Question

Many ions and compounds have very similar names, and 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(Il) 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

(a) \(CaS\) and \(CaHS\) (b) \(HBr\) and \(HBrO_3\) (c) \(AlN\) and \(Al(NO_2)_3\) (d) \(FeO\) and \(Fe_2O_3\) (e) \(NH_3\) and \(NH_4^+\) (f) \(K_2SO_3\) and \(KHSO_3\) (g) \(Hg_2Cl_2\) and \(HgCl_2\) (h) \(HClO_3\) and \(HClO_4\)

Step-by-step solution

(a) calcium sulfide and calcium hydrogen sulfide

For calcium sulfide, we have a calcium ion (Ca²⁺) and a sulfide ion (S²⁻). They combine in a 1:1 ratio, so the formula is: \(CaS\). For calcium hydrogen sulfide, we have a calcium ion (Ca²⁺) and a hydrogen sulfide ion (HS⁻). They combine in a 1:1 ratio, so the formula is: \(CaHS\).

(b) hydrobromic acid and bromic acid

Hydrobromic acid is a binary acid, which means it has hydrogen (H⁺) and a halogen (in this case, bromine) combined. The halogen forms a negative ion, which is the bromide ion (Br⁻). The formula of hydrobromic acid is: \(HBr\). Bromic acid is an oxyacid containing hydrogen (H⁺), bromine, and oxygen. The bromine forms a negative ion called bromate (BrO₃⁻). The formula of bromic acid is: \(HBrO_3\).

(c) aluminum nitride and aluminum nitrite

For aluminum nitride, we have aluminum (Al³⁺) and nitride (N³⁻) ions. They combine in a 1:1 ratio, so the formula is: \(AlN\). For aluminum nitrite, we have aluminum (Al³⁺) and nitrite (NO₂⁻) ions. They combine in a 1:3 ratio, so the formula is: \(Al(NO_2)_3\).

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

Iron(II) oxide has an iron ion with a +2 charge (Fe²⁺) and an oxide ion (O²⁻). They combine in a 1:1 ratio, so the formula is: \(FeO\). Iron(III) oxide has an iron ion with a +3 charge (Fe³⁺) and an oxide ion (O²⁻). They combine in a 2:3 ratio, so the formula is: \(Fe_2O_3\).

(e) ammonia and ammonium ion

Ammonia is a neutral compound with the formula: \(NH_3\). Ammonium ion is formed when ammonia gains a proton (H⁺), giving it a +1 charge. The formula of the ammonium ion is: \(NH_4^+\).

(f) potassium sulfite and potassium bisulfite

For potassium sulfite, we have potassium (K⁺) and sulfite (SO₃²⁻) ions. They combine in a 2:1 ratio, so the formula is: \(K_2SO_3\). For potassium bisulfite, we have potassium (K⁺) and bisulfite (HSO₃⁻) ions. They combine in a 1:1 ratio, so the formula is: \(KHSO_3\).

(g) mercurous chloride and mercuric chloride

Mercurous chloride, also called mercury(I) chloride, has mercury ions in the +1 oxidation state (Hg₂²⁺) and chloride ions (Cl⁻). They combine in a 1:2 ratio, so the formula is: \(Hg_2Cl_2\). Mercuric chloride, also called mercury(II) chloride, has mercury ions in the +2 oxidation state (Hg²⁺) and chloride ions (Cl⁻). They combine in a 1:2 ratio, so the formula is: \(HgCl_2\).

(h) chloric acid and perchloric acid

Chloric acid is an oxyacid containing hydrogen (H⁺), chlorine, and oxygen. The chlorine forms a negative ion called chlorate (ClO₃⁻). The formula of chloric acid is: \(HClO_3\). Perchloric acid is another oxyacid containing hydrogen (H⁺), chlorine, and oxygen. The chlorine forms a negative ion called perchlorate (ClO₄⁻). The formula of perchloric acid is: \(HClO_4\).

Key concepts

Ionic Compounds

Ionic compounds are formed from the electrostatic attraction between oppositely charged ions. These ions are usually metals and non-metals. Metals tend to lose electrons and form positive ions, while non-metals gain electrons to form negative ions. For example, in calcium sulfide (\(CaS\)), calcium (a metal) decays into a positive ion (\(Ca^{2+}\)) and sulfur (a non-metal) forms a negative ion (\(S^{2-}\)). Because both ions have equal and opposite charges, they come together in a simple 1:1 ratio to form a stable ionic compound.

Notably, the properties of ionic compounds often include:

• High melting and boiling points due to strong ionic bonds.
• Selective solubility in water, where they can dissolve and dissociate into their constituent ions.
• The ability to conduct electricity in the liquid state or when dissolved, because ions are free to move.

Binary Acids

Binary acids consist only of hydrogen and one other element, commonly a halogen. A famous example is hydrobromic acid (\(HBr\)). Here, the hydrogen ion (\(H^+\)) bonds with a halogen, like bromine (\(Br^-\)) to form the acid. In water, binary acids can dissociate, releasing the hydrogen ion which is responsible for acidic behavior.

Binary acids are characterized by:

• The presence of just two elements: hydrogen and a non-metal.
• Being compounds that often appear gaseous at room temperature or are soluble in water.
• Having names starting with 'hydro-' and ending with '-ic acid', as a standard naming convention. This helps differentiate them from oxyacids.

Oxyacids

Oxyacids are acids that contain hydrogen, oxygen, and another non-metal element. For instance, bromic acid (\(HBrO_3\)) includes bromine, oxygen, and hydrogen. These acids originate from the combination of their corresponding oxyanions with hydrogen ions.

An important point about oxyacids is their naming:

• The name is usually based on the oxyanion's name. If the oxyanion ends in '-ate', the acid name will end in '-ic acid'.
• For example, chlorate (\(ClO_3^−\)) forms chloric acid (\(HClO_3\)).
• Oxyacids play critical roles in biological systems and industrial applications, thanks to their reactivity and ability to donate protons.

Oxidation States

Oxidation states, or oxidation numbers, indicate the degree of oxidation of an atom in a molecule. They are important for balancing equations and understanding electron transfer in reactions.

For example, in iron oxides, iron can exhibit different oxidation states, impacting the compound's formula. In iron(II) oxide (\(FeO\)), iron is in the +2 state (\(Fe^{2+}\)). In iron(III) oxide (\(Fe_2O_3\)), it is in the +3 state (\(Fe^{3+}\)).

Recognizing oxidation states involves understanding:

• The rules for assigning oxidation numbers, such as that the sum of oxidation states in a neutral compound is zero.
• Oxidation states help describe chemical reactions where electrons are transferred, like redox reactions.
• They aid in predicting the formation and stability of different chemical species.