题干

下列有关实验的描述或操作错误的是(  )


A:提取海带中碘元素,为保证I完全氧化为I2,加入的氧化剂(H2O2或新制氯水)均应过量

B:纸上层析法通常以滤纸作为惰性支持物。滤纸纤维上的羟基具有亲水性,它所吸附的水作为固定相

C:制备硫酸亚铁铵晶体时,最后在蒸发皿中蒸发浓缩溶液时,只需小火加热至溶液表面出现晶膜为止,不能将溶液全部蒸干

D:减压过滤不宜用于过滤胶状沉淀或颗粒太小的沉淀

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答案(点此获取答案解析)

D

同类题4

    When I was young, my father had one of the first telephones in our neighborhood. I remember the shiny box on the wall. But I was too little to reach it. I could only listen to my mother talk on it.

    I discovered that inside the-wonderful box lived an amazing person whose name was Information Please. There was nothing she did not know.

    One day my mother went out. I accidentally hurt my finger when I was playing with a hammer. I walked around the house sucking my finger, finally seeing the telephone. Quickly I dragged a chair over and climbed up.

    “Information Please, ”I spoke into the receiver. A click or two and a small clear voice spoke into my ear. “Information.”

    “I hurt my finger…”I cried into the phone.

    “Isn't your mother home?” came the question.

    “Nobody's home but me.” I sobbed.

    “Are you bleeding?” the voice asked.

    “No,” I replied, “I hit my finger with the hammer and it hurts.”

    “Can you open your icebox?” she asked. I said I could.

    “Then take a little piece of ice and hold it to your finger.” said the voice.

    After that, I called “Information Please” for everything. I asked her for help with my geography and she told me where Philadelphia was. She helped me with my math. She told me her name was Sally.

    Then, there was the time my pet canary(金丝雀)died. I called “Information Please” and told Sally the sad story. “Why is it that birds sing so beautifully and bring joy to all families, only to end up as a pile of feathers?” She listened, then said quietly, “Paul, always remember that there are other worlds to sing in.” Somehow, I felt better.

    One day when I called “Information Please” again, a different voice answered “Information.”

    I asked for Sally. “Are you a friend?” she said.

    “Yes,” I answered.

    “I'm sorry to have to tell you this,” she said. “She died five days ago.” Before I could hang up she said, “Wait a minute. Did you say your name was Paul?”

    “Yes.”

    “Well, Sally left a message for you. The note said, ‘Tell him I still say there are other worlds to sing in. He'll know what I mean.'” I thanked her and hung up. I knew what Sally meant.