Problem 57 - Chemistry: Principles and Reactions

Question

Write balanced equations for the reaction of sulfur with the following metals to form solids that you can take to be ionic when the anion is \(\mathrm{S}^{2-}\). (a) potassium (b) magnesium (c) aluminum (d) calcium (e) iron (forming \(\mathrm{Fe}^{2+}\) ions)

Step-by-Step Solution

Answer

Question: Write balanced equations for the reaction of sulfur with the following metals, given that the anion in each case is S^(2-): (a) potassium, (b) magnesium, (c) aluminum, (d) calcium, (e) iron (forming Fe^2+ ions). Answer: (a) 2K + S → K₂S (b) Mg + S → MgS (c) 2Al + 3S → Al₂S₃ (d) Ca + S → CaS (e) Fe + S → FeS

Step 1: Identify the metal cations and their charges

First, we'll list the metals and their corresponding cations when reacting with sulfur: (a) potassium: K^+ (b) magnesium: Mg^2+ (c) aluminum: Al^3+ (d) calcium: Ca^2+ (e) iron (forming Fe^2+ ions): Fe^2+

Step 2: Balance the electrons to form ionic compounds

Now we'll balance the electrons for each reaction, ensuring that the net charge is zero. (a) potassium: K^+ + S^(2-) → K₂S (b) magnesium: Mg^2+ + S^(2-) → MgS (c) aluminum: 2Al^3+ + 3S^(2-) → Al₂S₃ (d) calcium: Ca^2+ + S^(2-) → CaS (e) iron (forming Fe^2+ ions): Fe^2+ + S^(2-) → FeS

Step 3: Write the balanced equations for each reaction

Finally, we'll write the balanced equations for the reaction of sulfur with each metal. (a) 2K + S → K₂S (b) Mg + S → MgS (c) 2Al + 3S → Al₂S₃ (d) Ca + S → CaS (e) Fe + S → FeS

Key Concepts

Ionic Compounds

In the world of chemistry, ionic compounds are substances composed of ions held together by electrostatic forces termed ionic bonding. An ion is an atom or molecule that has a net electrical charge because it has lost or gained one or more electrons. Ionic compounds typically form when metals react with nonmetals, with metals donating electrons to become positively charged cations, while nonmetals gain electrons to become negatively charged anions.

Understanding the formation of ionic compounds is crucial when balancing chemical equations, as seen in the provided textbook exercise. For instance, the reaction between a metal such as potassium (K) and sulfur (S) forms potassium sulfide (K₂S), an ionic compound where the potassium ion (K⁺) and sulfide ion (S²⁻) combine in a 2:1 ratio to ensure electrical neutrality.

These solid compounds are crystalline in nature, typically have high melting and boiling points, and conduct electricity when dissolved in water or melted, due to the movement of the free ions. Knowing the charge on the ions is essential for writing the correct formula for the compound and then for balancing the equation.

Chemical Reactivity of Metals

The chemical reactivity of metals plays a pivotal role in the reactions they undergo, including their ability to form compounds with nonmetals, like sulfur in the textbook exercise. Metals are positioned on the periodic table and can be ordered by their reactivity in a series known as the reactivity series or activity series.

Metals like potassium (K) and aluminum (Al) may willingly lose electrons to form cations, which combine with anions to create ionic compounds. Their reactivity is grounded in their electron configuration and the ease with which they can shed electrons to achieve a more stable electronic arrangement. This gives insight into the predicting reactions outcomes.

Factors Influencing Reactivity:

• Electron Configuration: Metals with fewer valence electrons lose them more readily, making them more reactive.
• Atomic Size: Larger atoms tend to lose electrons more easily because the outer electrons are further from the nucleus and less tightly held.
• Shielding Effect: Electrons in inner shells can shield outer electrons from the nucleus' pull, making them easier to lose.

When writing balanced chemical equations, understanding the reactivity of the metals involved is important as it dictates the product formed and the ratio of reactants required for a balanced equation.

Formation of Sulfides

Sulfides are compounds that contain the sulfide ion S²⁻, a combination of sulfur with a valence of -2. They are typically formed when sulfur reacts with metals, often resulting in the formation of solid ionic compounds, as showcased in the exercise where metals like magnesium (Mg) and calcium (Ca) react with sulfur to produce sulfides (MgS and CaS, respectively).

The sulfide ion is chemically characteristic due to its high charge and small size, which means it forms strong ionic bonds with metal ions, resulting in compounds with high lattice energies and considerable stability. These compounds often possess distinct properties such as high melting points and electrical conductivity in their molten state or when dissolved in water.

Applications of Sulfides:

• Ore Processing: Metal sulfides are often the primary source of metals in mining.
• Industrial Uses: Sulfides are used in the production of pigments and other chemicals.
• Electronics: Some metal sulfides have semiconducting properties.

When forming sulfides, the reactivity and oxidation state of the metal are key to determining the stoichiometry of the resultant sulfide, which is vital for correctly balancing the chemical equation.