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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.

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), AgC鈧侶鈧僌鈧� and SrI鈧� react to form AgI and Sr(C鈧侶鈧僌鈧�)鈧�. Ag鈦� swaps with Sr虏鈦�, and I鈦� with C鈧侶鈧僌鈧傗伝. 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.

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 FeSO鈧� and Ca(OH)鈧� are in aqueous form, denoting they are dissolved in water, enabling the ions to rearrange to form Fe(OH)鈧� and CaSO鈧�. Understanding aqueous solutions is key to predicting and explaining the outcomes of many chemical processes.