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Exam Tips for Chemistry Exam (Class 12)

Somak Chatterjee|Feb 20th, 2013 06:41pm

How to Revise:–

  • Don’t take stress.
  • Realize your grey-areas in the subject.
  • Do not study anything new before examination.
  • Divide your time in accordance with the weightage of chapters.
  • Start revising your notes and keep a glossary of important words.
  • Be well-versed with the format of paper and marks allotted to each chapter.
  • Practice CBSE sample papers and previous years’ board papers.
  • Take at least one mock test on your own by randomly selecting a sample test paper. Stick to the exact duration of the test. Do not take break in between. Try to simulate the exam conditions as far as possible.
  • Go through the NCERT solutions thoroughly.
  • Physical chemistry: Revise the laws, postulates, formulae and graphs
  • Inorganic chemistry: Revise the structures, oxidation states, chemical reactions and periodic trends.
  • Organic chemistry: Revise name reactions, distinction tests and IUPAC nomenclature.
  • Clear your doubts related to any topic immediately. You can always post your doubts on ‘Ask and Answer’ on meritnation.com and get expert help. Remember “Expert help is just a click away’.

During the Examination:–

  • Read the question paper thoroughly in the initial 15 minutes.
  • Mark the questions you are confident in answering.
  • Write the correct question numbers for the answers.
  • Do not leave sheets blank in between your answers.
  • In the answer-sheet write the answers of all questions of one section at one place. Also, all the parts of a question need to be answered in sequence.
  • Avoid leaving any answer blank. Try to write the closest answer you remember.
  • Draw lines for rough work on the right hand side of the answer sheet. This would minimize the chances of errors in noting down the answer (especially the numeric values) from rough calculations done on some other page of the answer sheet.
  • In the answer sheet, use black or blue coloured ink only.
  • Underline the keywords in the answer.
  • All equations must be balanced. A reaction, which is not balanced, is not an equation.

Ques: Complete the following chemical reaction equations: (i) P4 + SO2Cl2 → (ii) XeF4 + H2(CBSE 2010 Set 3, Q 30)

Model Ans:
(i) P4 + 10 SO2Cl2 → 4 PCl5 + 10 SO2
(ii) 6 XeF4 + 12 H2O → 4 Xe + 2 XeO3 + 24 HF + 3 O2

  • Reasoning questions carry one mark each and demand to-the point and precise answer.

Ques: NF3 is an exothermic compound but NCl3 is endothermic compound.  (CBSE 2010 Set 3, Q 30)

Model Ans: The instability of NCl3 is due to the weak NCl bond. This is due to the large difference in the size of nitrogen and chlorine atoms. On the other hand, atoms of both nitrogen (75 pm) and fluorine (72 pm) are small sized. Thus, bonding in NF3 is quite strong and it is an exothermic compound.

Ques: Account for the following: (CBSE 2009 Set 1, Q 23)

(i) NH3 is a stronger base than PH3.

(ii) Sulphur has a greater tendency for catenation than oxygen.

(iii) Bond dissociation energy of F2 is less than that of Cl2.

Model Ans: (i) On moving from nitrogen to phosphorus, i.e., down the group, the atomic size increases. As the size of the central atom increases, the lone pair of electrons occupy a larger volume. Consequently, the electron density, and hence, the basic strength decrease. Thus, NH3 is a stronger base than PH3.

(ii) The tendency for catenation depends upon the bond energy. The bond energy of a sulphur molecule is more than that of an oxygen molecule. Thus, the sulphur − sulphur bond strength is higher, and as a result, the tendency of catenation is also higher. Sulphur shows catenation up to eight atoms.

(iii) Bond dissociation energy of fluorine is less than that of chlorine. It is due to the low value of electron affinity of small-sized fluorine. Also, the value of enthalpy of hydration of fluorine is much higher than that of chlorine.

  • Attempting numericals: Start the answer by writing the skeleton formula in standard notation followed by substitution of values with units. Numericals carry step-wise marking. At times it happens that due to lack of time these questions remain unattempted. In that case, even if you write the general formula and substitute the values, you manage to score half of the total marks alloted to the question.

Ques: A solution prepared by dissolving 1.25 g of oil of winter green (methyl salicylate) in 99.0 g of benzene has a boiling point of 80.31 °C. Determine the molar mass of this compound. (B.P. of pure benzene = 80.10 °C and Kb for benzene = 2.53 °C kg mol−1)    (CBSE 2010 Set 3, Q 21)

  • Conversion of units should be taken care of. The final answer must be written with units.
  • Always support your answers with structures, examples, equations and graphs even if the question does not ask for it.
  • Memory-based questions are usually asked from the chapters like polymers, chemistry in everyday life, biomolecules and surface chemistry.

Example :

Ques: Define the term, “homopolymerisation” giving an example.

(2012 CBSE Set 1, Q8 Polymer)

Ques: What is meant by coagulation of a colloidal solution? Describe briefly any three methods by which coagulation of lyophobic sols can be carried out.

(2012 CBSE Set 1, Q11 Surface Chemistry)

Ques: What is meant by (i) Peptide linkage (ii) biocatalysts?

(2012 CBSE Set 2, Q14 Biomolecules)

Ques: Explain the following terms giving one example of each type:

(i) Antacids,

(ii) Disinfectants,

(iii) Enzymes.

(2012 CBSE Set 3, Q27 Chemistry in Everyday Life)

A little hard work with a little smartness will make you come out with flying colours in the upcoming chemistry examination. So focus on time management, topic-wise revision, self-assessment and then Chemistry will be a pleasant and successful experience for you!!!

All the Best!

Team Meritnation

Add Comment Total Comments (4)

  • 1. praju  |  January 17th, 2014 at 11:41 pm

    ur awesome yar…….
    thank u for such a nice guidance…..

  • 2. nitesh  |  February 24th, 2013 at 6:06 pm

    which is this reaction vutz smit reaction

  • 3. munnawar kahn  |  February 21st, 2013 at 1:58 pm

    thanks for solve

  • 4. Samuel  |  February 20th, 2013 at 8:54 pm

    thank you

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