The scientist used the law of conservation of mass, which states that matter cannot be created or destroyed in a chemical reaction. Since all the reactants (12.7 grams of Cu and 3.2 grams of S) are expected to fully react, the total mass of the products (copper sulfide, Cu2S) should equal the total mass of the reactants, resulting in a predicted total of 15.9 grams (12.7 g + 3.2 g).
2Cu + S → Cu2S
Copper (Cu) reacts with sulfur (S) to form copper sulfide as shown in the equation. A scientist adds 12.7 grams of Cu to 3.2 grams of S to start the reaction.
In this reaction, all of the copper and all of the sulfur react. Before running the experiment, the scientist expected the products of the reaction will be a total of 15.9 grams of copper sulfide (Cu2S). In 1-2 sentences, explain the law that the scientist used to predict that the product of the reaction would be 15.9 grams of copper sulfide.
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The scientist applied the law of conservation of mass, which asserts that the total mass of reactants must equal the total mass of products in a chemical reaction. By calculating the combined mass of the reactants (12.7 grams of Cu and 3.2 grams of S), the scientist predicted that the products would total 15.9 grams of copper sulfide (Cu2S), as all material is conservatively accounted for in the reaction.