Question

Commercial cold packs and hot packs are available for treating athletic injuries. Both types contain a pouch of water and a dry chemical. When the pack is struck, the pouch of water breaks, dissolving the chemical, and the solution becomes either hot or cold. Many hot packs use magnesium sulfate, and many cold packs use ammonium nitrate. Write reactions to show how these strong electrolytes break apart when they dissolve in water

Short answer

Magnesium sulfate (\(MgSO_4\)) and ammonium nitrate (\(NH_4NO_3\)) are strong electrolytes that dissociate in water. The dissociation reactions are: 1. \(MgSO_4(s) \xrightarrow{H_2O} Mg^{2+}(aq) + SO_4^{2-}(aq)\) 2. \(NH_4NO_3(s) \xrightarrow{H_2O} NH_4^{+}(aq) + NO_3^{-}(aq)\)

Step-by-step solution

1. Magnesium sulfate dissolving in water

1. Write the chemical formula of magnesium sulfate: Magnesium sulfate has the chemical formula \(MgSO_4\). 2. Identify the ions that magnesium sulfate breaks into: When dissolved in water, magnesium sulfate breaks into magnesium ions and sulfate ions. The ions are: - Magnesium ion(\(Mg^{2+}\)) - Sulfate ion(\(SO_4^{2-}\)) 3. Write the balanced dissociation reaction: When magnesium sulfate dissolves in water, it dissociates into its ions as follows: \[MgSO_4(s) \xrightarrow{H_2O} Mg^{2+}(aq) + SO_4^{2-}(aq)\]

2. Ammonium nitrate dissolving in water

1. Write the chemical formula of ammonium nitrate: Ammonium nitrate has the chemical formula \(NH_4NO_3\). 2. Identify the ions that ammonium nitrate breaks into: When dissolved in water, ammonium nitrate breaks into ammonium ions and nitrate ions. The ions are: - Ammonium ion(\(NH_4^+\)) - Nitrate ion(\(NO_3^-\)) 3. Write the balanced dissociation reaction: When ammonium nitrate dissolves in water, it dissociates into its ions as follows: \[NH_4NO_3(s) \xrightarrow{H_2O} NH_4^{+}(aq) + NO_3^{-}(aq)\]

Key concepts

Electrolyte Dissociation

When a chemical substance dissolves in water, it may undergo a process called electrolyte dissociation. During this transformation, the chemical compound breaks down into its constituent ions, which then disperse throughout the solution. This process is essential because it enables the compound to conduct electricity, given that ions carry positive or negative charges. For example, when a compound dissociates, it releases free-moving charged particles in the water, effectively turning the solution into an electrolyte.
In general, this process occurs with acids, bases, and salts when they dissolve. Understanding this concept is crucial for predicting how different substances react in aqueous solutions. It is particularly relevant in contexts like sports medicine, where substances such as those in cold or hot packs break down to offer therapeutic benefits.
Here's a simple breakdown of how this works: a solid compound might look stable, but when water molecules surround it, they pull the ions apart due to the polar nature of water. This dissociation is represented in chemical equations by showing reactants on one side and the resulting ions on the other. The notations often include the state of each component in the reaction, such as aqueous \((aq)\) to denote that the ions are dissolved in solution.

Magnesium Sulfate

Magnesium sulfate is a well-known compound, often referred to as Epsom salt. It has the chemical formula \(MgSO_4\). Upon dissolving in water, magnesium sulfate dissociates into magnesium ions \((Mg^{2+})\) and sulfate ions \((SO_4^{2-})\). These ions are crucial because they provide the compound’s reactivity and ability to function effectively in its applications.
Magnesium ions are essential in various biological processes, including muscle function and energy production. This makes magnesium sulfate an ideal component in hot packs, as the dissociation produces heat energy, resulting in a warming effect. This reaction can be particularly soothing for sore muscles, aiding in the relief of tension and pain.
When representing the dissociation of magnesium sulfate in water, the balanced chemical equation is formulated as:

\[MgSO_4(s) \xrightarrow{H_2O} Mg^{2+}(aq) + SO_4^{2-}(aq)\]
This equation indicates that a solid magnesium sulfate \((s)\) is transformed into aqueous ions in solution, illustrating the principle of electrolyte dissociation in action.

Ammonium Nitrate

Ammonium nitrate, with the molecular formula \(NH_4NO_3\), is widely used in various applications, particularly in cold packs for treating injuries. When ammonium nitrate dissolves in water, it undergoes dissociation, breaking into ammonium ions \((NH_4^+)\) and nitrate ions \((NO_3^-)\). This dissociation is exothermic, meaning it absorbs heat from its surroundings, which results in a cooling sensation.
This makes ammonium nitrate particularly useful for instant cold packs, as the reaction effectively lowers the temperature, providing quick relief for injuries and inflammation. Understanding how ammonium nitrate dissociates is important not only for practical applications but also for comprehending broader chemical concepts such as thermodynamics and reaction mechanics.
The dissociation is represented by the chemical equation:

\[NH_4NO_3(s) \xrightarrow{H_2O} NH_4^{+}(aq) + NO_3^{-}(aq)\]
This balanced equation demonstrates how solid ammonium nitrate \((s)\) transitions into its component ions in an aqueous solution, showcasing another example of electrolyte dissociation.