Problem 54 - Chemistry Matter and Change

Question

Copper sulfide is formed when copper and sulfur are heated together. In this reaction, 127 \(\mathrm{g}\) of copper reacts with 41 \(\mathrm{g}\) of sulfur. After the reaction is complete, 9 \(\mathrm{g}\) of sulfur remains unreacted. What is the mass of copper sulfide formed?

Step-by-Step Solution

Answer

The mass of copper sulfide formed is 159 g.

Step 1: Identify the total mass of the reactants

We start by adding the mass of copper and sulfur that are initially present. Copper has a mass of 127 g and sulfur has a mass of 41 g. Thus, the total initial mass of reactants is 127 g + 41 g = 168 g.

Step 2: Determine the mass of leftover sulfur

After the reaction, it is given that 9 g of sulfur remains unreacted. This means that not all of the sulfur was used to form copper sulfide.

Step 3: Calculate the mass of sulfur that reacted

To find the mass of sulfur that reacted, subtract the mass of leftover sulfur from the total initial mass of sulfur. Thus, 41 g - 9 g = 32 g of sulfur reacted with copper.

Step 4: Add the masses of the reacted substances

The mass of the substances that reacted to form copper sulfide is the mass of the copper plus the mass of the reacted sulfur. So, we add 127 g of copper and 32 g of sulfur, which gives 159 g.

Step 5: Conclude the mass of copper sulfide formed

Since no other products are formed and this is a closed system, by the conservation of mass, the total mass of the copper sulfide must be equal to the total mass of copper and sulfur that reacted. Therefore, the mass of copper sulfide formed is 159 g.

Key Concepts

Understanding Stoichiometry

Stoichiometry is a fundamental concept in chemistry that deals with the quantitative relationships between the reactants and products in a chemical reaction. It allows us to predict how much product will form from a given amount of reactant or how much reactant is needed to fully use up another reactant.

In the case of copper sulfide formation, stoichiometry helps us understand how much sulfur reacts with a given mass of copper to form copper sulfide.

• Step 1: Calculate the molar masses of the substances involved.
• Step 2: Using the masses from the exercise, determine the mole ratios of copper and sulfur.
• Step 3: Apply the mole ratios to find how much of each substance reacts.

By knowing these ratios, we can determine the mass of the products formed, which in this exercise, guided us in calculating the mass of copper sulfide produced.

The Law of Conservation of Mass

The law of conservation of mass states that in a closed system, the total mass of the reactants will be equal to the total mass of the products. This principle is a cornerstone in understanding chemical equations. It implies that matter cannot be created or destroyed in a chemical reaction.

In the given problem, we see this law applied. Initially, copper and sulfur together weigh 168 g. After the reaction, sulfur and copper form copper sulfide, and the mass must remain the same unless some mass escapes the system, which is not the case here.

• Before the reaction: Copper + Sulfur = 168 g
• After the reaction: Copper sulfide + Unreacted sulfur = 168 g

By applying this law, when 9 g of sulfur remains unreacted, we could calculate the mass of copper sulfide formed by subtracting the unreacted mass from the total.

Formation of Copper Sulfide

Copper sulfide is a compound formed when copper and sulfur chemically combine in a reaction. It exemplifies the formation of a binary compound, meaning it is composed of two different elements.

When copper, a metal, reacts with sulfur, a non-metal, they form a compound usually **CuS** or **Cu2S**, depending on the particular stoichiometry.

• Copper sulfide can appear in different forms and is used in applications like defense materials, batteries, and semiconductors.
• In this reaction, 127 g of copper reacts with 32 g of the available sulfur to form 159 g of copper sulfide.

This chemical reaction process illustrates the transformation from reactants (copper and sulfur) to a new resultant product (copper sulfide), emphasizing the interactions at the atomic level during compound formation.