Question

Write a balanced chemical equation showing how each metal oxide reacts with HI. (a) \(\mathrm{MgO}\) (b) \(\mathrm{K}_{2} \mathrm{O}\) (c) \(\mathrm{Rb}_{2} \mathrm{O}\) (d) \(\mathrm{CaO}\)

Short answer

(a) \(\mathrm{MgO} + 2\mathrm{HI} \rightarrow \mathrm{MgI}_2 + \mathrm{H}_2\mathrm{O}\) (b) \(\mathrm{K}_2\mathrm{O} + 2\mathrm{HI} \rightarrow 2\mathrm{KI} + \mathrm{H}_2\mathrm{O}\) (c) \(\mathrm{Rb}_2\mathrm{O} + 2\mathrm{HI} \rightarrow 2\mathrm{RbI} + \mathrm{H}_2\mathrm{O}\) (d) \(\mathrm{CaO} + 2\mathrm{HI} \rightarrow \mathrm{CaI}_2 + \mathrm{H}_2\mathrm{O}\)

Step-by-step solution

Identify the Reactants

The given metal oxides are (a) \(\mathrm{MgO}\), (b) \(\mathrm{K}_2\mathrm{O}\), (c) \(\mathrm{Rb}_2\mathrm{O}\), (d) \(\mathrm{CaO}\) and they all react with hydrogen iodide (HI).

Write the Unbalanced Equations

Write down the initial, unbalanced reaction for each metal oxide with HI: (a) \(\mathrm{MgO} + \mathrm{HI} \rightarrow \) (b) \(\mathrm{K}_2\mathrm{O} + \mathrm{HI} \rightarrow \) (c) \(\mathrm{Rb}_2\mathrm{O} + \mathrm{HI} \rightarrow \) (d) \(\mathrm{CaO} + \mathrm{HI} \rightarrow \)

Determine the Products

The products of each reaction are water (\(H_2O\)) and the corresponding metal iodide: (a) \(\mathrm{MgI}_2\) (b) \(\mathrm{KI}\) (c) \(\mathrm{RbI}\) (d) \(\mathrm{CaI}_2\)

Balance the Equations

Balance the chemical equations by adjusting coefficients to get the same number of each type of atom on both sides of the equation: (a) \(\mathrm{MgO} + 2\mathrm{HI} \rightarrow \mathrm{MgI}_2 + \mathrm{H}_2\mathrm{O}\) (b) \(\mathrm{K}_2\mathrm{O} + 2\mathrm{HI} \rightarrow 2\mathrm{KI} + \mathrm{H}_2\mathrm{O}\) (c) \(\mathrm{Rb}_2\mathrm{O} + 2\mathrm{HI} \rightarrow 2\mathrm{RbI} + \mathrm{H}_2\mathrm{O}\) (d) \(\mathrm{CaO} + 2\mathrm{HI} \rightarrow \mathrm{CaI}_2 + \mathrm{H}_2\mathrm{O}\)

Key concepts

Chemical Reactions

Chemical reactions are processes where substances, known as reactants, transform into different substances called products. This change occurs through the breaking and forming of chemical bonds.
For example, when metal oxides react with hydrogen iodide (HI), a chemical reaction takes place, resulting in the formation of a metal iodide and water. Here's the key: in a chemical reaction, the total mass of the reactants equals the total mass of the products, due to the conservation of mass. To portray this correctly, we must balance the equations, which is a crucial aspect of chemistry.

Stoichiometry

Stoichiometry is essentially the 'accounting' of chemistry. It involves quantitatively analyzing the relationships between the reactants and products in a chemical reaction.
In the provided exercise, stoichiometry is used to balance the chemical equations by ensuring that there are equal numbers of atoms for each element on both sides of the equation. This is done by adjusting coefficients—the numbers placed before compounds—to reflect the quantity of molecules involved in the reaction.

• For instance, if two hydrogen iodide (HI) molecules are needed to react completely with one metal oxide molecule, then the coefficient of HI will be '2' in the balanced equation.

Metal Oxides

Metal oxides are compounds composed of metal atoms and oxygen. They are typically basic (alkaline), and they react with acids to form salts and water—a type of reaction called a neutralization reaction.
In our exercise, the metal oxides react with hydrogen iodide, an acid, to produce metal iodides and water. The challenge here is that different metal oxides might require different amounts of hydrogen iodide to balance the equation, since the metal atoms can have varying valences.

Hydrogen Iodide

Hydrogen iodide (HI) is a diatomic molecule consisting of hydrogen and iodine. As an acid, it readily donates a proton (hydrogen ion) in reactions with bases, such as metal oxides.
In the reactions from our exercise, HI behaves as an acid and reacts stoichiometrically with the metal oxides to yield water and metal iodides. Because HI is a reactant in our exercise, understanding its behavior is integral to correctly balancing the chemical equations and grasping the stoichiometry of the reactions.