题干

已知:草酸钙[CaC2O4]比碳酸钙受热易分解,CaC2O4
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CaCO3+CO↑.将12.8gCaC2O4固体加热一段时间后剩余5.6g固体.下列说法正确的是(   )

A:剩余固体为混合物

B:剩余固体中含有钙元素的质量为4.0g

C:将剩余固体溶于足量水中,其溶质质量为7.6g

D:将加热产生的气体全部通入足量澄清石灰水中,生成5.0g固体

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答案(点此获取答案解析)

B

同类题3

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    The old man walked with a cane (拐杖) slowly into the restaurant. His poor jacket, patched (打补丁的) trousers, and worn-out shoes made him stand out from the usual Saturday morning breakfast crowd. Unforgettable were his pale blue eyes that sparkled (闪光) like diamonds, large rosy cheeks, and thin lips that held a steady smile. He walked toward a table by the window. A young waitress watched him and ran over to him, saying, “Here, Sir. Let me give you a hand with that chair.” Without a word, he smiled and nodded a thank you. She pulled the chair away from the table. Supporting him with one arm, she helped him move in front of the chair, and get comfortably seated. Then she pushed the table up close to him, and leaned his cane against the table where he could reach it. In a soft, clear voice he said, “Thank you, Miss.” “You're welcome, Sir.” She replied. “My name is Mary. I'll be back in a moment. If you need anything, just wave at me.”

    After he had finished a hearty meal of pancakes, bacon, and hot lemon tea, Mary brought him the change, helping him up from his chair and out from behind the table. She handed him his cane, and walked with him to the front door. Holding the door open for him, she said, “Come back and see us, Sir!” He nodded a thank you and said softly with a smile, “You are very kind!”

    When Mary went to clean his table, she was shocked. Under his plate she found a business card and a note written on the napkin, under which was a $ 100 bill. The note on the napkin read, “Dear Mary, I respect you very much, and you respect yourself, too. It shows by the way you treat others. You have found the secret of happiness. Your kind gestures will shine through those who meet you.”

    The man she had served was the owner of the restaurant. This was the first time that she, or any of his employees, had seen him in person.