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1.
《昭通师范高等专科学校学报》2017,(5):48-50
通过实验,得出昭通大山包党参中的多糖含量.根据多糖溶于水但不溶于乙醇选用水提醇沉法粗提昭通大山包党参中的多糖,再用丙酮和石油醚的混合液(V∶V=1∶1)除粗糖中的脂肪及脂溶性杂质,并用正丁醇和氯仿的混合液(V∶V=1∶5)除蛋白(Sevage法)得到多糖纯品.所得昭通大山包党参中多糖的含量为4.61%. 相似文献
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周存峰 《数理化学习(高中版)》2008,(4):49-50
请认真分析比较下面两道涉及铝沉淀的图象.例1图1是向MgCl2和AlCl3混合液中,先加入NaOH溶液后又滴加盐酸,所得沉淀y(mol)与试剂体积V(mL)之间的关系.以下结论不正确的是()(A)NaOH和盐酸的分界点是6mL处(B)原混合液中c(Al3 )∶c(Mg2 )∶c(Cl-)=1∶1∶5(C)c(NaOH)∶c(HCl)=2∶1(D 相似文献
3.
磷酸三丁脂萃取-火焰原子吸收光度法测定金 总被引：1，自引：0，他引：1
研究了稀释剂的选择、王水浓度、TBP浓度、温度、振荡时间和相比等对萃取金的影响,提出以20%(V/V)的磷酸三丁脂—乙酸丁脂溶液直接从20%(V/V)王水介质中萃取金(Ⅲ),然后用火焰原子吸收光度法测定.以乙酸丁脂为稀释剂,在20%(V/V)的王水介质中,TBP浓度为20%(V/V)、常温下、人工振荡90 s或机器振荡30 s、有机相与水相比为1∶4金均能被萃取完全. 相似文献
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电解质溶液中离子浓度大小比较问题是高考的热点,也是学习的难点.现结合一些典型例题对常见类型进行梳理,以明确解题思路.类型一单一溶液中各离子浓度的比较(1)弱电解质的电离是微弱的.多元弱酸溶液分步电离,电离程度逐级减弱.如H3S溶液中:c(H2S)>c(H+)>c(HS-)>c(S2-).(2)弱电解质离子的水解是微弱的(双水解除外).多元弱酸的正盐溶液中,弱酸根离子分步水解,水解程度逐级减弱.如 相似文献
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从表面上看Ag~ 离子氧化能力应比Ag(NH_3)_(2~ )离子强,因为E_(Ag~o) /Ag=0.799(V),而=0.373(V)。但实际上硝酸银溶液不能直接被醛还原产生“银镜”,而必须被氨络合以后才能反应。 AgNO_3水溶液由于水解原因呈弱酸性,pH值约5左右。Ag~ 离子和NO_(3~-)离子均有较强的氧化性,根据它们在酸性溶液中标准电极电势的大小,不难判断NO_(3~-)离子比Ag~ 离子氧化能力强: 相似文献
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电解质溶液是重要的基础理论之一,它与物质结构理论、化学平衡理论有着密切的联系,并且与化学实验、化学计算互相渗透,对理解及应用能力的要求较高.随着人们环保意识的增强,与溶液知识相关的废水分析与处理问题,将会与离子共存、pH求算及中和滴定等一起融入未来的高考试题中.一、命题基点1.电解质和非电解质(1)电解质和非电解质比较(2)强、弱电解质的比较2.电解质溶液酸碱性的表示方法(1)水的离子积常数(2)溶液的pH、pOH与pKw3.盐类的水解(1)正盐溶液的酸碱性(2)盐类的水解规律(3)影响盐类水解的因素(4)酸式盐溶液的酸碱性4.溶液中的三守… 相似文献
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《中学生数理化(高中版)》2006,(4)
一、盐类的水解 (1)盐类水解的实质:盐电离出来的一种或多种离子与水电离出来的 H 或OH-结合生成弱电解质,从而促进了水的电离． (2)盐类水解的规律:有弱才水解,无弱不水解;谁弱谁水解,谁强显谁性;越弱越水解,都弱双水解．例1 在纯碱溶液中滴入酚酞,溶液变红．若在该溶液中再滴入过量的氯化钡溶液,所观察到的现象是 (以离子方程式和简要文字 相似文献
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龙德清 《郧阳师范高等专科学校学报》2002,22(6):33-35
通过硫酸水解,将木屑中的纤维素转化为葡萄糖,在催化剂作用下,用硝酸将其氧化,制取了草酸.经研究,本法最佳配料比及工艺条件为:干木屑∶硫酸(50%)∶硝酸(65%)∶催化剂=30g∶30mL∶4mL∶0.03g,浸泡水解时间为4h以上,反应时间5h以上,反应温度控制在65～70℃.所得草酸纯度为97.5%,收率达50%.对产品理化数据指标及工艺环保措施进行了分析. 相似文献
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《中学生数理化(高中版)》2018,(4)
<正>一、盐类水解原理1.定义:在溶液中,盐电离出来的阴离子或阳离子与水所电离出来的H+或OH-结合生成弱电解质,这种作用叫做盐类的水解。2.盐类水解的实质:使水的电离平衡发生移动。3.盐类水解的结果:盐的溶液呈现出不同程度的酸碱性。4.盐类水解的条件:(1)盐必须能溶于水中;(2)生成盐的酸或碱是弱酸或弱碱(有弱 相似文献
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陈世华 《数理化学习(高中版)》2006,(11)
五、碱性高锰酸钾溶液氧化烯烃并酸化,生成羧酸指点迷津:不饱知键直接相连的碳原子上有氢的烯烃或炔烃被酸性高锰酸钾氧化生成—COOH,常常利用产物逆推烃的结构.例6(2005年高考天津理综卷)Ⅰ.某天然油脂A的分子式为C57H106O6.1mol该油脂水解可得到1mol甘油、1mol不饱和脂肪酸B和2mol直链饱和脂肪酸C.经测定B的相对分子质量为280,原子个数比为C∶H∶O=9∶16∶1.(1)写出B的分子式:;(2)写出C的结构简式:;C的名称是.(3)写出含5个碳原子的C的同系物的同分异构体的结构简式:.Ⅱ.RCH=CHR′与碱性KMnO4溶液共热后酸化,发生双键断裂生成羧… 相似文献
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《海外英语》2007,(4):36
There are numbers of crossroads on our long and unpredictable life journey where we totally have no idea about which direction to choose. No matter what our decision is, we should not turn back, but face the music and go ahead instead. I am this kind of girl who always does try without regretting, one example is how I dealt with my love. 相似文献
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Migration occurs behind a variety of reasons and has a great effect on the whole world. People may migrate in order to improve their economic situation, or in order to escape civil strife, persecution, and environmental disasters. The impact of migration is complex, bringing both benefits anddisadvantages. This paper briefly talks about the causes of migration, the allocation of benefits, and the ways in which individual countries and the international community deal with this important subject. 相似文献
14.
Sister Carrie is one of the most controversial characters in American literature.Thought as a "fallen woman" firstly,she was defined as a "new woman" by some critics later. However, by digging into the motivaton behind the whole process of Carrie's "success", the relationship between Carrie and her creator (the author), the social conditions of then American, it can be found that Carrie has never been free-standing on her thought and she has never found her real-sdf even after becoming a famous actress. In a society dominated by mass consumerism Carrie is only an adherent of her own desires. She also is a representative of all those country girls flooded into cities, a symbol and a sacrifice of the urbanization of America in a time countryside was overcome by cities. 相似文献
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RUZBEHANI Mohsen 《重庆大学学报(英文版)》2004,3(1):20-25
1.IntroductionOne-cyclecontrolmethod,whichwasproposedaboutonedecadeago[1],hasbecomeanattractivemethodinspecialfieldssuchaspowerfactorcorrection[2-6],switchingamplifiers[7,8],etc.Themainideaofthiscontrollerisbasedonintegrationofdiodevoltageinone-cycleandforcesittobeexactlyequaltothereferencevalue.Themainadvantageofthiscontrollerisitsrealtimeabilitytorejectthevariationofinputvoltage[1].Despitethisgreatability,ithasnogoodperformancesinrejectingofloaddisturbanceandfollowingreferencecommands.Espec… 相似文献
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Rajesh Kanoi 《海外英语》2007,(1):52
Today, Sunday morning, I sit thinking and typing at my computer. My thoughts are in my homeland, India and my body is in China. The body is here and mind there for a good reason. Mr. Hu is president and I am resident and both are in each other's countries (what a difference the absence of one small letter makes!). Mr. Hu will return in a few days and I will stay on longer. 相似文献
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正A One day a pig went to the stable(马棚)to see his good friend,an oldhorse,and was going to stay there forthenight.Night came and it was time forsleep.The pig went into the straw heap(稻草堆)and lay comfortably.A longtime passed,but the horse was stillstanding there and did not move.Thepig asked the horse why he did not go tosleep."Standing like this is the begin-ning ofsleeping,"answered the horse. 相似文献
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《今日中学生》2014,(9)
正1.Any fool can count the seeds in an apple.Only God can count all the apples in one seed.2.Happy families are all alike;every unhappy family is unhappy in its own way.3.Memories are the key not to the past,but to the future.4.Sometimes in the dark you see what you want to see.5.There is a great difference between 相似文献
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《重庆大学学报(英文版)》2014,(2)
正Scope and Policy The Journal of Chongqing University-English Edition(JCQU-E)is a peerreviewed journal publishing research articles in multiple disciplines of science and technology,covering civil and environmental engineering,chemical engineering,biotechnology,mechanical and electrical engineering,computer and data processing,mining,metallurgy,materials science,and interdisciplines thereof. 相似文献