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Ch.22 - Chemistry of the Nonmetals
Chapter 22, Problem 36

Complete the exercises below. Explain the following observations: a. For a given oxidation state, the acid strength of the oxyacid in aqueous solution decreases in the order chlorine > bromine > iodine. b. Hydrofluoric acid cannot be stored in glass bottles. c. HI cannot be prepared by treating NaI with sulfuric acid. d. The interhalogen ICl₃ is known, but BrCl₃ is not.

Verified step by step guidance
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Step 1: For part (a), consider the electronegativity of the halogens. Chlorine is more electronegative than bromine and iodine, which means it can stabilize the negative charge on the conjugate base better, making the oxyacid stronger.
Step 2: For part (b), understand the chemical interaction between hydrofluoric acid (HF) and glass. HF reacts with silicon dioxide (SiO₂) in glass to form silicon tetrafluoride (SiF₄) and water, which is why it cannot be stored in glass bottles.
Step 3: For part (c), consider the reaction between NaI and sulfuric acid. Sulfuric acid is a strong oxidizing agent and can oxidize iodide ions (I⁻) to iodine (I₂), preventing the formation of HI.
Step 4: For part (d), analyze the stability of interhalogen compounds. ICl₃ is stable because iodine can expand its octet to accommodate more than eight electrons, while bromine in BrCl₃ would not be stable due to its inability to expand its octet effectively.
Step 5: Summarize the key concepts: electronegativity affects acid strength, chemical reactivity of HF with glass, redox reactions preventing HI formation, and octet expansion influencing interhalogen stability.

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Oxidation States and Acid Strength

The strength of an oxyacid is influenced by the electronegativity and oxidation state of the central atom. As the electronegativity decreases down the group in the periodic table, the ability of the central atom to stabilize the negative charge on the conjugate base diminishes, leading to weaker acids. Thus, for oxyacids with the same oxidation state, chlorine is a stronger acid than bromine, which is stronger than iodine.
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Reactivity of Hydrofluoric Acid

Hydrofluoric acid (HF) is unique due to its ability to form strong hydrogen bonds and its reactivity with silica, a major component of glass. This reactivity can lead to the etching of glass, making it unsuitable for storage in glass containers. Instead, HF is typically stored in plastic bottles to prevent reactions that could compromise the container.
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Interhalogen Compounds

Interhalogen compounds are formed between different halogens and can exhibit varying stability based on the size and electronegativity of the halogens involved. While ICl₃ is stable due to the larger size of iodine allowing for effective overlap with chlorine, BrCl₃ is not known because bromine's size and electronegativity do not favor the formation of a stable compound with chlorine, leading to instability and decomposition.
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