问题 问答题

某些食品的包装袋内一个装有白色颗粒状固体的小纸袋,上面写着“干燥剂,主要成分是生石灰”

(1)生石灰(CaO)可作干燥剂的理由是(用化学方程式表示)______.

(2)对它作了一系列探究,获得较多收益,其实验方案如下:

问题与猜想 实验步骤  实验现象 实验结论
 问题1:小纸袋中的物质能否继续作干燥剂?取足量小纸袋中固体放入烧杯中,加适量的水,触摸杯壁. _______________不能作干燥剂 
 问题2:猜想变质后的物质可能是______________________ ______________ _________________ 
(3)对它还有一个要再探究的新问题是:______.

答案

(1)生石灰与水极易反应生成氢氧化钙,故选CaO+H2O═Ca(OH)2

(2)对它的探究是分两个方面进行的:问题一是氧化钙不能做干燥剂,从表中的信息可以看出是利用氧化钙与水反应放出大量的热进行的.问题二:固体的成分检验主要依据下列知识:根据生石灰在空气中易吸收空气中的水变成氢氧化钙,氢氧化钙又易于空气中的二氧化碳反应生成碳酸钙的特点可知它可能为混合物为Ca(OH)2和CaCO3的混合物;再根据氢氧化钙的溶液呈碱性,能使酚酞试液变红,碳酸钙与盐酸反应生成是澄清石灰水变浑浊

故答案为:

问题与猜想 实验步骤 实验现象实验结论
问题1:小纸袋中的物质能否继续作干燥剂?取足量小纸袋中固体放入烧杯中,加适量的水,触摸杯壁. 杯壁温度无变化不能作干燥剂
问题2:猜想变质后的物质可能是氢氧化钙和碳酸钙的混合物取固体放入烧杯中加适量的水,溶解滴入酚酞试液,再滴加稀盐酸.酚酞变红,产生气泡,把气体通入澄清石灰水,溶液变混氢氧化钙和碳酸钙的混合物
(3)此题未开放题只要结合此题的物质问题合理即为正确.答案为:通过什么方法可重新让它做干燥剂

单项选择题
阅读理解

At a certain time in our lives we consider every place as the possible sites(地点) for a house. I have thus searched the country within a dozen miles of where I live. In imagination I have bought all the farms, one after another, and I knew their prices.

The nearest thing that I came to actual ownership was when I bought the Hollowell place. But before the owner completed the sale with me, his wife changed her mind and wished to keep it, and he offered me additional dollars to return the farm to him. However, I let him keep the additional dollars and sold him the farm for just what I gave for it.

The real attractiong of the Hollowell farm to me were its position, being about two miles from the village, half a mile from the nearest neighbor, bounded(相邻) on one side by the river, and separated from the highway by a wide field. The poor condition fo the house and fences showed that it hadn’t been used for some time. I remembered from my earliest trip up the river that the house used to be hidden behind a forest area, and I was in a hurry to buy it before the owner finished getting out some rocks, cutting down the apples trees, and clearing away some young trees which had grown up in the fields. I wanted to buy it before he made any more of his improvements. But it turned out as I have said.

I was not really troubled by the loss. I had always had a garden, but I don’t thing I was ready for a large farm. I believe that as long as possible it is better to live free and uncommitted (无牵挂的). It makes but little difference whether you own a farm or not.

小题1:What do we know about the author?

A.He wanted to buy the oldest farm near where he lived.

B.He made a study of many farms before buying.

C.He made money by buying and selling farms.

D.He had the money to buy the best farm in the country.小题2:Why did the author decide to buy the Hollowell place?

A.It was of good market value.

B.It was next to the highway.

C.It was in a good position.

D.It was behind a nice garden.小题3:Why did the author want to buy the farm in a hurry?

A.He was afraid the owner might changes his mind.

B.He hoped to enlarge the forest on the farm.

C.He wanted to keep the farm as it was.

D.He was eager to become a farm owner.小题4:The underlined words “the loss” in the last paragraph refer to ___.

A.the money the author lost in buying the farm

B.the sale of the garden in the Hollowell place

C.the removal of the trees around the house

D.the failure to possess the Hollowell place小题5:What does the author believe as important in life?

A.To own a farm

B.To satisfy his needs

C.To be free from worries

D.To live in the countryside