Hydrogen halides (HF, HCl, HBr, HI) are highly reactive compounds that have many industrial and laboratory uses. (a) In the laboratory, HF and \(\mathrm{HCl}\) can be generated by reacting \(\mathrm{CaF}_{2}\) and \(\mathrm{NaCl}\) with concentrated sulfuric acid. Write appropriate equations for the reactions. (Hint: These are not redox reactions.) (b) Why is it that HBr and HI cannot be prepared similarly-that is, by reacting NaBr and NaI with concentrated sulfuric acid? (Hint: \(\mathrm{H}_{2} \mathrm{SO}_{4}\) is a stronger oxidizing agent than both \(\mathrm{Br}_{2}\) and \(\mathrm{I}_{2} .\) ) (c) HBr can be prepared by reacting phosphorus tribromide \(\left(\mathrm{PBr}_{3}\right)\) with water. Write an equation for this reaction.

Understanding chemical reaction equations is vital in the study of chemistry. These equations are symbolic representations of chemical reactions, showing the reactants that interact and the products that are formed as a result.

For instance, the reaction of calcium fluoride (\textbf{CaF}\(_2\)) with sulfuric acid (\textbf{H}\(_2\)\textbf{SO}\(_4\)) to produce hydrogen fluoride (\textbf{HF}) and calcium sulfate (\textbf{CaSO}\(_4\)) is represented as:

• \textbf{CaF}\(_2\) + \textbf{H}\(_2\)\textbf{SO}\(_4\) \rightarrow 2\textbf{HF} + \textbf{CaSO}\(_4\)

Similarly, sodium chloride (\textbf{NaCl}) reacts with sulfuric acid to yield hydrogen chloride (\textbf{HCl}) and sodium sulfate (\textbf{Na}\(_2\)\textbf{SO}\(_4\)):

• 2\textbf{NaCl} + \textbf{H}\(_2\)\textbf{SO}\(_4\) \rightarrow 2\textbf{HCl} + \textbf{Na}\(_2\)\textbf{SO}\(_4\)

These equations must be balanced, meaning the number of atoms for each element is equal on both sides. This follows the law of conservation of mass, which states that matter cannot be created or destroyed in a chemical reaction.

When writing reaction equations, we must consider factors like the physical states of the reactants and products, reaction conditions (such as temperature and pressure), and whether the reaction is spontaneous or requires a catalyst.

Sulfuric acid (\textbf{H}\(_2\)\textbf{SO}\(_4\)) is a highly important chemical in industry and laboratory processes due to its distinct properties. It's known for being a dense, colorless, oily liquid that is highly soluble in water, releasing heat upon dilution.

As a strong mineral acid, sulfuric acid has significant dehydrating properties, meaning it can remove water from other substances. This ability is utilized in various reactions, including the conversion of carbohydrates to carbon and water.

Another critical property of sulfuric acid is its strong oxidizing power, especially in its concentrated form. It can oxidize many metals (except noble metals like gold and platinum) and non-metals, which makes it hazardous but also useful in various chemical syntheses and industrial processes.

Moreover, concentrated sulfuric acid is a strong dehydrating agent and can cause severe burns when it comes into contact with organic materials, highlighting the importance of careful handling when working with this corrosive substance.

The preparation of gases in the laboratory requires an understanding of various chemical reactions and the properties of the reactants and products. Standard methods involve the combination of solid and liquid chemicals to produce a gas as one of the products.

One common method for gas generation is the action of acids on metals, salts, or other compounds. For example, in the preparation of hydrogen halides like hydrogen fluoride (\textbf{HF}) and hydrogen chloride (\textbf{HCl}), acid-base reactions are conducted using sulfuric acid with metal halides, such as calcium fluoride or sodium chloride.

However, not all halides can be prepared this way, because the conditions that facilitate the production of hydrogen fluoride and hydrogen chloride can lead to oxidation or other unwanted reactions with other halogen compounds. In such cases, alternative methods like the reaction of phosphorus tribromide (\textbf{PBr}\(_3\)) with water to form hydrogen bromide (\textbf{HBr}) are used:

• \textbf{PBr}\(_3\) + 3\textbf{H}\(_2\)\textbf{O} \rightarrow 3\textbf{HBr} + \textbf{H}\(_3\)\textbf{PO}\(_3\)

Safety is paramount when gases are prepared in the lab, requiring adequate ventilation, the use of fume hoods, and protective equipment to prevent inhaling toxic or corrosive vapors.