问题 问答题

已知:①在化工生产中,原料往往不能全部转化成产品;②工业上常用电解纯净的饱和食盐水的方法来得到烧碱溶液,再经过浓缩,蒸发等步骤制造固体烧碱.现要分析一种仓库里的固体烧碱样品.

(1)猜测一下,该烧碱样品中可能含有哪些杂质?

(2)设计一个实验方案,来证实你的猜测是正确的.

实验步骤实验现象实验结论

答案

(1)电解纯净的饱和食盐水的方法来得到烧碱时,NaCl不能全部转化为产品,可以推测出烧碱样品中可能含有NaCl,又由于烧碱生产和贮存过程中会吸收空气中的CO2 而生成Na2CO3,还可以推测烧碱样品中可能含有Na2CO3

(2)设计实验方案来验证猜测是正确的,实质是验证样品中Cl-和CO32--的存在,检验Cl-通常用AgNO3溶液和稀硝酸;检验CO32-通常用酸溶液,为防止对Cl-鉴别产生干扰,酸溶液只能用稀硝酸,实验方案设计中一定要注意排除CO32-

Cl-鉴别的干扰以及OH-对Cl-鉴别的干扰;

故答案为:

(1)可能含有NaCl和Na2CO3(2)见下表

实验步骤实验现象实验结论
把固体烧碱溶于水  
取少量溶液,滴入稀酸有气体逸出有Na2CO3
取少量溶液,先滴入过量稀硝酸,再滴入硝酸银溶液

(或者取少量溶液,先滴入足量硝酸银溶液,再滴入过量硝酸)

有气体逸出,滴入硝酸银溶液后有白色沉淀(或者:先有沉淀生成,滴入过量稀硝酸后,部分沉淀溶解,并有气体逸出)有NaCl

判断题
单项选择题

Vienna was one of the music centers of Europe during the classical period, and Haydn, Mozart, and Beethoven were all active there. As the (1) of the Holy Roman Empire (which included parts of present-day Austria, Germany, Italy, Hungary, Czech and Slovakia), it was a (2) cultural and commercial center (3) a cosmopolitan character. Its population of almost 250,000 (in 1800) made Vienna the fourth largest city in Europe. All three (4) masters were born elsewhere, but they were (5) to Vienna to study and to seek (6) . In Vienna, Haydn and Mozart became close friends and influenced each other’s musical (7) . Beethoven traveled to Vienna at sixteen to play for Mozart; at twenty-two, he returned to study with Haydn.

Aristocrats from all over the Empire spent the winter in Vienna, sometimes bringing their private (8) . Music was an important part of court life, and a good orchestra was a (9) of prestige. Many of the nobility were excellent musicians.

Much music was heard in (10) concerts where aristocrats and wealthy commoners played (11) professional musicians. Mozart and Beethoven often earned money by performing in these intimate concerts. The nobility (12) hired servants who could (13) as musicians. An advertisement in the Vienna Gazette of 1789 (14) : " Wanted, for a house of the gentry, a manservant who knows how to play the violin well. "

In Vienna there was also (15) music, light and popular in (16) . Small street bands of wind and string players played at garden parties or under the windows of people (17) to throw (18) money. Haydn and Mozart wrote many outdoor entertainment (19) , (20) they called divertimentos or serenades. Vienna’s great love of music and its enthusiastic demand for new works made it the chosen city of Haydn, Mozart and Beethoven.

19()

A.music

B.melody

C.pieces

D.series