Question

The following hydrogen halides $\left( {HF,HCl,HBr{\text{ }}\operatorname{and} {\text{ HI}}} \right)$ 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

Hydrogen halides are diatomic inorganic compounds that dissolve in water to give acids that are known as hydrohalic acids. As the bond length of $H - X$ increases, bond energy decreases which makes the release of ${H^ + }$ easier and has the greater acidic strength.

Complete step by step answer:
As we know that hydrogen halides are diatomic inorganic compounds with general $HX$ where $X = F,Cl,Br,I$ .Hydrogen halides are the colourless gases at the room temperature and produce steamy fumes in moist air. Hydrogen halides are water soluble gases. Hydrogen halides can be formed easily by the direct reaction of hydrogen gas with the required halogen molecule. As the size of halides ion increases, the bond length of $H - X$ increases. Longer the bond length, weaker is $H - X$ bond and less energy is required to break it and liberate ${H^ + }$ ion. More easily the ${H^ + }$ ions liberated, more is the acidic behavior. Hence acidic strength each form in water depends on the strength of $H - X$ bond. Hence according this $HI$ is the most strongest hydrogen halide acid whereas $HF$ is the least acidic, which is correct. Moreover the hydrogen halides are colourless gases at STP conditions. From $HCl$ to $HI$ , the boiling point increases due to increase in intermolecular wander wool forces. Upon dissolving these halides in water, hydrogen halides give corresponding acids. The acids form are very strong reflecting their tendency to ionize in aqueous solution. We have already discussed the strength of acid. We also got to know that the acid each hydrogen halide forms in water is based on the strength of the bond. Thus only the third statement is correct.
Hence option (C) is the correct answer.

Note: Out of all hydrogen halides, $HF$ is most stable and less acidic due to high electronegativity of fluorine atoms. $HI$ is the strongest reducing agent out of all hydrogen halides as it has low thermal stability as compared to all other hydrogen halides. It can release hydrogen atoms easily to reduce the other compound.