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 (a) calcium sulfide and calcium hydrogen sulfide, (b) hydrobromic acid and bromic acid, (c) aluminum nitride and aluminum nitrite, (d) iron(II) oxide and iron(III) oxide, (e) ammonia and ammonium ion, (f) potassium sulfite and potassium bisulfite, (g) mercurous chloride and mercuric chloride, (h) chloric acid and perchloric acid.

Short answer

The correct chemical formulas for the given ions and compounds are: (a) Calcium sulfide: \(CaS\); Calcium hydrogen sulfide: \(Ca(HS)_2\) (b) Hydrobromic acid: \(HBr\); Bromic acid: \(HBrO3\) (c) Aluminum nitride: \(AlN\); Aluminum nitrite: \(Al(NO2)_3\) (d) Iron(II) oxide: \(FeO\); Iron(III) oxide: \(Fe2O3\) (e) Ammonia: \(NH3\); Ammonium ion: \(NH4^+\) (f) Potassium sulfite: \(K2SO3\); Potassium bisulfite: \(KHSO3\) (g) Mercurous chloride: \(Hg2Cl2\); Mercuric chloride: \(HgCl2\) (h) Chloric acid: \(HClO3\); Perchloric acid: \(HClO4\)

Step-by-step solution

(a) Calcium sulfide and calcium hydrogen sulfide

Calcium sulfide has one calcium ion (Ca^2+) and one sulfide ion (S^2-). To write its formula, we simply combine these ions together and balance them by their charges: Ca^2+ + S^2- -> \(CaS\) Calcium hydrogen sulfide contains one calcium ion (Ca^2+) and one hydrogen sulfide ion (HS^-). To write its formula, we combine the ions together and balance them by their charges: Ca^2+ + 2(HS^-) -> \(Ca(HS)_2\)

(b) Hydrobromic acid and bromic acid

Hydrobromic acid is formed when a hydrogen ion (H^+) combines with a bromide ion (Br^-): H^+ + Br^- -> \(HBr\) Bromic acid is formed when a hydrogen ion (H^+) combines with a bromate ion (BrO3^-): H^+ + BrO3^- -> \(HBrO3\)

(c) Aluminum nitride and aluminum nitrite

Aluminum nitride has one aluminum ion (Al^3+) and one nitride ion (N^3-). To write its formula, we simply combine these ions together and balance them by their charges: Al^3+ + N^3- -> \(AlN\) Aluminum nitrite contains one aluminum ion (Al^3+) and one nitrite ion (NO2^-). To write its formula, we combine the ions together and balance them by their charges: Al^3+ + 3(NO2^-) -> \(Al(NO2)_3\)

(d) Iron(II) oxide and iron(III) oxide

Iron(II) oxide has one iron(II) ion (Fe^2+) and one oxide ion (O^2-). To write its formula, we simply combine these ions together and balance them by their charges: Fe^2+ + O^2- -> \(FeO\) Iron(III) oxide has one iron(III) ion (Fe^3+) and one oxide ion (O^2-). To write its formula, we combine the ions together and balance them by their charges: 2(Fe^3+) + 3(O^2-) -> \(Fe2O3\)

(e) Ammonia and ammonium ion

Ammonia is a neutral molecule with the chemical formula: \(NH3\) Ammonium ion is formed when ammonia molecule gains a hydrogen ion (H^+): \(NH3\) + H^+ -> \(NH4^+\)

(f) Potassium sulfite and potassium bisulfite

Potassium sulfite contains one potassium ion (K^+) and one sulfite ion (SO3^2-). To write its formula, we combine the ions together and balance them by their charges: 2(K^+) + SO3^2- -> \(K2SO3\) Potassium bisulfite contains one potassium ion (K^+) and one hydrogen sulfite ion (HSO3^-). To write its formula, we combine the ions together and balance them by their charges: K^+ + HSO3^- -> \(KHSO3\)

(g) Mercurous chloride and mercuric chloride

Mercurous chloride (also known as mercury(I) chloride) has one mercury(I) ion (Hg2^2+) and two chloride ions (Cl^-). To write its formula, we combine the ions together and balance them by their charges: Hg2^2+ + 2(Cl^-) -> \(Hg2Cl2\) Mercuric chloride (also known as mercury(II) chloride) has one mercury(II) ion (Hg^2+) and two chloride ions (Cl^-). To write its formula, we combine the ions together and balance them by their charges: Hg^2+ + 2(Cl^-) -> \(HgCl2\)

(h) Chloric acid and perchloric acid

Chloric acid is formed when a hydrogen ion (H^+) combines with a chlorate ion (ClO3^-): H^+ + ClO3^- -> \(HClO3\) Perchloric acid is formed when a hydrogen ion (H^+) combines with a perchlorate ion (ClO4^-): H^+ + ClO4^- -> \(HClO4\)

Key concepts

Ionic Compounds

Ionic compounds are composed of positively and negatively charged ions that are held together by electrostatic forces. These forces create a neutral compound overall, as the total positive charge equals the total negative charge. In ionic compounds:

• Metals typically form positive ions (cations) by losing electrons.
• Nonmetals form negative ions (anions) by gaining electrons.
• For example, in calcium sulfide, calcium (Ca\(^{2+}\)) loses two electrons becoming a cation, while sulfide (S\(^{2-}\)) gains two electrons becoming an anion.

To write the formula for an ionic compound, ensure that the charges are balanced. This might involve using subscripts in the chemical formula.

• The compound formula for calcium sulfide is simply \( CaS \) because the charges already balance out (both are 2).
• In cases like calcium hydrogen sulfide, two hydrogen sulfide ions (HS\(^-\)) balance one calcium ion (Ca\(^{2+}\)). This results in the formula \( Ca(HS)_2 \).

Polyatomic Ions

Polyatomic ions are ions composed of two or more atoms covalently bonded, that carry a charge, given the molecule a 'cluster' of atoms functionality. These ions behave like a single unit in the context of ionic compounds.
Some common polyatomic ions include:

• Nitrite (NO\(_2^-\))
• Sulfate (SO\(_4^{2-}\))
• Ammonium (NH\(_4^+\))
• Hydroxide (OH\(^-\))

Understanding polyatomic ions is key to naming compounds like aluminum nitrite (Al(NO\(_2\))_3), where you need to manage the overall charge by using multiple ions to balance the charges with the metal ion.The formula \( Al(NO_2)_3 \) arises from one aluminum ion (Al\(^{3+}\)) requiring three nitrite ions (NO\(_2^-\)) to neutralize the charges. It's crucial to recognize the different endings and prefixes (such as sulfite vs. sulfate) represent different numbers of oxygen atoms, thus changing the charge of ions and ultimately the formula.

Acid Nomenclature

Naming acids properly is crucial because they are fundamental components in chemistry with varying properties and uses. Acids can be simple binary compounds or complex oxyacid structures depending on the presence of oxygen.

• Binary Acids: These typically consist of hydrogen combined with a nonmetal, named using the 'hydro-' prefix plus the suffix '-ic' on the nonmetal. For example, hydrobromic acid (HBr).
• Oxyacids: These include hydrogen combined with a polyatomic ion containing oxygen. The name is based on the ion:
  • The '-ate' ions form '-ic' acids, like bromic acid (HBrO\(_3\)).
  • The '-ite' ions form '-ous' acids, like chlorous acid (HClO\(_2\)).
  • Addition of 'per-' or 'hypo-' prefixes can indicate more or less oxygen, respectively, as seen with chloric acid (HClO\(_3\)) versus perchloric acid (HClO\(_4\)).

Understanding these naming conventions helps distinguish each acid's composition and nature, and prevents confusion amongst similarly described compounds.