问题 推断题

右图是一定条件下相关物质的转化关系,其中A是只含两种元素的纯净物,B、C、E、F均是初中常见的无色无味的气体。

(1) 写出下列物质的化学式C____ E_____ F_____ H______。

(2) 写出符合反应③的一个化学反应方程式:          

(3) 写出反应②的化学反应方程式:           

答案

O2   CO2   H2   CaCO3    Fe+2HCl==FeCl2+H2↑  2CO+O2 2CO2

题目分析:根据题意,E通入澄清石灰水,有白色沉淀H生成,即E能使澄清的石灰水变浑浊,因此E是二氧化碳,则H是碳酸钙;又因为B、C两种无色无味的气体点燃能生成E二氧化碳,则可知B、C分别为一氧化碳和氧气中的一种;而A是只含两种元素的纯净物,且A能与气体B在高温下反应,生成E二氧化碳和D,且D能与稀盐酸反应,生成气体F;若B为一氧化碳,则A应为金属氧化物,D为金属单质,且只要是活泼金属,即能与稀盐酸反应产生氢气,故F为氢气,符合题意。

(1)根据上面的分析,可知C是氧气,故化学式为O2;E是二氧化碳,故化学式为CO2;F是氢气,故化学式为H2;H是碳酸钙,,故化学式为CaCO3

(2)根据题意,反应③是活泼金属与稀盐酸的反应,生成相应的盐和氢气,故符合要求的化学反应方程式可以是Fe+2HCl=FeCl2+H2↑。

(3)反应②是一氧化碳和氧气反应生成二氧化碳,故反应的化学方程式为2CO+O2 2CO2

点评:在解此类题时,先要找准“题眼”,即有特征的物质或反应现象等,再根据题中的条件进行有目的假设,然后沿着假设进行推导,只要各步都满足,假设就成立,如不满足,可再假设,再验证。

选择题
阅读理解

Many adults in the United States can remember crying the nursery rhyme in the street "Hot cross buns!" But only a few people realize this was an early form of advertising.

Written advertisements probably began with hieroglyphics more than three thousand years ago, but only a few people could read these symbols. So merchants made signs with pictures or hung their tools over their doors to identify their businesses.

In the time of the Roman Empire, wall paintings were a popular form of advertisement. An ad for a play, or some other performance was painted on part of a building or on a wall around a city. People often advertised a house for rent or a freshwater bath in this way, too.

Today, large wall signs are still used for outdoor advertising. But outdoor advertising is only a small fraction of the total advertising. About forty per -cent of all ads are printed in daily newspapers. Radio commercials also provide this kind of information. Some people think they are the best form of advertising because radio broadcasts reach almost everyone in a nation.

Advertisements in magazines and on television reach many people, too. However, usually only large companies can advertise on a national network, because TV commercials shown across the country can cost many thousands of dollars.

Then there are ads that are almost part of daily living. If you use public transportation, you will see large printed ads, called ear cards, on buses and taxis and in trains. Ads are painted on the trucks that deliver products people are buying or selling.

小题1:Which is the passage mainly discussing?

A.Modern advertising

B.Significance of advertising

C.Development of advertising

D.Origin of advertising小题2:Which of the following is the original form of advertising?

A.Signs with pictures

B.Wall signs

C.Street crying

D.Wall painting小题3:Which of the following can best replace the underlined word “hieroglyphics” in Paragraph 2?

A.A signal

B.A signature

C.A symbol

D.A form小题4:Why did the merchants make signs with pictures or hang their tools over their doors ?

A.To have their houses decorated.

B.To make their business known by public.

C.To enable people to learn how to read

D.To advertise their houses to rent小题5:Radio commercials are the best form of advertising because ____________.

A.they can be heard everywhere in a country

B.they are cheap and fast

C.they are most recently developed

D.they can be understood by those who can neither read nor write