Question

Write the chemical formula for each of the following compounds, and indicate the oxidation state of the group 6 A element in each: (a) selenous acid, (b) potassium hydrogen sulfite, (c) hydrogen telluride, (d) carbon disulfide, (e) calcium sulfate.

Short answer

The chemical formulas and oxidation states of the group 6 A elements for the given compounds are: (a) selenous acid - H2SeO3, Se is +4; (b) potassium hydrogen sulfite - KHSO3, S is +4; (c) hydrogen telluride - H2Te, Te is -2; (d) carbon disulfide - CS2, S is -2; (e) calcium sulfate - CaSO4, S is +6.

Step-by-step solution

(a) Selenous Acid

Selenous acid is an oxoacid containing selenium, hydrogen, and oxygen. Its chemical formula is H2SeO3. The oxidation state of selenium (Se) in this compound can be determined as follows: Let the oxidation state of Se be x. We know that: x + 2(+1) + 3(-2) = 0 x = +4 So, the oxidation state of Se in selenous acid is +4.

(b) Potassium Hydrogen Sulfite

Potassium hydrogen sulfite is a salt containing potassium (K), hydrogen (H) and sulfite ions (SO3^2-). Its chemical formula is KHSO3. The oxidation state of sulfur (S) in the sulfite ion can be determined as follows: Let the oxidation state of S be x. We know that: x + 3(-2) = -2 x = +4 So, the oxidation state of S in potassium hydrogen sulfite is +4.

(c) Hydrogen Telluride

Hydrogen telluride is a covalent compound containing hydrogen (H) and tellurium (Te). Its chemical formula is H2Te. In this compound, Te has an oxidation state equal to the charge found on its accompanying H atoms. As hydrogen carries an oxidation state of +1, the oxidation state of Te in hydrogen telluride is -2.

(d) Carbon Disulfide

Carbon disulfide is a covalent compound containing carbon (C) and sulfur (S). Its chemical formula is CS2. The oxidation state of sulfur (S) in this compound can be determined as follows: Let the oxidation state of S be x. We know that: +4 + 2(x) = 0 x = -2 So, the oxidation state of S in carbon disulfide is -2.

(e) Calcium Sulfate

Calcium sulfate is a salt containing calcium (Ca) and sulfate ions (SO4^2-). Its chemical formula is CaSO4. The oxidation state of sulfur (S) in the sulfate ion can be determined as follows: Let the oxidation state of S be x. We know that: x + 4(-2) = -2 x = +6 So, the oxidation state of S in calcium sulfate is +6.

Key concepts

Oxidation State Determination

Oxidation states, sometimes known as oxidation numbers, are essential in understanding the electron exchange in chemical reactions. They provide insights into how elements interact in compounds. The oxidation state of an element in a compound is determined based on certain rules. For example, the sum of the oxidation states in a neutral compound is zero. For polyatomic ions, the sum equals the charge of the ion.

Determining the oxidation state involves :-

• Assigning oxidation states to known elements, such as hydrogen (+1) and oxygen (-2) in most cases.
• Using algebra to solve for the unknown oxidation state.

In selenous acid (H₂SeO₃), we assign +1 for hydrogen and -2 for oxygen, leading to selenium having an oxidation state of +4. Similarly, in other compounds like potassium hydrogen sulfite (KHSO₃) and calcium sulfate (CaSO₄), using similar methods reveals the oxidation state of sulfur to be +4 and +6, respectively.

Oxoacids

Oxoacids are acids that contain oxygen, hydrogen, and another element, often forming an anion with higher electronegativity than oxygen. This category includes compounds like selenous acid (H₂SeO₃). In oxoacids:

• Hydrogen is typically bonded to oxygen, which is bonded to the central atom (in this case, selenium).
• Oxygen usually has an oxidation state of -2.

In these acids, the central atom's oxidation state is essential to the compound's reactivity. For selenous acid, the calculation shows the oxidation state of selenium to be +4. Understanding such acids is crucial as they play significant roles in organic chemistry and environmental processes.

Covalent Compounds

Covalent compounds form when two or more nonmetals share electrons. In these cases, atoms hold onto their electrons more tightly and share them between bonded atoms, leading to lower electronegativity differences. Hydrogen telluride (H₂Te) and carbon disulfide (CS₂) are examples of covalent compounds.

Characteristics of covalent compounds include:

• Sharing of electrons between atoms.
• Formulas that often reflect the ratio of atoms in the simplest whole number terms.

In hydrogen telluride for instance, tellurium pairs with hydrogen, exhibiting an oxidation state of -2, which differs from its usual elemental state. Understanding covalent bonds is fundamental as it affects everything from molecular stability to the boiling and melting points of substances.

Ionic Compounds

Ionic compounds arise from the transfer of electrons between metals and nonmetals, resulting in a structure composed of positive and negative ions held by electrostatic forces. They typically form solid structures known as crystal lattices. For example, calcium sulfate (CaSO₄) exemplifies an ionic compound.

Key attributes of ionic compounds include:

• Formed via electron transfer, creating cations and anions.
• Usually have high melting and boiling points.
• Conduct electricity when dissolved in water, due to ion dissociation.

Analyzing ionic compounds like CaSO₄ involves determining the oxidation state of sulfur and identifying the way calcium ions bond with the sulfate anion, showcasing the compound's stability and its role in industrial applications.