Question

Sodium amide \(\left(\mathrm{NaNH}_{2}\right)\) reacts with water to produce sodium hydroxide and ammonia. Describe this reaction as a Brønsted acid-base reaction.

Short answer

Water acts as the Brønsted acid, donating a proton to the amide ion, which acts as the base.

Step-by-step solution

Write the Chemical Equation

The reaction involves sodium amide \( \mathrm{NaNH}_{2} \) and water \( \mathrm{H}_{2}\mathrm{O} \). The products formed are sodium hydroxide \( \mathrm{NaOH} \) and ammonia \( \mathrm{NH}_{3} \). The chemical equation is:\[\mathrm{NaNH}_{2} + \mathrm{H}_{2}\mathrm{O} \rightarrow \mathrm{NaOH} + \mathrm{NH}_{3}\]

Identify Brønsted Acids and Bases

In a Brønsted acid-base reaction, the acid donates a proton (\(\mathrm{H}^{+}\)), and the base accepts a proton. In this equation, water (\(\mathrm{H}_{2}\mathrm{O}\)) donates a proton to the amide ion (\(\mathrm{NH}_{2}^{-}\)), thus acting as a Brønsted acid. The amide ion (part of \(\mathrm{NaNH}_{2}\)) accepts the proton, acting as the base.

Products in Acid-Base Terms

When the amide ion (\(\mathrm{NH}_{2}^{-}\)) accepts a proton from water (acting as a base), it becomes ammonia (\(\mathrm{NH}_{3}\)). The water molecule, losing the proton, becomes hydroxide ion (\(\mathrm{OH}^{-}\)), which pairs with sodium to form sodium hydroxide (\(\mathrm{NaOH}\)).

Write the Proton Transfer

The proton transfer involved in this reaction can be represented as:\[\mathrm{NH}_{2}^{-} + \mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{NH}_{3} + \mathrm{OH}^{-}\]This highlights the transfer of a proton from water to the amide ion.

Key concepts

Sodium Amide

Sodium amide, chemically represented as \(\text{NaNH}_2\), plays a crucial role in the reaction with water to form sodium hydroxide and ammonia. Sodium amide consists of the sodium cation (Na\(^+\)) and the amide ion (\(\text{NH}_2^-\)). It is recognized for its ability to deprotonate other molecules, which means it can remove a proton (H\(^+\)) from one molecule and attach it to itself or another molecule.

In this context, the amide ion acts as a Brønsted base during its reaction with water. It seizes a proton from the water molecule, indicating its fundamental property as a strong base which emerges when it accepts a proton. This capacity to accept a proton highlights the amide ion's role within sodium amide as a critical player in Brønsted acid-base reactions.

Proton Transfer

Proton transfer forms the core of Brønsted acid-base reactions. In our specific reaction, it describes the movement of a proton from the water molecule to the amide ion. It is crucial in understanding the transformation of reactants to products when sodium amide reacts with water.

The step-by-step change involves water, a Brønsted acid, donating a proton. Water loses a proton and becomes a hydroxide ion \(\text{OH}^-\). On the flip side, the amide ion, \(\text{NH}_2^-\), transforms into ammonia, \(\text{NH}_3\), by accepting that proton. This transfer showcases the unique interchange: one molecule acts as a proton donor while the other acts as an acceptor, fulfilling the basic requirement of a Brønsted acid-base reaction.

Hydroxide Ion

A hydroxide ion, represented by \(\text{OH}^-\), is a key product of our reaction between sodium amide and water. When water donates a proton to the amide ion, it results in the formation of the hydroxide ion. This entire process hinges on the removal of a \(\text{H}^+\) from water, which turns the water molecule into the \(\text{OH}^-\) ion.

In the resulting solution, the hydroxide ion pairs with sodium ions from sodium amide, leading to the creation of sodium hydroxide. The presence of hydroxide ions in the solution indicates basicity, meaning that the solution has a potential to neutralize acids. This basic nature of hydroxide ions often gives rise to their utility in numerous chemical reactions and industrial processes.

Sodium Hydroxide

Sodium hydroxide, often known as lye or caustic soda, is a final product of our chemical reaction. Represented by \(\text{NaOH}\), it results from the union of sodium ions from sodium amide and hydroxide ions formed when water loses a proton. Sodium hydroxide is a strong base commonly used in various applications from manufacturing to cleaning.

It highlights the transformation due to the transfer of protons; where initially, sodium amide reacts with water, leads to the formation of sodium hydroxide and ammonia. This reaction exemplifies key aspects of Brønsted acid-base chemistry, where one substance acts as a proton donor and the other as a proton acceptor, finalizing in the creation of two distinctive compounds.