问题 选择题

50℃时,等质量的两份饱和Ca(OH)2溶液,一份冷却至20℃得溶液甲;另一份加少量CaO后,恢复温度至50℃得溶液乙.则甲、乙两溶液共同的是(  )

A.Ca(OH)2的溶解度

B.溶质的质量

C.溶剂的质量

D.溶液的质量分数

答案

A、甲在20℃的溶解度大于乙溶液在50℃的溶解度,则溶解度不相同,故A错误;

B、甲溶液降温时溶解度变大,由饱和溶液变为不饱和溶液,但溶质和溶剂质量都不变,而乙中加入少量的生石灰,生石灰会与水反应生成氢氧化钙,溶剂的质量会减小,故溶质的质量也会减少,故B错误;

C、甲溶液降温时溶解度变大,由饱和溶液变为不饱和溶液,但溶质和溶剂质量都不变,而乙中加入少量的生石灰,生石灰会与水反应生成氢氧化钙,溶剂的质量会减小,故C错误;

D、因甲的溶质和溶剂不变,与由原50℃时溶解度来计算的结果相同,则质量分数不变,而乙有溶质析出时仍然时饱和溶液,可根据50℃的溶解度来计算,则甲、乙溶液的溶质的质量分数相同,故D正确;

故选D.

阅读理解

阅读理解。

     We know that many animals do not stay in one place. Birds, fish and other animals move from one

place to another at a certain time. They move for different reasons: most of them move to find food more

easily, but others move to get away from places that are too crowded.

     When cold weather comes, many birds move to warmer places to find food. Some fishes give birth

in warm water and move to cold water to feed. The most famous migration(迁移) is probably the

migration of the fish, which is called "salmon". This fish is born in fresh water but it travels many miles to

salt water. There it spends its life. When it is old, it returns to its birthplace in fresh water. Then it gives

birth and dies there. In northern Europe, there is a kind of mouse. They leave their mountain homes when

they become too crowded. They move down to the low land. Sometimes they move all the way to the

seaside, and many of them are killed when they fall into the sea.

     Recently, scientists have studied the migration of a kind of lobster(龙虾). Every year, when the

season of bad weather arrives, the lobster get into a long line and start to walk across the floor of the

ocean. Nobody knows why they do this, and nobody knows where they go.

     So, sometimes we know why humans and animals move from one place to another, but at other

times we don't. Maybe living things just like travel.

1. Most animals move from one place to another at a certain time to _____.

A.  find food more easily                    

B. enjoy warmer weather

C. give birth                          

D. find beautiful places

2. The mice in northern Europe move when _____.  

A. they need fresh water            

B. the weather is bad

C. the place gets too crowded          

D. they haven't enough food

3. This passage is mainly about _____.    

A. why animals move from one place to another

B. how animals can find food easily

C. new discoveries of animals traveling

D. some problems with traveling 

单项选择题