Question

Why isn't hydrochloric acid used in a direct reaction with copper to prepare the \(\mathrm{CuCl}_{2}\) solution?

Short answer

Copper doesn't directly react with hydrochloric acid to prepare \(\mathrm{CuCl}_{2}\) solution because it is less reactive and doesn't readily react with dilute acids like hydrochloric acid. Instead, copper first reacts with a more reactive acid, such as nitric acid, to form copper nitrate. Then, copper nitrate can react with hydrochloric acid to form the desired \(\mathrm{CuCl}_{2}\) solution.

Step-by-step solution

Understanding Copper Reactivity

Copper is a relatively less reactive metal, and it doesn't readily react with dilute acids like hydrochloric acid. The reactivity series of metals dictates that metals above hydrogen in the series can displace hydrogen from dilute acids, but copper is below hydrogen in the reactivity series, so it doesn't directly react with hydrochloric acid.

Understanding the reaction with other acids

Copper can react with more reactive acids, such as nitric acid, to produce copper nitrate. The reaction is as follows: \( \mathrm{Cu + 4HNO_{3} \rightarrow Cu(NO_{3})_{2} + 2NO_{2} + 2H_{2}O} \) In this reaction, nitric acid acts as an oxidizing agent, oxidizing the copper metal to form copper nitrate.

Formation of \(\mathrm{CuCl}_{2}\) using Copper Nitrate

Once we have copper nitrate, we can easily convert it into \(\mathrm{CuCl}_{2}\) by reacting it with hydrochloric acid. The reaction proceeds as follows: \( \mathrm{Cu(NO_{3})_{2} + 2HCl \rightarrow CuCl_{2} + 2HNO_{3}} \) In this reaction, chloride ions from hydrochloric acid replace the nitrate ions, and copper chloride is formed along with the regeneration of nitric acid.

Conclusion

So, the reason why hydrochloric acid isn't used in a direct reaction with copper to prepare \(\mathrm{CuCl}_{2}\) solution is that copper is less reactive and doesn't readily react with hydrochloric acid as it does with more reactive acids, such as nitric acid. To prepare \(\mathrm{CuCl}_{2}\) solution, we need to first react copper with nitric acid to form copper nitrate, and then react the copper nitrate with hydrochloric acid to form \(\mathrm{CuCl}_{2}\).

Key concepts

Copper Reactivity

Exploring the reactivity of copper is essential to understand why certain chemical reactions occur or, more intriguingly, why they don't. Copper, a doughty member of the transition metals, sits quite comfortably below hydrogen in the reactivity series. This series, akin to a leaderboard of chemical eagerness, ranks metals based on their propensity to lose electrons and form positive ions.

Given its laid-back nature in the reactivity lineup, copper doesn't aggressively pursue a reaction with hydrochloric acid to produce hydrogen gas and a copper chloride solution. Instead, it prefers not to displace hydrogen from the acid due to its lower placement in the reactivity hierarchy. This basic concept explains a lot about copper's behavior in various chemical reactions, including why stronger, more persuasive oxidizing agents, such as nitric acid, are required to coax it into reacting.

Metal-Acid Reactions

Delving into metal-acid reactions unveils the science behind the bubbling and fizzing often observed in the lab. These reactions are notorious for showcasing the rowdy metals higher up in the reactivity series willing to kick out hydrogen from dilute acids and take its place. However, copper stands apart with its 'too cool for school' attitude, maintaining a strict no-entry policy for such reactions.

What's happening at the molecular level involves a metal atom tossing its electrons to the hydronium ions in the acid. This gives birth to hydrogen gas and the metal's salt. But copper, lounging below hydrogen, lacks the enthusiasm to make this exchange, which is why hydrochloric acid treated with copper remains silent, free of the gaseous fanfare. Therefore, to stir things up, one has to look beyond the usual suspects in the acid locker and opt for a more persuasive one, like nitric acid, to initiate the dance of atoms resulting in a compound like copper nitrate.

Copper Chloride Preparation

The journey to preparing copper chloride is a bit like a culinary recipe that requires a two-step process to achieve the desired flavor— or in this case, chemical compound. Copper's initial reluctance to react with hydrochloric acid means chemists can't take the direct route to produce copper chloride. However, copper does agree to react with nitric acid, a more demanding oxidizing agent, showcasing a lively chemical interaction that results in copper nitrate as the first product.

Next comes the pivotal step where copper nitrate meets hydrochloric acid. This encounter facilitates the exchange of companions from nitrate ions to chloride ions, with nitric acid being regenerated, akin to a polite swapping of dance partners. This two-phase process, robust yet more circuitous, achieves the end goal: a concoction of copper chloride, a compound useful in various applications, crystallizing the art and subtlety in chemical preparation.