Chem Notes 1st Year Chap 6
Important Questions
Q Why it is necessary to reduce the pressure inside the discharge tube to get cathode rays ?
Ans: The conductance of electricity trough discharge tube does not occur at ordinary pressure because the molecules gas inside the tube hinders the movement of electrons between the electrodes therefore the number of molecules inside the tube is reduced by decreasing the pressure to get the cathode rays.
Q How positive rays are produced?
Ans: The positive rays are produced when high speed of cathode rays strike the molecules of a gas enclosed in the discharge tube. They knock out electrons from the gas molecules and positive ions are produced which start moving towards the cathode thus giving rise to the positive rays.
M+ e- ------------> M + 2e-
Q Whichever the gas used in the discharge tube the nature of cathode rays remains the ame why ?
Ans: Cathode rays are emitted from the cathode when voltage is applied inside the discharge tube at very low pressure and not from the gas inside the tube. The characteristics of the cathode rays are independent of the nature material making cathode and the gas inside the tube. There the nature of cathode rays remains the same which ever the gas is used inside the tube.
Q Why the e/m of cathode rays is just equal to the electrons ?
Ans: Actually, the cathodes rays is the beam of fast moving electrons therefore the e/m value of cathode rays is just equal to the electrons and is same for all the gases.
Q Jstify that cathode rays are material particles with negative charge.
Ans: The cathode rays can derive a small paddle wheel placed in their path. This shows that these rays are the material particles having momentum i.e mass and velocity. When the cathode rays are passed through the electric field these are deflected towards the positive plate indicating that they have negative charge.
Q e/m value of positive rays is different for the gases bot remains same for cathode raus. Explain.
Ans: Positive rays are produced by the ionization of gas molecules inside the tube and characteristics of positive rays vary from gas to gas therefore the e/m value of positive rays different for different gases as each has its own characteristics positive ion whereas in case of cathode rays they are always fast moving electrons what ever the gas may be in tube and hence its e/m value remains same for all gases.
Q e/m values of positive rays obtained from the hydrogen gas is 1836 times less than that of cathode rays. Why ?
Ans: e/m value of the positive rays depend upon the nature of gas inside the tube heavier the gas smaller will its e/m value. Since mas of hydrogen is 1836 time heavier than that of electrons therefore the e/m value of hydrogen is 1836 time more than that of electron.
Q Prove that cathode rays move in a straight line or it can cast the shadow of an opaque object placed in their path.
Ans: in 1869, Hittrof observed that these rays cast a sharp shadow when the opaque object is placed in their path. This showed that the cathode rays travel in straight line perpendicular to the surface of cathode.
Q What are the particles formed by the decay of free neutron ?
Ans: Free neutron decay into a proton with the emission of an electron and neutrino.
on ---------> P + e + on
Q Different between the slow and fast neutrons .
Ans: The neutrons moving the energy of 1.2 MeV are called neutrons where as the neutrons moving with energy less than the 1eV are termed as the slow neutrons.
Q How the slow neutron can be more effective than the fast neutrons ?
Ans: The slow neutrons are more effective in nuclear fission as they are being captured by the nucleus and results in its disntegration e.g when slow neutron hit Cu metal then y-radiation is emitted with the formation of radioactive Cu which is converted into Zn.
Cu + n ---------> Cu +
Cu -------------> Zn + e
Q How did Rutherford's model proved existence of nucleus of atom ?
Ans: Rutherford bombarded the beam of alpha particles on thin gold foil and observed that some ( only a few ) particles were deflected backward. Theses re-bouncing alpha particles must have collided with the heavy portion of atoms with positive charge called the nucleus.
Q Write down the drawback of Rutherford atomic model.
Ans: The revolving electrons being negatively charged should emit the energy continuously. The orbit of electron should become smaller until finally it falls into the nucleus. But in reality it never falls
Nature of spectrum : If the electron emits energy continuously we should get the Continuous Spectrum Actually atoms give Line Spectrum
Q Define Spectrum.
Ans: The visual display of the dispersion of the components of white ligh when it is passed trough a prism is called the spectrum.
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Q Why it is necessary to reduce the pressure inside the discharge tube to get cathode rays ?
Ans: The conductance of electricity trough discharge tube does not occur at ordinary pressure because the molecules gas inside the tube hinders the movement of electrons between the electrodes therefore the number of molecules inside the tube is reduced by decreasing the pressure to get the cathode rays.
Q How positive rays are produced?
Ans: The positive rays are produced when high speed of cathode rays strike the molecules of a gas enclosed in the discharge tube. They knock out electrons from the gas molecules and positive ions are produced which start moving towards the cathode thus giving rise to the positive rays.
M+ e- ------------> M + 2e-
Q Whichever the gas used in the discharge tube the nature of cathode rays remains the ame why ?
Ans: Cathode rays are emitted from the cathode when voltage is applied inside the discharge tube at very low pressure and not from the gas inside the tube. The characteristics of the cathode rays are independent of the nature material making cathode and the gas inside the tube. There the nature of cathode rays remains the same which ever the gas is used inside the tube.
Q Why the e/m of cathode rays is just equal to the electrons ?
Ans: Actually, the cathodes rays is the beam of fast moving electrons therefore the e/m value of cathode rays is just equal to the electrons and is same for all the gases.
Q Jstify that cathode rays are material particles with negative charge.
Ans: The cathode rays can derive a small paddle wheel placed in their path. This shows that these rays are the material particles having momentum i.e mass and velocity. When the cathode rays are passed through the electric field these are deflected towards the positive plate indicating that they have negative charge.
Q e/m value of positive rays is different for the gases bot remains same for cathode raus. Explain.
Ans: Positive rays are produced by the ionization of gas molecules inside the tube and characteristics of positive rays vary from gas to gas therefore the e/m value of positive rays different for different gases as each has its own characteristics positive ion whereas in case of cathode rays they are always fast moving electrons what ever the gas may be in tube and hence its e/m value remains same for all gases.
Q e/m values of positive rays obtained from the hydrogen gas is 1836 times less than that of cathode rays. Why ?
Ans: e/m value of the positive rays depend upon the nature of gas inside the tube heavier the gas smaller will its e/m value. Since mas of hydrogen is 1836 time heavier than that of electrons therefore the e/m value of hydrogen is 1836 time more than that of electron.
Q Prove that cathode rays move in a straight line or it can cast the shadow of an opaque object placed in their path.
Ans: in 1869, Hittrof observed that these rays cast a sharp shadow when the opaque object is placed in their path. This showed that the cathode rays travel in straight line perpendicular to the surface of cathode.
Q What are the particles formed by the decay of free neutron ?
Ans: Free neutron decay into a proton with the emission of an electron and neutrino.
on ---------> P + e + on
Q Different between the slow and fast neutrons .
Ans: The neutrons moving the energy of 1.2 MeV are called neutrons where as the neutrons moving with energy less than the 1eV are termed as the slow neutrons.
Q How the slow neutron can be more effective than the fast neutrons ?
Ans: The slow neutrons are more effective in nuclear fission as they are being captured by the nucleus and results in its disntegration e.g when slow neutron hit Cu metal then y-radiation is emitted with the formation of radioactive Cu which is converted into Zn.
Cu + n ---------> Cu +
Cu -------------> Zn + e
Q How did Rutherford's model proved existence of nucleus of atom ?
Ans: Rutherford bombarded the beam of alpha particles on thin gold foil and observed that some ( only a few ) particles were deflected backward. Theses re-bouncing alpha particles must have collided with the heavy portion of atoms with positive charge called the nucleus.
Q Write down the drawback of Rutherford atomic model.
Ans: The revolving electrons being negatively charged should emit the energy continuously. The orbit of electron should become smaller until finally it falls into the nucleus. But in reality it never falls
Nature of spectrum : If the electron emits energy continuously we should get the Continuous Spectrum Actually atoms give Line Spectrum
Q Define Spectrum.
Ans: The visual display of the dispersion of the components of white ligh when it is passed trough a prism is called the spectrum.
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