问题 问答题

某无色澄清溶液,可能含有以下离子中的几种:Cl-、Ba2+、Cu2+、Br-、C

O2-3
、S
O2-4
K+.取该溶液进行下述实验:

①取少量溶液进行焰色反应,透过钴玻璃观察到火焰呈紫色;

②另取部分溶液,加入盐酸,产生的气体能使澄清石灰水变浑浊;

③另取部分溶液,滴入几滴氯水,再加入少量四氯化碳,振荡静置,四氯化碳层呈橙红色;

④另取部分溶液,加入过量BaCl2溶液,产生白色沉淀;用稀硫酸和该沉淀反应,有气体生成,同时有白色沉淀;

⑤取④中部分滤液,加入AgNO3溶液,有白色沉淀,加稀硝酸沉淀不溶解.

根据上述实验现象推断,原溶液中肯定存在的离子是______;

肯定不存在的离子是______;可能存在的离子是______.

答案

①透过钴玻璃观察到火焰呈紫色,说明溶液中一定存在K+

②加入盐酸,产生的气体能使澄清石灰水变浑浊,说明一定存在CO32-,一定不存在与CO32-反应的离子:Ba2+、Cu2+

③橙红色的为溴单质,说明原溶液中一定存在Br-

④沉淀可能为硫酸钡和碳酸钡,由于用稀硫酸溶解沉淀,所以无法判断是否存在SO42-,但是一定存在CO32-

⑤由于④中进入了氯化钡,引进了Cl-,无法判断是否存在Cl-

根据以上分析可知,溶液中一定存在的离子为:K+、CO32-、Br-,一定不存在的离子为:Ba2+、Cu2+,可能存在的离子为:SO42-、Cl-

故答案为:K+、CO32-、Br-;Ba2+、Cu2+;SO42-、Cl-

单项选择题
阅读理解

阅读理解

     Endangered languages are languages that wouldn't exist any longer, much like endangered species of

plants or animals. Languages are considered to be endangered when parents are no longer teaching the

language to their children and are not using it actively in everyday life. A language is considered to nearly

disappear when it is spoken by only a few elderly native speakers.

     The world faces enormous challenges in order to protect different kinds of languages. Of the more than 6,912 languages, half may be in danger of disappearing in the next several decades.

     It is caused by many reasons: small numbers of speakers, the regular use of other languages, attitudes

towards their languages, moving of the younger population, government policies, and languages used in

education and so on. A language may lack important things such as a body of literature, and people who

read and write it. A language may also lack prestige (声望) and support of its speakers.

     The survival of a language is also threatened when speakers move to other areas where different

languages are spoken, or when government policies improve the use of a specific language in school,

official business and the media. These situations encourage people to learn the wider-known language and may cause them, especially the young, to stop using their mother tongue. Often those speaking

lesser-known languages will choose to learn a more prestigious language with the hope of greater

economic opportunities. Most of the world's parents are teaching their children English, French, Spanish,

Chinese, Arabic, Russian or some other main languages instead of their own languages for social and

economic reasons.

1. What's the main idea of this passage?

A. Languages in the world.

B. Reasons why languages become endangered.

C. What an endangered language is.

D. Languages spoken by few speakers.

2. About _________ languages will probably disappear in this century according to the passage.

A. more than 6,912

B. more than 3,456

C. 6,912

D. less than 3,456

3. Which of the following best shows the structure of the passage?

①=Paragraph1②=Paragraph2③=Paragraph3④=Paragraph4

4. We can infer that the best way to maintain an endangered language is to _________.

A. forbid the speakers to move about

B. pass laws to protect the language

C. raise the salaries of the people who speak the language

D. teach the language to young children and encourage people to speak it as much as possible

5. All of the following about languages are true EXCEPT __________.

A. many languages will be probably endangered in this century

B. government policies have a big effect on languages

C. the endangered language is a language that is spoken by few people

D. languages are related to their speakers' social and economic position