Session Ending Examination (2015-16) Chemistry CBSE Class - XI

Time: 3 Hrs. M.M: 70

General Instructions:

1. Question 1 to 5 one mark.
2. Question 6 to 10 each two mark.
3. Question 11 to 22 each three mark.
4. Question 23 is value based question and carry four marks.
5. Questions 24 to 26 each five mark.

Section A

1. When <math>\alpha</math> -rays hit a thin foil of gold, very few <math>\alpha</math> -particles are deflected back. What does it prove?
2. Calculate the number of atoms of each type in 5.3 g of <math>Na.CO_3</math>.
3. Critical temperatures of ammonia and carbon dioxide are 405.5 K and 304.10 K

respectively. Which of these gases will liquefy first when you start cooling from 500 K to their critical temperature?

1. Why does table salt get wet in rainy season?
2. What orbitals can overlap to form a <math>\sigma</math> – bond and which orbitals can do so to form a <math>\pi</math> – bond?

Section B

1. What is hybrid state of central atom in the following? <math>NO_3^-</math>, <math>BF_4^-</math>, <math>PF_5</math>, <math>IF_5</math> and <math>CO_2</math>.

1. Using van der Waals equation, calculate the constant 'a' when two moles of a gas confined

in a four litre flask exerts a pressure of 11.0 atmosphere at a temperature of 300 K. The value of 'b' is 0.05 L <math>mol^{-1}</math>.

1. (i) What are conjugate acid-base pairs?
2. What are amphoteric substance? Give one example.
3. What are allotropes? List two characteristic differences between diamond and graphite which are allotropes of carbon.

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1. Indentify the species I and II as electrophiles (E) or nucleophiles (Nu) in the reactions
2. <math>(CH_3)_2 \overset{\bullet}{O}:+B(CH_3)_3 \longrightarrow (CH_3)_2 O + \overline{B}(CH_3)_3</math>

1. <math>: C_N :+ CH_3Br \longrightarrow H_3C : CN + : Br</math>
2. <math>H: C = CH + : NH_2^- \longrightarrow H - C = C: + : NH_3</math>

1. <math>CH_{\frac{3}{2}}CH = O + :SO_3 H_{\frac{3}{11}} \longrightarrow CH_{\frac{3}{2}} - CH - SO_3 H</math>

Section C

Arrange the elements of second row in order of increasing second ionisation enthalpies.

1. <math>0.145dm^3</math> of hydrogen gas is collected over water at <math>23°C</math> and total pressure of

<math>99085Nm^{-2}</math>. If the vapour pressure of water at <math>23^{\circ}C</math> is <math>2973Nm^{-2}</math>, what is the pressure exerted by the dry gas? Also calculate the volume of dry gas? Under NTP conditions?

1. What volume of 0.6 M HCl has enough hydrochloric acid to react exactly with 25 mL of aqueous NaOH having concentration of 0.5 M?

1. When a certain metal was irradiated with a light of frequency <math>3.2 \times 10^{16} Hz</math>, the

photoelectrons had twice the kinetic energy as emitted when the same metal was irradiated with light of frequency <math>2.0 \times 10^{16} Hz</math>. Calculate the threshold frequency <math>(v_0)</math> of the metal.

1. Calculate the kinetic energy of moving electron which has a wavelength of 4.8 pm (mass

of electron = <math>9.11 \times 10^{-31} kg</math>, h = <math>6.63 \times 10^{-34} J_5</math>).

1. Explain the difference in the reactivity of the group, metals with water.

<math>\mathbf{or}</math>

1. What is the oxidation state of K in <math>KO_2</math>?
2. LiH is more stable than NaH. Explain.
3. Why are alkali metal halides soluble in water?
4. Draw the resonance structure of the following compounds
5. <math>CH_2 = CH - \ddot{C}l</math>:
6. <math>CH_1 = CH - CH = CH_2</math>

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