Question

If the HCl molecule is completely polarised, the expected value of dipole moment is \[6.12\] (debye), but the experimental value of dipole moment is \[1.03\text{ }D\]. Calculate the percentage ionic character.
A. 17
B. 83
C. 50
D. Zero
E. 90

Answer 1

Hint: Ionic character percentage can be calculated by the ratio of the experimental value of dipole moment to the expected value of dipole moment and multiplied by 100. Given a molecule, HCl is unsymmetrical so its dipole moment has value otherwise the symmetrical molecule’s dipole moment is zero. The value of the dipole moment depends on the electronegativity of the molecule.

Complete Step by Step Answer:
Given a molecule, HCl is polar as the electronegativity difference between the atoms of the molecule lies between 0.5 to 1.7. As there is a good electronegativity difference, the dipole moment will also exist and the expected value of the dipole moment is \[6.12\text{ }D\].

A dipole moment depends on the magnitude of charge which gets separated and on the distance with which charge gets separated. And this gives an idea about the ionic character so, with the dipole moment \[6.12\text{ }D\], the HCl molecule has good ionic character as compared to the ionic character according to the experimentally observed value of dipole moment, which is \[1.03\text{ }D\].

To calculate the exact ionic character of the HCl molecule we need to determine the percentage of ionic character with the help of two values of dipole moment.
To find the percentage of ionic character divide the experimental value of dipole moment by the observed value of dipole moment followed by the multiplication with 100 such as
$Percentage \ of \ ionic \ character = \dfrac{Experimental \ value \ of \ dipole \ moment}{Observed \ value \ of \ dipole \ moment} \times 100$
\[Percentage\text{ }of\text{ }ionic\text{ }character\text{ }=\text{ }1.03/6.12\times 100\]
\[Percentage\text{ }of\text{ }ionic\text{ }character\text{ }=\text{ }17%\text{ }approx.\]
Thus, the correct option is A.

Note: It is important to note that if a molecule is polar it means polar covalent (out of non-polar covalent and polar covalent). Because of this, HCl bond is polar but still its less ionic character is less (not completely ionic). Non-polar covalent will have even less ionic character than polar covalent ionic character. If the bond has great polarity (electronegativity difference greater than 1.4) means ionic then the ionic character will increase and the covalent character decreases.