问题 问答题

实验室可用NaBr、浓H2SO4、乙醇为原料制备少量溴乙烷:

C2H5-OH+HBr

H2SO4
C2H5Br+H2O

已知反应物的用量为:0.30mol NaBr(s);0.25mol C2H5OH(密度为0.80g-cm-3);36mL浓H2SO4(质量分数为98%,密度为1.84g-mL-1);25mL水.试回答下列问题.

(1)该实验应选择图中的a装置还是b装置?______.

(2)反应装置中的烧瓶应选择下列哪种规格最合适______

A.50mL   B.100mL    C.150mL    D.250mL

(3)冷凝管中的冷凝水的流向应是______

A.A进B出            B.B进A出             C.从A进或B进均可

(4)可能发生的副反应为:______、______、______(至少写出3个方程式).

(5)实验完成后,须将烧瓶内的有机物蒸出,结果得到棕黄色的粗溴乙烷,欲得纯净溴乙烷,应采用的措施是______.

答案

(1)由题给信息,知该反应为:C2H5-OH+HBr

H2SO4
C2H5Br+H2O,反应需要加热,所以应采用装置a,

故答案为:a;

(2)烧瓶的规格与所盛液体的体积有关,加热时烧瓶内液体的体积应小于烧瓶的容积的

2
3

V(C2H5OH)=

0.25mol×46g?mol-1
0.80g?cm-3
=14cm-3=14mL,忽略混合时体积变化,混合后液体的总体积约为36mL+25mL+14mL=75mL,所以150mL的烧瓶最合适,故答案为:C; 

(3)冷凝时,水需充满冷凝器,为了防止冷凝器冷凝时,受热不均匀破裂,冷凝水应下进上出.故答案为:B;

(4)可能发生的副反应有:C2H5OH脱水生成乙烯和乙醚;浓H2SO4氧化HBr;C2H5OH脱水炭化等反应.故答案为:

C2H5OH

浓硫酸
170℃
C2H4↑+H2O     2C2H5OH 
浓硫酸
140℃
C2H5OC2H5+H2O

2HBr+H2SO4(浓)

 加热 
.
 
Br2+SO2↑+2H2O       C2H5OH+2H2SO4(浓)
2C+2SO2↑+5H2O

C+2H2SO4(浓)

  △  
.
 
CO2↑+2SO2↑+2H2O(任意选取3个反应即可)

(5)棕黄色的粗溴乙烷,是由于溴乙烷溶解了Br2的缘故,可用质量分数小于5%的稀NaOH溶液洗涤除去,采用稀NaOH溶液,是为了防止C2H5Br的水解.

故答案为:将粗溴乙烷和稀NaOH(aq)的混合物放在分液漏斗中用力振荡,并不断放气,至油层无色,分液可得纯溴乙烷.

填空题
阅读理解

You’re out to dinner. The food is delicious and the service is fine. You decide to leave a big fat tip. Why? The answer may not be as simple as you think.

Tipping, psychologists have found, is not just about service. Instead, studies have shown that tipping can be affected by psychological reactions to a series of different factors from the waiter’s choice of words to how they carry themselves while taking orders to the bill’s total.

“Studies before have shown that mimicry (模仿) brings into positive feelings for the mimicker,” wrote Rick van Baaren, a social psychology professor. “These studies show that people who are being mimicked become more generous toward the person who mimics them.”

So Rick van Baren divided 59 waiters into two groups. He requested that half serve with a phrase such as, “Coming up!” Those in the other half were instructed to repeat the orders and preferences back to the customers. Rick van Baaren then compared their take-home(实得收入). The results were clear---it pays to mimic your customer. The copycat waiters earned almost double the amount of tips to the other group.

Leonard Green and Joel Myerson, psychologists at Washington University in St. Louis, found the generosity of a tipper may be limited by his bill. After research on the 1,000 tips left for waiters, cab drivers, hair stylists, they found tip percentages in these three areas dropped as customers’ bills went up.

“That’s also a point of tipping,” Green says. “You have to give a little extra to the cab driver for being there to pick you up and something to the waiter for being there to serve you. If they weren’t there you’d never get any service. So part of the idea of a tip is for just being there.”

小题1:According to the passage, a customer gives the cab driver a tip for ____.

A.driver’s politeness

B.being there

C.driver’s attitudes

D.driver’s mimicry小题2:According to the passage, which of the following will be likely to show the right change of the tip percentages for the three areas researched?

小题3:According to the passage, we know the writer seems to _________.

A.oppose Mr. Green’s idea about tipping

B.support the opinions of Mr. Green and Rick van Baaren about tipping

C.give his generous tip to the waiters very often

D.think part of Mr. Green’s explanation is reasonable