小明想测定某石灰石样品中碳酸钙的质量分数，他取一块石灰石样品_爱下问搜题

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问题计算题

小明想测定某石灰石样品中碳酸钙的质量分数，他取一块石灰石样品，将其敲碎后，称出6g放入烧杯内（烧杯质量为20 g）加入50 g某一定溶质质量分数的稀盐酸，用玻璃棒搅拌充分反应至不再产生气泡为止。反应所需时间（t)与烧杯内剩物质的总质量（m）的关系如图所示

试回答：

（1）将石灰石样品敲打粉碎的目的是

（2）反应结束后 * * 生二氧化碳质量是多少？

（3）石灰石样品中碳酸钙的质量分数是多少？（5分）（保留到1％）

答案

（1）将石灰石样品敲打粉碎的目的是增大反应物接触面，加速反应速率。（2）2．2g （3）83%

题目分析：（1）将石灰石样品敲打粉碎的目的是增大反应物接触面，加速反应速率。

（2）反应结束后 * * 生二氧化碳的质量=76g-73．8g=2．2g

（3）设石灰石样品中碳酸钙的质量为xg

CaCO₃+2HCl=CaCl₂+H₂O+CO₂↑

100 44

x 2．2g

x = 5g

石灰石样品中碳酸钙的质量分数=×100% = 83%

解答题

下列是某种营养生殖方式的操作系列图，请根据你的认识和动手实践经验据图回答：

（1）此种生殖方式叫______，B表示______，C表示______．

（2）要使植物体成活，操作时的关键是______．

（3）请将此种生殖方式的操作顺序用图中字母和箭头（→）表示出来．______．

（4）你认为采用这种生殖方式的优点是：______．

单项选择题

Since life began eons ago, thousands of creatures have come and gone. Some, such as the dinosaurs, became extinct due to naturally changing ecologic conditions. More recent threats to life forms are humans and their activities. Man has drained marshes, burned prairies, dammed and diverted rivers. Some of the more recent casualties of man’’s expansion have been the dodo, great auk, passenger pigeon, Irish elk, and Steller’’s sea cow. Sadly, we can no longer attribute the increasing decline in our wild animals and plant species to "natural" processes. Many species are dying out because of exploitation, habitat alteration or destruction, pollution, or the introduction of new species of plants and animals to an area. As mandated by Congress, protecting endangered species, and restoring them to the point where their existence is no longer jeopardized, is the primary objective of the U.S. Fish and Wildlife Service’’s Endangered Species Program.

The tone of this passage is________.

A．nationalistic

B．pro-wildlife

C．anti-wildlife

D．feminist