Problem 4 - Chemistry: Principles and Reactions

Question

WEB Write a balanced net ionic equation for the reaction of each of the following aqueous solutions with \(\mathrm{OH}^{-}\) ions. (a) ammonium nitrate (b) sodium dihydrogen phosphate \(\left(\mathrm{NaH}_{2} \mathrm{PO}_{4}\right)\) (c) \(\mathrm{Al}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}{\underline{\phantom{xx}}}^{3+}\)

Step-by-Step Solution

Answer

Question: Write balanced net ionic equations for the reactions of the following aqueous solutions with hydroxide ions, \(\mathrm{OH}^{-}\): (a) Ammonium nitrate (b) Sodium dihydrogen phosphate (c) \(\mathrm{Al}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}{\underline{\phantom{xx}}}^{3+}\) Answer: (a) \(\mathrm{NH}_{4}^{+} + \mathrm{OH}^{-} \rightarrow \mathrm{NH}_{3} + \mathrm{H}_{2}\mathrm{O}\) (b) \(\mathrm{H}_{2} \mathrm{PO}_{4}^{-} + \mathrm{OH}^{-} \rightarrow \mathrm{HPO}_{4}^{2-} + \mathrm{H}_{2}\mathrm{O}\) (c) \(\mathrm{Al}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}{\underline{\phantom{xx}}}^{3+} + 3\mathrm{OH}^{-} \rightarrow \mathrm{Al}\left(\mathrm{OH}\right)_{3} + 6\mathrm{H}_{2}\mathrm{O}\)

Step 1: (a) Reaction of ammonium nitrate with hydroxide ions

We are given the aqueous solution ammonium nitrate. The formula for ammonium nitrate is \(\mathrm{NH}_{4} \mathrm{NO}_{3}\). The hydroxide ions are denoted by \(\mathrm{OH}^{-}\). The reaction can be written as: $$\mathrm{NH}_{4} \mathrm{NO}_{3} + \mathrm{OH}^{-} \rightarrow$$ Now, we need to predict the products. Ammonium will react with hydroxide ions to produce water and ammonia. The products will be ammonia (\(\mathrm{NH}_{3}\)), nitrate ion (\(\mathrm{NO}_{3}^{-}\)), and water (\(\mathrm{H}_{2}\mathrm{O}\)). Write the balanced chemical equation: $$\mathrm{NH}_{4} \mathrm{NO}_{3} + \mathrm{OH}^{-} \rightarrow \mathrm{NH}_{3} + \mathrm{NO}_{3}^{-} + \mathrm{H}_{2}\mathrm{O}$$ Finally, we write the balanced net ionic equation by removing the spectator ions: $$\mathrm{NH}_{4}^{+} + \mathrm{OH}^{-} \rightarrow \mathrm{NH}_{3} + \mathrm{H}_{2}\mathrm{O}$$

Step 2: (b) Sodium dihydrogen phosphate reacting with hydroxide ions

The given aqueous solution is sodium dihydrogen phosphate, which has the formula \(\mathrm{NaH}_{2} \mathrm{PO}_{4}\). The hydroxide ions are denoted by \(\mathrm{OH}^{-}\). Write the reaction as: $$\mathrm{NaH}_{2} \mathrm{PO}_{4} + \mathrm{OH}^{-} \rightarrow$$ Now, we need to predict the products. When the sodium dihydrogen phosphate reacts with hydroxide ions, it forms water and sodium monohydrogen phosphate. Write the balanced chemical equation: $$\mathrm{NaH}_{2} \mathrm{PO}_{4} + \mathrm{OH}^{-} \rightarrow \mathrm{NaHPO}_{4} + \mathrm{H}_{2}\mathrm{O}$$ Our net ionic equation does not include sodium ions as it's a spectator ion, and we get: $$\mathrm{H}_{2} \mathrm{PO}_{4}^{-} + \mathrm{OH}^{-} \rightarrow \mathrm{HPO}_{4}^{2-} + \mathrm{H}_{2}\mathrm{O}$$

Step 3: (c) Reaction of \(\mathrm{Al}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}{ }^{3+}\) with hydroxide ions

We have the complex ion \(\mathrm{Al}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}{\underline{\phantom{xx}}}^{3+}\) reacting with hydroxide ions, \(\mathrm{OH}^{-}\). $$\mathrm{Al}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}{\underline{\phantom{xx}}}^{3+} + \mathrm{OH}^{-} \rightarrow$$ When the complex ion reacts with hydroxide ions, it will form an insoluble aluminum hydroxide and release water. Write the balanced chemical equation: $$\mathrm{Al}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}{\underline{\phantom{xx}}}^{3+} + 3\mathrm{OH}^{-} \rightarrow \mathrm{Al}\left(\mathrm{OH}\right)_{3} + 6\mathrm{H}_{2}\mathrm{O}$$ Since there are no spectator ions in this reaction, the net ionic equation is the same as the balanced chemical equation: $$\mathrm{Al}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}{\underline{\phantom{xx}}}^{3+} + 3\mathrm{OH}^{-} \rightarrow \mathrm{Al}\left(\mathrm{OH}\right)_{3} + 6\mathrm{H}_{2}\mathrm{O}$$

Key Concepts

Aqueous Solutions

An aqueous solution is a solution in which the solvent is water. This type of solution is very common in chemistry, particularly because water is known as the "universal solvent," capable of dissolving many different substances. When a substance dissolves in water, it typically dissociates into its individual ions, making them available for chemical reactions. For example, when ammonium nitrate

• dissolves in water, it separates into ammonium ions ( ⁺ ) and nitrate ions ( ^- ).
• Similarly, sodium dihydrogen phosphate disassociates into sodium ( ⁺ ) and dihydrogen phosphate ions ( ^- ).

In solutions, these ions move freely, which allows them to react with hydroxide ions ( ^- ) as seen in the given exercises.
This key ability to move and react is what makes aqueous solutions particularly vital in the study and practice of chemistry.

Hydroxide Ions

Hydroxide ions ( ^- ) are an important component of many chemical reactions, especially those that involve bases. They play a crucial role in the formation of water when they react with hydrogen ions (H ⁺ ) or other positively charged ions.
In the context of these reactions, hydroxide ions:

• React with ammonium ions ( ⁺ ) to produce ammonia ( ₃ ) and water.
• Can neutralize weak acids like those in sodium dihydrogen phosphate to form water.

Hydroxide ions are ubiquitous in many basic solutions and understanding their interactions with other chemicals helps in predicting the outcomes of chemical reactions.

Chemical Reactions

Chemical reactions tell us how different substances combine or change into new substances. In chemistry, writing equations for these reactions is essential.
For instance, in the case of ammonium nitrate reacting with hydroxide ions, knowing the starting materials allows us to predict that ammonia and water will form.
Similarly, sodium dihydrogen phosphate reacts with hydroxide ions to produce sodium monohydrogen phosphate and water.

• The type of reaction occurring can be decomposition, synthesis, or a replacement.
• Net ionic equations highlight the involvement of specific ions in a reaction.
• Spectator ions don't participate in the actual chemical change, and are often omitted in net ionic equations.

Net ionic equations simplify reactions by showing only the ions that actually take part in the change, giving us a clearer picture of the reaction's core chemistry.

Reaction Products

The outcome of a chemical reaction, known as the reaction products, gives rise to new chemical compounds. These products are a direct result of the reorganization of atoms and the net charge must be balanced.
For example, in our exercises:

• When ammonium nitrate and hydroxide ions react, the products are ammonia ( ₃ ), nitrate ions, and water.
• In the reaction with sodium dihydrogen phosphate, the products include sodium monohydrogen phosphate and water.
• In the aluminum complex reaction, aluminum hydroxide and water are formed.

Understanding what products are formed in a reaction helps not just in completing equations correctly but also in predicting the physical and chemical properties of the resulting solution. Identifying reaction products is vital for deducing reaction mechanisms and for practical applications in fields such as environmental science and engineering.