Problem 135 - Chemistry and Chemical Reactivity

Question

Two beakers sit on a balance; the total mass is \(167.170 \mathrm{g} .\) One beaker contains a solution of \(\mathrm{KI}\) the other contains a solution of \(\mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2} .\) When the solution in one beaker is poured completely into the other, the following reaction occurs: $$2 \mathrm{KI}(\mathrm{aq})+\mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{aq}) \rightarrow 2 \mathrm{KNO}_{3}(\mathrm{aq})+\mathrm{PbI}_{2}(\mathrm{s})$$ What is the total mass of the beakers and solutions after reaction? Explain completely.

Step-by-Step Solution

Answer

The total mass remains 167.170 g after the reaction.

Step 1: Understanding the Problem

We need to determine the total mass of the beaker system before and after the chemical reaction occurs. According to the problem, two solutions are poured together, and a reaction takes place.

Step 2: Recognizing Conservation of Mass

In any chemical reaction, according to the law of conservation of mass, the mass of the reactants equals the mass of the products. No mass is lost in the reaction.

Step 3: Identifying Initial Mass

We are given that the total mass of the two beakers and their solutions before any chemical reaction takes place is 167.170 g.

Step 4: Applying the Law of Conservation of Mass

Since the law of conservation of mass dictates that mass is neither created nor destroyed, the total mass of the system after the reaction must also be 167.170 g.

Step 5: Conclusion

The reaction between the solutions in the beakers does not alter the total mass of the system. Although different substances may form, the total mass remains constant due to conservation of mass.

Key Concepts

Chemical Reactions

Chemical reactions are fascinating processes where substances, known as reactants, transform into new substances, called products.
During these reactions, the atoms in the reactants rearrange themselves to form new chemical bonds, resulting in products with different properties.
For instance, in the given chemical reaction: - Two molecules of potassium iodide - Combine with one molecule of lead(II) nitrate - To form two new molecules of potassium nitrate and a molecule of lead iodide. This process highlights how new substances can be created while adhering to specific stoichiometric proportions. The balanced chemical equation is crucial as it ensures that the number of each type of atom is the same on both sides of the reaction.
Thus, chemical reactions are essential for transforming matter and are fundamental to chemistry and various scientific applications.

Law of Conservation of Mass

The Law of Conservation of Mass is a critical principle in chemistry, stating that mass cannot be created or destroyed in a chemical reaction.
This means that the mass of the reactants always equals the mass of the products. In our exercise, the reaction involves combining solutions of potassium iodide and lead nitrate, which results in the formation of potassium nitrate and solid lead iodide.
Despite these changes in state and composition, the total mass remains constant. To better grasp this, consider the initial mass of the beaker system, which is given as 167.170 g.
After the reaction, even though solid lead iodide has formed, the total mass of the system remains 167.170 g.
Thanks to the Law of Conservation of Mass, we can confidently state that no mass is lost during the process. This principle helps ensure that calculations in chemistry are accurate and reliable, especially when predicting the outcomes of reactions.

Stoichiometry

Stoichiometry is a branch of chemistry that deals with the quantitative relationships between the amounts of reactants and products in a chemical reaction.
It uses the balanced chemical equation to ensure that calculations and reactions are performed correctly. In the given exercise, stoichiometry is utilized to balance the chemical reaction: - The equation shows that 2 moles of KI react with 1 mole of Pb(NO extsubscript{3}) extsubscript{2} - To create 2 moles of KNO extsubscript{3} and 1 mole of PbI extsubscript{2}. Balancing equations is important because it allows chemists to predict the exact amounts of substances consumed and produced.
Understanding stoichiometry is essential for various applications, such as determining reactant quantities needed or predicting product yields. By applying stoichiometry, students can explore the precision and elegance of chemical reactions, opening up a world of scientific discovery.