问题 选择题

在试管中注入某红色溶液,给试管加热,溶液颜色逐渐变浅,则原溶液可能是(  )

①滴有石蕊的H2SO4溶液      ②滴有酚酞的氨水溶液

③滴有酚酞的氢氧化钠溶液   ④滴有酚酞的饱和氢氧化钙溶液

⑤滴有酚酞的Na2CO3溶液     ⑥溶有SO2的品红溶液.

A.②⑥

B.②④

C.①③⑤

D.②④⑥

答案

①滴有石蕊的H2SO4溶液显示红色,加热以后,溶液颜色不变,故①错误;

②滴有酚酞的氨水溶液显示红色,因为氨水显碱性,解热后,氨水受热容易分解放出氨气,导致碱性减弱,溶液颜色逐渐变浅,故②正确;

③滴有酚酞的氢氧化钠溶液显示红色,氢氧化钠受热稳定,加热后碱性几乎不变,溶液颜色不变,故③错误;

④滴有酚酞的饱和氢氧化钙溶液显示红色,加热后,氢氧化钙的溶解度随着温度的升高而降低,所以溶液碱性减弱,溶液颜色逐渐变浅,故④正确;

⑤滴有酚酞的Na2CO3溶液显示红色,其中碳酸根离子水解程度受温度的影响,温度高,水解程度大,碱性增强,所以溶液颜色逐渐变深,故⑤错误;

⑥二氧化硫有漂白性,使品红溶液褪色,但加热后,其与品红结合生成的无色物质不稳定,分解,二氧化硫从溶液中逸出,品红又显红色,故⑥错误.

故选B.

阅读理解

阅读理解。

     People know the dangers of fires. It's good for a family to learn how to prepare for a fire. Here are sonic

suggestions:

     Put a smoke a1arm in the house. Smoke from a fire causes the alarm to go off The alarm makes a loud

sound. The sound tells everyone to leave the house at once.

     Make escape (逃脱) plans. They should know all the ways out of the house. If there is a fire, everyone

follows the plan to get out. Part of the plan is to check all the windows to make sure they can be opened

easily.

     Buy fire extinguishers (灭火器) in the house, Everyone in the family should know how to use them.

     Practise for a fire. They do fire practice because they teach children about fire safety. Everyone in. the

family should know the following fire rules:

    ★ Don't open a hot door! The tire can grow more quickly if you open the door.

    ★ Stay close to the floor! Smoke can be more dangerous than fire, The best air is near the floor because

smoke rises.

    ★ What will you do if your hair or clothes start to burn? First, stop! Don't run! The fire burns faster

because of more air. Drop! Fall to the floor. Then roll! Turning over and over will make the fire go out. Put

a blanket (毯子) around you to keep air away from the fire that may still be on you.

    There are many possible causes for fires. A wise family is ready all the time. If there is a fire, don't forget

to call 119 for help.

1. What does it mean when a smoke alarm rings at home?

A. You have to get up.

B. Water is running to the floor.

C. Something is burning.

D. Someone breaks your window.

2. The writer advises people to do the following to prepare for a fire except that _________.

A. they practise for a fire

B. they make escape plans

C. they buy fire extinguishers

D. they use electrical cookers

3. When a fire happens, _________ if you open the hot door.

A. the fire will grow more quickly

B. the electricity will be cut off

C. the door will soon be on fire

D. the house will fall down

4. What are the right steps you should take when your hair or clothes catch fire?

A. Stop, run, roll.

B. Step, drop, roll.

C. Run, drop, roll.

D. Roll, drop, stop.

5. What is the best title for this passage?

A. The Dangers of a Fire.

B. The Causes of a Fire.

C. Learn to Use a Fire Extinguisher.

D. Be Ready for a Fire.

选择题