问题 问答题

氢氧化钠溶液中滴入几滴无色酚酞试液,酚酞显红色.氢氧化钠溶液中主要存在的粒子是H2O、Na+和OH-,哪一种粒子能使指示剂变色呢?

(1)提出假设:______.

(2)实验探究:

①在第一支试管中加入2ml水,再滴入几滴酚酞试液,现象是______.

②在第二支试管中加入2ml氯化钠溶液,再滴入几滴酚酞试液,现象是______.

(3)结论:原假设______.(填成立或不成立)

(4)拓展实验:

①在第三支试管中加入2ml氯化钡溶液,再滴入几滴酚酞试液,酚酞不变色.

②在第四支试管中加入2ml氢氧化钡溶液,再滴入几滴酚酞试液,现象是______.

答案

(1)因氢氧化钠溶液中主要存在的粒子是H2O、Na+和OH-

又实验探究中的①和②是H2O、Na+遇酚酞是否变色,

则可提出假设OH-能使无色酚酞试液显红色来探究,

故答案为:OH-能使无色酚酞试液显红色;

(2)①根据观察可知,水中加入酚酞,不变色,故答案为:不变色;

②根据观察可知,氯化钠溶液中滴入酚酞,不变色,故答案为:不变色;

(3)由探究①和②可知,H2O、Na+遇酚酞都不变色,

则遇酚酞变色的原因是溶液中存在OH-,即假设OH-能使无色酚酞试液显红色成立,

故答案为:成立;

(4)因氢氧化钡溶液中存在OH-,则氢氧化钡溶液中滴入几滴酚酞试液,溶液变红,

故答案为:显红色.

单项选择题
阅读理解

阅读表达。

     A common concern we often hear with regard to single

children is whether one child necessarily means a lonely child.

Many single-child parents feel a dilemma associated with their

decision to have only one child. There are no other children in the

family for the child to associate with, and this may lead to the

child feeling lonely at times, especially during vacations.

      Another common argument against having just one child is

that an only child may be more spoiled than one with brothers or

sisters. Many people believe that a single child will not have

learned to negotiate with others, and respect the give-and-take

involved in many relationships. Some think this may leave the

child less able to interact well with people his or her own age than

one who has been raised with brothers or sisters.

      However, for some single-child parents, particularly those

with busy careers, the pressures of giving time and energy to a

second child can seem too great,resulting in them electing to have

no more children. For other parents, the financial burden of having

a second child may be the prime consideration. Still others believe

that, ______, the parents can give,and the child can receive,

more quality time and attention. This often leads to increased self-

respect which, combined with increased independence, can lead

to the child being more confident.

1.What is the best title of the passage?  ( Please answer within10 words. )

____________________________________________________________________

2. Which sentence in the passage can be replaced by thefollowing one?

     Many single-child parents feel it hard to decide whether to  have only one child.

____________________________________________________________________

3. Please fill in the blank in the third paragraph with proper words or phrases to complete the sentence.

( Please answer within 10 words.)

____________________________________________________________________

4.  Would you like to have a brother or sister in your family? Why?( Please answer within 30 words.)

_____________________________________________________________________

5. Translate the underlined sentence in the second paragraph into Chinese.

______________________________________________________________________