问题 实验题

某校化学课外小组为了鉴别碳酸钠和碳酸氢钠两种自色固体,用不同的方法做了以下实验,如图I~Ⅳ所示。

(1)只根据图I、Ⅱ所示实验,能够达到实验目的的是          (填装置序号)。

(2)图I所示实验前要先检验气密性,则检验气密性的方法是:关闭分液漏斗活塞,将导管口浸入水中,                                                                ,则气密性良好。

(3)图Ⅲ、Ⅳ所示实验均能鉴别这两种物质,但比较图Ⅲ和图Ⅳ两组实验,图Ⅳ实验的优点是                                                                   

(4)若用图Ⅳ实验验证碳酸钠和碳酸氢钠的稳定性,则试管B中装入的固体最好是      (填化学式)。

(5)除去碳酸钠固体中少量碳酸氢钠的方法是                                        (填化学方程式)。

答案

(1)图Ⅱ或Ⅱ(共1分)

(2)用双手握住左侧试管,导管口有气泡冒出,松开手后,导管口形成一水柱(共2分;每个给分点给1分)

(3)可以同时进行对比实验,有利于比较分析(共1分;从对比实验的角度回答即给分)

(4)NaHCO3(共1分)

(5)2NaHCO3Na2CO3+CO2↑+H2O (共2分)

题目分析:(1)Na2CO3、NaHCO3都能与稀盐酸反应,均产生能使澄清石灰水变浑浊的气体,故I不能用于二者的鉴别;Na2CO3、NaHCO3与稀盐酸反应机理不同,后者比前者反应快得多,II的气球膨胀的速率不同,可用于鉴别二者;(2)由气密性检查常用方法可知,关闭分液漏斗活塞,将导管口浸入水中,用双手握住左侧试管,导管口有气泡冒出,松开手后,导管口形成一水柱,说明装置气密性好;(3)图III只能先后检验Na2CO3、NaHCO3受热时的稳定性,而图IV则可以同时进行对比实验,有利于比较分析;(4)受热温度:A>B,则二者之中分别应盛Na2CO3、NaHCO3;(5)Na2CO3受热不会分解,2NaHCO3Na2CO3+CO2↑+H2O。2CO3、NaHCO3、物质的检验和提纯等相关知识。

单项选择题
阅读理解

Valentine’s Day is named for Saint Valentine an early Christmas churchman who reportedly helped young lovers. Valentine was killed for his Christian beliefs on February 14 more than 1700 years ago, but the day that has his name is even earlier than that.

More than 2,000 years ago, the ancient Romans celebrated a holiday for lovers. As part of the celebration, girls wrote their names on pieces of paper and put them in a large container. Boys reached into the container and pulled one out. The girl whose name was written on the paper became his lover or sweet heart for a year.

Lovers still put their names on pieces of paper and they sent each other Valentine’s Day cards that tell of their love. Sometimes they also sent gifts, like flowers of chocolate candy. Americans usually send these gifts and cards through the mail system. But some used another way to send this message. They have it printed in a newspaper. The cost is usually a few dollars. Some of the messages are simple and short “Jane, I love you very much”. Others say more. This one, for example, “Dan, Roses are red. Violets are blue. I hope you love me as much as I love you. Forever. May.”

Most of the newspapers that print such messages are local, but USA Today is sold throughout the United States, and 90 other countries as well. This means someone can send a Valentine message to lover in a far-away city or town almost anywhere in the world. These messages cost 80 dollars and more. An employee of USA Today says readers can have a small heart or rose printed along with their messages this year. Will this kind of Valentine’s Day message reach the one you love? Well, just make sure he or she reads the newspaper.

1. When was the day named after Valentine?

A. More than 1700 years ago before Valentine’s death  

B. More than 2000 years ago

C. On February 24                              

D. It is not mentioned in the passage.

2. Which is not true about the Roman holiday?

A. Girls put into a container large pieces of paper with their own names on them.

B. Boys and girls became sweet hearts by chance

C. Girls and boys were not lovers for a year.

D. It was celebrated as a holiday for lovers

3. What is the cost of printing a message to show one’s love? It’s _______________.

A. a few dollars                   B. 80 dollars, and more                C. very expensive

D. a few dollars in a local newspaper and 80 dollars in USA Today

4. What can be inferred from the passage?

A. The ancient Roman girls were more open and easy-going than boys

B. Valentine was killed for helping lovers

C. Readers of USA Today can send roses to their lovers along with printed messages

D. Valentine was honored by people for his firm Christian belief and warm heart

5. What is the purpose of the passage?

A. To briefly introduce the origin of Valentine’s Day and the modern style.

B. To advertise for USA Today.

C. To tell you that Americans are open to express their love

D. To sell roses on Valentine’s Day.