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同类题1

像科学家一样“做科学”——探秘氢氧化钠
实验室有一瓶长期暴露在空气中的氢氧化钠固体样品,观察发现,样品表面出现了大量的白色粉末.某兴趣小组的同学对该样品进行了探究.请回答下列问题:
(1)实验证明,这份氢氧化钠已经变质,但不能确定是否完全变质.请你从下列药品中选择合适的试剂,探究氢氧化钠是否完全变质.
药品:蒸馏水、酚酞试液、稀盐酸、氯化钙溶液.
你的实验方案是
                                                                                                                                                                                                                                         .
用化学方程式表示该实验中所依据的化学反应原理:                         .
(2)如果给你一份未知浓度的稀硫酸,要求通过定量实验,测定氢氧化钠变质的程度(即样品中氢氧化钠的含量),请你给出具体的实验方案.
实验方案
反应的化学方程式
 
 
 
(3)实验证明,氢氧化钠部分变质,请你设计一个提纯该样品的实验方案,以得到纯净的氢氧化钠固体.
提纯样品应采用的试剂是                                           .
实验方案
反应的化学方程式
 
 
 

同类题5

根据短文内容,从短文后的选项中选出能填入空白处的最佳选项。选项中有两项为多余选项。

    When a New Yorker was hiking in Europe, his Swiss friend kept saying “Listen to that!” but he didn't hear anything. His ears were accustomed to loud city noises and it was days before he was able to notice the sound of a bird. ____. There is background music in restaurants, bars, stores, rest rooms, elevators, and when you are waiting on the telephone. Russell Baker blames “society's determination to entertain you whether you like it or not”.

    ____, but in practice they avoid it. They drive with the car radio turned up, switch on the television when they get home, and exercise while listening to music on headphones. ____ They can buy things in stores, but they do not have enough human contact. So they fill their lives with sound.

    ____. Young men play their car stereos loudly in order to create a personal environment around them. Like animals, they are marking a territory to warn rivals away and to attract a mate.

    It may also be true that the brain itself wants excitement just as the stomach insists on food. ____ This seems extreme. Perhaps we would be better off if we sought periods of silence to provide balance.

A. Sometimes the reason for the noise is primitive

B. The noise suggests that people have a spiritual problem

C. They spend too much time in elevators and the like

D. Unlike in the past, we now have modern technology to supply a constant flood of sounds

E. For most of us, silence has become a rare experience

F. A good response would be to use our brains to improve modern technology

G. People may say they yearn for quiet