Science (English Medium) कक्षा १२ - CBSE Question Bank Solutions for Chemistry

An amorphous solid “A” burns in air to form a gas “B” which turns lime water milky. The gas is also produced as a by-product during roasting of sulphide ore. This gas decolourises acidified aqueous \[\ce{KMnO4}\] solution and reduces \[\ce{Fe^{3+}}\] to \[\ce{Fe^{2+}}\]. Identify the solid “A” and the gas “B” and write the reactions involved.

The reaction \[\ce{Ar\overset{+}{N2}Cl- ->[Cu/HCl] ArCl + N2 + CuCl}\] is anmed as ______.

Which of the following cannot be prepared by Sandmeyer’s reaction?

(i) Chlorobenzene

(ii) Bromobenzene

(iii) Iodobenzene

(iv) Fluorobenzene

Arrange the following compounds in increasing order of dipole moment.

\[\ce{CH3CH2CH3, CH3CH2NH2, CH3CH2OH}\]

Which of the following terms are correct about enzyme?

(i) Proteins

(ii) Dinucleotides

(iii) Nucleic acids

(iv) Biocatalysts

Activation energy for the acid catalysed hydrolysis of sucrose is 6.22 kJ mol^–1, while the activation energy is only 2.15 kJ mol^–1 when hydrolysis is catalysed by the enzyme sucrase. Explain.

Assertion: In presence of enzyme, substrate molecule can be attacked by the reagent effectively.

Reason: Active sites of enzymes hold the substrate molecule in a suitable position.

Give reasons to support the answer:

3-Hydroxy pentan-2-one shows positive Tollen’s test.

Define coagulation.

State the Hardy-Schulze rule.

What is electrophoresis?

Define the following term:

Coagulation

Why a negatively charged sol is obtained when AgNO₃ solution is added to KI solution?

Write the structures of A, B and C in the following reaction:

Illustrate Sandmeyer's reaction with an equation.

What type of semiconductor is obtained when silicon is doped with boron? 

After watching a programme on TV about the adverse effects of junk food and soft drinks on the health of school children, Sonali, a student of Class XII, discussed the issue with the school principal. Principal immediately instructed the canteen contractor to replace the fast food with the fibre and vitamins rich food like sprouts, salad, fruits etc. This decision was welcomed by the parents and the students. 

After reading the above passage, answer the following questions:

(a) What value are expressed by Sonali and the Principal of the school?

(b) Give two examples of water-soluble vitamins.

Although phenoxide ion has more number of resonating structures than carboxylate ion, carboxylic acid is a stronger acid than phenol. Give two reasons.

Give reasons for the following observations: Addition of alum purifies the water

Write the name of the vitamin responsible for the coagulation of blood.