Chemistry Objective Questions & Answers on “Towards Quantum Mechanical Model of the Atom”.
1. Who found out about dual behavior of a matter?
a) De Broglie
b) Bohr
c) Rutherford
d) Thomson
Answer: a
Clarification: A French physicist named Louis de Broglie proposed that matter exhibits both particle and wave like nature. This means that like photons, electrons also should have both momentum and wavelength.
2. A ball of mass 0.5kg is moving with velocity 6.626 m/s. What’s the wavelength of that ball?
a) 1 x 10-34 m
b) 2 x 10-34 m
c) 2 x 10-32 m
d) 2 x 10-3 m
Answer: b
Clarification: Louis de Brogie gave the realation between momentum and wavelength as λ = h/p. Here h is Planck’s constant, whose value is 6.626 x 10-34 J/s. Wavelength = h/mv = 2 x 10-34 m (momentum p = mass m x velocity v).
3. Mass of a photon is given by 3.313 x 10-34 kg. Find it’s wavelength.
a) 0.67A°
b) 0.67nm
c) 0.37A°
d) 1.67A°
Answer: a
Clarification: Louis de Brogie gave the realation between momentum and wavelength as λ = h/p. Here h is Planck’s constant, whose value is 6.626 x 10-34 J/s. Wavelength = h/mc = 6.626 x 10-34 Js/(3.313 x 10-34 kg x 3 x 108 m/s) = 0.67A°.
4. Determining the exact position and velocity of an electron is impossible at a time.
a) True
b) False
Answer: a
Clarification: A German physicist, Werner Heisenberg stated Heisenberg’s principle of uncertainty, that states that determining the exact position and velocity of an electron is impossible at a time, as a result of dual nature of matter and radiation.
5. As per Heisenberg’s principle of uncertainty, the relation between relative momentum and relative position is __________
a) independent
b) equal
c) directly proportional
d) inversely proportional
Answer: d
Clarification: Heisenberg’s principle of uncertainty states that the product of relative momentum and velocities is equal to greater than the h/4π, where is “h” is the Planck’s constant and is equal to 6.626 x 10-34 Js.
6. The uncertainty of a ball is given by 0.5A°. Then calculate the uncertainty in momentum.
a) 2.055 x 10-24 kgm/s
b) 1.015 x 10-24 kgm/s
c) 1.055 x 10-24 kgm/s
d) 1.095 x 10-24 kgm/s
Answer: c
Clarification: Heisenberg’s principle of uncertainty states that Δx. Δp ≥ h/4π, x is position, p is momentum and “h” is the Planck’s constant and is equal to 6.626 x 10-34 Js. Relative momentum Δp = h/4πΔx = 1.055 x 10-24 kgm/s.
7. If the uncertainties in position and momentum are equal, then the uncertainty in position is given by ____
a) √h/4π
b) √h4π
c) √h/4
d) √h/π
Answer: a
Clarification: As we know, Heisenberg’s principle of uncertainty states that Δx. Δp ≥ h/4π, x is position, p is momentum and “h” is the Planck’s constant. Δx = Δp; Δx. Δx = h/4π; Δx = √h/4π
8. If the kinetic energy of an electron is 5J. Find out its wavelength.
a) 0.313 x 1015 m/s
b) 3.013 x 1015 m/s
c) 3.310 x 1015 m/s
d) 3.313 x 1015 m/s
Answer: d
Clarification: We know that the mass of an electron is 9.1 x 10-31 kg. Given that the kinetic energy of an electron is 5J. K.E = mv2/2 and by substituting we get v = √1.098 x 1031 m/s = 3.313 x 1015m/s.
9. An object has a mass of 6 kg and velocity of 10 m/s. The speed is measured with 5% accuracy, then find out Δx in m.
a) 0.12676 x 10-34
b) 0.1566 x 10-34
c) 0.176 x 10-34
d) 0.276 x 10-34
Answer: c
Clarification: Speed’s uncertainty is 10 x 5/100 = 0.5 m/s. We have Heisenberg’s principle of uncertainty i.e. Δx. Δp ≥ h/4π. Δx = h/2mπ. Therefore uncertainty in position = 6.626 x 10-34 Js/12 x 3.1416 = 0.176 x 10-34.
10. Δx. Δp ≥ h/4π.
a) True
b) False
Answer: a
Clarification: Heisenberg’s principle of uncertainty states that the product of relative momentum and velocities is equal to greater than the h/4π, where is “h” is the Planck’s constant and is equal to 6.626 x 10-34 Js. Hence the above statement is true.