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问题 实验题

（6分）某学生设计了如下实验方法分离NaCl和CaCl2两种固体混合物。

（1）B溶液是           ，加入过量B溶液的原因是                                     ，

反应的离子方程式是                                   。

（2）经此实验方法分离得到的NaCl，经分析含有杂质，若要得到纯净的NaCl，还应补充实验操作，其反应的离子方程式是                                                                   。

答案

（6分）（1）Na2CO3（写化学式），原因是使Ca2+沉淀完全

反应的离子方程式是Ca2+ + CO32- = CaCO3↓   

（2）Ag + + Cl-  = AgCl↓

单项选择题

Imagine fishermen walking down to the seashore, ready to carry out their early morning routine of preparing their boats and net. (51) they hope for a good catch of fish. But to their (52) , a horrible sight meets their still sleepy eyes. Thousands of fish have been washed ashore dead. The cause of this mass destruction—A red tide!

Red tides are a global (53) . They have been observed on both the Atlantic and the Pacific coasts of the United States and Canada. They have also occurred in many other places. Though relatively few people are (54) them, red tides are not new.

In the Philippines, a red tide was first seen in the province of Bataan in 1908. Since then, red tides have been seen in many other (55) . A Philippines red tide expert told us that " (56) the fish kills, the Philippines has documented 1, 926 eases of dead shellfish poisoning caused by red tides. "

The term "red tide" (57) the discoloration of water that sometimes occurs in certain areas of the ocean or sea. Although the color is often red, it may also be (58) of brown or yellow. The World Book Encyclopedia reports that "the discolored areas may range from (59) a few square yards to more than 2,600 square kilometers. "

What causes such discoloration Red tides are generally caused by several species of single-celled organisms. These tiny organisms have hair-like projections which they use to (60) themselves in water.

59().

A. less than

B. more than

C. as much as

D. as little as
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单项选择题

人绒毛膜促性腺激素产生于

A．合体滋养细胞 B．妊娠黄体
C．胎膜
D．脐带
E．羊水
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