Problem 113 - Chemistry The Central Science

Question

Because many ions and compounds have very similar names, there is great potential for confusing them. Write the correct chemical formulas to distinguish between \((\mathbf{a})\) calcium sulfide and calcium hydrogen sulfide, \((\mathbf{b})\) hydrobromic acid and bromic acid \((\mathbf{c})\) aluminum nitride and aluminum nitrite,\((\mathbf{d})\)iron(II) oxide and iron(III) oxide,\((\mathbf{e})\)ammonia and ammonium ion, \((\mathbf{f})\)potassium sulfite and potassium bisulfite,\((\mathbf{g})\) mercurous chloride and mercuric chloride, \((\mathbf{h})\) chloric acid and perchloric acid.

Step-by-Step Solution

Answer

The correct chemical formulas for each pair are: (a) Calcium sulfide: CaS and calcium hydrogen sulfide: Ca(HS)_2. (b) Hydrobromic acid: HBr and bromic acid: HBrO_3. (c) Aluminum nitride: AlN and aluminum nitrite: Al(NO_2)_3. (d) Iron(II) oxide: FeO and iron(III) oxide: Fe_2O_3. (e) Ammonia: NH_3 and ammonium ion: NH_4^(+). (f) Potassium sulfite: K_2SO_3 and potassium bisulfite: KHSO_3. (g) Mercurous chloride: Hg_2Cl_2 and mercuric chloride: HgCl_2. (h) Chloric acid: HClO_3 and perchloric acid: HClO_4.

Step 1: (a) Calcium sulfide and calcium hydrogen sulfide

For calcium sulfide, we have the calcium ion Ca^(2+) and the sulfide ion S^(2-). The correct chemical formula is obtained by balancing the charges, which results in CaS. For calcium hydrogen sulfide, we have the calcium ion Ca^(2+) and the hydrogen sulfide ion HS^(-). Balancing the charges results in the correct chemical formula: Ca(HS)_2.

Step 2: (b) Hydrobromic acid and bromic acid

Hydrobromic acid is a strong acid with a hydrogen ion H^(+) and the bromide ion Br^(-). Putting them together, we get the chemical formula: HBr. Bromic acid is a weak acid containing a hydrogen ion H^(+) and the bromate ion BrO_3^(-). Combining them, we get the chemical formula: HBrO_3.

Step 3: (c) Aluminum nitride and aluminum nitrite

For aluminum nitride, we have the aluminum ion Al^(3+) and the nitride ion N^(3-). Balancing the charges, we get the chemical formula: AlN. For aluminum nitrite, we have the aluminum ion Al^(3+) and the nitrite ion NO_2^(-). Balancing the charges results in the chemical formula: Al(NO_2)_3.

Step 4: (d) Iron(II) oxide and iron(III) oxide

Iron(II) oxide contains an iron(II) ion Fe^(2+) and an oxide ion O^(2-). Balancing the charges, we get the chemical formula: FeO. Iron(III) oxide contains an iron(III) ion Fe^(3+) and an oxide ion O^(2-). Balancing the charges, we get the chemical formula: Fe_2O_3.

Step 5: (e) Ammonia and ammonium ion

Ammonia is a neutral compound with the molecular formula NH_3. Ammonium ion is a positively charged polyatomic ion formed when ammonia gains a proton (H^(+)). Its chemical formula is NH_4^(+).

Step 6: (f) Potassium sulfite and potassium bisulfite

For potassium sulfite, we have the potassium ion K^(+) and the sulfite ion SO_3^(2-). Balancing the charges, we get the chemical formula: K_2SO_3. For potassium bisulfite, we have the potassium ion K^(+) and the bisulfite ion HSO_3^(-). Balancing the charges, we get the chemical formula: KHSO_3.

Step 7: (g) Mercurous chloride and mercuric chloride

Mercurous chloride contains the mercurous ion Hg_2^(2+) and the chloride ion Cl^(-). Balancing the charges, we obtain the chemical formula: Hg_2Cl_2. Mercuric chloride contains the mercuric ion Hg^(2+) and the chloride ion Cl^(-). Balancing the charges results in the chemical formula: HgCl_2.

Step 8: (h) Chloric acid and perchloric acid

Chloric acid is a weak acid containing a hydrogen ion H^(+) and the chlorate ion ClO_3^(-). The chemical formula for chloric acid is HClO_3. Perchloric acid is a strong acid containing a hydrogen ion H^(+) and the perchlorate ion ClO_4^(-). The chemical formula for perchloric acid is HClO_4.

Key Concepts

Ionic Compounds

Ionic compounds are made up of charged particles called ions. These ions are usually formed when atoms lose or gain electrons to achieve a stable electron configuration, usually resembling that of noble gases. In an ionic compound, the positive ions, known as cations, and negative ions, known as anions, come together in a fixed ratio to balance each other's charges.
This results in a compound that is electrically neutral overall.

Let's consider the example of calcium sulfide (CaS).

• Calcium ion: Ca\(^{2+}\)
• Sulfide ion: S\(^{2-}\)

When they combine, each calcium ion pairs with one sulfide ion, resulting in the formula CaS, where the charges balance out.

Similarly, the formula for iron(III) oxide is Fe\(_2\)O\(_3\). It contains:

• Iron ion: Fe\(^{3+}\) (iron in the +3 oxidation state)
• Oxide ion: O\(^{2-}\)

To balance the charges, two Fe\(^{3+}\) ions are needed for every three O\(^{2-}\) ions. Thus, the formula is Fe\(_2\)O\(_3\).

Understanding the charges of the ions involved is crucial to writing the correct formula for any ionic compound.

Acid Nomenclature

Acid nomenclature is the system of naming acids based on their chemical composition. Acids are substances that release hydrogen ions (H\(^+\)) when dissolved in water. Their names often reflect the anions they form upon ionization.

There are two main types of acids:

• Binary acids: These consist of hydrogen and one other non-metal element, like HBr (hydrobromic acid).
• Oxyacids: These are more complex and contain hydrogen along with oxygen and another element. An example is HBrO\(_3\), where the anion is bromate (BrO\(_3^-\)), making it bromic acid.

When naming acids, the suffixes and prefixes provide clues about their composition. For example:

• "-ic" suffix in bromic acid alludes to the higher number of oxygens.
• "hydro-" prefix (as in hydrobromic acid) indicates a binary acid without oxygen.

Equilibrium between naming systems and memorizing common acid names is a helpful approach to mastering acid nomenclature.

Polyatomic Ions

Polyatomic ions are ions composed of two or more atoms bonded together, that collectively form a charged entity.
They play an important role in forming various compounds.

These ions often involve a combination of different elements, resulting in unique and specific chemical properties.
Understanding polyatomic ions is essential when dealing with compounds like aluminum nitrite (Al(NO\(_2\))\(_3\)) and perchloric acid (HClO\(_4\)).

The nitrite ion, NO\(_2^-\), is a polyatomic ion. Its presence in compounds like aluminum nitrite requires balancing to ensure the resulting compound is neutral. Since Al\(^{3+}\) has a 3+ charge, it pairs with three NO\(_2^-\) ions to balance the charges.

Similarly, the perchlorate ion, ClO\(_4^-\), forms part of perchloric acid. As a strong oxyacid, it contains one hydrogen ion paired with a perchlorate ion.

Some common polyatomic ions include:

• Sulfite: SO\(_3\)^{2-}
• Phosphate: PO\(_4\)^{3-}
• Ammonium: NH\(_4\)^+

Familiarity with these ions and their charges helps in recognizing and writing chemical formulas for compounds containing polyatomic ions.