问题 问答题

常温下由两种常见的气体A和B组成的混合物,合气体中只含经分析混碳和氢 两种元素,并且A的相对分子质量大于B的相对分子质量,不论A和B以何种比例混合,碳元素与氢元素的质量比总小于3:1,由此可确定A的化学式是______;B的化学式是______;这样判断的理由是______.若上述气体中碳元素与氢元素的质量   比为6:5,则混合气体中A与B的质量之比为______.

答案

不论A和B以何种比例混合,碳元素与氢元素的质量比总小于3:1,说明A和B中碳元素与氢元素的质量比均小于或者等于3:1,即碳原子和氢原子个数比均小于或者等于

3
12
1
1
=1:4.在初中化学中,满足条件的只有甲烷和氢气.A的相对分子质量大于B的相对分子质量,则A为CH4,B为H2

由于在CH4分子中,C、H的质量比为3:1,在CH4中混入任何比例的H2都将使C、H的质量比小于3:1.

设A的质量为xg,B的质量为1g,则

3x
4
:(
x
4
+1
)=6:5.则x=
8
3
;故A与B的质量之比为
8
3
g:1g=8:3.

故答案为:CH4;H2;在CH4分子中,C、H的质量比为3:1,在CH4中混入任何比例的H2都将使C、H的质量比小于3:1;8:3.

单项选择题 A3/A4型题
阅读理解

Since the first Earth Day in 1970,American have gotten a lot “greenter” toward the environment . “We didn’t know at that time there even was an environment,let alone that there was a problem with it,”says Bruce Anderson,president of Earth Day USA.

But what began as nothing important in public affairs has grown into a social movement .Business people,political leaders, university professors,and especially millions of grass-roots Americans are taking part in the movement. “The understanding has increased many ,many times,”says Gaylord Nelson,the fromer govermor from Wisconsin,who thought up the first According to US government reports , emissions (排放)from cars and trucks have dropped from 10.3 million tons a year to 5.5 tons .The number of cities producing CO beyond the standard has been reduced from 40 to 9 .Although serious problems still remain and need to be dealt with , the world is a safer and healthier place .A kind of “Green thinking ” has become part of practices .

Great improvement has been achieved .In 1988 there were only 600 recycling programs ,; today in 1995 there are about 6,600 .Advanced lights ,motors , and building designs have helped save a lot of energy and therefore prevented pollution .

Twenty –five years ago , there were hardly any education programs for environment .Today , it’s hard to find a public school , university , or law school that does not have such a kind of program .” Until we do that , nothing else will change! ” say Bruce Anderson .

小题1:According to Anderson , before 1970, Americans had little idea about ___

A.the social movement

B.recycling techniques

C.environmental problems

D.the importance of Earth Day小题2:Where does the support for environmental protection mainly come from?

A.The grass –roots level

B.The business circle

C.Government officials

D.University professors小题3:What have Americans achieved in environmental protection ?

A.They have cut car emissions to the lowest

B.They have settled their environmental problems

C.They have lowered their CO levels in forty cities.

D.They have reduced pollution through effective measures .小题4:What is especially important for environmental protection according to the last paragraph ?

A.Education

B.Planning

C.Green living

D.CO reduction