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问题 填空题

有一种氯化钠与氯化钾的混合物，它所含钾与钠的物质的量之比为3∶1，求：

(1)混合物中氯化钾的质 量分数。

(2)含1 mol Cl－的混合物的质量。

答案

(1)79.3%(2)70.5 g

题目分析：（1）则设混合物中有1mol的氯化钠，则氯化钾有3mol，混合物的总质量=1*58.5+3*74.5=282g，所以氯化钾的质量分数=(74.5*3/282)*100%=79.3%

(2)总的氯离子为1mol，所以氯化钾为0.75mol,氯化钠为0.25mol,所以混合物的质量="0.75*74.5+0.25*58.5=70.5" g

点评：本题抓住在氯化钾中，氯离子的物质的量等于钾离子的物质的量等于氯化钾的物质的量，而且计算过程中需要对物质的量与质量间的换算非常熟练。

单项选择题

（）负责公安系统审计人员岗位资格证书管理工作。

A.公安部消防局审计处

B.公安部审计局

C.总队审计处

D.公安部政治部
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单项选择题

Government officials reported three new cases of mad cow, bringing the total so far this year to 99. Last year, France recorded just 31 cases of the mad cow disease. The rising numbers are in part (1) a new testing program that focuses on cows that are most (2) . That program has (3) 39 cases. But still 60 new cases were identified in the usual way, (4) were found in 1999. Many scientists (5) that this year, five years after safety precautions were (6) , the number of cases would be (7) .

The rise in cases has (8) some scientists to question whether the disease can be transmitted in ways not yet understood. Scientists are still (9) the disease, first recognized in cows in 1986.

It appears that it is not caused by a bacteria, virus or fungus, but (10) infectious particles called prion, perhaps (11) a virus or other agent. The disease kills cells in the brain, (12) it spongy and full of holes.

France has taken more steps to (13) safety than most European countries, (14) refusing to take English beef (15) the European Union. But some scientists believe that France has not been (16) in imposing the ban on feed that (17) animal pans.

Some French officials hope that the sudden interest in mad cow disease will mean that French consumers will become educated about it, thereby recognizing that French beef is actually (18) controlled. Every cow is given a passport at birth, and extensive information about its parentage and (19) it was raised must be (20) to any slaughterhouse. When a diseased animal is found, the entire herd is destroyed.

16（）

A.affective

B.efficient

C.effective

D.affect
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