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

Which two elements among the following belong to the same period Al, Si, Ba and O?

1. Why liquids diffuse slowly as compared to gases?

1. A gas is filled into a bulb connected to an open limb manometer. The level of mercury in

the open arm is 2.1 cm lower than that in the other arm of manometer. The atmospheric pressure is 720 mm. What is the pressure of the gas?

1. Heat capacity is an extensive property but specific heat is intensive property. Comment on the statement.
2. Boron forms no compounds in unipositive state but thallium in unipositive state is quite stable. Explain.

Section B

6. Cyanogen (CN), is known as a pseudohalogen because it has some properties similar to halogens. It is composed of two CN's joined together. Do the two CN's join through the carbon or the nitrogen (i. e., C - N - N - C or N - C - C - N)?

1. <math>CO_2</math> is heavier than <math>N_2</math> and <math>O_2</math> gases present in the air but it does not form the lower layer of the atmosphere. Explain.
2. Calculate
3. mass of 2.5 g atoms of magnesium,
4. gram atom in 1.4 g of nitrogen (Atomic mass <math>Mg = 24</math>, <math>N = 14</math>)

1/5

Or Calculate the mass of

1. 1 molecule of N₂
2. 100 molecules of sucrose <math>(C_{12}H_{22}O_{11})</math>.

What happens when (give chemical equation only)

1. sodium is exposed to moist air?
2. sodium reacts with water?

Name one reaction in which water acts

1. as an oxidising agent and
2. as a reducing agent?

Section C

1. The threshold wavelength for emitting photons from a metal is <math>6.0 \times 10^3 \, \text{Å}</math>. What would be the wavelength of radiation to produce photoelectrons having twice the kinetic energy of those produced by radiation of wavelength <math>_{3\times10^3}</math> Å?
2. The wavelength of the first line in the Balmer series is 656 nm. Calculate the wavelength of the second line and the limiting line in Balmer series.
3. A student while measuring pressure and volume of a gas at constant temperature forgot to record some of the observations as follows.

Pressure (torr) 100 125 (-) 200 Volume (mL) 80 (-) 32 40

Calculate the missing observations. Name the law used in your calculations.

1. Give the balanced equations for the reactions that form the basis for the following redox titrations
2. Titration of potassium permanganate for estimation of ferrous ions.
3. Titration of iodine against sodium thiosulphate (iodimetric titration).
4. Iodometric titration for estimation of cupric ions.

1. The degree of dissociation of <math>N_2O_4</math> into <math>NO_2</math> at one atmospheric pressure and 313 K is

0.310. Calculate <math>\,K_{\,\textstyle z}\,</math> of the dissociation reaction at this temperature. What will be the degree of dissociation at 10 atmospheric pressure at the same temperature? 2/5