Problem 33 - Chemistry An Atoms First Approach

Question

Of the hydrogen halides, only HF is a weak acid. Give a possible explanation.

Step-by-Step Solution

Answer

HF is a weak acid among hydrogen halides due to the stronger bond between hydrogen and fluorine and the higher electronegativity of fluorine. These factors make it more difficult for HF to dissociate and release H+ ions in a solution, compared to other hydrogen halides.

Step 1: Identify the hydrogen halides

Hydrogen halides are binary compounds of hydrogen with halogen elements, and they include the following: hydrogen fluoride (HF), hydrogen chloride (HCl), hydrogen bromide (HBr), and hydrogen iodide (HI).

Step 2: Understand acidity strength

The strength of an acid is determined by its ability to donate a proton (H+) to a solution. A strong acid will dissociate completely, releasing more H+ ions, while a weak acid will only partially dissociate, releasing fewer H+ ions.

Step 3: Analyze bond strength

One of the factors affecting the acidity of a compound is the strength of the bond between hydrogen and the halogen atom. The weaker the bond, the easier it is for the compound to dissociate and release H+ ions. The bond strength decreases as the size of the halogen atoms increases, meaning that the bond between hydrogen and fluorine (in HF) is stronger compared to that with other halogens, making it more difficult to dissociate and release H+ ions.

Step 4: Consider electronegativity

Another essential factor in determining acidity is the electronegativity of the halogen atoms. A higher electronegativity implies that the atom has a greater ability to attract the shared electron pair in the molecule. Fluorine is the most electronegative element, meaning it holds the electrons more tightly compared to the other halogen atoms. This strong attraction further results in the HF bond being difficult to dissociate, thus making HF a weak acid.

Step 5: Conclusion

The reason why HF is a weak acid among hydrogen halides is due to its stronger bond between hydrogen and fluorine, and the higher electronegativity of fluorine. These factors make it more difficult for HF to dissociate and release H+ ions in a solution, making it a weak acid compared to the other hydrogen halides.