Question

Write the formula for (a) permanganic acid, (b) sulfurous acid, and (c) dichromic acid.

Short answer

The chemical formulas are (a) \(HMnO_4\) for permanganic acid, (b) \(H_2SO_3\) for sulfurous acid, and (c) \(H_2Cr_2O_7\) for dichromic acid.

Step-by-step solution

Identify permanganic acid

To write the formula for permanganic acid, recognize that 'permanganic' refers to the presence of the permanganate ion. The permanganate ion has the formula \(MnO_4^-\). Since acids typically combine a hydrogen ion (\(H^+\)) with an anion, we can deduce that permanganic acid must contain hydrogen and permanganate ions.

Write the formula for permanganic acid

Combining one hydrogen ion with the permanganate ion yields \(HMnO_4\bspace\), which is the chemical formula for permanganic acid.

Identify sulfurous acid

Sulfurous acid involves the presence of the sulfite ion, which has the formula \(SO_3^{2-}\). Combining this ion with hydrogen ions will yield the formula for sulfurous acid.

Write the formula for sulfurous acid

Since the sulfite ion carries a 2- charge, it will combine with two hydrogen ions to maintain electrical neutrality. Therefore, the formula for sulfurous acid is \(H_2SO_3\).

Identify dichromic acid

Dichromic acid involves the presence of the dichromate ion. The dichromate ion has the formula \(Cr_2O_7^{2-}\). Like sulfurous acid, it will combine with two hydrogen ions to balance the charge.

Write the formula for dichromic acid

By adding two hydrogen ions to the dichromate ion, we get the formula for dichromic acid, which is \(H_2Cr_2O_7\).

Key concepts

Permanganic Acid Formula

Understanding the formula for permanganic acid starts with identifying its key component: the permanganate ion. As explained in the step-by-step solution, the permanganate ion is symbolized by \(MnO_4^-\bspace\). To form the acid, this negatively charged ion must be combined with a positively charged hydrogen ion (\(H^+\)).

When these ions combine, they create the stable compound permanganic acid, where only one hydrogen ion is needed to balance the single negative charge of the permanganate ion, resulting in the chemical formula \(HMnO_4\bspace\). This formula represents a compound that is used in various oxidation reactions due to the manganese ion's high oxidation state.

Sulfurous Acid Formula

The sulfurous acid formula is a classic exercise in balancing charges to create a neutral compound. Its key constituent, the sulfite ion, is represented by \(SO_3^{2-}\bspace\). The charge on the sulfite ion indicates that two hydrogen ions (each with a charge of \(H^+\)) are necessary to neutralize the overall charge.

By joining these ions, we obtain the formula for sulfurous acid: \(H_2SO_3\bspace\). A distinguishing aspect of sulfurous acid is its role as a reducing agent in solutions, and its use as a preservative due to its capability to inhibit the growth of bacteria and fungi.

Dichromic Acid Formula

The chemical behavior of dichromic acid is delineated by its formula, which hinges on the dichromate ion \(Cr_2O_7^{2-}\bspace\). Much like with sulfurous acid, we encounter a polyatomic ion with a 2- charge that needs to be neutralized. The solution involves adding two hydrogen ions \(H^+\) to the dichromate ion to maintain electrical neutrality.

The result of this combination is the formula for dichromic acid: \(H_2Cr_2O_7\bspace\). Dichromic acid is not commonly encountered in simple aqueous solutions due to its strong oxidizing properties and is instead used in chemical syntheses and industrial processes.

Acid Nomenclature

The nomenclature of acids is an essential aspect of chemistry that allows clear and effective communication among scientists. When dealing with inorganic acids, the name often provides clues about its composition. The suffix '-ic' typically indicates an acid with a higher oxidation number of its central atom, while '-ous' suggests a lower oxidation number.

In the case of sulfurous acid \(H_2SO_3\bspace\), the central sulfur atom has a lower oxidation state compared to sulfuric acid (\(H_2SO_4\bspace\)). Similarly, for permanganic acid (\(HMnO_4\bspace\)), the 'ic' suffix reflects manganese's higher oxidation state compared to manganeous acid. Thus, acid nomenclature is not arbitrary but provides insight into the chemical characteristics of the compound.

Polyatomic Ions

Polyatomic ions are charged entities composed of two or more atoms covalently bonded together. These ions are pivotal in the formation of various compounds, including acids. Understanding the charge and composition of these ions is crucial when predicting the formulas of the compounds they form.

Examples of polyatomic ions include the sulfate ion \(SO_4^{2-}\bspace\), the permanganate ion \(MnO_4^-\bspace\), and the dichromate ion \(Cr_2O_7^{2-}\bspace\). When writing chemical formulas for compounds containing these ions, their charges must be balanced with corresponding numbers of hydrogen ions or other counterions to form neutral species, as demonstrated with the sulfurous acid and dichromic acid.