Question

Complete and balance each of the following doublereplacement reactions: (a) \(\mathrm{AgC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}(a q)+\operatorname{SrI}_{2}(a q) \rightarrow\) (b) \(\mathrm{FeSO}_{4}(a q)+\mathrm{Ca}(\mathrm{OH})_{2}(a q) \rightarrow\)

Short answer

(a) \(2\mathrm{AgC}_{2}\mathrm{H}_{3}\mathrm{O}_{2} + \mathrm{SrI}_{2} \rightarrow 2\mathrm{AgI} + \mathrm{Sr(C}_{2}\mathrm{H}_{3}\mathrm{O}_{2})_{2}\); (b) \(\mathrm{FeSO}_{4} + \mathrm{Ca(OH)}_{2} \rightarrow \mathrm{Fe(OH)}_{2} + \mathrm{CaSO}_{4}\).

Step-by-step solution

Identify the Products for Reaction (a)

To determine the products of the double replacement reaction between AgC₂H₃O₂(aq) and SrI₂(aq), swap the anions between the two cations: Ag⁺ will pair with I⁻ to form AgI, and Sr²⁺ will pair with C₂H₃O₂⁻ to form Sr(C₂H₃O₂)₂. The initial reaction is: \[\mathrm{AgC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}(aq) + \operatorname{SrI}_{2}(aq) \rightarrow \mathrm{AgI}(s) + \mathrm{Sr} (\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2})_{2}(aq)\]

Balance the Equation for Reaction (a)

Check if the reaction is balanced. Ensure the number of atoms for each element matches on both sides. Here's the balanced equation: \[\mathrm{2AgC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}(aq) + \operatorname{SrI}_{2}(aq) \rightarrow \mathrm{2AgI}(s) + \mathrm{Sr} (\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2})_{2}(aq)\]

Identify the Products for Reaction (b)

Similarly, swap the anions between FeSO₄(aq) and Ca(OH)₂(aq): Fe²⁺ pairs with OH⁻ to form Fe(OH)₂, and Ca²⁺ pairs with SO₄²⁻ to form CaSO₄. The initial reaction is: \[\mathrm{FeSO}_{4}(aq) + \mathrm{Ca(OH)}_{2}(aq) \rightarrow \mathrm{Fe(OH)}_{2}(s) + \mathrm{CaSO}_{4}(s)\]

Balance the Equation for Reaction (b)

Check and adjust coefficients to balance the chemical equation if needed. In this case, each side already has the same number of atoms for each element: \[\mathrm{FeSO}_{4}(aq) + \mathrm{Ca(OH)}_{2}(aq) \rightarrow \mathrm{Fe(OH)}_{2}(s) + \mathrm{CaSO}_{4}(s)\]

Conclusion: Summary of Balanced Equations

Reaction (a): \[\mathrm{2AgC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}(aq) + \operatorname{SrI}_{2}(aq) \rightarrow \mathrm{2AgI}(s) + \mathrm{Sr} (\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2})_{2}(aq)\]. Reaction (b): \[\mathrm{FeSO}_{4}(aq) + \mathrm{Ca(OH)}_{2}(aq) \rightarrow \mathrm{Fe(OH)}_{2}(s) + \mathrm{CaSO}_{4}(s)\].

Key concepts

Chemical Equation Balancing

Balancing chemical equations is a critical skill in chemistry. It ensures that the same number of each type of atom is present on both sides of the equation. This reflects the law of conservation of mass, which states that matter cannot be created or destroyed. To balance an equation, follow these steps:

• Identify each type of atom involved in the reaction.
• Count the number of atoms for each element on both the reactant and product sides.
• Adjust coefficients (the numbers in front of compounds) to balance the atoms. Do not change subscripts, as this alters the substance's identity.

Balancing involves some trial and error, but practice will make it easier. Let's look at Reaction (a) for example. The initial reaction is \[\mathrm{AgC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}(aq) + \operatorname{SrI}_{2}(aq) \rightarrow \mathrm{AgI}(s) + \mathrm{Sr} (\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2})_{2}(aq)\]To balance, adjust coefficients: \[\mathrm{2AgC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}(aq) + \operatorname{SrI}_{2}(aq) \rightarrow \mathrm{2AgI}(s) + \mathrm{Sr} (\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2})_{2}(aq)\] Now, we have equal numbers of each atom on both sides.

Anion-Cation Reactions

Double replacement reactions, also known as double displacement reactions, involve the exchange of anions and cations between two reacting ionic compounds. These reactions typically occur in aqueous solutions and result in the formation of new compounds, one of which is often a precipitate, a gas, or a weak or non-electrolyte. Here's how anion-cation reactions work:

• Anions (negatively charged ions) swap places with cations (positively charged ions) between the two compounds.
• The general form is: \(AB + CD \rightarrow AD + CB \)

In Reaction (a), AgC₂H₃O₂ and SrI₂ react to form AgI and Sr(C₂H₃O₂)₂. Ag⁺ swaps with Sr²⁺, and I⁻ with C₂H₃O₂⁻. Observing such swaps helps in predicting the products of the reaction accurately.
This kind of reaction is common in solution chemistry and often results in the formation of a precipitate, like AgI, which is not soluble in water.

Aqueous Solutions Chemistry

In chemistry, aqueous solutions play a significant role in many types of reactions, including double replacement reactions. An aqueous solution occurs when a substance is dissolved in water, indicated by the label (aq) in chemical equations. Let's explore some key points about aqueous solutions:

• Water serves as the solvent, dissolving the reactants into ions, which can move freely and react with one another.
• This environment facilitates the exchange of ions, crucial for reactions like double replacement where cations and anions swap partners.
• Aqueous reactions can result in different types of products, such as a precipitate, gas, or water.

In Reaction (b), both FeSO₄ and Ca(OH)₂ are in aqueous form, denoting they are dissolved in water, enabling the ions to rearrange to form Fe(OH)₂ and CaSO₄. Understanding aqueous solutions is key to predicting and explaining the outcomes of many chemical processes.