The Foundations of Chemistry

(HF) 2 (aq)
H 2 O(
) 34 H 3 O
(aq)
HF 2 (aq) K
 5

The order of increasing acid strengths of the aqueous hydrohalic acids is:

HFHClHBrHI

The only acid used in industry to a greater extent than HCl is H 2 SO 4. Hydrochloric

acid is used in the production of metal chlorides, dyes, and many other commercially

important products. It is also used on a large scale to dissolve metal oxide coatings from

iron and steel prior to galvanizing or enameling.

Hydrofluoric acid is used in the production of fluorine-containing compounds and for

etching glass. The acid reacts with silicates, such as calcium silicate, CaSiO 3 , in the glass

to produce a very volatile and thermodynamically stable compound, silicon tetrafluoride,

SiF 4.

CaSiO 3 (s)
6HF(aq)88nCaF 2 (s)
SiF 4 (g)
3H 2 O(
)

THE OXOACIDS (TERNARY ACIDS) OF THE HALOGENS

Table 24-5 lists the known oxoacids of the halogens, their sodium salts, and some trends

in properties. Only three oxoacids, HClO 4 , HIO 3 , and H 5 IO 6 , have been isolated in anhy-

drous form. The others are known only in aqueous solution. In all these acids the H is

bonded through an O.

The only oxoacid of fluorine that has been prepared is unstable hypofluorous acid,

HOF. Aqueous hypohalous acids(except HOF) can be prepared by reaction of free halo-

gens (Cl 2 , Br 2 , I 2 ) with cold water. The smaller the halogen, the farther to the right the

equilibrium lies.

X 2 
H 2 O 34 HX 
 HOX (XCl, Br, I)

hydrohalic acid hypohalous acid

Hypohalitesalts can be prepared by reactions of the halogens with colddilute bases.

24-7

950 CHAPTER 24: Some Nonmetals and Metalloids

0 ^1 
^1

In HOF the oxidation states are
F1, H
1, O0.

These reactions all involve
disproportionationof the halogen.

TABLE 24-5 Oxoacids of the Halogens and Their Salts

Thermal Oxidizing
Stability Oxidizing Power and
Oxidation Name and Acid Power Sodium Name Thermal Hydrolysis Nature of
State Acid of Acid Strength of Acid Salt of Salt Stability of Anion Halogen

 1 HXO hypohalous NaXO sodium XF, Cl, Br, I

(HOX) acid (NaOX) hypohalite


 3 HXO 2 halous NaXO 2 sodium XCl, Br (?)

acid halite


 5 HXO 3 halic NaXO 3 sodium XCl, Br, I

acid halate


 7 HXO 4 perhalic NaXO 4 sodium XCl, Br, I

acid perhalate

 7 H 5 XO 6 paraperhalic several sodium XI only

acid types paraperhalates

Increase Increases Increases Increase