Complete the exercises below. Write a balanced equation for each of the following reactions. a. Hydrogen selenide can be prepared by the reaction of an aqueous acid solution on aluminum selenide. b. Sodium thiosulfate is used to remove excess Cl₂ from chlorine-bleached fabrics. The thiosulfate ion forms SO₄²⁻ and elemental sulfur, while Cl₂ is reduced to Cl⁻.

Balancing chemical equations is essential to ensure that the law of conservation of mass is upheld, meaning the number of atoms of each element must be the same on both sides of the equation. This involves adjusting coefficients in front of compounds to achieve equal numbers of each type of atom. For example, in the reaction of aluminum selenide with an acid, one must account for all reactants and products to write a balanced equation.

Acid-base reactions involve the transfer of protons (H⁺ ions) between reactants. In the context of the first reaction, an aqueous acid reacts with aluminum selenide, leading to the formation of hydrogen selenide. Understanding the properties of acids and bases, including their ability to donate or accept protons, is crucial for predicting the products of such reactions.

Redox (reduction-oxidation) reactions involve the transfer of electrons between species, resulting in changes in oxidation states. In the second reaction, sodium thiosulfate acts as a reducing agent, reducing chlorine gas (Cl₂) to chloride ions (Cl⁻) while itself being oxidized to sulfate ions (SO₄²⁻) and elemental sulfur. Recognizing the roles of oxidizing and reducing agents is vital for understanding the electron transfer processes in these reactions.