问题 选择题

我们国家现在已全面禁止销售含磷洗涤剂。含磷洗涤剂中的Na5PxO10会造成水的

污染,该物质中磷元素的化合价为+5价,则x的值为(   )。

A.1

B.2

C.3

D.4

答案

答案:C

分析:根据物质的化学式为Na5PxO10,利用各种元素的化合价及化合物中元素的正负化合价的代数和为0来计算得出P的原子个数.

解:在Na5PxO10中,钠元素的化合价为+1价,磷元素的化合价为+5价,氧元素的化合价为-2价,

因化合物中各元素的化合价的代数和为0,

则(+1)×5+(+5)×x+(-2)×10=0

解得x=3

故选C.

点评:本题考查化合价的规律和原则,学生应熟悉常见元素的化合价并能用化合价计算的原则来求化合物中某元素的原子个数.

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阅读理解。

     American this year will swallow 15,000 tons of aspirin, one of the safest and most effective drugs

invented by man. The most popular medicine in the world today, it is an effective pain reliever. Its bad

effects are relatively mild and it is cheap.

     For millions of people suffering from arthritis (关节炎). It is the only thing that works. Aspirin, in

short, is truly the 20th-century wonder drug. It is also the second largest suicide drug and is the leading

cause of poisoning among children. It has side effects that, although relatively mild, are largely unrecognized

among users.

     Although aspirin was at first sold by a German company in1899, it has been around much longer than

that. Hippocrates, in ancient Greek, understood the medical value of the leaves and tree bark which today

are known to contain salicylates (水杨酸碱), the chemical in aspirin. During the 19th century, there was

a great deal of experimentation in Europe with this chemical, and it led to the introduction of aspirin. By 1915,

aspirin tablets were available in the United States.

     A small quantity of aspirin (two-grain tablets) relieves pain and inflammation. It also reduces fever by

interfering with (干预) some of the body's reactions.

1. The passage is written to ______.

A. suggests us using more aspirin

B. reminds us of the side effects of aspirin

C. gives us a whole view of aspirin

D. discusses the good effects of aspirin

2. According to the author, aspirin ______.

A. is very safe

B. first appeared in 1899

C. can be harmful to children

D. can hardly be dangerous

3. Generally speaking, the author seems to be ______.

A. in favour of aspirin

B. against the use of aspirin

C. not interested in aspirin

D. careful in using aspirin

4. What is the best title for this passage?

A. How to Use Aspirin

B. Why I Take Aspirin

C. The Most Popular Medicine

D. The Side Effects of Aspirin