Question

Write the chemical formula for each of the following compounds, and indicate the oxidation state of the halogen or noble-gas atom in each: (a) chlorate ion, (b) hydroiodic acid, (c) iodine trichloride, (d) sodium hypochlorite, (e) perchloric acid, (f) xenon tetrafluoride.

Short answer

(a) The chemical formula for the chlorate ion is \(ClO_3^-\), and the oxidation state of chlorine is +5. (b) The chemical formula for hydroiodic acid is \(HI\), and the oxidation state of iodine is -1. (c) The chemical formula for iodine trichloride is \(ICl_3\), and the oxidation state of iodine is +3. (d) The chemical formula for sodium hypochlorite is \(NaClO\), and the oxidation state of chlorine is +1. (e) The chemical formula for perchloric acid is \(HClO_4\), and the oxidation state of chlorine is +7. (f) The chemical formula for xenon tetrafluoride is \(XeF_4\), and the oxidation state of xenon is +4.

Step-by-step solution

(a) Chlorate ion

The chlorate ion is a polyatomic ion consisting of one chlorine atom and three oxygen atoms, and has a -1 charge. Therefore, its chemical formula is \(ClO_3^-\). To determine the oxidation state of the chlorine atom, let's set up the equation: \(1 \cdot Cl + 3 \cdot O = -1\) Oxygen has a fixed oxidation state of -2: \(1 \cdot Cl + 3 \cdot -2 = -1\) Solving for the chlorine's oxidation state: \(1 \cdot Cl = 5\) \(Cl = +5\) The oxidation state of chlorine in chlorate ion is +5.

(b) Hydroiodic acid

Hydroiodic acid is a binary acid consisting of hydrogen and iodine. Its chemical formula is \(HI\). The oxidation state of hydrogen in most compounds is +1. Since the compound is neutral, the oxidation state of iodine will be -1. The oxidation state of iodine in hydroiodic acid is -1.

(c) Iodine trichloride

Iodine trichloride consists of one iodine atom and three chlorine atoms. Its chemical formula is \(ICl_3\). The oxidation state of chlorine in this compound is -1, so we can set up the equation: \(1 \cdot I + 3 \cdot -1 = 0\) Solving for the iodine's oxidation state: \(1 \cdot I = 3\) \(I = +3\) The oxidation state of iodine in iodine trichloride is +3.

(d) Sodium hypochlorite

Sodium hypochlorite is a compound consisting of sodium, chlorine, and oxygen, and it's an ionic compound. Its chemical formula is \(NaClO\). Sodium has an oxidation state of +1, and oxygen has an oxidation state of -2. We need to determine the oxidation state of chlorine: \(1 \cdot +1 + 1 \cdot Cl + 1 \cdot -2 = 0\) Solving for the chlorine's oxidation state: \(1 \cdot Cl = 1\) \(Cl = +1\) The oxidation state of chlorine in sodium hypochlorite is +1.

(e) Perchloric acid

Perchloric acid is an oxoacid that consists of hydrogen, chlorine, and oxygen. Its chemical formula is \(HClO_4\). The oxidation state of hydrogen in most compounds is +1, and oxygen has an oxidation state of -2. We can determine the oxidation state of chlorine: \(1 \cdot +1 + 1 \cdot Cl + 4 \cdot -2 = 0\) Solving for the chlorine's oxidation state: \(1 \cdot Cl = 7\) \(Cl = +7\) The oxidation state of chlorine in perchloric acid is +7.

(f) Xenon tetrafluoride

Xenon tetrafluoride is a compound consisting of one xenon atom and four fluorine atoms. Its chemical formula is \(XeF_4\). The oxidation state of fluorine in most of its compounds is -1. We can determine the oxidation state of xenon: \(1 \cdot Xe + 4 \cdot -1 = 0\) Solving for the xenon's oxidation state: \(1 \cdot Xe = 4\) \(Xe = +4\) The oxidation state of xenon in xenon tetrafluoride is +4.

Key concepts

Chemical Formulas

A chemical formula is a concise way of expressing information about the atoms that constitute a particular chemical compound. These formulas use symbols from the periodic table, numbers, and sometimes other symbols to indicate elements and their proportions in a compound.
For example, the compound sodium chloride contains one sodium (Na) and one chlorine (Cl) atom per formula unit, making its chemical formula NaCl.
When writing chemical formulas, it's essential to:

• Identify the elements involved.
• Determine the number of each type of atom in a compound.
• Consider the charges of ions, especially in ionic compounds, to ensure neutrality.

Formulas are not only important for naming compounds but also for understanding their stoichiometry and reactions they may undergo in chemical reactions.

Polyatomic Ions

Polyatomic ions are charged species, consisting of two or more atoms bonded together. Unlike monatomic ions, which are single atoms with a charge, polyatomic ions have multiple atoms. As a group, they can gain or lose electrons to achieve a stable electronic configuration.
These ions can be positive (cations) or negative (anions), with most being anions. Examples include the sulfate ion \( (SO_4^{2-}) \), phosphate ion \( (PO_4^{3-}) \), and the chlorate ion \( (ClO_3^-) \).
Polyatomic ions form the fundamental building blocks of many ionic compounds, where they often pair up with counter ions to balance charges.
When dealing with polyatomic ions:

• Always consider the entire group's charge.
• Learn common names and formulas as they occur frequently in chemical reactions.
• Ensure charge balance when they are part of a larger compound.

Mastery of polyatomic ions greatly aids in understanding and predicting the formation and reactivity of compounds.

Binary Acids

Binary acids are simple acids that consist of two elements: hydrogen and a non-metal element. They form when hydrogen combines directly with halogens like fluorine, chlorine, bromine, and iodine. The general formula for binary acids is HX, where H is hydrogen and X is a halogen.
An example is hydroiodic acid, which has the formula HI. In aqueous solution, binary acids ionize to release hydrogen ions (H+) and the corresponding anion (X-).
Important points to remember about binary acids include:

• They are called binary because of the two-element composition.
• They are typically named using the prefix "hydro-", followed by the base name of the non-metal, and the suffix "-ic".
• They vary in strength; some are strong acids like hydrochloric acid (HCl), while others are weak.

Understanding binary acids is fundamental to grasping acid-base reactions and their role in different chemical processes.

Oxoacids

Oxoacids are acids that contain hydrogen, oxygen, and another element (often a non-metal). They are characterized by having at least one hydrogen atom bonded to an electronegative oxygen atom, which can be released as a proton (H+) in solution.
An example is perchloric acid (HClO_4), where the hydrogen atom is bonded to an oxygen in a molecular structure containing chlorine and multiple oxygens.
When studying oxoacids, keep these points in mind:

• They are named based on the central non-metal and the oxyanion they derive from.
• The strength of oxoacids generally increases with the number of oxygen atoms bonded to the central atom.
• They play crucial roles in various biological and chemical processes, such as in buffering and catalysis.

Understanding the properties and naming conventions of oxoacids is crucial for predicting their behavior in chemical reactions and their interactions with bases.