1. (a) Calculate the number of oxygen atoms in 0.10 mole of Na2CO3.10H2O.
(b) If one mole of sulphur weighs 32 grams, what is the mass (in grams) of 1 atom of sulphur?
(c) Identify the correct formula for ammonium sulphate from the following formula:
(NH4)(SO4)3,(NH4)2SO4,NH4(SO4)2
2. How were cathode rays produced using a discharge tube? Give four properties of cathode rays.
Why does e/m ratio of negatively charged particles remain constant for all gases? Draw a neat
and labelled diagram of a cathode ray tube.
3.(a) What are the postulates of Bohr’s model of an atom?
(b) Show diagrammatically the electron distributions in Sodium, Lithium and Aluminium atoms.
Answers
Since 1 mole of Na2CO3.10H20 = 6.022 X1023molecules of Na2CO3.10H20
So 0.1 mol of Na2CO3.10H2O will have = 6.022 X1023 X0.1 molecules of Na2CO3.10H20
Now we know that each molecule contains 13 O-atoms,
Total no. of O- atoms = 6.022 X1022 X 13
hence O2 molecules will be = 6.022 X1022 X 13 /2= 6.022 X1022 X 6.2
Now further, 6.022 X1023 molecules of Oxygen = 1 mol Oxygen gas .
Thus, 6.022 X1022 X 6.2 molecules of Oxygen will contain= 6.022 X1022 X 6.2 / 6.022 X1023 moles of oxygen
= 0.62 mol of oxygen
Now as one mol oxygen = 32 gm of oxygen
So, 0.62 mol oxygen = 32 X 0.62= 19.84 gm of Oxygen gas.
(b)
6.022*1023atoms weight=32g
1 atoms weight=32/6.022*1023
(c)(NH4)2SO4
2..
cathode rate were composed of a previously unknown negatively charged particle, which was later named the electron.Cathode ray tubes(CRTs) use a focused beam of electrons deflected by electric or magnetic fields to create the image on a television screen it was started by a J.J Thomson.
4.Properties of cathode rays:-
They are deflected from their rectilinear path by electrostatic and magnetic fields and behave in the manner of a stream of negatively charged particles.
They can impart negative charge to objects in their paths.
They can cause ionization in gases.
They cast shadows if some target is placed in their path.
The negatively charged particles are electrons. The mass and charge of an electron is same irrespective of the substance (element or compound) it is generated. Hence, e/m or charged mass ratio is constant and independent of the type of gas.
3.(a)
•An electron can make a transition from a stationary state of higher energy E2 to a state of lower energy E1and in doing so, it emits a single photon of frequency,
ν=E2−E1h where h is the planck's constant.
Conversely, on absorbing an energy, E2−E1 when the electron is at energy E1, the electron can make a transition from E1 to E2.
•Only those orbits are allowed for which the angular momentum of the electron is an integral multiple of h2π,
Thus, L=nh2π where n=0,1,2,.....
•
An electron can revolve around the nucleus in certain fixed orbits of definite energy without emission of any radiant energy. Such orbits are called stationary orbits.
Explanation:
1.(a)
Since 1 mole of Na2CO3.10H20 = 6.022 X1023molecules of Na2CO3.10H20
So 0.1 mol of Na2CO3.10H2O will have = 6.022 X1023 X0.1 molecules of Na2CO3.10H20
Now we know that each molecule contains 13 O-atoms,
Total no. of O- atoms = 6.022 X1022 X 13
hence O2 molecules will be = 6.022 X1022 X 13 /2= 6.022 X1022 X 6.2
Now further, 6.022 X1023 molecules of Oxygen = 1 mol Oxygen gas .
Thus, 6.022 X1022 X 6.2 molecules of Oxygen will contain= 6.022 X1022 X 6.2 / 6.022 X1023 moles of oxygen
= 0.62 mol of oxygen
Now as one mol oxygen = 32 gm of oxygen
So, 0.62 mol oxygen = 32 X 0.62= 19.84 gm of Oxygen gas.
(b)
6.022*1023atoms weight=32g
1 atoms weight=32/6.022*1023
(c)(NH4)2SO4
2..
cathode rate were composed of a previously unknown negatively charged particle, which was later named the electron.Cathode ray tubes(CRTs) use a focused beam of electrons deflected by electric or magnetic fields to create the image on a television screen it was started by a J.J Thomson.
4.Properties of cathode rays:-
They are deflected from their rectilinear path by electrostatic and magnetic fields and behave in the manner of a stream of negatively charged particles.
They can impart negative charge to objects in their paths.
They can cause ionization in gases.
They cast shadows if some target is placed in their path.
The negatively charged particles are electrons. The mass and charge of an electron is same irrespective of the substance (element or compound) it is generated. Hence, e/m or charged mass ratio is constant and independent of the type of gas.
3.(a)
•An electron can make a transition from a stationary state of higher energy E2 to a state of lower energy E1and in doing so, it emits a single photon of frequency,
ν=E2−E1h where h is the planck's constant.
Conversely, on absorbing an energy, E2−E1 when the electron is at energy E1, the electron can make a transition from E1 to E2.
•Only those orbits are allowed for which the angular momentum of the electron is an integral multiple of h2π,
Thus, L=nh2π where n=0,1,2,.....
•
An electron can revolve around the nucleus in certain fixed orbits of definite energy without emission of any radiant energy. Such orbits are called stationary orbits