题干

根据我国现行的食品质量标准,0~6个月的婴儿奶粉中蛋白质的含量为12%~l8%.现有一种待测婴儿奶粉,请你尝试完成鉴定实验.

(一)实验目的:鉴定该待测婴儿奶粉蛋白质含量是否符合食品质量标准.

(二)实验原理:蛋白质与双缩脲试剂发生作用,产生紫色反应.

(三)材料用具:相同浓度的标准婴儿奶粉溶液和待测婴儿奶粉溶液,双缩脲试剂A液(质量浓度为0.1g/mL的NaOH溶液)、B液(质量浓度为0.01g/mL的CuSO4溶液),试管和滴管等.

(四)实验步骤:

①取两支试管编号甲、乙,向甲试管中加入2mL的标准婴儿奶粉溶液,向乙试管中加入2mL的____.标准婴儿奶粉在本实验中起____作用.

②分别向两支试管中加入2mL的____溶液,振荡、摇匀.

③再分别向两支试管中加入3~4滴____溶液,振荡、摇匀,比较颜色变化.

④在预测结果中,如果甲、乙两试管颜色基本一致说明____

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答案(点此获取答案解析)

\u5f85\u6d4b\u5a74\u513f\u5976\u7c89\u6eb6\u6db2,\u5bf9\u7167,A\uff08\u6216NaOH\uff09\uff08\u53cc\u7f29\u8132\u8bd5\u5242A\uff09,B\uff08\u6216CuSO4\uff09\uff08\u53cc\u7f29\u8132\u8bd5\u5242B\uff09,\u5f85\u6d4b\u5a74\u513f\u5976\u7c89

同类题3

完形填空

    I had just arrived in this Asian country for a one-year teaching position. One day, I took the subway to visit some ancient palaces and temples in the downtown. The following account of what happened to me has taught me much about culture 1.

    Since all the 2 were taken, I stood. Suddenly, I felt someone pulling on my bag. 3 I probably was in someone's way, I moved over slightly. But in one quick motion(动作), I felt my bag removed from my back, and in a flash it was 4. I turned around to see who the thief was. I looked at the people standing behind me, but didn't see my bag or any 5. My heart sank and I began to 6.

    I glanced around the car only to find directly across from me was an elderly lady, and sitting on her lap was my 7. I tried to get it back from her lap. But as I began to 8 it up, she quickly grabbed(抓住) it back and held onto it. I looked around at the people standing beside me, and those sitting beside her, but no one took any 9 of the situation. Trying not to cause a(an) 10, I tried to negotiate through gestures. I used my hands as best as I could, but she 11 my requests for my bag and pointed to my back. She picked up my bag, showing how 12 it was. I finally began to understand. She was holding my bag to13 me.

    At the next stop, a middle-aged woman got on the crowded subway. Another elderly woman sitting down took her bag, 14 it on her lap. They didn't talk; 15 this older woman was more than pleased to sit with this stranger's bag on her lap throughout her journey.

    As the subway pulled into the main downtown station and I was getting ready to get off, the woman 16 handed me back my bag. But 17 I had a chance to thank her, she had disappeared into the crowd.

    Sadly, this considerate custom was more 18 to me than if I had been robbed. Everyone back home had heard of being robbed—that was 19 city behavior—but having a stranger hold onto someone's bag out of 20, in a city of twelve million people—that was truly unusual.