Questions
State and explain law of definite proportion ?
A chemical compound always contains the same elements combined together in the same proportion by mass.
Example : Carbon dioxide can be obtained by many methods.
Its formula : co2 mass ratio --------> 12:32 simple ratio--------> 3:8
Define Atomic mass unit (amu) or unified mass(u). What is its value ?
One atomic mass unit is equal to one-twelfth(1/12) the mass of an atom of carbon-12.
1 amu (u)= 1.66056* 10-24 g.
Define mole ?
Mole is the amount of a substance which contain 6.022 * 1023 particles (Avogadro's number)
1 Mole= 22.4 L at STP (Molar volume at STP).
What is limiting reagent (limiting reactant) ?
The reactant that is consumed completely in a reaction is called limiting reagent (limiting reactant) .
Explain Rutherford's alpha ray scattering experiment ? Give its important observations and conclusions ?
Rutherford bombarded thin gold foil by alpha particles (positive charge) and the movements of rays are detected by circular zinc sulphide screen.
| Observations | Conclusions | |
| 1 | Most of the alpha particles passed through the gold foil without any deflections. | Most of the space in an atom is empty. |
| 2 | A few alpha particles were deflected through small angles. | A heavy positive centre is present at the centre of the atom called nucleus. |
| 3 | Very few alpha particles are deflected back (1800). | Nucleus is very small in size. |
Explain line spectrum of hydregon ?
| Series | Spectral region | n1 | n2 |
| Lyman series | Ultraviolet | 1 | 2,3 |
| Balmer series | Visible | 2 | 3,4 |
| Paschen series | infrared | 3 | 4,5 |
| Brackett series | infrared | 4 | 5,6 |
| Pfund series | infrared | 5 | 6,7 |
What are the postulates of Bohr atom model ?
(i) The electrons in an atom revolve around the nucleus in circular paths called orbits. These orbits have definite energies called energies shells or energy levels.
(ii) As long as electrons remain in a particular orbit, it does not lose or gain energy.
(iii) Energy is emitted or absorbed by an atom only when an electron in it moves from one orbit to other.
What are the merits of Bohr atom model ?
(i) Bohr's model can explain the stability of an atom.
(ii) Bohr's model can explain the atomic spectrum of hydrogen.
What are the merits of Bohr atom model ?
(i) Bohr's model can explain the stability of an atom.
(ii) Bohr's model can explain the atomic spectrum of hydrogen.
What are the draw backs of Bhor atom model ?
(i) It cannot explain de Broglie concept of dual nature of matter.
(ii) It cannot explain Heisenberg's uncertainty principle.