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我省巢湖市石灰石资源丰富．滨湖中学化学兴趣小组计划研究繁昌一石灰石矿山的碳酸钙含量．它们选取了100克石灰石样品，在其中加入足量的稀盐酸，测得生成的二氧化碳质量与反应时间的关系如图所示．请你分析并计算后回答：

（1）反应生成的二氧化碳质量为______克；

（2）此石灰石样品中碳酸钙的质量分数是多少？

答案

（1）由图中曲线可知生成二氧化碳的质量为33g．

（2）设样品中碳酸钙的质量分数为x．

CaCO3+2HCl=CaCl2+H2O+CO2↑

100                  44

100g×x              33g

100
44
=
100g×x
33g
，x=75%

答：（1）33；

（2）此石灰石样品中碳酸钙的质量分数为75%．

选择题

给画线的字选择正确的解释。     

“之”在字典中的解释：A．动词，往，   去。B．代词，代替人或事物。C．结构助词。没有意义。

D．代词，这或那。   

1．卜算子·送鲍浩然之浙东。    (     )   

2．这是他采用的缓兵之计。    (     )   

3．之二虫，该杀耶！    (     )

4．妈妈对小刚说：“做事要多思，不能操之过急。”    (     )
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填空题

Americans’ (1) impulses keep generating surprises. Charitable giving plays an even larger role in the (2) . Demand for nonprofit services gets proportionately bigger as a locality’s (3) rises. The philanthropy of the wealthy may not hinge on tax (4) to the degree many believe. The US (5) the world in levels of charitable activity. Some experts see charity as a (6) trait of the US, more than (7) or business. But those forces may be (8) , as many nonprofits, from healthcare to classical music are selling (9) in a marketplace alongside for-profit (10) . Charity is no mere (11) activity. It pays off for society in ways that may (12) the rates of return on many traditional investments. Charity not only helps those on the (13) end but also strengthens the (14) of society at large. Moreover, it appears to make the givers themselves more (15) . The pattern that conservatives are better givers than (16) is less about politics than about charity-linked (17) most common to conservatives, religious commitment, marriage and children, and entrepreneurship. The main point is that more Americans, regardless of ideology, embrace giving as a tool for (18) . The urge to make a difference, and to take (19) in it, outweighs (20) considerations.
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