25 POINTS FOR THIS Copper (Cu) reacts with sulfur (S) to form copper sulfide. A scientist adds 12.7 grams of Cu to 3.2 grams of S to start the reaction. At the end of the experiment, there are 15.9 grams of copper sulfide. In this reaction, all of the copper and all of the sulfur react. The scientist then tries to add 13.7 grams of Cu to 3.2 grams of S. There are still 15.9 grams of copper sulfide at the end, but some copper is also left over. In 1-2 sentences, explain how to calculate the amount of remaining copper. Use the law of conservation of mass in the explanation.