Question

The observed dipole moment of Hydrochloric acid - HCl is 1.3 D. If the bond length of HCl is 1.3 $\overset{o}{{A}}\,$, then the percent ionic character of $H-Cl$ bond is nearly:
(Charge on electron = $4.8\times {{10}^{-10}}esu$)
a. 50 %
b. 40 %
c. 30 %
d. 17 %

Answer 1

Dipole arises due to the separation of negative and positive charges in an element. It is equal to the product of charge on individual atoms and the distance between them. Dipole moment arises due to the difference in electronegativity between atoms in a compound.

Complete step by step answer:
In the lower classes, we have studied the dipole moment and relating parameters. Let us now see the concept in detail.
Dipole moment arises due to the separation of charges within a molecule, which is due to the electronegativity difference between the atoms. It is equal to the product of charge and distance between atoms.
The value of ionic character in any compound is equal to the ratio of the experimental value to theoretical value. Percentage ionic character is equal to the value of ionic character multiplied by 100. i.e.,
$$ ionic character = $\dfrac{{{\mu }_{practical}}}{{{\mu }_{theoretical}}}\times 100$
Given,
${{\mu }_{practical}}$= 1.3 D
Charge on electron =${{\mu }_{theoretical}}=4.8\times {{10}^{-10}}esu$
Therefore,
${{\mu }_{theoretical}}$ = charge on electron (in esu) x bond length
= 4.8$\times {{10}^{-10}}\times$1.3$\overset{o}{{A}}\,$
= 6.24$\times {{10}^{-10}}$ $\overset{o}{{A}}\,$
By substituting these values in the above equation, we have
$$ ionic character = $\dfrac{1.3\times {{10}^{-10}}}{6.24\times {{10}^{-10}}}\times 100\approx 17$
Therefore, the answer is option (d) – If the bond length of HCl is 1.3 $\overset{o}{{A}}\,$ then the percent ionic character of H-Cl bond is nearly $17$.
So, the correct answer is “Option (d)”.

Additional Information: Dipole moment is measured in a unit known as Debye, which is denoted by ‘D’.

Note: Hydrochloric acid is actually a covalent compound. But due to the electronegativity difference between the two elements, it has an ionic nature. Chlorine has an electronegativity of 3.16, whereas Hydrogen has an electronegativity of 2.2. Therefore, Chlorine develops a delta negative charge and hydrogen develops a delta positive charge.