问题
问答题 简答题
离心泵的抽空有什么现象？
答案
参考答案：
泵在运行中，突然发生噪音、振动并伴随扬程、流量、效率的降低，电机电流的减少，压力表的指示压力剧烈波动，如果更严重一睦，压力表回零，打法上量。
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离心泵的抽空有什么现象？
参考答案：
泵在运行中，突然发生噪音、振动并伴随扬程、流量、效率的降低，电机电流的减少，压力表的指示压力剧烈波动，如果更严重一睦，压力表回零，打法上量。
Charlotte Whitehead was born in England in 1843, and moved to Montreal, Canada at the age five with her family. While her ill elder sister throughout the years, Charlotte discovered she had a(an) in medicine. At 18 she married and a family. Several years later, Charlotte said she wanted to be a . Her husband supported her decision. , Canadian medical schools did not women students at the time. Therefore, Charlotte went to the United States to study at the Women’s Medical College in Philadelphia. It took her five years to her medical degree. Upon graduation, Charlotte to Montreal and set up a private . Three years later, she moved to Winnipeg, Manitoba, and there she was once again a doctor. Many of her patients were from the nearby timber and railway camps. Charlotte herself operating on damaged limbs and setting bones, in addition to delivering all the babies in the area. But Charlotte had been practicing without a license. She had a doctor’s license in both Montreal and Winnipeg, but was . The Manitoba College of Physicians and Surgeons, an all-male board, wanted her to her studies at a Canadian medical college! Charlotte refused to her patients to spend time studying what she already knew. So in 1887, she appeared to the Manitoba Legislature to a license to her but they, too, refused. Charlotte to practice without a license until 1912. She died four years later at the age of 73. In 1993, 77 years after her , a medical license was issued to Charlotte. This decision was made by the Manitoba Legislature to honor “this courageous and pioneering woman.”
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（16分）某同学从网络上了解到菠菜中富含可溶性的两类正盐：草酸盐和碳酸盐。该同学欲用实验验证这一事实并检测其中草酸盐的含量。查阅资料得知草酸（H2C2O4）是一种二元有机弱酸，具有较强的还原性；草酸钙（CaC2O4）不溶于水能溶于稀硫酸。请回答下列问题：
（1）该学生将菠菜研磨成粉末、热水浸泡、过滤得到澄清溶液A。研磨菠菜使用的实验仪器的名称为 。
（2）设计实验方案验证菠菜中含有草酸盐和碳酸盐，补充完成预期现象和结论。
| 实验步骤 | 预期现象和结论 |
| 步骤1：调节溶液A至弱碱性，滴加足量CaCl2溶液。 | ①出现白色沉淀，说明菠菜中 。 |
| 步骤2：取步骤1的沉淀于试管中，加入足量的稀硫酸，沉淀完全溶解，并将产生的无色无味的气体通入澄清石灰水中。 | ② 。 |
| 步骤3：向步骤2得到的溶液中滴加几滴高锰酸钾溶液。 | ③ 。 |
①操作：取m g菠菜样品，将其中草酸盐全部转化为CaC2O4沉淀分离出来置于烧杯中，用过量的稀硫酸完全溶解后，溶液转入 中并加水配制成250mL溶液。每次移取25．00mL该溶液于锥形瓶中，用0．0100mol·L－1 KMnO4标准溶液滴定，平均消耗标准溶液V mL。KMnO4滴定实验时发生的离子方程式为 。
②计算：菠菜中草酸盐（以C2O42－计算）的质量分数为（可以只列式不化简） 。
③误差分析: 下列操作会使测定结果偏高的是 。
A．配制溶液时未洗涤烧杯和玻璃棒就加水定容
B．锥形瓶未干燥就加入待测液进行滴定
C．未用标准液润洗就加入标准液开始滴定
D．滴定前尖嘴处有气泡滴定后气泡消失
E．滴定后俯视读数