问题 单项选择题

During the past three years, the staff members of the Smithsonian Institution’s Family Folklore Project have interviewed hundreds of persons about their family folklore. To prepare for these interviews we drew upon our academic backgrounds in folklore and American studies, and upon our personal backgrounds as members of families, in addition, we reviewed the major instruction guides in genealogy, oral history, family history, and folklore fieldwork. Although these publications were all helpful in some way, no single book was completely adequate since family folklore combines aspects of all the above disciplines. Over time we have developed guidelines and questions that have proven successful for us; we hope that the following suggestions will be helpful to anyone who wishes to collect the folklore of his or her own family.

The assumption of this passage is that

A.anyone can successfully interview people about their family folklore without prior training.

B.American history is inherent in the family folklore of Americans.

C.American history and folklore of Americans have no connections.

D.no guidelines are needed in the interviews.

答案

参考答案:B

填空题
实验题

(12分)尖晶石型锰酸锂(LiMn2O4)是一种环保绿色能源新型材料。实验室通过下列方法制取:将MnO2和Li2CO3按4︰1的物质的量比配料,球磨3~5小时,然后升温至600℃~750℃,保温24小时,自然冷却至室温得产品。

(1)保温24小时的目的是____________________________________________________。

(2)写出该反应的化学方程式_________________________________________________。

(3)实验室测定锰酸锂中锰的平均化合价的实验步骤如下:

步骤1:准确称取0.1g左右的尖晶石型锰酸锂试样于锥形瓶中,加入5mL稀硫酸、10.00mL 0.2000mol/L草酸钠(Na2C2O4)标准溶液,于80℃水浴加热溶解;

步骤2:待试样全部溶解,立即用浓度为0.2000mol/L的高锰酸钾溶液滴定至终点;

步骤3:计算样品得电子的物质的量n;

步骤4:将溶液中Mn2+氧化为Mn3+,再用硫酸亚铁铵标准溶液滴定,记录实验数据,计算出样品中Mn元素的质量为m;

步骤5:将实验步骤1-4重复2次。

已知反应: 2Mn3++C2O42-=2Mn2++2CO2↑;Mn4++C2O42-=Mn2++2CO2

2MnO4+5C2O42-+16H+="2" Mn2++10 CO2↑+8H2O

①步骤2中,为判断滴定终点,_________(填“需要”或“不需要”)加入指示剂。

②步骤4中,滴定时盛放硫酸亚铁铵标准溶液的玻璃仪器是___________________。

③请用样品得电子的物质的量n和样品中Mn元素的质量m来表示样品中Mn元素的化合价=_____。