Question

Starting with elemental phosphorus \(\left(\mathrm{P}_{4}\right)\), show how you would prepare phosphoric acid.

Short answer

Burn phosphorus in oxygen, then dissolve the resulting phosphorus pentoxide in water.

Step-by-step solution

Reacting Phosphorus with Oxygen

First, elemental phosphorus ( \( ext{P}_4\)) is burned in an excess of oxygen to produce phosphorus pentoxide. The chemical reaction is: \[\mathrm{P}_{4} + 5\mathrm{O}_{2} \rightarrow \mathrm{P}_{4}\mathrm{O}_{10}\].

Dissolve Phosphorus Pentoxide in Water

Next, phosphorus pentoxide \(\mathrm{P}_{4}\mathrm{O}_{10}\) is reacted with water to form phosphoric acid \(\mathrm{H}_{3}\mathrm{PO}_{4}\). This reaction is as follows: \[\mathrm{P}_{4}\mathrm{O}_{10} + 6\mathrm{H}_{2}\mathrm{O} \rightarrow 4\mathrm{H}_{3}\mathrm{PO}_{4}\].

Key concepts

Phosphorus

Phosphorus is a fascinating and essential element widely used in many chemical processes. It is denoted by the symbol \(P\) and has an atomic number of 15 on the periodic table.
One of its most common allotropes is white phosphorus, which contains tetrahedral \(\mathrm{P}_4\) molecules. This form of phosphorus is highly reactive and needs careful handling.
In its elemental form, white phosphorus is often used as a starting material to synthesize other phosphorus compounds, such as phosphoric acid.

• White phosphorus is sensitive to heat and light.
• It reacts readily with oxygen and can be hazardous in its elemental state.

Understanding how phosphorus behaves in reactions is crucial for producing compounds safely.

Phosphorus Pentoxide

Phosphorus pentoxide is a compound formed when phosphorus reacts with oxygen. Its chemical formula is \(\mathrm{P}_4\mathrm{O}_{10}\), although it's commonly simplified to \(\mathrm{P}_2\mathrm{O}_5\) in some contexts due to its empirical formula.
This compound is crucial as an intermediate in producing phosphoric acid.
When phosphorus pentoxide comes in contact with water, it undergoes a chemical transformation to create phosphoric acid.

• It appears as a white crystalline solid.
• Highly reactive with water, leading to rapid conversion to an acid.
• Used in the dehydration process in a variety of chemical reactions.

As a drying agent, it effectively removes moisture due to its hygroscopic nature.

Chemical Reaction

Chemical reactions are processes where reactants transform into products through the breaking and forming of chemical bonds. In our case, the transformation from elemental phosphorus to phosphorus pentoxide, and subsequently to phosphoric acid, involves several such reactions.
Specifically, the reaction of phosphorus with oxygen is known as a combustion Reaction.
These transformations require precise conditions, like sufficient temperature and controlled environments, to proceed efficiently.

• Reactions are represented by balanced chemical equations.
• Involve changes in energy, often releasing or absorbing heat.
• Can be categorized into different types, like synthesis, decomposition, and combustion.

Understanding reaction mechanisms is vital for the efficient and safe production of chemicals.

Oxygen

Oxygen is a diatomic molecule represented as \(\mathrm{O}_2\) and is essential for life and numerous chemical reactions. In the context of phosphoric acid synthesis, oxygen plays a pivotal role in the first reaction involving phosphorus.
Combining elemental phosphorus with oxygen leads to the formation of phosphorus pentoxide via a combustion process.

• Oxygen is a powerful oxidizing agent.
• Essential for combustion reactions.
• Supports the transformation of phosphorus into valuable compounds.

In most reactions, oxygen works to alter the oxidation state of the other elements involved, facilitating an array of chemical processes.

Elemental Phosphorus

Elemental phosphorus, particularly in its white phosphorus form, is a tetratomic molecule known for its reactivity. Represented as \(\mathrm{P}_4\), it is the starting material in many synthesis processes, including that of phosphoric acid.
When exposed to air, white phosphorus can ignite spontaneously due to its high reactivity with oxygen.
It must be stored under water or inert gases to prevent unwanted reactions.

• Vital for synthesizing essential phosphorus compounds.
• Handling requires careful safety measures.
• Combines with elements such as oxygen and chlorine in chemical production.

By understanding and controlling the reactions of elemental phosphorus, we can safely produce valuable industrial chemicals.