Hydrohalic acids Hydrofluoric acid

When this reaction involves fluorine, it is explosive, but it becomes less and less violent as we substitute chlorine, bromine, and iodine. The hydrogen halides dissolve in water to form hydrohalic acids. Hydrofluoric acid (HF) is a weak acid (that is, it is a... 

It is common practice to refer to the molecular species HX and also the pure (anhydrous) compounds as hydrogen halides, and to call their aqueous solutions hydrohalic acids. Both the anhydrous compounds and their aqueous solutions will be considered in this section. HCl and hydrochloric acid are major industrial chemicals and there is also a substantial production of HF and hydrofluoric acid. HBr and hydrobromic acid are made on a much smaller scale and there seems to be little industrial demand for HI and hydriodic acid. It will be convenient to discuss first the preparation and industrial uses of the compounds and then to consider their molecular and bulk physical properties. The chemical reactivity of the anhydrous compounds and their acidic aqueous solutions will then be reviewed, and the section concludes with a discussion of the anhydrous compounds as nonaqueous solvents. 

In contrast to the other three hydrohalic acids, HF is a weakly dissociating acid. One consequence of this property is that ion exchange is superior to distillation for HF reprocessing [Da3]. When diluted in water HF dissociates into H+, F and various hydrofluoric species such as HF2- and (HF)2 according to the reactions ... 

Down a group, bond strength is the most important factor. Acid strength increases as bond strength decreases. A weaker bond means that the hydrogen atom is more easily pulled away from the atom to which it is attached. For example, hydrofluoric acid is a stronger acid than water, but HF is the weakest of the hydrohalic acids because the H-F bond is relatively strong. 

Hydrohalic acids can cause cleavage of the ether. Hydrofluoric acid, HF, doesn t work as well as the other acids in the group (HCl, HBr, or HI)-Secondary and tertiary ethers undergo reaction, while methyl and primary ethers undergo Sp 2 reaction. A generic example is in Figure 3-34, and the mechanism is in Figure 3-35. 

Of the hydrohalic acids FIF, HC1, HBr, and HI, hydrofluoric acid is the only weak acid. Which of these acids has a positive value of pka ... 

Hydrohalides dissolve easily in water to form hydrohalic acids and undergo virtually complete ionic dissociation (equation 84). All the hydrohalic acids, except HF, are very strong acids. Although AHF is one of the most acidic liquids, as measured by its Hammett function, hydrofluoric acid is a weak acid. 

Diorgano tellurium oxides react with hydrohalic acids by regenerating the diorgano tellurium dihalides, the common starting materials for the preparation of diorgano tellurium oxides. The reactions with hydrochloric acid, hydrobromic acid , and hydroiodic acid, therefore, are not of synthetic importance. The reaction with hydrofluoric acid , however, is a convenient way of preparing diorgano tellurium difluorides. 

Hydrofluoric acid is a weak acid, whereas all other hydrohalic acids (HCl, HBr, and HI) are strong acids. 

The hydrogen halides form hydrohalic add solutions when dissolved in water. These solutions have the characteristic properties of acids, such as reactions with active metals to produce hydrogen gas. —(Section 4.4) Hydrofluoric acid also reacts readily with silica (Si02) and with silicates to form hexafluorosilicic acid (H2SiFg) ... 

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