问题 问答题

计算:

(1)已知,NH4Cl的溶解度:90℃:72g,40℃:46g,现将90℃时的NH4Cl饱和溶液300g,蒸发掉50g水后仍回到90℃会析出NH4Cl晶体______g;然后降温至40℃,又会析出NH4Cl晶体______g.

(2)某温度时,将25gCuSO4-5H2O晶体溶解在31g水中,恰好达到饱和,计算硫酸铜在该温度下的溶解度.

答案

(1)根据溶解度的定义可以知道,90℃时NH4Cl的溶解度为72g,所以蒸发掉50g水后仍回到90℃,能够析出36g氯化铵;

设90℃时300g饱和的NH4Cl溶液中含有溶质的质量为x,则:

x
300g
=
72g
100g+72g

解得:x=126g

所以蒸发掉50g水后溶液中溶质的质量为:126g-36g=90g

40℃NH4Cl的溶解度46g,所以设若降温至40℃能够析出溶质的质量为y,则:

90g-y
300g-50g-36g-y
=
46g
100g+46g

解得:y=33g

(2)设25gCuSO4?5H2O晶体中含结晶水的质量为z

25g×

5×(16+1×2)
64+32+16×4+5×(16+1×2)
×100%=8g

设硫酸铜在该温度下的溶解度为a,则:

25g-8g
25g+31g
=
a
100g+a

解得:a=44g

答:硫酸铜在该温度下的溶解度为44g.

故答案为:(1)36;33;

(2)44g.

阅读理解

阅读理解

     SOUTHPORT, ENGLAND-A British teaching union famous for strange ideas has supported

proposal to employ dogs as classroom assistants.

     At the annual conference of the Professional Association of Teachers in Southport, northwest

of England, one person suggested properly trained dogs be able to keep order in primary schools.

They can round up lost children and protect those who experience unfortunate "accidents". Wendy

Dyble, a Shetland Islands woman who teaches children up to age seven, made it clear to her fellow

friends that she was not  "barking mad". They obviously believed her, supporting her idea by 16

votes to 13, with a total of 63 abstentions (弃权).

     She said big dogs could help round up children, keep  them in line, lick up the milk they spill on

the floor and provide the extra eyes that a teacher needs to keep order."A big dog would also be

helpful in breaking up fights and looking for lost property, like gym shoes or dolls, " Dyble said at

the conference."The dog will also be useful in sniffing out smells that children do not own up to, "

she added."It would be nice for the teacher not to have to go round sniffing each child to find the

culprit (犯错的人). "

     The idea was greeted by the Dog Defense League but less so by bigger teaching unions.A

spokesman for Education Secretary David Blunkett, who is blind, said his guide dog was always

popular with pupils when he visited schools.The Professional Association of Teachers, with around

35,000 members, is the smallest teaching union in Britain.It has an honour for occasional strange

ideas.

     Earlier this week, its annual conference here suggested stopping exams because they lead to stress

and introducing selection at the age of 12 based on physical coordination and manual skill in the use

of hand.

1. According to the writer's opinion, to employ dogs as classroom assistants________.

A. is a wonderful idea

B. can improve the relation between children and animals

C. is beyond ordinary people's minds

D. can make some teachers lose jobs

2. What Dyble said at the conference________.

A. gained some support from the members

B. frightened everyone at the conference

C. interested everyone at the conference

D. caused some trouble to trained dogs

3. A spokesman for Education Secretary________.

A. once used a dog as a classroom assistant

B. sang high praise for Dyble' s idea

C. would employ dogs as teachers

D. benefited much from dogs

4. The last paragraph of this passage________.

A. has nothing to do with the topic of this passage

B. shows there are too many exams in British schools

C. provides further facts about the teaching union

D. shows the writer's anger to the union

单项选择题