Problem 10 - Chemical Principles: The Quest for Insight

Question

The following acids are also used in chemical laboratorics, although they are less common than those in the preceding exercise. Write the formulas of (a) perchloric acid; (b) hypochlorous acid; (c) hypoiodous acid; (d) hydrofluoric acid; (c) phosphorous acid; (f) periodic acid.

Step-by-Step Solution

Answer

The formulas are: (a) HClO4, (b) HClO, (c) HIO, (d) HF, (e) H3PO3, (f) HIO4.

Step 1 - Identify elements in each acid

Recognize the prefix and root in each acid’s name to determine its constituent elements and its ion form.

Step 2 - Determine the charges

Use the periodic table and chemical nomenclature rules to determine the charges of the ions in each acid.

Step 3 - Write the formulas of the acids

Combine the hydrogen (H) cation with the anion for each acid, making sure that the overall charge is neutral (total positive charges equals total negative charges).

Step 4 - List the formulas

(a) Perchloric acid contains the perchlorate anion (ClO4-). Formula: HClO4.(b) Hypochlorous acid contains the hypochlorite anion (ClO-). Formula: HClO.(c) Hypoiodous acid contains the hypoiodite anion (IO-). Formula: HIO.(d) Hydrofluoric acid contains the fluoride anion (F-). Formula: HF.(e) Phosphorous acid contains the phosphite anion (HPO3^2-). Formula: H3PO3.(f) Periodic acid contains the periodate anion (IO4-). Formula: HIO4.

Key Concepts

Chemical Nomenclature

Understanding chemical nomenclature, which is essentially the naming system of compounds, is crucial for students to write chemical formulas accurately. The names of acids often give clues about their composition and structure. For instance, the prefix ‘hydro-’ in hydrofluoric acid tells us that the compound is an acid that consists of hydrogen and a non-metal. Similarly, the prefix ‘per-’ as in perchloric acid indicates a higher oxygen content than in chloric acid.

Using the example of perchloric acid, the root ‘chlor’ refers to the element chlorine, and the suffix ‘-ic’ suggests that it is in the form of its highest common oxidation state, in this case, perchlorate \textbf{(ClO4\(^-\))}. Learning to recognize these prefixes, roots, and suffixes can simplify the process of writing chemical formulas. The key is to match the names of acids with the appropriate anion and combine with hydrogen ions to balance the charge.

Acid Formula Determination

When it comes to determining the formula of acids, there's a systematic method students can follow. Firstly, identify the central element and the associated oxyanion if it's an oxyacid. For example, in hypochlorous acid, ‘hypo-’ indicates fewer oxygen atoms than the common oxyacid of chlorine, which is chlorous acid. The oxyanion for hypochlorous acid is thus hypochlorite \textbf{(ClO\(^-\))}.

Once the oxyanion is established, the formula can be determined by adding enough hydrogen ions (\textbf{H\(^+\)}) to neutralize the negative charge of the anion, resulting in a neutral compound. Keep in mind that some acids, like phosphorous acid, have a more complex polyatomic anion, such as phosphite \textbf{(HPO3\(^{2-}\))}, which requires three hydrogen ions for charge balance, forming \textbf{H3PO3}. Recognizing these details is an essential step before you can successfully write the correct formula for an acid.

Periodic Table Charges

Having knowledge of the periodic table charges is indispensable for writing chemical formulas. Elements in the periodic table are organized in a way that allows us to infer their common ion charges based on their group (column). For instance, halogens like chlorine typically form anions with a charge of \(^-1\), as in the case of hypochlorous acid (\textbf{ClO\(^-\)}).

Transition metals can have multiple possible charges, which is often indicated in the compound’s name using Roman numerals. Nonmetals found on the right side of the periodic table usually form anions with negative charges. Understanding these patterns provides a foundation for predicting the charge balance required in chemical compounds. The concept of electronegativity is also important, as it influences how atoms will gain or lose electrons to form ions, which is the basis of writing formulas for acids and other compounds.