Question

The following hydrogen halides(HF, HCl, HBr and HI) are all polar molecules. The strength of the acid each forms in water is based on which of the following?
I. The polarity of the molecule
II. The size of the molecule
III. The strength of the bond
(A) I only
(B) II only
(C) III only
(D) I and III
(E) II and III

Answer 1

Hint: The acidic strength of the halogen acids depends on how stronger the bond is between the halogen acids. Stronger the bond between them, lesser is the acidic strength and vice-versa. Now find the correct statement.

Complete step by step answer:
First of all, we should know what polar molecules are. Polar molecules are those in the one acquires positive charge and the other acquires the negative charge due to the difference in their electronegativities and in such molecules there are ionic bonds between the atoms.
Now, we can determine the acidic strength of all the above given acids i.e. HF, HCl, HBr and HI on the basis of their bond strength. Stronger the bond strength between the atoms of the H-X ,lesser will be the acidic character of the halogen acid and vice-versa.
As we move down the group, the bond strength decreases because the size of the atom increases and thus, the acidic character increases.
So, HI being bigger in size, has the lowest value of the bond strength and thus, will have the highest acidic character.
On the other hand, HF being smaller in size, has the highest value of the bond strength and thus, will have the lowest acidic character.
Thus, the order of acidic character is as;
HI > HCl > HBr> HF

Hence, the strength of the acid i.e. the acidic strength depends on the bond strength.
So, option(C) is correct.

Note: Always remember that the in the periodic table,
1. size decreases as move from left to right and hence bond strength increases and thus, the acidic character decreases.
2. size increases as move from top to bottom and hence bond decreases and thus, acidic character increases.