Question

37. What type of concept associated with dispersion forces is depicted below? Page 6 Electrostatic attraction Helium atom 1 Helium atom 2 8 (b) A) Capillary action B) Polarizability C) Molecularity D) Dynamic equilibrium E) Liquid crystal formation

Answer 1

Solution 37):-

"Polarization" is the concept associated with the dispersion forces shown in figure.

Polarization, in simple words, is the partial or complete separation of positive and negative charges in atoms or molecules. The atoms of helium are electrically symmetrical and do not possess any dipole moment. However, a slight relative displacement of the nuclei or the electrons may develop a temporary (instantaneous) dipole moment in a helium atom. At the moment, a He atom develops a temporary dipole moment, it can polarize other He atom and may change it into an induced dipole. The two helium atoms thus can be held by electrostatic forces called London forces.

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​​​​​​Solution 38):-

NH₃ + H₂O   $\rightleftharpoons$ NH₄ ⁺ + OH^-

The ICE Table:-

Kb = [NH4+] [OH-] / [NH3] = (x).(x) / (0.20 - x)

(1.8 × 10^-5) = x² / (0.20 - x)

Taking, (0.20 - x) = 0.20 because the value of x is very small.

Now,

(1.8 × 10^-5) = x² / (0.20)

Or, x² = 3.6 × 10^-6

Or, x = 1.9 × 10^-3

x = [OH^-] = 1.9 × 10^-3 M

pOH = -log₁₀ [OH^-] = -log₁₀ (1.9 × 10^-3) = 2.72

pH = 14 - pOH = 14 - 2.72 = 11.28

Thus, pH of the 0.20 M NH3 solution is = 11.28

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