问题 计算题

(10分)小强买来一包黄铜(铜、锌合金),包装说明如右图,他对包装说明上的质量分数产生了疑问,他称取20g黄铜样品放入烧杯中,然后往烧杯中加入稀硫酸93.7g,恰好完全反应,反应后称得烧杯内物质共113.5g。

(1)反应产生氢气          g。

(2)通过计算判断该黄铜样品中铜的质量分数是否与包装说明相符(计算结果精确到0.1%,下同)。

(3)计算反应后所得溶液中溶质的质量分数是多少?

答案

(1)  0.2  (2)因为67.5%<70%,所以与包装说明不相符  (3)16.1%

题目分析:1、由于黄铜中只有锌与稀硫酸反应放出氢气,因此反应前后烧杯内物质总质量减小的部分即为产生氢气的质量,因此反应产生的氢气质量为:20+93.7-113.5=0.2克;

2、要计算黄铜的质量分数,先得计算出铜的质量。我们先可以根据氢气的质量计算出锌的质量,再用黄铜总质量减去锌的质量,即可得出铜的质量。而第(3)小题中要计算的溶质质量分数,就是反应生成的硫酸锌的质量分数,可以根据化学方程式计算硫酸锌的质量,再用硫酸锌的质量除以总溶液的质量即可。

解:设Zn质量为x, ZnSO4质量为y

Zn +H 2SO4 = ZnSO4 + H2↑                         …………1分

65  161   2

x         y      0.2g                           …………1分

                                      …………1分

x=6.5g    y=16.1g                                 …………1分

该黄铜样品中Cu质量分数=×100%=67.5%          …………1分

因为67.5%<70%,所以与包装说明不相符                      …………1分

反应后溶质质量分数=×100%=16.1%     …………2分

答:略

点评:本题解题关键在于找出氢气的质量。

判断题
阅读理解

阅读理解。

     These days, if you still think the cell phone is just for talking, you'll get laughed at. Yes, it's true, voice-

only handsets have become out of date. Today's do-it-all mobiles have a lot in common with the computer.

The only difference may be that they fit in your pocket and you pay by the minute to use them. Some of the

things a cell phone can do for you will be available this year:

      Surf at speed

      Cell phones that let you use the Web have been around for years. So, what's new? Well, faster third-

generation (3G) networks that let you surf at anywhere. This then allows a carrier to send video, music, and

games to your phone. Possible choices are from LG Electronics VX 8000 and Motorola V1150.

      Listen as you go

      The problem with most cell phone MP3 players is that they hold only a handful of songs. But, that's about

to change. Sony Ericsson's new W800i can hold around 150 songs in its 500 MB memory. And Samsung's

SPH-V5400 even comes with a 1.5 GB hard drive. Mobile phones may eventually replace mini-MP3 players,

especially for teens.

      Say cheese

      Camera cell phones are not new either. But, most of them have limitations: around 1-megapixel (百万像

素). But new technology has made 2-megapixel units more common, and 3-megapixel units are showing up

soon. Some 2-megapixel models, like Sony Ericsson's K750i, offer limited zoom and focus controls. Others,

like LG's recent A7110, can even capture 30 minutes of full-motion video.

      Portable TV

      You say you like"watching TV"? That's what Samsung MM-A700 wants to give you. The new model lets

users watch popular TV programmes-for a fee. Other choices are Nokia's 6620, Sanyo's MM7400 and NEC's

N940. The NEC model lets you watch public TV-no fee. 

      The above are just a handful of what you'll see in the coming months. Further down the road, your mobile

phone may play a host of other roles, such as mobile credit card, position locator... So what is there that a cell

phone can't do?

1. Which of the following models should you choose to listen to the music? [ ]

A. Samsung's SPH-V5400 and Nokia's 6620.

B. Sony Ericsson's W800i and Samsung's SPH-V5400.

C. Sony Ericsson's W800i and NEC's N940.

D. Sanyo's MM7400 and NEC's N940.

2. What's the difference between NEC's N940 and other models? [ ]

A. It allows you to surf the Internet at a high speed.

B. It can capture 30 minutes of full-motion video.

C. It can hold as many as 150 songs.

D. It lets you watch public TV for free.

3. Which of the following statements is TRUE according to the passage? [ ]

A. All the functions of the models mentioned in the passage are completely new.

B. Camera cellphones of 3-megapixel units will appear soon.

C. It is certain that a cellphone can do anything in the near future.

D. Today's do-it-all mobiles have nothing in common with the computer.

4. This passage may be _____. [ ]

A. an introduction to some new models of cellphones

B. an advertisement trying to persuade you to buy new cellphones

C. a science fiction trying to attract readers' attention

D. a survey to find the development of cellphones