Problem 2 - Chemistry and Chemical Reactivity

Question

The reaction of elemental phosphorus and excess oxygen produces \(\mathrm{P}_{4} \mathrm{O}_{10} .\) Name the compound. (a) phosphorus oxide (b) phosphoric acid (c) phosphorus decaoxide (d) tetraphosphorus decaoxide

Step-by-Step Solution

Answer

The correct name is (d) tetraphosphorus decaoxide.

Step 1: Understanding the Chemical Reaction

The problem describes a chemical reaction where elemental phosphorus reacts with oxygen to form a compound. The chemical formula for this compound given in the question is \( \mathrm{P}_4 \mathrm{O}_{10} \). This tells us that there are 4 phosphorus atoms and 10 oxygen atoms in one molecule of this compound.

Step 2: Interpreting the Chemical Name

The chemical formula \( \mathrm{P}_4 \mathrm{O}_{10} \) needs to be translated into a chemical name. In systematic chemical naming (IUPAC nomenclature), the prefixes 'tetra-' and 'deca-' are used to indicate quantities of four and ten, respectively. Therefore, \( \mathrm{P}_4 \mathrm{O}_{10} \) is called tetraphosphorus decaoxide.

Step 3: Identifying the Correct Option

Comparing the constructed chemical name from the previous step against the provided options, we see that option (d) 'tetraphosphorus decaoxide' correctly describes \( \mathrm{P}_4 \mathrm{O}_{10} \). Options (a), (b), and (c) either lack the proper numerical prefixes or describe different compounds.

Key Concepts

Phosphorus Oxides

Phosphorus oxides are compounds composed of phosphorus and oxygen. These compounds can vary in the number of phosphorus and oxygen atoms they contain. The main types of phosphorus oxides are based on different oxidation states and combinations of these two elements. The most common phosphorus oxides are

• Phosphorus trioxide ( \( \mathrm{P}_4 \mathrm{O}_6 \) ), which has four phosphorus atoms and six oxygen atoms.
• Phosphorus pentoxide ( \( \mathrm{P}_4 \mathrm{O}_{10} \) ), which is essentially the full oxidation of phosphorus and is commonly encountered.

Phosphorus pentoxide, also known as tetraphosphorus decaoxide, is a significant oxide due to its use in industries for dehydration reactions. It forms via the reaction of elemental phosphorus with excess oxygen, as outlined in the exercise. By recognizing the different phosphorus oxides, we can deduce their roles in various chemical reactions.

IUPAC Naming System

The IUPAC naming system, or International Union of Pure and Applied Chemistry nomenclature, establishes standard rules for naming chemical compounds. This helps chemists communicate unambiguously.For binary compounds such as phosphorus oxides, the naming convention often uses Greek prefixes to determine the number of atoms of each element present. In the case of \( \mathrm{P}_4 \mathrm{O}_{10} \), the prefix 'tetra-' is used for four phosphorus atoms, and 'deca-' for ten oxygen atoms. As a consequence, the IUPAC name for \( \mathrm{P}_4 \mathrm{O}_{10} \) is tetraphosphorus decaoxide. When naming compounds:

• Identify the number of atoms with appropriate Greek prefixes (e.g., 'mono-' for one, 'di-' for two, 'tri-' for three, etc.).
• The more electronegative element (oxygen in this case) is named second.
• Follow the same naming rule for other similar compounds, adapting the prefix according to the number of atoms.

The IUPAC naming system allows chemists from around the world to be on the same page when discussing chemical substances.

Chemical Reaction Interpretation

Interpreting a chemical reaction requires understanding the formulae of the reactants and products. For the given reaction, elemental phosphorus ( \( \text{P} \)) reacts with excess oxygen ( \( \text{O}_2 \)) to form \( \mathrm{P}_4 \mathrm{O}_{10} \). Each element's subscript indicates how many atoms are contained in a molecule of the substance.The formula \( \mathrm{P}_4 \mathrm{O}_{10} \) reveals that during the reaction, four phosphorus atoms have bonded with ten oxygen atoms. This indicates the complete oxidation of phosphorus when there's a surplus of oxygen, yielding phosphorus pentoxide.Here are steps to interpret such a chemical reaction:

• Balance the chemical equation to understand the stoichiometry. This helps establish the ratio of reactants to products.
• Recognize the oxidation state changes in the elements involved (phosphorus is fully oxidized in this reaction).
• Write the resulting compound's chemical formula to compare with possible chemical names using IUPAC naming.

By correctly interpreting chemical reactions, we gain valuable insights into the process, assisting in predicting reaction outcomes and identifying the resultant compounds.