :

\( \mathrm{[Ag(CN)_2]} \) \( \mathrm{[Ag(NH_3)_2]} \)

(II) What is the coordination number of the central metal ion in the following complexes ?

\( \mathrm{[Fe(C_2O_4)_3]^{3-}} \) and \( \mathrm{[Cr(NH_3)_3Cl_3]} \)

(III) Draw a geometrical isomer of the complex \( \mathrm{[CoCl_2(en)_2]^+} \), which is optically active.

(ii) Using valence bond theory, explain the hybridization of \( \mathrm{[Ni(CO)_4]} \) and its magnetic behaviour.

[Atomic number : Ni = 28]

(i) For first order reaction, calculate the ratio between the time taken to complete \( \frac{3}{4} \)th of the reaction and the time taken to complete half of the reaction.

(ii) (I) What is meant by a complex reaction ?

(II) Give an example of a pseudo first order reaction.

(i) A first order reaction is 20% complete in 10 minutes. Calculate the time taken when 80% of the reaction will be completed.

[Given : log 5 = 0.7, log 4 = 0.6]

(ii) For a chemical reaction \( \mathrm{R \rightarrow P} \), variation in \( \ln[\mathrm{R}] \) vs. time (t) graph is given below :

(I) Predict the order of the reaction.

(II) Write the slope of the curve.

Organic compounds containing carbonyl group as the functional group are aldehydes, ketones and carboxylic acids. The carbon-oxygen double bond is polarised due to higher electronegativity of oxygen as compared to carbon. Aldehydes are generally more reactive than ketones in nucleophilic addition reactions due to steric and electronic reasons. They react with HCN, Sodium bisulphite, Grignard reagent and a number of ammonia derivatives like Hydroxylamine, Hydrazine, Semicarbazide, etc. Aldehydes and ketones undergo various reactions due to the acidic nature of \( \alpha \)-hydrogen. Aldehydes and ketones having at least one \( \alpha \)-hydrogen atom undergo a reaction in the presence of dilute alkali as a catalyst to form \( \beta \)-hydroxy aldehydes or \( \beta \)-hydroxy ketones. On the other hand, aldehydes which do not possess an \( \alpha \)-hydrogen undergo self-oxidation and reduction in the presence of concentrated alkali.

Draw the structure of the semicarbazone of cyclohexanone.

Atomic radii is a useful property for determining many aspects of chemistry of elements such as physical and chemical properties. The periodic table greatly assists in finding a number of trends. The transition metals belong to group 3 - 12 and are generally characterised by partially filled d-orbitals in the free elements or their cations. The atomic radii of transition metals show a small decrease from left to right across a period, then remain nearly constant, and finally, slight increase towards the end of the series. The trend is a result of interplay between the increasing nuclear charge and the increasing shielding effect from the filling of d-orbitals. Initially the nuclear charge dominates, leading to decrease in size, but as more d-electrons are added, their shielding becomes more effective, balancing the increased nuclear charge and causing the radii to become constant.

The increase in size between 3d and 4d metals is much greater than between the 4d and 5d metals. The atomic radii of 2^nd and 3^rd series are almost the same due to lanthanoid contraction. Increase in density is also observed on moving from left to right in a period.

Why is there not much change in the atomic radius of the transition metals with the increase in atomic number ?

Organic compounds containing carbonyl group as the functional group are aldehydes, ketones and carboxylic acids. The carbon-oxygen double bond is polarised due to higher electronegativity of oxygen as compared to carbon. Aldehydes are generally more reactive than ketones in nucleophilic addition reactions due to steric and electronic reasons. They react with HCN, Sodium bisulphite, Grignard reagent and a number of ammonia derivatives like Hydroxylamine, Hydrazine, Semicarbazide, etc. Aldehydes and ketones undergo various reactions due to the acidic nature of \( \alpha \)-hydrogen. Aldehydes and ketones having at least one \( \alpha \)-hydrogen atom undergo a reaction in the presence of dilute alkali as a catalyst to form \( \beta \)-hydroxy aldehydes or \( \beta \)-hydroxy ketones. On the other hand, aldehydes which do not possess an \( \alpha \)-hydrogen undergo self-oxidation and reduction in the presence of concentrated alkali.

From the compounds given below, identify which would undergo aldol condensation and which would undergo Cannizzaro reaction ?

Cyclohexanone, Benzaldehyde, Methanal, 2-Methylpentanal

Atomic radii is a useful property for determining many aspects of chemistry of elements such as physical and chemical properties. The periodic table greatly assists in finding a number of trends. The transition metals belong to group 3 - 12 and are generally characterised by partially filled d-orbitals in the free elements or their cations. The atomic radii of transition metals show a small decrease from left to right across a period, then remain nearly constant, and finally, slight increase towards the end of the series. The trend is a result of interplay between the increasing nuclear charge and the increasing shielding effect from the filling of d-orbitals. Initially the nuclear charge dominates, leading to decrease in size, but as more d-electrons are added, their shielding becomes more effective, balancing the increased nuclear charge and causing the radii to become constant.

The increase in size between 3d and 4d metals is much greater than between the 4d and 5d metals. The atomic radii of 2^nd and 3^rd series are almost the same due to lanthanoid contraction. Increase in density is also observed on moving from left to right in a period.

Why do transition metals have high \( \Delta_{a}H^{\circ} \) ?

Organic compounds containing carbonyl group as the functional group are aldehydes, ketones and carboxylic acids. The carbon-oxygen double bond is polarised due to higher electronegativity of oxygen as compared to carbon. Aldehydes are generally more reactive than ketones in nucleophilic addition reactions due to steric and electronic reasons. They react with HCN, Sodium bisulphite, Grignard reagent and a number of ammonia derivatives like Hydroxylamine, Hydrazine, Semicarbazide, etc. Aldehydes and ketones undergo various reactions due to the acidic nature of \( \alpha \)-hydrogen. Aldehydes and ketones having at least one \( \alpha \)-hydrogen atom undergo a reaction in the presence of dilute alkali as a catalyst to form \( \beta \)-hydroxy aldehydes or \( \beta \)-hydroxy ketones. On the other hand, aldehydes which do not possess an \( \alpha \)-hydrogen undergo self-oxidation and reduction in the presence of concentrated alkali.

Why is \( \alpha \)-hydrogen of carbonyl group acidic in nature ?

Organic compounds containing carbonyl group as the functional group are aldehydes, ketones and carboxylic acids. The carbon-oxygen double bond is polarised due to higher electronegativity of oxygen as compared to carbon. Aldehydes are generally more reactive than ketones in nucleophilic addition reactions due to steric and electronic reasons. They react with HCN, Sodium bisulphite, Grignard reagent and a number of ammonia derivatives like Hydroxylamine, Hydrazine, Semicarbazide, etc. Aldehydes and ketones undergo various reactions due to the acidic nature of \( \alpha \)-hydrogen. Aldehydes and ketones having at least one \( \alpha \)-hydrogen atom undergo a reaction in the presence of dilute alkali as a catalyst to form \( \beta \)-hydroxy aldehydes or \( \beta \)-hydroxy ketones. On the other hand, aldehydes which do not possess an \( \alpha \)-hydrogen undergo self-oxidation and reduction in the presence of concentrated alkali.

Arrange the following compounds in increasing order of reactivity towards nucleophilic addition reactions :

Butanone, Propanone, Propanal, Ethanal

Atomic radii is a useful property for determining many aspects of chemistry of elements such as physical and chemical properties. The periodic table greatly assists in finding a number of trends. The transition metals belong to group 3 - 12 and are generally characterised by partially filled d-orbitals in the free elements or their cations. The atomic radii of transition metals show a small decrease from left to right across a period, then remain nearly constant, and finally, slight increase towards the end of the series. The trend is a result of interplay between the increasing nuclear charge and the increasing shielding effect from the filling of d-orbitals. Initially the nuclear charge dominates, leading to decrease in size, but as more d-electrons are added, their shielding becomes more effective, balancing the increased nuclear charge and causing the radii to become constant.

The increase in size between 3d and 4d metals is much greater than between the 4d and 5d metals. The atomic radii of 2^nd and 3^rd series are almost the same due to lanthanoid contraction. Increase in density is also observed on moving from left to right in a period.

Give reasons for the following :

(i) The second and third series of transition metals resemble each other much more than they resemble the first series (3d).

(ii) Transition metals show variable oxidation states.

(a) What is meant by invert sugar ?

(b) What happens when glucose reacts with nitric acid ? Write the reaction involved.

(c) Name the disease caused by the deficiency of Vitamin \( \mathrm{B_1} \).

Atomic radii is a useful property for determining many aspects of chemistry of elements such as physical and chemical properties. The periodic table greatly assists in finding a number of trends. The transition metals belong to group 3 - 12 and are generally characterised by partially filled d-orbitals in the free elements or their cations. The atomic radii of transition metals show a small decrease from left to right across a period, then remain nearly constant, and finally, slight increase towards the end of the series. The trend is a result of interplay between the increasing nuclear charge and the increasing shielding effect from the filling of d-orbitals. Initially the nuclear charge dominates, leading to decrease in size, but as more d-electrons are added, their shielding becomes more effective, balancing the increased nuclear charge and causing the radii to become constant.

The increase in size between 3d and 4d metals is much greater than between the 4d and 5d metals. The atomic radii of 2^nd and 3^rd series are almost the same due to lanthanoid contraction. Increase in density is also observed on moving from left to right in a period.

Why is Zn a non-transition element ?

(a) "Haloalkanes react with KCN to form alkyl cyanides as the main product, whereas with AgCN, they form isocyanides as the main product." Explain the statement.

(b) Complete the given equation :

\( \xrightarrow[\Delta]{\text{Conc. } \mathrm{H_2SO_4}} \)

The resistance and conductivity of a conductivity cell containing 0.1 mol \( \mathrm{L^{-1}} \) KCl solution are 100 ohms and \( 1.29 \times 10^{-2} \ \mathrm{S\ cm^{-1}} \), respectively. If the resistance of the same cell filled with 0.02 mol \( \mathrm{L^{-1}} \) KCl solution is 520 ohms, calculate conductivity and molar conductivity of 0.02 mol \( \mathrm{L^{-1}} \) KCl solution.

(a) Mention any two types of RNA molecules.

(b) How is glycogen different from starch ?

(c) Explain the \( \beta \)-pleated sheet structure of proteins.

(a) What happens when chlorobutane is treated with Na metal in the presence of dry ether ?

(b) Arrange the following compounds in increasing order of their boiling points :

1-Bromobutane, 1-Iodobutane, Butane, 1-Chlorobutane

10 g of a non-volatile solute is dissolved in 200 g of water to make a solution. It has a vapour pressure of 31.84 mm Hg at 308 K.

Calculate the molar mass of the solute.

[Given : Vapour pressure of pure water at 308 K = 32 mm Hg]

(a) Arrange the following compounds in the decreasing order of their acidic strength :

Phenol, 4-Nitrophenol, 2,4,6-Trinitrophenol

(b) Why are alcohols more soluble in water than hydrocarbons of comparable molecular masses ?

(c) Name the reagent used in the oxidation of a primary unsaturated alcohol to an aldehyde.