Question

Aqueous sodium hydroxide reacts with white phosphorous to form phosphine and: (a) \(\mathrm{P}_{2} \mathrm{O}_{3}\) (b) \(\mathrm{P}_{2} \mathrm{O}_{5}\) (c) \(\mathrm{NaH}_{2} \mathrm{PO}_{2}\) (d) \(\mathrm{Na}_{3} \mathrm{PO}_{3}\)

Short answer

The other product is sodium hypophosphite \((\mathrm{NaH}_2\mathrm{PO}_2)\).

Step-by-step solution

Understanding the Reactants and Products

We know that white phosphorous (P₄) reacts with sodium hydroxide (NaOH) in water to form phosphine (PH₃) and another product. Phosphorous generally forms compounds with oxygen-containing ions in such reactions.

Writing the General Reaction Equation

The typical equation for the reaction of P₄ with NaOH is: \[\text{P}_4 + \text{NaOH} + \text{H}_2\text{O} \rightarrow \text{PH}_3 + \text{NaH}_2\text{PO}_2\] This equation shows that phosphorous reacts with sodium hydroxide and water to produce phosphine and sodium hypophosphite.

Solving for the Additional Product

From the equation, the additional compound formed alongside phosphine (PH₃) is sodium hypophosphite (NaH₂PO₂). This matches with option (c) \(\mathrm{NaH}_2\mathrm{PO}_2\).

Key concepts

Sodium Hydroxide

Sodium hydroxide, often known as NaOH, is a powerful alkaline compound widely used in various chemical reactions and industrial processes. It's commonly referred to as caustic soda due to its potent ability to cause chemical burns if it comes into contact with the skin. This makes it critical to handle sodium hydroxide with proper safety precautions. NaOH dissolves readily in water to form an alkaline solution, which can neutralize acids and act as a base in reactions. It's commonly used in the manufacturing of soaps, paper, and textiles. In the context of chemical reactions, sodium hydroxide can react with a variety of substances, including organic compounds like phosphorous. Specific to our exercise, sodium hydroxide reacts with white phosphorous in the presence of water to produce phosphine and sodium hypophosphite. The reaction underscores NaOH's role as a reactant that facilitates the breaking down of phosphorous compounds, showcasing its versatility in forming new substances.

White Phosphorous

White phosphorous is a highly reactive allotrope of phosphorous, primarily known for its ability to ignite spontaneously in air. It's typically stored underwater to prevent accidental ignition due to its high reactivity with oxygen. This reactivity is crucial in many chemical processes, such as the one described in the exercise. White phosphorous (P₄) is composed of four phosphorous atoms arranged in a tetrahedral configuration. Its distinctive attribute is its propensity to react with strong bases like sodium hydroxide. This characteristic is leveraged in our reaction scenario, where white phosphorous reacts with NaOH and water. The reaction is as follows:

• White phosphorous accepts oxygen and hydrogen from the aqueous sodium hydroxide solution, leading to the formation of phosphine (PH₃).
• The breakdown of white phosphorous also contributes to the production of sodium hypophosphite (NaH₂PO₂), completing the cycle of transformation.

Understanding the properties of white phosphorous is key to appreciating its role and behavior in such reactions.

Phosphine

Phosphine is a compound with the chemical formula PH₃. It's a colorless, flammable gas that is highly toxic and associated with a distinct odor reminiscent of decaying fish. Phosphine is used in various industrial and agricultural applications, primarily as a pesticide and a chemical warfare agent due to its potent toxicity. In the chemical reaction provided, phosphine is one of the main products formed when white phosphorous reacts with sodium hydroxide and water. The production of phosphine in this reaction highlights the reduction of phosphorous and the release of hydrogen as a byproduct. The formation of PH₃ involves the white phosphorous molecule combining with hydrogen from the water to yield phosphine gas:

• The reaction emphasizes phosphine's status as a key secondary compound resulting from the decomposition and transformation of white phosphorous in alkaline conditions.

This reaction notes how phosphine can emerge under specific chemical conditions, illustrating its broader relevance in industrial chemistry.

Sodium Hypophosphite

Sodium hypophosphite, chemically denoted as NaH₂PO₂, is the salt produced in the reaction between white phosphorous and sodium hydroxide in water. It is a valuable reducing agent, often employed in electroplating processes, particularly for nickel plating due to its effective ability to deposit metal. In this particular chemical reaction, the creation of sodium hypophosphite signifies the introduction of phosphorous into a stable ionic form. Here, sodium hypophosphite is formed alongside phosphine. As the reaction progresses:

• Sodium hypophosphite acts as both a product and an indication of the reaction's progression where the P₄ molecule is broken down.
• The conversion to NaH₂PO₂ illustrates the transformation of phosphorous from its highly reactive elemental form to a more stable compound.

Understanding sodium hypophosphite’s creation and role in chemical reactions is crucial, as it serves as a vital component in various industrial applications due to its reducing properties.