问题 实验题

硫酸亚锡(SuSO4)是一种重要的硫酸盐,广泛应用于镀锡工业。某研究小组设计SnSO4制备路线如下:

查阅资料:

I.酸性条件下,锡在水溶液中有Sn2+、Sn4+两种主要存在形式,Sn2+易被氧化。

II.SnC12易水解生成碱式氯化亚锡[Sn(OH)Cl]。

回答下列问题:

(1)SnC12粉末需要加浓盐酸进行溶解,请用化学方程式说明原因___________________。

(2)在SnC12溶液中加入Sn粉的作用有两个:①调节溶液pH ②_________________。

(3)操作I中使用的玻璃仪器有___________________。

(4)该小组通过下列方法测定所用锡粉的纯度(杂质不参与反应):

①将试样溶于盐酸中,发生的反应为:Sn+2HCl═SnCl2+H2↑;

②加入过量的FeCl3,发生的反应为:SnCl2+ FeCl3= SnCl4+ FeCl2

③用已知浓度的K2Cr2O7滴定生成的Fe2+,发生的反应为:6FeCl2+K2Cr2O7+14HCl═6FeCl3+2KCl+2CrCl3+7H2O

滴定时,K2Cr2O7溶液应该装在____________(填“酸式”或“碱式”)滴定管中。

若取2.0g锡粉,经上述各步反应后,共用去0.100mol/L K2Cr2O7溶液40.00mL,锡粉中锡的质量分数是____________________。

答案

(1)SnCl2+H2OSn(OH)Cl+HCl(2)防止Sn2+被氧化(3)漏斗、玻璃棒、烧杯(4)酸式;71.4%

题目分析:(1)SnCl2易水解生成碱式氯化亚锡,存在平衡SnCl2+H2OSn(OH)Cl+HCl,加入盐酸,使该平衡向左移动,抑制Sn2+水解;(2)由题意知Sn2+易被氧化,加入Sn粉除调节溶液pH外,还防止Sn2+被氧化;(3)由流程图可知,操作Ⅰ是从溶液中得到含结晶水的晶体,只能采取蒸发浓缩、冷却结晶、过滤、洗涤得到,故用到的玻璃仪器为漏斗、玻璃棒、烧杯;(4)碱式滴定管的胶管与重铬酸钾溶液会有一定的氧化和吸附,影响浓度;令锡粉中锡的质量分数为x,则:

Sn~Sn2+~2Fe3+~2Fe2+K2Cr2O7计算.

119g                            mol

2.0g×x               0.100mol/L×0.040L

=

解得x=71.4%,

单项选择题
单项选择题

I came across an old country guide the other day. It listed all the tradesmen in each village in my part of the country, and it was impressive to see the great variety of services which were available on one’s own doorstep in the late Victorian countryside.

Nowadays a superficial traveler in rural England might conclude that the only village tradesmen still flourishing were either selling frozen food to the inhabitants or selling antiques to visitors. Nevertheless, this would really be a false impression. Admittedly there has been a contraction of village commerce, but its vigor is still remarkable.

Our local grocer’s shop, for example, is actually expanding in spite of the competition from supermarkets in the nearest town. Women sensibly prefer to go there and exchange the local news while doing their shopping, instead of queueing up anonymously at a supermarket. And the proprietor knows well that personal service has a substantial cash value.

His prices may be a bit higher than those in the town, but he will deliver anything at any time. His assistants think nothing of bicycling down the village street in their lunch, hour to take a piece of cheese to an old-age pensioner who sent her order by word of mouth with a friend who happened to be passing. The more affluent customers telephone their shopping lists and the goods are on their doorsteps within an hour. They have only to hint at a fancy for some commodity outside the usual stock and the grocer a red-faced figure, instantly obtains it for them.

The village gains from this sort of enterprise, of course. But I also find it satisfactory because a village shop offers one of the few ways in which a modest individualist can still get along in the world without attaching himself to the big battalions of industry or commerce.

Most of the village shopkeepers I know, at any rate, are decidedly individualist in their ways. For exampie, our shoemaker is a formidable figure: a thick-set, irritable man whom children treat with marked respect, knowing that an ill-judged word can provoke an angry eruption at any time. He stares with contempt at the pairs of cheap, mass-produced shoes taken to him for repair: has it come to this, he seems to be saying, that he, a craftsman, should have to waste his skills upon such trash But we all know he will in fact do excellent work upon them. And he makes beautiful shoes for those who can afford such luxury.

In what way is the village shoemaker a “formidable figure”()

A. He seems to pay little attention to public opinion

B. He refuses to mend cheap, mass-produced shoes

C. He is bad-tempered as well as an excellent craftsman

D. He has very high standards of workmanship