The scientist used the law of conservation of mass, which states that in a closed system, the total mass of the reactants before a chemical reaction is equal to the total mass of the products after the reaction. Since 12.7 grams of copper and 3.2 grams of sulfur are combined, the expected mass of the product, copper sulfide (Cu2S), is 12.7 grams + 3.2 grams = 15.9 grams.
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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