问题 选择题

下面是我校实验室中一瓶硫酸试剂标签上的部分内容.据此分析说法正确的是(  )

硫酸   化学纯(CP)(500mL)

品名:硫酸

化学式:H2SO4

相对分子质量:98

密度:1.84g/cm3质量分数:98%

A.该硫酸的物质的量浓度为9.2mol/L

B.取该硫酸与等质量的水混合后,硫酸的物质的量浓度为9.2mol/L

C.配置200mL4.6mol/L的稀硫酸需取该硫酸50mL

D.该硫酸与等体积的水混合后溶液的质量分数小于49%

答案

A.由c=

1000ρw
M
可知,c=
1000×1.84×98%
98
=18.4mol/L,故A错误;

B.设质量为m,则硫酸的质量分数

m×98%
2m
=49%,浓度越小,密度越小,则硫酸的物质的量浓度小于9.2mol/L,故B错误;

C.由混合前后溶质的物质的量不变,V×18.4mol/L=0.2L×4.6mol/L,解得V=50mL,故C正确;

D.设体积为V,则

1.84×V×98%
1.84V+V
>49%,故D错误;

故选C.

完形填空

However difficult you find it to arrange your time, it will pay off in the long run if you set aside a certain part of the day for studying - and stick to it. __小题1:__ But don't forget to make sure that you have enough left for recreational activities or simply to be “with” yourself: reading a novel or watching a television programme.

As part of your weekly schedule, it is also advisable to consider exactly what you have to do in that week, and make sure that you handle the most significant tasks first. __小题2:__

On a physical level, make sure you have an area or space for studying. __小题3:__ If you always study in the same place, preferably a room of your own, you will find it easier to adjust mentally to the activity when you enter that area. You should have everything that you might need at hand.

Make sure that all the physical equipment that you use, such as a desk, chair etc. is at good height for you. If you use a personal computer, there are plenty of guidelines available from the movement on angles, lighting and the like.   __小题4:__

If you are working on topic your teacher has set, but finding it hard to concentrate, it may be that you actually need to take your mind right off it for a period of time.  __小题5:__ After a period away from the test, having not thought about it at all, you may return to it refreshed and full of ideas.

A.It's wise to leave the easier or less urgent areas of your work until later.

B.It's all too easy to read something and then forget where it came from.

C.Consult these and avoid the typical student aches and pains.

D.“Airing the mind” can work wonders sometimes.E.Make use of equipment that is available to you .

F.It is best to make a weekly schedule.

G.Don't do it just anywhere.

单项选择题 A1型题