Problem 85 - Chemistry Matter and Change

Question

Predict Consider the fact that all of the following are stable compounds. What can you infer about the oxidation state of phosphorus in its compounds? $$\mathrm{PH}_{3}, \mathrm{PCI}_{3}, \mathrm{P}_{2} \mathrm{H}_{4}, \mathrm{PCI}_{5}, \mathrm{H}_{3} \mathrm{PO}_{4}, \mathrm{Na}_{3} \mathrm{PO}_{3}$$

Step-by-Step Solution

Answer

In the given stable compounds of phosphorus, we can determine its oxidation states to be -3 in PH3, +3 in PCl3 and Na3PO3, -2 in P2H4, and +5 in PCl5 and H3PO4. This indicates that phosphorus exhibits a wide range of oxidation states and is a chemically versatile element capable of forming various stable compounds.

Step 1: Determine the oxidation state of hydrogen, oxygen, and chlorine

For each compound, we need to use known oxidation states of certain elements: - In most compounds, hydrogen has an oxidation state of +1. - In most compounds, oxygen has an oxidation state of -2. - In most compounds, halogens like chlorine have an oxidation state of -1.

Step 2: Determine the oxidation state of phosphorus in each compound

Using the rules from step 1, we can determine the oxidation state of phosphorus in each compound. Let's denote the oxidation state of phosphorus as x. 1. PH3: \(1*(+1) + x = 0\) \(x = -3\) 2. PCl3: \(3*(-1) + x = 0\) \(x = +3\) 3. P2H4: \(2x + 4*(+1) = 0\) \(x = -2\) 4. PCl5: \(5*(-1) + x = 0\) \(x = +5\) 5. H3PO4: \(3*(+1) + x + 4*(-2) = 0\) \(x = +5\) 6. Na3PO3: \(3*(+1) + x + 3*(-2) = 0\) \(x = +3\)

Step 3: Analyze oxidation state of phosphorus in these compounds

From the oxidation states we calculated for phosphorus in each compound, we can infer that phosphorus can exhibit a wide range of oxidation states, including -3, -2, +3, and +5. This shows that phosphorus is a chemically versatile element capable of forming a variety of stable compounds with different oxidation states.

Key Concepts

Phosphorus Compounds

Phosphorus is a fascinating element that forms a variety of compounds through diverse chemical interactions. Its ability to bond with different elements like hydrogen, chlorine, and oxygen leads to unique compounds such as phosphine (\(PH_3\)), phosphorus trichloride (\(PCl_3\)), and phosphoric acid (\(H_3PO_4\)).

• Phosphine (\(PH_3\)) is a simple hydride of phosphorus.
• Phosphorus trichloride (\(PCl_3\)) is used as a reagent in the chemical industry.
• Phosphorus pentachloride (\(PCl_5\)) is used in organic synthesis.
• Phosphoric acid (\(H_3PO_4\)) is essential in industrial applications and food processing.
• Sodium phosphite (\(Na_3PO_3\)) is used in electroplating and water treatment.

Phosphorus's chemistry is greatly versatile, allowing for the formation of both simple and complex compounds. Each compound's stability is partially determined by the oxidation state of phosphorus, which can significantly affect its chemical properties. This ability makes phosphorus a key player in both biological and industrial chemistry.

Chemical Stability

Chemical stability refers to the ability of a compound to remain unchanged under specified conditions. Phosphorus compounds exhibit a wide range of stability, influenced heavily by the oxidation state of the phosphorus atom. In stable compounds, phosphorus can exist in different oxidation states such as -3, -2, +3, and +5. This versatility in oxidation states allows phosphorus to form stable compounds under varying environmental conditions. Factors that contribute to the chemical stability of phosphorus compounds include:

• Oxidation state: Different oxidation states lend stability by forming specific stable bonds.
• Bond strengths: Stable compounds typically contain strong covalent bonds.
• Electron configuration: The arrangement of electrons affects how easily a compound will react chemically.
• Environmental conditions: Temperature, pressure, and pH levels can affect compound stability.

Understanding chemical stability is crucial in predicting how phosphorus compounds behave during chemical reactions. This stability is important for applications in industries such as agriculture, where phosphorus is a critical nutrient.

Oxidation Number Determination

Oxidation numbers are theoretical constructs used to understand the electron transfer in chemical reactions. Determining the oxidation number of phosphorus in a compound can provide insight into the type of chemical bonding and interaction occurring. For phosphorus compounds, this process involves:Start by knowing oxidation state rules for common elements in a compound:

• Hydrogen is usually +1.
• Oxygen is usually -2.
• Chlorine is typically -1.

Apply these rules to phosphorus compounds to calculate the oxidation number of phosphorus. For example, in \(PH_3\), phosphorus pairs with three hydrogen atoms, each with a +1 state, which means phosphorus balances with -3. Using algebraic methods, the oxidation number of phosphorus can be determined by balancing known oxidation states:- In \(PCl_3\), 3 chlorine atoms contribute -1 each, leading to phosphorus being +3.- In \(H_3PO_4\), phosphorus is +5 to balance out the -8 from oxygen and +3 from hydrogen.Ultimately, recognizing oxidation numbers helps decipher the reactive capabilities of phosphorus in chemical compounds. Understanding this concept is vital for students to predict the chemical behavior and formation of various phosphorus compounds.