9701 · 11.2
The chemical properties of the halogen elements and the hydrogen halides — FAQ
Frequently asked questions for 9701 The chemical properties of the halogen elements and the hydrogen halides. Direct answers first, then deeper explanation — then practise with marking.
Why is fluorine so reactive if the F-F bond is not particularly weak?
While the F-F bond is stronger than the I-I bond, it is anomalously weak for its size due to repulsion between the lone pairs on the small, adjacent fluorine atoms. This weak bond, combined with fluorine's extremely high electronegativity and the very strong bonds it forms with other elements, contributes to its extreme reactivity.
If the H-F bond is the most polar, why isn't HF the strongest acid?
Acidity in water is about how easily the H-X bond breaks to release a proton. The H-F bond is exceptionally strong (high bond enthalpy). The energy required to break this bond is so large that it outweighs the effect of the bond's polarity. Therefore, HF dissociates only slightly in water, making it a weak acid.
What is the practical use of the disproportionation of chlorine?
The reaction of chlorine with cold, dilute sodium hydroxide produces a solution containing sodium chlorate(I), which is the active ingredient in household bleach. It is used for its oxidising properties in cleaning and disinfecting.