试题与答案

(09苏州)、某课外活动小组为了测定一批石灰石中碳酸钙的质量分数,将石灰 石样品

题型:计算题

题目:

(09苏州)、某课外活动小组为了测定一批石灰石中碳酸钙的质量分数,将石灰

石样品研成粉末,然后取一定量的石灰石粉末与过量稀盐酸充分反应(假设石灰石中的杂质

既不和酸反应,也不溶于水),过滤、洗涤、干燥后称量滤渣质量的数据如下表:

实验序号样品的质量/g滤渣的质量/g
第一次3.40.3
第二次3.60.4
第三次5.00.5
 

(1)该样品中碳酸钙质量分数的平均值为:   ▲   (结果精确到0.1%)。

(2)引起三次实验数据差异的操作原因可能是:      ▲       

(3)若利用题(1)的结果,煅烧100t这种石灰石,理论上最多能得到氧化钙多少吨?(结果精确到0.1t)

答案:

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The safety of ships at sea does not depend only on the arrangements made in the ships themselves. Dangerous coasts and rocks may be seen in the daytime, (51) they are a threat to safe navigation at night. Lighthouses are therefore erected at such places to (52) sailors of the danger. Modern lighthouses are put up at all dangerous places near the courses (53) by ships. On some rocky coasts several lighthouses may be built not far from each other, and (54) the sailors on a ship may know which is which, they have (55) arrangements of lights. One lighthouse will give a single flash at regular (56) , another may give two flashes; a third may give two followed by one; and so on. (57) watching the lights the navigator is able to decide exactly where he is, and he can set his (58) with confidence. In the approaches to some ports two continuous lights are set up, one above (59) but some distance behind; when they appear from the sea one above the other, the ship is on the right course; but if they do not, the captain knows that he is (60) his course and likely to strike a rock or the bottom of the sea.

A.On

B.After

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D.By

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