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Chemistry Open Book Exam

Candidates are required to give their answers in their own words as far as practicable. All the questions are compulsory. Figures in the margin indicate the full marks.



1. Answer the following questions based on the above graph. (first ionization energy vs atomic number).

a. Why on moving from Be to B does the value of the first ionization energy drop? (1)
b. He has a higher peak than Ne and Ar. Explain. (1)
c. Compare the first ionization energy of Cl and Ar with reason. (1)
d. Name any two elements from the given graph which impart a characteristic color during a flame test. (1)
e. Explain the trend of first ionization energy in a period of the periodic table. 


2. You are provided three test tubes labelled A, B and C containing alkane, alkene and alkyne. How do you know which test tube contains alkane, alkene and alkyne? Explain your answer with suitable reactions involved. Also explain the acidic nature of ethyne. Compare the electronegativity of carbon present in ethane, ethene and ethyne. (3+1+1)


3. Complete the following equations and balance them by the oxidation number method or ion-electron method. Indicate the oxidizing agent and the reducing agent present in the equations. Also prove that redox reaction occurs simultaneously from the following reactions. 

Describe any two applications of redox reactions.


4. Answer the following:

a. Write the principle involved in the manufacture of sulphuric acid by contact process. (2)
b. Why is sulphur trioxide not directly absorbed by water to give sulphuric acid in the manufacture of sulphuric acid by contact process? (1)
c. Calculate the percentage composition of sulphuric acid. (1)
d. In what condition is the product of the pressure and volume of a certain amount of ideal gas constant? (1)
e. 273 ml of a gas is taken in a vessel at 0°C. What will be the volume of gas at -10°C? (1)
f. Suggest the chemical reaction by which carbon monoxide is obtained by using organic molecules with concentrated sulphuric acid. (1)
g. Carbon monoxide is a poisonous gas. Explain the chemical process. (1)


5. Answer the following questions.

a. Complete the table given below. 

AtomAtomic numberNucleon NumberNo. of each subatomic
Mg1224?
Al1327?

 b. 35Cl and 37Cl are the isotopes of chlorine. Calculate the difference in the number of neutrons between them. (1)
c. While calculating the relative mass of an atom, the mass of electrons is not used in the calculation. Why? (1)
d. Why was the Thomson watermelon atomic model discarded by the Rutherford atomic model? Explain. (2)
e. How does Bohr's atomic model explain the origin of hydrogen spectra? (3)


6. Answer the following:

a. Rock salt is an example of halide ore, which is cheap and most abundant. Explain the principle of any one compound manufactured from rock salt. (2)
b. The bond angles of PF3, PCl3, PBr3 and PI3 are 97° , 100° , 101.5° and 102° respectively. Compare these bond angles on the basis of VSEPR theory. (2)
c. Draw an orbital picture of the following molecules.
i. CH4 ii. NH3 iii. H2O iv. C2H2 (2)
d. Calculate the number of sigma bonds and pi bonds present in the following molecules.
i. 2-Methylbut-2-ene ii. Ethane nitrile iii. Acetone. iv. Formaldehyde (2)


7. You are a chemist and are provided a fund of one million dollars. As a chemist, how will you utilize the fund for the economic development of the country? (8)

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