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Ch.4 - Reactions in Aqueous Solution
Chapter 4, Problem 113b

Phosphorus can have several different oxidation numbers ranging in value from -3 to +5. (b) Based on oxidation numbers, which phosphorus oxide compound from part (a) was formed by combustion with a limited supply of oxygen?

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insert step 1> Identify the possible oxidation states of phosphorus, which range from -3 to +5.
insert step 2> Recall that in a combustion reaction with a limited supply of oxygen, the compound formed will have phosphorus in a lower oxidation state compared to when there is an excess of oxygen.
insert step 3> Consider the common phosphorus oxides: P4O6 and P4O10.
insert step 4> Determine the oxidation state of phosphorus in each oxide: In P4O6, phosphorus has an oxidation state of +3, and in P4O10, it has an oxidation state of +5.
insert step 5> Conclude that P4O6 is the phosphorus oxide formed by combustion with a limited supply of oxygen, as it has a lower oxidation state (+3) compared to P4O10 (+5).

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Oxidation Numbers

Oxidation numbers are a way to keep track of electrons in chemical compounds. They indicate the degree of oxidation of an atom in a molecule, helping to determine how many electrons are gained or lost during a reaction. For phosphorus, oxidation numbers can range from -3 to +5, reflecting its ability to form various compounds depending on the reaction conditions.
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Combustion Reactions

Combustion reactions involve the reaction of a substance with oxygen, typically producing heat and light. In the case of phosphorus, combustion can lead to the formation of different oxides depending on the availability of oxygen. A limited supply of oxygen often results in the formation of lower oxidation state oxides, such as phosphorus trioxide (P2O3), rather than higher oxidation state oxides like phosphorus pentoxide (P2O5).
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Phosphorus Oxides

Phosphorus oxides are compounds formed from phosphorus and oxygen, with varying oxidation states. The most common oxides include phosphorus trioxide (P2O3) and phosphorus pentoxide (P2O5). The specific oxide formed during combustion depends on the oxidation state of phosphorus and the amount of oxygen available, influencing the properties and reactivity of the resulting compound.
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