Problem 92 - Chemistry and Chemical Reactivity

Question

Ammonium sulfide, (NH,) \(_{2} \mathrm{S}\), reacts with \(\mathrm{Hg}\left(\mathrm{NO}_{3}\right)_{2}\) to produce HgS and \(\mathrm{NH}_{4} \mathrm{NO}_{3}\) (a) Write the overall balanced equation for the reaction. Indicate the state (s, aq) for each compound. (b) Name each compound. (c) What type of reaction is this?

Step-by-Step Solution

Answer

(a) \((NH_4)_2S_{(aq)} + Hg(NO_3)_2_{(aq)} \rightarrow HgS_{(s)} + 2 NH_4NO_3_{(aq)}\); (b) Ammonium sulfide, mercury(II) nitrate, mercury(II) sulfide, ammonium nitrate; (c) Double displacement reaction.

Step 1: Write the Unbalanced Equation

The reaction involves ammonium sulfide ((NH\(_4\))\(_2\)S) and mercury(II) nitrate (Hg(NO\(_3\))\(_2\)). To find the products, consider that ammonium nitrate (NH\(_4\)NO\(_3\)) forms while mercury(II) sulfide (HgS) is a precipitate. The unbalanced equation is: \((NH_4)_2S_{(aq)} + Hg(NO_3)_2_{(aq)} \rightarrow HgS_{(s)} + NH_4NO_3_{(aq)}\).

Step 2: Balance the Chemical Equation

To balance the number of each type of atom on both sides of the equation, we need two ammonium nitrates for every one molecule of ammonium sulfide. The balanced chemical equation is: \((NH_4)_2S_{(aq)} + Hg(NO_3)_2_{(aq)} \rightarrow HgS_{(s)} + 2 NH_4NO_3_{(aq)}\).

Step 3: State Symbols

The states of the compounds are included in the equation: aqueous for ammonium sulfide and mercury(II) nitrate, solid for mercury(II) sulfide, and aqueous for ammonium nitrate.

Step 4: Naming the Compounds

- \((NH_4)_2S\) is called ammonium sulfide.- \(Hg(NO_3)_2\) is called mercury(II) nitrate, also known as mercuric nitrate.- \(HgS\) is mercury(II) sulfide, also known as mercuric sulfide.- \(NH_4NO_3\) is ammonium nitrate.

Step 5: Determine the Reaction Type

This reaction is a double displacement reaction, also known as a metathesis reaction, where the ions of the two compounds exchange places to form two new compounds: one of which is a precipitate in this case.

Key Concepts

Balancing Chemical Equations

Balancing chemical equations is an essential skill in chemistry. It ensures that the same number of each type of atom appears on both sides of the equation. This reflects the law of conservation of mass, which states that matter cannot be created or destroyed in a chemical reaction.

To balance a chemical equation, follow these steps:

• Write the Unbalanced Equation: Identify the reactants and products, then write their chemical formulas. For example, in this reaction, we start with ammonium sulfide, \((NH_4)_2S\), and mercury(II) nitrate, \(Hg(NO_3)_2\), forming mercury(II) sulfide, \(HgS\), and ammonium nitrate, \(NH_4NO_3\).
• Count Atoms for Each Element: Tally the number of each type of atom present on both sides of the equation.
• Adjust Coefficients: Modify the coefficients (the numbers in front of compounds) to balance the atoms. Start with elements that appear in only one reactant and one product. Here, balancing the nitrogen atoms by placing a coefficient of 2 in front of \(NH_4NO_3\) balances the equation as: \((NH_4)_2S_{(aq)} + Hg(NO_3)_2_{(aq)} \rightarrow HgS_{(s)} + 2 NH_4NO_3_{(aq)}\).
• Double-Check Results: Ensure all atoms balance and that coefficients are in the lowest possible ratio - for simplicity and accuracy.

Types of Chemical Reactions

Chemical reactions come in various types, and identifying them can help predict product formation and understand reaction mechanisms. One common type is the double displacement reaction (also known as a metathesis reaction). In a double displacement reaction, two compounds exchange ions to form two new compounds. This can sometimes result in the formation of a precipitate, an insoluble solid that forms out of the solution.

In the given reaction, ammonium sulfide and mercury(II) nitrate react through ion exchange producing mercury(II) sulfide, a solid, and ammonium nitrate, which remains in aqueous solution.

• Double Displacement: These reactions generally involve ions in two aqueous solutions exchanging partners to form two new compounds.
• Precipitation Reaction: When a solid forms from the reaction, it is called a precipitation reaction. Here, \(HgS\) is the precipitate.

By understanding the type of reaction, you can identify possible reaction products and anticipate the nature of chemical transformations.

Chemical Compounds Naming

Naming chemical compounds follows established rules and conventions that allow chemists to easily communicate complex structures. Here is how some of the compounds in the exercise are named:

• Ammonium Sulfide \((NH_4)_2S\): Composed of ammonium ions \(NH_4^+\) and sulfide ions \(S^{2-}\). The name reflects these ions.
• Mercury(II) Nitrate \(Hg(NO_3)_2\): Contains mercury ions \(Hg^{2+}\) and nitrate ions \(NO_3^-\). The (II) indicates the oxidation state of the mercury, critical for understanding its reactivity and naming.
• Mercury(II) Sulfide \(HgS\): Known for its distinct orange-red color, it consists of mercury ions \(Hg^{2+}\) and sulfide ions \(S^{2-}\). The name hints at the oxidation state and chemical composition.
• Ammonium Nitrate \(NH_4NO_3\): Formed by ammonium ions \(NH_4^+\) and nitrate ions \(NO_3^-\). Widely used in fertilizers, highlighting how naming conveys information about usage.

The systematic naming provides clear identification, ensuring that chemists worldwide can accurately interpret formulas and rely on consistent terminology. Understanding the naming conventions thus aids in mastering chemistry communication.