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某校化学研究性学习小组的同学对一瓶敞口放置的氢氧化钠产生了兴趣，甲乙两组同学围绕这瓶氢氧化钠进行了一系列的探究活动．

______①氢氧化钠是否完全变质②样品中碳酸钠的质量分数是多少？

______①氢氧化钠与二氧化碳反应生成碳酸钠和水．

②向氢氧化钠和碳酸钠混合物中加入盐酸时，盐酸先与氢氧化钠反应，再与碳酸钠反应；

______实验一：探究氢氧化钠固体的变质情况．

①取少量该固体样品置于试管中，向其中加入稀盐酸，发现有气泡产生，说明该样品中含有碳酸钠，由此可确定该固体已发生变质．则反应方程式为：______．

②如果氢氧化钠已经完全变质，甲组同学认为取少量固体溶于水，向其中滴加无色酚酞后，溶液应呈无色，乙组同学思考后认为甲组同学的想法是错误的，原因是：______

．

③为探究该固体中是否还有未变质的氢氧化钠，同学们又进行了如下表所示的实验．请将下表填写完整．

实验目的实验操作现象结论或化学方程式
除去碳酸钠取少量该固体样品溶于水配成溶液，滴加适量的氯化钙溶液，充分反应后过滤

______

有关反应的化学方程式为

______

检验是否含有氢氧化钠向过滤后的滤液中滴入____________该样品中含有氢氧化钠
实验二：测定其中碳酸钠的质量分数

______

①甲组同学：称取20.00样品，放入过量的盐酸直到反应停止，共收集到4.40g二氧化碳．（设计思路：根据样品与盐酸反应生成二氧化碳的质量求出碳酸钠的质量，再计算样品中碳酸钠的质量分数．）

②乙组同学：称取20.00g样品，加水配成溶液，向溶液中加入过量的澄清石灰水．过滤、洗涤、干燥，共得到白色沉淀10.00g．（设计思路：根据样品与石灰水反应生成沉淀碳酸钙的质量，先求出碳酸钠的质量，再计算样品中碳酸钠的质量分数．）

______根据两组同学的实验结果，请你帮助他们计算出样品中碳酸钠的质量分数：（任选一组写出计算过程）

______

（1）在交流时，老师问同学们“能否用上述实验所得的数据计算出样品中氢氧化钠的质量分数”，甲乙两组的同学都一致认为可以．但小明思考后，觉得甲、乙两种方案都不妥，理由是：______．

（2）小明又重新设计新方案：先用电子秤准确称取20.00g变质的NaOH样品放入锥形瓶中，用电子秤秤得锥形瓶及样品的总质量为70.00g，再把175.00g7.3%稀盐酸平均分成7份依次加入样品中，每次充分反应用电子秤秤得锥形瓶及所盛物质的质量，实验数据记录如下：

加入盐酸的次数第一次第二次第三次第四次第五次第六次第七次
锥形瓶及所盛物质的总质量95.00120145170192.8215.6240.6
（2）请根据上述实验数据，计算样品中氢氧化钠的质量分数为______

（不要写出计算过程）

答案

实验一：①盐酸和碳酸钠反应生成氯化钠、水和二氧化碳，反应方程式为Na2CO3+2HCl=2NaCl+H2O+CO2↑；

②因为碳酸钠和氢氧化钠溶液都显碱性，使酚酞试液变成红色，所以不能先用酚酞试液检验；

③氯化钙和碳酸钠反应生成碳酸钙白色沉淀和氯化钠，氢氧化钠溶液能使酚酞试液变红．

实验目的实验操作现象结论或化学方程式
除去碳酸钠取少量该固体样品溶于水配成溶液，滴加适量的氯化钙溶液，

充分反应后过滤

白色沉淀有关反应的化学方程式为

Na2CO3+CaCl2=2NaCl+CaCO3↓

检验是否含有氢氧化钠向过滤后的滤液中滴入酚酞试液变红该样品中含有氢氧化钠
实验二：【解决问题】①设碳酸钠质量为x

Na2CO3+2HCl=2NaCl+H2O+CO2↑

106                   44

x                    4.4g

106
x
=
44
4.4g
     x=10.6g

 样品中碳酸钠的质量分数=

10.6g
20g
×100%=53.0% 

答：样品中碳酸钠的质量分数53.0%．  

或②设碳酸钠质量为y

Na2CO3+CaCl2=2NaCl+CaCO3↓

106                 100

y                   10.00g

  

106
y
=
100
10.00g
     y=10.6g

样品中碳酸钠的质量分数=

10.6g
20g
×100%=53.0% 

答：样品中碳酸钠的质量分数53.0%．   

【交流与反思】（1）氢氧化钠具有吸水性，样品中除去碳酸钠不只有氢氧化钠还有水，故甲、乙两种方案都不妥；

（2）盐酸先和氢氧化钠反应，没有气体生成，所以开始溶液质量不变，氢氧化钠反应完毕后盐酸再和碳酸钠反应生成二氧化碳气体，质量会减少．

由题中数据分析可知，前四次溶液质量没有变化，所以前四次反应的盐酸和氢氧化钠消耗的．

氢氧化钠消耗盐酸的质量为175.00g×4/7=100.0g

设样品中氢氧化钠的质量为x．

NaOH+HCl=NaCl+H2O

40     36.5

x      100．Og×7.3%

40
x
=
36.5
100.0g×7.3%
       x=8.0g

样品中氢氧化钠的质量分数=

8.0g
20g
×100%=40.0%

答：样品中氢氧化钠的质量分数为40.0%．

故答案为：实验一：①Na2CO3+2HCl=2NaCl+H2O+CO2↑；

②产生白色沉淀；Na2CO3+CaCl2=2NaCl+CaCO3↓； 酚酞试液；变红；       

实验二：①设碳酸钠质量为x

Na2CO3+2HCl=2NaCl+H2O+CO2↑

106                   44

x                    4.4g

106
x
=
44
4.4g
     x=10.6g

 样品中碳酸钠的质量分数=

10.6g
20g
×100%=53.0% 

答：样品中碳酸钠的质量分数53.0%．  

或②设碳酸钠质量为y

Na2CO3+CaCl2=2NaCl+CaCO3↓

106                 100

y                   10.00g

  

106
y
=
100
10.00g
     y=10.6g

样品中碳酸钠的质量分数=

10.6g
20g
×100%=53.0% 

答：样品中碳酸钠的质量分数53.0%．

【交流与反思】（1）理由是：样品中有水，无法测出样品的氢氧化钠的质量；

（2）40.0%．

单项选择题

振动堆焊，焊至最后一圈时，停止（），关闭切削液。

A.横向移动

B.纵向移动

C.转动

D.移动
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单项选择题

Social-networking sites offer users easy ways to present idealized images of themselves, even if those ideals don’t always square with their real-world personalities. Psychology researcher Soraya Mehdizadeh has discovered a way to poke through the offline-online curtain: she has used Faeebook to predict a person’s level of narcissism and self-esteem.

Mehdizadeh, who conducted the study as an undergraduate at Toronto’s York University, gained access to the Faeebook accounts of 100 college students and measured activities like photo sharing, wall postings and status updates; she also studied how frequently users logged on and how often they remained online during each session. Her findings were published recently in Cyberpsyehology, Behavior and Social Networking.

After measuring each subject using the Narcissism Personality Inventory and Rosenberg Self-Esteem Scale, Mehdizadeh, who graduated from York this past spring, discovered narcissists and people with lower self-esteem were more likely to spend more than an hour a day on Facebook and were more prone to post self-promo-tional photos ( striking a pose or using Photoshop, for example). Narcissists were also more likely to showcase themselves through status updates (using phrases like "I’m so glamorous I bleed glitter") and wall activity (posting self-serving links like " My Celebrity Look-alikes" ).

Self-esteem and narcissism are often interrelated but don’t always go hand in hand. Some psychologists believe that narcissists--those who have a pervasive pattern of grandiosity, a need for admiration, as well as a lack of sympathy--unconsciously inflate their sense of self-importance as a defense against feeling inadequate. Not enough empirical research has been produced to confirm that link, although Mehdizadeh’s study seems to support it. Because narcissists have less capacity to sustain intimate or long-term relationships, Mehdizadeh thinks that they would be more drawn to the online world of virtual friends and emotionally detached communication.

Although it seems that Facebook can be used by narcissists to fuel their inflated egos, Mehdizadeh stops short of proclaiming that excessive time spent on Faeebook can turn regular users into narcissists. She also notes that social-networking sites might ultimately be found to have positive effects when used by people with low self-esteem or depression. "If individuals with lower self-esteem are more prone to using Facebook," she says, "the question becomes, ’ Can Facebook help raise self- esteem by allowing patients to talk to each other and help each other in a socially interactive environment’ I don’t think it’s necessarily a bad thing that people with low self-esteem use Facebook.

Facebook’s users（）

A.like to hide themselves

B.maybe show the characters that are different from the real ones

C. (are more likely to) upload the modified photos

D. are often used as the research
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