Problem 120 - Chemistry The Molecular Science

Question

If 1.5 mol Cu reacts with a solution containing 4.0 mol \(\mathrm{AgNO}_{3},\) what ions will be present in the solution at the end of the reaction? $$\mathrm{Cu}(\mathrm{s})+2 \mathrm{AgNO}_{3}(\mathrm{aq}) \longrightarrow \mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{aq})+2 \mathrm{Ag}(\mathrm{s})$$

Step-by-Step Solution

Answer

The solution contains \(\mathrm{Cu^{2+}}\), \(\mathrm{NO_3^-}\), and \(\mathrm{Ag^+}\) ions.

Step 1: Identify the Limiting Reactant

First, we need to identify the limiting reactant. The balanced chemical equation is \[ \mathrm{Cu} + 2 \mathrm{AgNO}_{3} \to \mathrm{Cu}(\mathrm{NO}_{3})_{2} + 2 \mathrm{Ag} \].For every 1 mol of \(\mathrm{Cu}\), 2 mol of \(\mathrm{AgNO}_{3}\) is required. We have 1.5 mol of \(\mathrm{Cu}\) and 4.0 mol of \(\mathrm{AgNO}_{3}\). Calculating the moles of \(\mathrm{AgNO}_{3}\) required: \(1.5 \times 2 = 3.0\) mol. Since 4.0 mol of \(\mathrm{AgNO}_{3}\) is present, \(\mathrm{Cu}\) is the limiting reactant.

Step 2: Calculate Remaining Reactants

Since \(\mathrm{Cu}\) is the limiting reactant, it will be completely consumed.Calculate the remaining \(\mathrm{AgNO}_{3}\):- Initial moles of \(\mathrm{AgNO}_{3}\) = 4.0 mol- Used moles of \(\mathrm{AgNO}_{3}\) = 3.0 mol- Remaining \(\mathrm{AgNO}_{3}\) = 4.0 - 3.0 = 1.0 mol

Step 3: Identify Ions in Solution

After completing the reaction, the solution will contain ions from the products and any unreacted substances.- \(\mathrm{Cu(\text{NO}_3)_2}\) dissolves to form \(\mathrm{Cu^{2+}}\) and \(\mathrm{NO_3^-}\) ions.- 1.0 mol of unreacted \(\mathrm{AgNO}_3\) will dissolve to give \(\mathrm{Ag^+}\) and \(\mathrm{NO_3^-}\) ions.Thus, the solution contains \(\mathrm{Cu^{2+}}\), \(\mathrm{NO_3^-}\), and \(\mathrm{Ag^+}\) ions.

Key Concepts

Balanced Chemical Equation

In chemical reactions, a balanced chemical equation is crucial as it signifies the conversation of mass, ensuring that the number of atoms for each element is the same on both sides of the equation. For instance, in the equation \( \mathrm{Cu} + 2 \mathrm{AgNO}_{3} \to \mathrm{Cu(NO}_{3})_{2} + 2 \mathrm{Ag} \), the numbers in front of the molecules and compounds are coefficients that balance the equation. They indicate how many molecules or moles of each substance participate in the reaction. This balance is essential to calculate how much product will form and what quantities of reactants are required. The equation shows that 1 mole of copper reacts with 2 moles of silver nitrate to produce copper(II) nitrate and silver. This balance helps us predict that for every 1.5 moles of copper, we would need 3 moles of silver nitrate for a complete reaction.

Reaction Stoichiometry

Stoichiometry involves the calculation and measurement of reactants and products in chemical reactions. It uses the relationships defined by a balanced chemical equation.

• For instance, in the reaction \( \mathrm{Cu} + 2 \mathrm{AgNO}_3 \to \mathrm{Cu(NO}_3)_2 + 2 \mathrm{Ag} \), the stoichiometric coefficients play a crucial role.
• If we begin with 1.5 moles of Cu, using stoichiometry, we calculate that 3 moles of AgNO\(_3\) are needed since each mole of Cu requires 2 moles of AgNO\(_3\) to react fully.
• This calculation allows us to determine the limiting reactant, which is the reactant that will be entirely used up, limiting the extent of the reaction.

In our problem, since only 3.0 moles of AgNO\(_3\) are required and we have 4.0 moles available, copper (1.5 moles) becomes the limiting reactant. Stoichiometry helps us make these determinations and predict the amounts of products and excess reactants after the reaction.

Ions in Solution

When ionic compounds dissolve in water, they dissociate into their respective ions. After the completion of the reaction \( \mathrm{Cu} + 2 \mathrm{AgNO}_3 \to \mathrm{Cu(NO}_3)_2 + 2 \mathrm{Ag} \), the solution contains a mixture of ions.

• The compound \( \mathrm{Cu(NO}_3)_2 \) dissociates to form copper ions \( \mathrm{Cu^{2+}} \) and nitrate ions \( \mathrm{NO}_3^- \).
• The unreacted silver nitrate \( \mathrm{AgNO}_3 \) also dissociates into silver ions \( \mathrm{Ag^+} \) and nitrate ions \( \mathrm{NO}_3^- \).

Thus, the resulting solution consists of \( \mathrm{Cu^{2+}} \), \( \mathrm{NO}_3^- \), and \( \mathrm{Ag^+} \) ions. Recognizing these ions helps in understanding the chemical dynamics within the solution, including reactions that will or will not proceed further. The presence of \( \mathrm{NO}_3^- \) ions from both substances reflects the need to consider all possible sources of ions when predicting the ionic content of the reaction mixture.