Unformatted text preview: paper industry, and in water treatment.
Bromine is used to prepare dibromoethane (BrCH2 CH2 Br) which is a gasoline additive, and silver bromide
(AgBr), used in photographic film. Iodine finds uses as a medicinal antiseptic. NaI is added to table salt to
prevent goiter, and silver iodide is used in cloud seeding.
EXAMPLE 21.7 Preparation of F 2
The chemistry of fluorine differs in many ways from that of the rest of the halogens. For instance, it cannot be
prepared by the electrolysis of an aqueous solution of its sodium salt, as Cl2 is prepared. Write chemical
equations to show the steps in the industrial process of making F2 . Give the source of the fluorine, and mention
why it cannot be prepared in aqueous solution.
•Method of Solution
The industrial process starts with the mineral fluorspar, CaF 2 . This is treated with sulfuric acid to make
CaF 2 (s) + H 2 SO4 (l) → 2HF(l) + CaSO4 (s)
The hydrogen fluoride is mixed with KF and electrolyzed
2HF(l) → H2 (g) + F2 (g) Back Forward Main Menu TOC Study Guide TOC Textbook Website MHHE Website Nonmetallic Elements and Their Compounds / 4 27
The F 2 molecule has such a strong attraction for electrons that it reacts violently with water, hot glass, and
most metals. If F2 were formed in an aqueous solution, it would immediately oxidize water to oxygen gas.
EXAMPLE 21.8 Reaction of Chlorine with Sodium Hydroxide
When chlorine is dissolved in base, a solution of aqueous sodium hypochlorite is formed. A 5.25% solution is
sold as liquid laundry bleach. Write the chemical equation for the reaction. Assign oxidation numbers and
identify the oxidizing agent and the reducing agent.
•Method of Solution
Cl 2 (g) + 2NaOH(aq) → NaCl(aq) + NaOCl(aq) + H2 O(l)
If we assign oxidation numbers to all the chlorine atoms, we can see that chlorine is both oxidized and reduced.
None of the other elements in the equation changes oxidation state. Thus chlorine is the oxidizing agent and the
0 0 –1 +1 Cl—Cl + 2NaOH → NaCl + NaOCl + H2 O
| oxidation | This is an example of a disproportionation reaction.
21. Which halogens are prepared by electrochemical oxidation?
Write a chemical equation for the preparation of elemental bromine from seawater.
Which of the hydrogen halides are strong acids in water?
Which halogen is the strongest oxidizing agent among all the elements.
Show the similarity of chlorine and bromine by writing equations for their reactions:
a. with I – ion.
b. with NaOH(aq).
______________________________________________________________________________ CONCEPTUAL QUESTIONS
2. Explain why hydrogen does not have a unique position in the periodic table.
Explain how Br2 can act as both an oxidi...
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