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Ch.3 - Mass Relationships in Chemical Reactions
Chapter 3, Problem 117a

A copper wire having a mass of 2.196 g was allowed to react with an excess of sulfur. The excess sulfur was then burned, yielding SO2 gas. The mass of the copper sulfide produced was 2.748 g. (a) What is the percent composition of copper sulfide?

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Determine the mass of sulfur that reacted by subtracting the mass of copper from the mass of copper sulfide: \( \text{mass of sulfur} = \text{mass of copper sulfide} - \text{mass of copper} \).
Calculate the percent composition of copper in the copper sulfide by dividing the mass of copper by the mass of copper sulfide and multiplying by 100: \( \%\text{Cu} = \left( \frac{\text{mass of copper}}{\text{mass of copper sulfide}} \right) \times 100 \).
Calculate the percent composition of sulfur in the copper sulfide by dividing the mass of sulfur by the mass of copper sulfide and multiplying by 100: \( \%\text{S} = \left( \frac{\text{mass of sulfur}}{\text{mass of copper sulfide}} \right) \times 100 \).
Verify that the sum of the percent compositions of copper and sulfur equals 100% to ensure the calculations are correct.
Summarize the percent composition of copper sulfide, listing the percent of copper and the percent of sulfur.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Percent Composition

Percent composition refers to the percentage by mass of each element in a compound. It is calculated by dividing the mass of the element in the compound by the total mass of the compound and then multiplying by 100. This concept is essential for determining the contribution of each element to the overall mass of a compound, which is crucial for solving the given problem.
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Stoichiometry

Stoichiometry is the branch of chemistry that deals with the quantitative relationships between the reactants and products in a chemical reaction. It allows chemists to predict the amounts of substances consumed and produced in a reaction based on balanced chemical equations. Understanding stoichiometry is vital for calculating the mass of copper sulfide produced from the reaction of copper and sulfur.
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Chemical Reaction and Products

A chemical reaction involves the transformation of reactants into products, often accompanied by a change in mass. In this case, copper reacts with sulfur to form copper sulfide (CuS). Recognizing the nature of the reaction and the products formed is crucial for determining the mass changes and calculating the percent composition of the resulting compound.
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