Question

Write a balanced equation for the preparation of (a) \(\mathrm{F}_{2}\) from HF. (b) \(\mathrm{Br}_{2}\) from \(\mathrm{NaBr}\). (c) \(\mathrm{NH}_{4}^{+}\) from \(\mathrm{NH}_{3}\)

Short answer

Question: Write out balanced equations for the following three reactions: (a) Preparation of \(\mathrm{F}_{2}\) from HF, (b) Preparation of \(\mathrm{Br}_{2}\) from \(\mathrm{NaBr}\) and (c) Preparation of \(\mathrm{NH}_{4}^{+}\) from \(\mathrm{NH}_{3}\). Answer: a) \(2\,\ce{HF} -> \ce{H2} + \ce{F2}\) b) \(2\,\ce{NaBr} + \ce{Cl2} -> 2\,\ce{NaCl} + \ce{Br2}\) c) \(\ce{NH3} + \ce{HX} -> \ce{NH4+} + \ce{X-}\)

Step-by-step solution

a. Preparation of \(\mathrm{F}_{2}\) from HF

One way to prepare \(\mathrm{F}_{2}\) from HF is by electrolysis. We can represent this process by the following balanced equation: $$2\,\ce{HF} -> \ce{H2} + \ce{F2}$$

b. Preparation of \(\mathrm{Br}_{2}\) from \(\mathrm{NaBr}\)

To prepare \(\mathrm{Br}_{2}\) from \(\mathrm{NaBr}\), we can use the following redox process in which chlorine gas (\(\ce{Cl2}\)) acts as an oxidizing agent to convert \(\mathrm{NaBr}\) into \(\mathrm{Br}_{2}\), while chlorine gets reduced to form \(\mathrm{NaCl}\). $$2\,\ce{NaBr} + \ce{Cl2} -> 2\,\ce{NaCl} + \ce{Br2}$$

c. Preparation of \(\mathrm{NH}_{4}^{+}\) from \(\mathrm{NH}_{3}\)

To prepare \(\mathrm{NH}_{4}^{+}\) from \(\mathrm{NH}_{3}\), the ammonia acts as a base and accepts a proton (\(\ce{H+}\)) from a generic acid (\(\ce{HX}\)) in an acid-base reaction. The balanced equation for this reaction is: $$\ce{NH3} + \ce{HX} -> \ce{NH4+} + \ce{X-}$$ Keep in mind that in a real context, \(\ce{X-}\) would represent specific anions depending on the acid used, but this generic equation covers any possible scenario where ammonia acquires a proton.

Key concepts

Chemical Reaction

A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. It involves making and breaking of chemical bonds, which results in the substances involved changing their chemical properties and composition. In the context of the exercises, each preparation method involves a chemical change.

For example, when preparing \(\mathrm{F}_{2}\) from HF, the HF molecules undergo an electrolysis reaction, leading to a change where hydrogen and fluorine atoms are separated, forming hydrogen gas (\(\mathrm{H}_{2}\)) and fluorine gas (\(\mathrm{F}_{2}\)). This represents the core idea of a chemical reaction where starting materials, referred to as reactants, transform into new substances, known as products. The ability to write balanced chemical equations is crucial for understanding chemical reactions as it ensures the law of conservation of mass is satisfied, meaning that atoms are neither created nor destroyed in the process.

Electrolysis

Electrolysis is a process that uses electric current to drive a non-spontaneous chemical reaction. It is one of the most common methods for decomposing chemical compounds, often used to separate elements from naturally occurring sources or compounds.

In the case of generating \(\mathrm{F}_{2}\) from HF, electrolysis provides the energy required to break the stable \(\ce{HF}\) molecules into their constituent elements. This process usually occurs in an electrolytic cell, where an external voltage source is connected to two electrodes submerged in an electrolyte solution. When the current is on, HF is decomposed, and the fluorine atoms are attracted to the anode resulting in \(\mathrm{F}_{2}\) gas, while hydrogen atoms move towards the cathode forming \(\mathrm{H}_{2}\) gas.

Redox Reaction

Redox reactions, or oxidation-reduction reactions, are chemical processes in which electrons are transferred between substances. The substance gaining electrons undergoes reduction, while the substance losing electrons is undergoing oxidation.

For instance, to prepare \(\mathrm{Br}_{2}\) from \(\mathrm{NaBr}\), we observe a redox reaction where chlorine gas (\(\ce{Cl2}\)) acts as an oxidizing agent, oxidizing the bromide ions (\(\mathrm{Br}^{-}\)) to bromine gas (\(\mathrm{Br}_{2}\)) while it itself is reduced to chloride ions, resulting in \(\mathrm{NaCl}\). Recognizing redox reactions and balancing the equations where they occur is fundamental to understanding these types of chemical reactions, as this shows the movement of electrons and the conserved nature of charge in a chemical process.

Acid-Base Reaction

Acid-base reactions are an important class of chemical reactions that involve the transfer of protons (\(\ce{H+}\)) between a proton donor (acid) and a proton acceptor (base).

As illustrated in the preparation of \(\mathrm{NH}_{4}^{+}\) from \(\mathrm{NH}_{3}\), ammonia functions as a base and accepts a proton from an acid (\(\ce{HX}\)), resulting in the formation of the ammonium ion (\(\mathrm{NH}_{4}^{+}\)) and the anion \(\mathrm{X}^{-}\). This process, where a base gains a hydrogen ion, is a fundamental aspect of acid-base chemistry. It must be considered when balancing chemical equations for reactions involving acids and bases to ensure the number of hydrogen ions and the overall charge on both sides of the equation is balanced.