APEEJAY SCHOOL, SAKET FIRST TERM EXAMINATION (2018-19) CHEMISTRY CLASS-XI

M.M.-70

TIME-3Hrs

GENERAL INSTRUCTIONS:

All questions are compulsory.

Question numbers 1 to 5 are very short answer questions and carry 1 marks each.

Questions numbers 6 to 12 are short answer questions and carry 2 marks each.

Question numbers 13 to 24 are short answer questions and carry 3 marks each.

. Question numbers 25 to 27 are long answer questions and carry 5 marks each.

Use log tables if necessary. 1

1. Why molality is preferred over molarity in expressing the concentration of a solution?
2. Which out of Cu2+, Fe2+ and Cr3+ has highest paramagnetism and why?
3. Define electronegativity.
4. Define the term bond order.

1

1. Gases possess characteristic critical temperatures which depend upon the magnitude of intermolecular forces between the gas particles. Critical temperature of ammonia and carbon dioxide are 405.5 K and 304.10 K. Which of these gases will liquefy first when you start cooling from 500 K to their critical temperature?

2

1. Commercially available concentrated hydrochloric acid contains 38% HCl by mass. What is the molarity of this solution? The density is 1.10 g/cm³.
2. Carbon is found to form two oxides, which contain 42.9% and 27.3% of carbon 2 respectively. Show that these figures illustrate the law of multiple proportion.

OR

Determine the molecular formula of an oxide of iron in which the mass percentage of iron and oxygen are 69.9 % and 30.1 % respectively, Given that the molar mass of oxide is 159.89 g mol-1. (Atomic mass of Fe = <math>55.85 \text{ g mol}^{-1}</math>)

1. Account the following: 2 Cations are smaller and anions are larger in radii than their parent atoms.
2. Cl has more negative electron gain enthalpy than F.
3. Explain why- 2
4. Be has higher ionization enthalpy than B?
5. First electron gain enthalpy of O is negative but second is positive?
6. Draw the box structure with orbital representation of the following molecules: 2
7. SF₄ ii.PCl₅ Predict the hybridization of the central metal atom and shape of the molecule.

1. How many <math>\sigma</math> and <math>\pi</math> bonds are present in the following? 2
2. CH₂=C=CH₂
3. CH₃-CH=CH-C≡CH
4. 13. Differentiate between bonding and anti-bonding molecular orbital. a ) State Dalton's law of partial pressure. 2<br>3
5. Derive relationship between partial pressure of a gas and its mole fraction in a mixture of two non reacting gases.

OR

1. Explain why during fire polishing of glass the sharp edges become smooth.
2. Derive relationship between molar mass and density of a gas.
3. a) Discuss the shape of BrF₃ on the basis of VSEPR theory. 3
4. On the basis of Molecular orbital theory explain, why is there an increase in bond

order in going from O2 to O2+ while a decrease in going from N2 to N2+?

1. 3 g of H₂ reacts with 29g of O₂ to form H₂O. 3
2. Which is the limiting reagent?
3. Calculate the maximum amount of H₂O that can be formed.
4. Calculate the amount of the reactant that is left unreacted.
5. a) Calculate the mole fraction of ethylene glycol (C₂H₆O₂) and water in a solution 3 containing 20% of C₂H₆O₂ by mass.
6. What is Gay Lussacs's law of gaseous volumes?
7. i) State and explain Heisenberg's uncertainty principle. 3
8. A golf ball has mass 40 g and speed 45 m s 1 If the speed can be measured with accuracy of 2%. Calculate the uncertainty in position of the golf ball.
9. An atom has 2K, 8L and 3M electrons. Write down its electronic configurations and 3 indicate in it.
10. no. of subshells
11. no. of orbitals
12. no. of s electrons
13. no. of unpaired electrons.
14. Amongst the elements of the third period (Na to Ar), Identify the element 3 with highest ionization enthalpy
15. with largest atomic radii
16. most reactive non metal
17. most reactive metal
18. an element that shows characteristic properties of metals as well as non-metal.
19. an element whose oxide is amphoteric in nature.
20. Give reasons: 3 Successive ionisation enthalpies are higher. Halogens have the highest negative electron gain enthalpy.
21. Electron gain enthalpy values of noble gases are positive while those of Be, Mg, N and P are almost zero.
22. Differentiate between Schottky & Frenkel defects. 3 Calculate the packing efficiency of a face centred cubic unit cell.
23. a) Write the half cell reaction and the overall cell reaction for the electrochemical cell 3