问题 填空题

某学生欲用已知物质的量浓度的醋酸来测定未知物质的量浓度的氢氧化钠溶液时,选择适当的指示剂。请填写下列空白:

(1)用标准醋酸滴定待测的氢氧化钠溶液时,从下列选项中选出最恰当的一项________。

 锥形瓶中溶液滴定管中溶液选用指示剂选用滴定管
A石蕊(乙)
B甲基橙(甲)
C酚酞(甲)
D石蕊(乙)
 

滴定时应左手握酸式滴定管的活塞,右手摇动锥形瓶,眼睛注视                        。直到加入一滴醋酸后,溶液颜色由       色变为    色,并在半分钟内溶液颜色不改变为止。

(2)下列操作中可能使所测氢氧化钠溶液的浓度值偏低的是        

A.酸式滴定管未用标准醋酸润洗就直接注入标准醋酸

B.滴定前盛放氢氧化钠溶液的锥形瓶用蒸馏水洗净后未干燥

C.酸式滴定管在滴定前有气泡,滴定后气泡消失

D.读取醋酸体积时,开始仰视读数,滴定结束后俯视读数

(3)某学生根据3次实验分别记录有关数据如表:

 待测氢氧化钠0.100mol/L醋酸的体积
滴定次数溶液的体积(ml)滴定前的刻度(ml)滴定后的刻度(ml)
第一次25.000.0024.98
第二次25.001.5627.86
第三次25.000.2225.24
 

依据上表数据计算该氢氧化钠溶液的物质的量浓度为             

(4)下图为上述25 mL NaOH溶液中逐滴滴加CH3COOH溶液过程中溶液pH的变化曲线,请回答:

①B点溶液呈中性,有人据此认为,在B点时NaOH与CH3COOH恰好完全反应,这种看法是否正确?________(选填“是”或“否”)。若不正确,则二者恰好完全反应的点是在AB区间还是BD区间内?________区间.(若正确,此问不答)。

②在D点时,溶液中c(CH3COO)+c(CH3COOH)________2c(Na)。(填“>”、“<”或“=”)

答案

(共12分)(1)C;注视锥形瓶内溶液颜色变化;红色;浅红色 (2)D

(3)0.10mol/L (4)①否;AB ②=

题目分析:(1)用标准醋酸滴定待测的氢氧化钠溶液时,锥形瓶中应该盛放待测液氢氧化钠。醋酸显酸性,则应该用酸式滴定管。醋酸钠水解溶液显碱性,因此应该选择酚酞作指示剂,因此答案选C;准确判断滴定终点是关键,所以滴定时应左手握酸式滴定管的活塞,右手摇动锥形瓶,眼睛注视锥形瓶内溶液颜色变化。酚酞的变色范围是8.2~10.0,所以滴定终点时的实验现象是直到加入一滴醋酸后,溶液颜色由红色变为浅红色,并在半分钟内溶液颜色不改变为止。

(2)中和滴定实验误差分析的总依据为:根据可知,由于C标、V待均为定植,所以C测的大小取决于V标的大小,即V标:偏大或偏小,则C测偏大或偏小。A、酸式滴定管未用标准醋酸润洗就直接注入标准醋酸,则醋酸的浓度被稀释,消耗醋酸的体积增加,所以测定结果偏高;B、滴定前盛放氢氧化钠溶液的锥形瓶用蒸馏水洗净后未干燥属于正确的操作,测定结果不变;C、酸式滴定管在滴定前有气泡,滴定后气泡消失,则导致消耗醋酸溶液的体积增加,测定结果偏高;D、读取醋酸体积时,开始仰视读数,读数偏大。滴定结束后俯视读数,读数偏小,因此电子消耗醋酸溶液的体积减少,测定结果偏低,答案选D。

(3)根据表中数据可知,三次实验中消耗醋酸溶液的体积分别是24.98ml、27.86ml-1.56ml=26.3ml、25.24ml-0.22ml=25.02ml。显然第二次实验误差偏大,应该舍去,实验消耗醋酸溶液体积的平均值==25.00ml。由于氢氧化钠溶液的体积也是25.00ml,因此该氢氧化钠溶液的物质的量浓度为0.100mol/L。

(4)①由于醋酸是弱酸,与氢氧化钠恰好反应时生成醋酸钠水解溶液显碱性,因此当溶液显中性时,二者并不没有恰好反应。二者恰好反应时溶液显碱性,因此二者恰好完全反应的点是在AB区间。

②当加入50ml醋酸溶液时,醋酸过量,所得溶液是由醋酸和醋酸钠构成的混合液,且二者的物质的量浓度相等,因此根据物料守恒可知c(CH3COO)+c(CH3COOH)=2c(Na)。

完形填空

阅读下面的短文,并根据短文后的要求答题(请注意问题后的字数要求)。

Most American teenagers used to spend their summer vacations holding multiple jobs. However, with the increase in gas prices, teenagers chose to stay at home instead of going out of the town. “I wish the prices would        .The expense of driving to places is affecting our daily life.”said Alicia, still a senior at Enochs High School in Modesto, California.

Alicia, who spent her summer at her dad’s house, said that there would be no point in getting a job. “The drive to my workplace is so long that I would hardly be making any profit because all my money would be going toward gas,”she said.

Teenagers are now forced to give up the pleasure of driving around the town without purpose.“Instead of driving around looking for something to do, I now find myself planning the way in advance so I don’t waste necessary gas,” said Stephen Macko, a student at Davis High School in Modesto.

What kinds of things are teenagers doing in order to conserve gas? Alicia saves gas by doing all of her things at one time so she doesn’t have to go home and leave again.

“I try to do it all in one trip so I don’t have to always be running around and wasting gas,”she said.“I know that when I go to lunch with my friends, we make sure to go somewhere near all of our houses so we save gas.”“But it’s hard, considering I drive a big truck. I also try to get a lift from my friends when they are going to places that I am going to.”said Stephen. Some try not to accelerate too much. Teenagers will have to continue changing their lifestyles unless the price of gas decreases. However, that might not be a bad thing.

小题1:What is the best title of this passage? ( Please answer within 10 words.)

                                                                   

小题2:Fill in the blank in the second paragraph with proper words or phrases to complete the sentence. ( Please answer within 7 words.)

                                                                  

小题3:Translate the underlined sentence in Paragraph 3 into Chinese.

                                                                  

小题4: Find a sentence in the passage to replace the following one.

There is such a long distance between my home and the workplace that I would make little money if I drive to work since the gas will cost all the money I earn.

                                                                  

小题5:List one example of what some teenagers do to save gas.

                                                                  

单项选择题