ASSIGNMENT – (HHW)
CLASS – XI
SUBJECT – CHEMISTRY
Instructions:
1. Submit neat work. This assignment must be handwritten.
3. Assignment should be submitted in a properly covered and labelled exercise copy (school
notebook).
4. Date of Submission: 18.06.2024.
5. All copies are to be collected by the Class monitor. Class, section, total number of copies
collected are to be written on a piece of paper and to be submitted to the Subject Teacher.
6. There will be no online submission. Submission beyond the due date will be dealt with
strictly.
Q1. A hypothetical electromagnetic wave is shown in the figure. Find out the wavelength of the
radiation.
(1)
Q2. Q1. The following data are obtained when dinitrogen and dioxygen react together to form
different compounds:
Mass of
Mass of
dinitrogen dioxygen
(i) 14 g
16 g
(ii) 14 g
32 g
(iii) 28 g
32 g
(iv) 28 g
80 g
Which law of chemical combination is obeyed by the above experimental data? Give its
statement.
(2)
Q3. Answer the following:
(2)
a) Calculate the sum of 7.21, 10.245, 0.0548 in terms of significant figure.
b) Two students performed the same experiment separately and each one of them recorded two
readings of mass which are given below. Correct reading of mass is 3.0 g. Based on given data,
identify the student(s) who is/are both precise and accurate.
Student
Readings
(i)
(ii)
A
3.01
2.99
B
3.05
2.95
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Q4. Calculate the radius (in pm) of Bohr’s 5th orbit for H-atom.
(Given, radius of first Bohr orbit = 53 pm)
(2)
Q5. In the reaction 2A + 4B → 3C + 4D, when 5 moles of A react with 6 moles of B, then
a) Which is the limiting reagent?
b) Calculate the amount of C formed?
(2)
Q6. Answer the following questions:
a) What is meant by quantisation of energy?
b) Mention one reason for the failure of the Bohr Model of Atom.
(2)
Q7. 45.4 L of dinitrogen reacted with 22.7 L of dioxygen and 45.4 L of nitrous oxide was
formed. Write the name and statement of the law that is obeyed in the reaction above.
(2)
Q8. A welding fuel gas contains carbon and hydrogen only. Burning a small sample of it in
oxygen gives 3.38 g carbon dioxide, 0.690 g of water and no other products. A volume of
10.0 L (measured at STP) of this welding gas is found to weigh 11.6 g. Calculate
(i) empirical formula (ii) molar mass and (iii) molecular formula of the gas. (2 + 0.5 + 0.5 = 3)
(Atomic mass: H = 1u, C = 12u, O = 16u. Take molar volume of a gas to be 22.4 L at STP)
Q9. The following is a case-based question. This question has an internal choice and
carries 4 marks. Read the passage carefully and answer the questions that follow.
The energy (E ) of a quantum of radiation is proportional to its frequency (ν ) and is expressed
by equation:
E = hυ
The proportionality constant, ‘h’ is known as Planck’s constant and has the value 6.626×10 –34 Js.
In 1887, H. Hertz performed a very interesting experiment in which electrons (or electric current)
were ejected when certain metals (for example potassium, rubidium, caesium etc) were exposed
to a beam of light. The phenomenon is called Photoelectric effect. The results observed in this
experiment were:
(i) The electrons are ejected from the metal surface as soon as the beam of light strikes the surface,
i.e., there is no time lag between the striking of light beam and the ejection of electrons from the
metal surface.
(ii) The number of electrons ejected is proportional to the intensity or brightness
of light.
(iii) For each metal, there is a characteristic minimum frequency,ν0 (also known as threshold
frequency) below which photoelectric effect is not observed. At a frequency ν > ν0, the ejected
electrons come out with certain kinetic energy. The kinetic energies of these electrons increase
with the increase of frequency of the light used.
The study of emission or absorption spectra is referred to as spectroscopy. The emission spectra
of atoms in the gas phase, on the other hand, do not show a continuous spread of wavelength
from red to violet, rather they emit light only at specific wavelengths with dark spaces between
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them. Such spectra are called line spectra or atomic spectra. The Swedish spectroscopist,
Johannes Rydberg, noted that all series of lines in the hydrogen spectrum could be described by
the following expression :
a) What are line spectra?
(1)
b) According to Planck, what is a ‘Quantum’?
(1)
c) Nitrogen laser produces radiation at a wavelength of 337.1 nm. If the number of photons
emitted is 5.6 × 1024, calculate the energy of this laser.
(Given: h = 6.6 x 10-34 Js, c = 3 x 108 ms-1)
(2)
OR
c) The Balmer series in the hydrogen spectrum corresponds to the transition from n 1 = 2 to
n2 = 3,4........... This series lies in the visible region. Calculate the wave number,
(in C.G.S. unit) of line associated with the transition in Balmer series when the electron
moves to n = 4 orbit. (RH = 109677 cm–1)
(2)
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