问题 选择题

已知某物质在20℃和40℃时的溶解度分别为10g和40g.某温下,将5g该物质加到20g水中,下列有关叙述正确的是(  )

A.20℃时所得溶液的质量为25g

B.40℃时所得溶液为饱和溶液

C.不管什么温度下,所得溶液中溶质的质量分数均为20%

D.该物质的溶解度随温度的升高而增大

答案

A、由物质在20℃时的溶解度为10g,则20g水溶解的物质的质量为

10g
100g
×20g=2g,即5g物质不能全部溶解,有固体不溶,则为饱和溶液,溶液质量为20g+2g=22g,故A错误;

B、由物质在40℃时的溶解度为40g,则20g水溶解的物质的质量为

40g
100g
×20g=8g,即5g物质能全部溶解,还能再溶解3g物质才饱和,所得溶液为不饱和溶液,故B错误;

C、20℃时所得溶液中溶质的质量分数为

2g
22g
×100%=0.091%,40℃时所得溶液中溶质的质量分数为
5g
5g+20g
×100%=20%,故C错误;

D、因物质在20℃和40℃时的溶解度分别为10g和40g,则温度越高,溶解度越大,即该物质的溶解度随温度的升高而增大,故D正确;

故选D.

填空题
单项选择题

Some politicians are scurrying about with much zest and anticipation. It’s time, their polls inform them, to find the quick fix for what they have determined is a society plagued by the irregular heartbeat of deficient values.

But there are contradictions that intrude on this denunciatory atmosphere. If there are moral omissions in the society, they cannot be sealed by instant, slenderly based attacks on entertainment. The plain fain fact is we are rearranging our priorities in the wrong way.

We are today misplacing our energies and our funding by directing all sorts of incentives to high schools and colleges. Too late. The moral scaffolding has been built by then, for better or worse. How then to begin this revision of life conduct We must introduce in pre-school, and keep alive through grade five, a new school course.

The course could be titled, "What is right, and what is plainly wrong. " For 30 minutes each day, the teacher would illuminate for these very young children what William Faulkner labeled "the old verities", the words that construct and implement the daily moral grind in every durable society must engage if it is to be judged a "just" society.

These are words like duty, honor, service, integrity, pity, pride, compassion and sacrifice, plus the clear admonition that violence is wrong. To the teaching of the meaning of those words must be added that cleansing rule of treating other people as you would want them to treat you. And most of all to make sure that these kids understand with growing clarity that home, school and church are the sanctuaries for their later life.

There is a grand simplicity to this kind of school course. It enters a child’s mind early, burrowing deep into those recesses of the human brain that even today advanced medical science has not been able to penetrate.

If you ask enough people, you will find that most of us remember our first-or second-grade teacher. I remember Miss Corbett and Miss Walker, who read to us before we really understood, but the words had weight and allure. We listened and, without really knowing it, we learned and saved what we learned. Perhaps it was because what we heard in those early school years was the first entry into our learning vessel.

Absent this kind of early instruction, absent the building of this moral shield, no congressional law, no presidential executive order, no fiery rhetoric will salvage a child’s conduct nor locate a missing moral core.

By mentioning one’s first-or second-grade teacher, the author intends to convey an idea that ().

A. for young children training in listening is more valued than that in reading

B. teachers at elementary level of schools are the best teachers

C. one’s early education influences him/her all his/her life

D. one’s early school years are the best time in his/her memory