试题与答案

我国部分地区暴发H7N9型禽流感时。为了防止禽流感蔓延,人们将家禽捕杀、掩埋,并

题型:填空题

题目:

我国部分地区暴发H7N9型禽流感时。为了防止禽流感蔓延,人们将家禽捕杀、掩埋,并在禽舍和掩埋坑中洒上大量熟石灰。

(1)熟石灰属于         (填“酸”“碱”或“盐”)。用熟石灰处理硫酸厂废水中的硫酸,其化学方程式为                                                 

(2)熟石灰的溶解度曲线如下图所示,30 ℃时,将1 g熟石灰加入100 g水中充分搅拌、过滤,若不计溶液损失,得到溶液的质量是         g。将该溶液降温到20 ℃,溶液中溶质的质量分数将              (填序号)。

A.不变        B.增大        C.减小

答案:

(1)碱       Ca(OH)2 + H2SO4 = CaSO4 + 2H2O    (2)100.15       A

题目分析:(1)碱是指电离出来的阴离子全部是氢氧根离子的化合物,熟石灰能电离出钙离子和氢氧根离子,所以熟石灰属于碱;反应物是氢氧化钙和硫酸反应生成硫酸钙和水,用观察法配平,所以方程式是:Ca(OH)2 + H2SO4 = CaSO4 + 2H2O;(2)30℃时氢氧化钙的溶解度是0.15g,所以30℃时,将1g熟石灰加入100g水中充分搅拌,只能溶解0.15g溶质,所得溶液质量为100g+0.15g=100.15g;将该溶液降温到20℃,溶解度增大,溶液变为不饱和,但不溶解的溶质被过滤掉,所以溶质和溶剂质量都没变,所得溶液的溶质质量分数不变。

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题型:阅读理解

“I can’t concentrate.” “My mind wanders when I try to study.” Lack of concentration is one of the most common complaints heard at school.

We all have the ability to concentrate. Think of the times when you were attracted to a super novel or the times when you were playing your guitar or piano. But at other times your mind races from one thing to another. Here are some tips.

Rest from time to time. Remember to take short breaks. Lectures are usually 50 minutes long, and that’s about the length of time most people can direct their attention to one task. But that’s just an average. Your concentration time might be shorter (20-35 minutes) or longer (perhaps 90 minutes).When you take a break, you get more oxygen to your brain! When we sit for long periods, blood tends to be pooled in our lower body and legs. Get up and walk around the room for a couple of minutes. As a result, more oxygen is carried to the brain and you can concentrate better.

_______________If you study one subject for a long time, you may find it hard to concentrate. Many students improve their concentration by changing one subject to another every one to two hours. In this way you can pay more attention to something that’s different.

Reward yourself. Give yourself a reward when you’ve completed a task. The task might be small, such as staying with a difficult paper until you’ve finished. But giving yourself a reward can help you be more interested in doing other tasks.

Increase your activity level. Your concentration wanders more easily if you just read an article straight through. Instead, take the heading for each part and turn it into a question. For this part, that would be, “How can I increase my activity level while studying?” Then study that part to answer that question. Do this routinely. The questions give us a focus for each part and increase our involvement(参与).

小题1:According to Paragraph 3, what’s the purpose of walking around?

A.To help us stay fit.

B.To benefit our lower body.

C.To provide the brain with more oxygen.

D.To increase our concentration time to 90 minutes.小题2:What’s the best title for Paragraph 4?

A.Study for one hour each time.

B.Do something difficult.

C.Study in different ways.

D.Change subjects.小题3:In the last paragraph, the writer suggests that______.

A.we just read the heading of some articles

B.we do our best to read an article straight through

C.we ask ourselves questions about what we are reading

D.we ask other people questions about the article we are reading小题4:The writer wrote the passage to______.

A.encourage us to try to concentrate

B.teach us how to concentrate while studying

C.give us the reasons for a lack of concentration

D.list the benefits we can get from concentration

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