CBSE Board Exam 2020: Check Important Questions of Class 12th Chemistry SubjectArfa Javaid
The CBSE Class 12th Chemistry Examination will be held on March 7, 2020. The students who are appearing for CBSE Class 12th Examination can go through the important questions mentioned in this article. The questions mentioned in this article are based on the previous year question papers, sample papers and NCERT textbooks.
CBSE Important Questions for Class 12th Chemistry Marks Wise
1 Mark Questions:
1- (CH3)3C—CHO does not undergo aldol condensation. Comment.
2- How is Brownian movement responsible for the stability of sols?
3- ZnO crystal on heating acquires the formula Zn 1+x O. Give reason.
4- Low spin configuration are rarely observed in tetrahedral coordination entity formation. Explain.
5- Write the name of the biodegradable polymer used in orthopaedic devices.
6- The IUPAC name of the compound shown below is:
2 Marks Questions:
1- (i) Allyl chloride can be distinguished from Vinyl chloride by NaOH and silver nitrate test. Comment.
(ii) Alkyl halide reacts with Lithium aluminium hydride to give alkane. Name the attacking reagent which will bring out this change.
2- Calculate the molality of ethanol solution in which the mole fraction of water is 0.88.
3- Calculate the number of lone pairs on the central atom in the following molecule and predict the geometry. XeF4
4- The rate of a reaction depends upon the temperature and is quantitatively expressed as
i) If a graph is plotted between log k and 1/T, write the expression for the slope of the reaction?
ii) If at under different conditions Ea1 and Ea2 are the activation energy of two reactions If Ea1 = 40 J / mol and Ea2 = 80 J / mol. Which of the two has a larger value of the rate constant?
5- What is meant by Vapour phase refining? Write any one example of the process which illustrates this technique, giving the chemical equations involved.
6- Calculate the emf of the following cell at 298 K :
Cr(s) / Cr3+ (0.1M) // Fe2+ (0.01M) / Fe(s)
[Given : E0Cell = + 0.30 V]
3 Marks Questions:
1- The rate constant for a first-order reaction is 60 s-1. How much time will it take to reduce 1g of the reactant to 0.0625 g?
2- (i) Write the expression for Freundlich’s equation to describe the behaviour of adsorption from solution.
(ii) What causes charge on sol particles?
(iii) Name the promoter used in the Haber’s process for the manufacture of ammonia.
3- (i) Which vitamin deficiency causes rickets?
(ii) Name the base that is found in the nucleotide of RNA only.
(iii) Glucose on reaction with acetic acid gives glucose Penta acetate. What does it suggest about the structure of glucose?
4- The magnetic moments of a few transition metal ions are given below:
Metal ion Magnetic moment(BM)
(at no. Sc = 21, Ti =22, Cr = 24, Ni = 28)
Which of the given metal ions :
(i) has the maximum number of unpaired electrons?
(ii) forms colourless aqueous solution?
(iii) exhibits the most stable +3 oxidation state?
5-. Answer the following questions:
(a) Which of the following electrolytes is most effective for the coagulation of AgI/Ag+ sol?
MgCl2, K2SO4, K4[Fe(CN)6]
(b)What happens when a freshly precipitated Fe(OH)3 is shaken with a little amount of dilute solution of FeCl3.
(c) Out of sulphur sol and proteins, which one forms macromolecular colloids?
6- Define and write an example for the following :
(a) Broad-spectrum antibiotics.
5 Marks Questions:
1- (a) When a chromite ore (A) is fused with an aqueous solution of sodium carbonate in free excess of air, a yellow solution of compound (B) is obtained. This solution is filtered and acidified with sulphuric acid to form a compound (C). Compound (C) on treatment with the solution of KCl gives orange crystals of compound (D). Write the chemical formulae of compounds A to D.
(b) Describe the cause of the following variations with respect to lanthanoids and actinoids:
(i) Greater range of oxidation states of actinoids as compared to lanthanoids.
(ii) Greater actinoid contraction as compared to lanthanoid contraction.
(iii) Lower ionisation enthalpy of early actinoids as compared to the early lanthanoids.
2- How will you convert:
(i) Aniline into Fluorobenzene.
(ii) Benzamide into Benzylamine.
(iii) Ethanamine to N, N-Diethylethanamine.
(b) Write the structures of A and B in the following:
3- (a) Account for the following:
(i) Direct nitration of aniline yields a significant amount of meta derivative.
(ii) Primary aromatic amines cannot be prepared by Gabriel phthalimide synthesis.
(b) Carry out the following conversions:
(i) Ethanoic acid into methenamine.
(ii) Aniline to p-Bromoaniline.
(c) Arrange the following in increasing order of basic strength:
Aniline, p-nitroaniline and p-toluidine.
4- Identify the type of defect shown in the following figure:
(i) What type of substances shows this defect?
(ii) A metal crystallizes in a body-centred cubic structure. If ‘a’ is the edge length of its unit cell, ‘r’ is the radius of the sphere. What is the relationship between ‘r’ and ‘a’?
(iii) An element with molar mass 63 g / mol forms a cubic unit cell with an edge length of 360.8 pm. If its density is 8.92 g/ cm3. What is the nature of the cubic unit cell?
5- (a) Account for the following:
(i) CH3CHO is more reactive than CH3COCH3 towards reaction with HCN.
(ii) 2-Fluorobutanoic acid is a stronger acid than 3-Fluorobutanoic acid.
(b) Write the chemical equations to illustrate the following name reactions:
(i) Etard reaction.
(ii) Rosenmund’s reaction.
(c) Give the mechanism of cyanohydrin formation when carbonyl compounds react with HCN in the presence of alkali.
6- (a) Apply Kohlrausch law of independent migration of ions, write the expression to determine the limiting molar conductivity of calcium chloride.
(b) Given are the conductivity and molar conductivity of NaCl solutions at 298K at different concentrations:
Conductivity S cm-1
Molar conductivity S cm2 mol-1
106.74 x 10-4
55.53 x 10-4
23.15 x 10-4
Compare the variation of conductivity and molar conductivity of NaCl solutions on dilution. Give reason.
(c) 0.1 M KCl solution offered resistance of 100 ohms in a conductivity cell at 298 K. If the cell constant of the cell is 1.29 cm-1, calculate the molar conductivity of KCl solution.
These were some of the important questions from previous year question paper, sample papers and the NCERT textbooks. Students can also check other important articles from the links given below.