List of top Chemistry Questions asked in CBSE CLASS XII

Consider the decomposition of hydrogen peroxide \( (\mathrm{H_2O_2}) \) as per the equation given below : \[ 2\mathrm{H_2O_2} \xrightarrow[\text{Alkaline medium}]{I^-} 2\mathrm{H_2O} + \mathrm{O_2} \] The mechanism for this reaction was found to be : Step I : \( \mathrm{H_2O_2} + I^- \longrightarrow \mathrm{H_2O} + IO^- \) (slow) Step II : \( \mathrm{H_2O_2} + IO^- \longrightarrow \mathrm{H_2O} + I^- + \mathrm{O_2} \) (fast) (a) Write the rate law expression. (b) Determine the order of reaction with respect to \( \mathrm{H_2O_2} \), \( I^- \) and overall order of reaction. (c) What is the molecularity of the reaction in Step II ?
Following reaction takes place in one step:

\(2A + B \rightarrow 2C\)

How will the rate of above reaction change if the volume of the reaction vessel is decreased to one third of its original volume? Will there be any change in the order of reaction with the reduced volume?
An organic compound (X) has the molecular formula \(C_5H_{10}O\). Draw structures for (X) if it:
(I) does not give Tollen's test but gives a positive iodoform test.
(II) does not give Tollen's test and iodoform test but undergoes Aldol condensation.
(III) undergoes Cannizzaro's reaction.

Conductivity of \( 2.5 \times 10^{-4} \) M methanoic acid solution is \( 5.25 \times 10^{-5} \) S cm\(^{-1}\).

(a) Calculate its molar conductivity.

(b) Calculate its degree of dissociation.

[Given : \( \lambda^{\circ}_{(\mathrm{H^+})} = 349.5 \) S cm\(^2\) mol\(^{-1}\) and \( \lambda^{\circ}_{(\mathrm{HCOO^-})} = 50.5 \) S cm\(^2\) mol\(^{-1}\)]

Explain the Finkelstein reaction.

(a) Define 'Denatured Protein' with an example.

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

(c) Name the disease caused by the deficiency of Vitamin C.

(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.



Draw the structures of major monohalo products in each of the following :

(a)

(b)



A reaction \( \mathrm{A \rightarrow B} \) follows second order kinetics. How will the rate of reaction be affected if the concentration of (i) A is increased by three times, and (ii) A is reduced to half ?

Write the reactions taking place at anode and cathode in a lead storage battery, when it is in use.

(a) Write two structural differences between DNA and RNA.

(b) Which component of starch is a branched chain polymer of \( \alpha \)-D-(+)-glucose ? Write its one characteristic feature.

(c) Which types of bonds hold the polypeptide chains in fibrous proteins ?

(i) Give a chemical test to distinguish between Propanal and Propanone.

(ii) Which of the given acids is stronger and why ? \( \mathrm{F_3C{-}C_6H_4{-}COOH} \) or \( \mathrm{H_3C{-}C_6H_4{-}COOH} \)

(iii) Complete the given reaction sequence :

\[ \mathrm{CH_3CH_2CH_2COOC_2H_5} \xrightarrow{\mathrm{NaOH}} \mathrm{A + C_2H_5OH} \]

\[ \mathrm{A} \xrightarrow{\mathrm{H_3O^+}} \mathrm{B} \]

Match Column I with Column II and choose the correct option :

Column IColumn II
a. Osmotic pressurei. \( \Delta \mathrm{T_f} = \mathrm{K_f}\,m \)
b. Elevation of boiling pointii. \( \pi = CRT \)
c. Depression of freezing pointiii. \( \frac{\mathrm{P_1^0 - P_1}}{\mathrm{P_1^0}} = \frac{\mathrm{W_2 \times M_1}}{\mathrm{M_2 \times W_1}} \)
d. Relative lowering of vapour pressureiv. \( \Delta \mathrm{T_b} = \mathrm{K_b}\,m \)

(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.



The electrical resistance of a column of 0.05 M KOH solution of area 0.5 cm\(^2\) and length 50 cm is 2.5 \(\times\) 10\(^4\) ohm. Calculate its molar conductivity.

(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 :

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

(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 ?

(a) What are anomers ? Explain.

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

(c) Name the disease caused by the deficiency of Vitamin B\(_{12}\).

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.

(ii) Draw the structure of the semicarbazone of cyclohexanone.

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.

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

Butanone, Propanone, Propanal, Ethanal

(a) When alkyl chlorides are treated with aqueous KOH, alcohol is formed, whereas when alkyl chlorides are treated with alcoholic KOH, alkenes are formed. Explain.

(b) Complete the given equation :

\( \mathrm{C_6H_5Cl} + \mathrm{CH_3COCl} \xrightarrow{\text{Anhyd. } \mathrm{AlCl_3}} \)

(i) Give a chemical test to distinguish between benzaldehyde and ethanal.

(ii) Which of the given acids is stronger and why ?

\( \mathrm{CH_2FCH_2CH_2COOH} \) or \( \mathrm{CH_2CHFCH_2COOH} \)

(iii) Complete the given equation :

\( \mathrm{C_6H_5COOC_2H_5} \; \overset{\mathrm{H_3O^+}}{\rightleftharpoons} \)

(a) Mention any two bases present in DNA.

(b) Which component of starch is an unbranched chain polymer of \( \alpha \)-D-(+) glucose ? Write its one characteristic feature.

(c) Write the name of the linkage present between amino acids. How is it represented ?

(a) Write the IUPAC name of the given compound :

\( \mathrm{H_2C=C(CH_3)-CH(Br)-CH_2Br} \)

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

1-Chlorobutane, Isopropyl chloride, 1-Chloropropane

A reaction is of first order with respect to A and of second order with respect to B. How is the rate of reaction affected, when the concentration of (i) both A and B are doubled, and (ii) A is doubled and B is reduced to half ?

A galvanic cell functions like an electrolytic cell when :