水中氧的含量测定步骤如下: 步骤1:水中的氧在碱性溶液中将Mn2+氧化为MnO(

题型:计算题

问题:

水中氧的含量测定步骤如下:

步骤1:水中的氧在碱性溶液中将Mn2+氧化为MnO(OH)2

步骤2:加入碘离子将生成的MnO(OH)2再还原成Mn2+离子。

步骤3:用硫代硫酸钠标准溶液滴定步骤2中生成的碘。

有关的测定数据如下:

1:Na2S2O3溶液的标定。取25.00 mL KIO3标准溶液(KIO3浓度:174.8 mg·L-1)与过量KI在酸性介质中反应,用Na2S2O3溶液滴定,消耗12.45 mL。

2:取20.0°C下新鲜水样103.5mL,按上述测定步骤滴定,消耗Na2S2O3标准溶液11.80 mL。已知该温度下水的饱和O2含量为9.08 mg·L-1

3.在20.0°C下密闭放置5天的水样102.2 mL,按上述测定步骤滴定,消耗硫代硫酸钠标准溶液6.75 mL。

5-1 写出上面3步所涉及的化学反应方程式。

5-2    计算标准溶液的浓度(单位mol·L-1)。

5-3 计算新鲜水样中氧的含量(单位mg·L-1)。

5-4 计算陈放水样中氧的含量(单位mg·L-1)。

5-5 以上测定结果说明水样具有什么性质?

考点:化学科学探究
题型:计算题

Over 60﹪of pupils in South African schools choose English for learning and teaching, but only 7﹪of pupils speak English as their home language, a recent South Africa survey shows.

Out of the country’s 12.2 million pupils only 851,536 speak English at home, yet 7.6 million pupils choose English as their favorite language of learning and teaching. Zulu is the most widely spoken home language, spoken by over 3.1 million pupils. However, less than a third of them choose to be taught in Zulu. The same thing is true of Pedi-speaking pupils, only a third of such pupils choosing to be taught in their home language. Besides English,

Afrikaans is the only language that has more pupils choosing it as their language of instruction than it has pupils who speak it at home. In primary schools, most pupils will choose African languages. As early as grade four, many would choose English or Afrikaans in their lessons.

The rising number of English-learning pupils is mainly caused by social and cultural reasons. English is the most common spoken language in official and public life in South Africa, the survey reports. In April 2011, the leaders of higher education and training said that they would take some steps to improve the university teaching and prevent the continuing decline of African languages. They suggested that in future every South African university student could be required to learn at least one African language in order to complete their studies at school.

小题1: We can learn from the passage that most South African pupils__________.

A.speak English both at home and at school

B.are required to learn two languages at school

C.choose English as their primary school language

D.are expected to speak their native language at home.小题2: It can be inferred from the passage that__________________.

A.Afrikaans is the most popular home language in South Africa

B.it’s easier for South African pupils to learn Afrikaans at school.

C.the number of South African pupils learning Afrikaans has increased

D.many South African pupils use Afrikaans at school instead of at home.小题3: The underlined word “decline” in the last paragraph is closest in meaning to “_________”.

A.going downhill

B.spreading widely

C.growing upwards

D.developing further小题4: What is the survey in the passage mainly about?

A.The use of native languages in South African families.

B.The language choice and use among South African pupils.

C.The progress in South Africa’s language teaching education

D.The spread of English at schools in South Africa.

题型:计算题

阅读下面的文章,回答问题。 

一个正常的搜索引擎,其核心功能自然是网页搜索。那搜索结果应该怎样排序才最好呢?实际上,在谷歌主导互联网搜索之前,人们为此伤透脑筋。很显然,搜索引擎应该把重要的网页放到搜素结果中比较靠前的地方。这个方案很容易想到,但是解决的方法却没有想象的那么简单。 

在谷歌诞生之前那段时间,流行的网页排名算法都很类似,它们都使用了一个非常简单的思想:越是重要的网页,访问量就会越大。许多大公司就通过统计网页的访问量来进行网页排名。但是这种排名算法有两个很显著的问题:一是只能够抽样统计,所以统计数据不一定准确,而且访问量的波动会比较大,想要得到准确的统计需要大量的时间和人力,还只能维持很短的有效时间;二是访问量并不一定能体现网页的“重要程度”——可能一些比较早接触互联网的网民还记得,那时有很多人推出了专门“刷访问量”的服务。有没有更好的方法,不统计访问量就能够为网页的重要度排序呢? 

就是在这种情况下,1996年初,谷歌公司的创始人,当时还是美国斯坦福大学研究生的佩奇和布林开始了对网页排序问题的研究。在1999年,一篇以佩奇为第一作者的论文发表了,论文中介绍了一种叫PageRank的算法,这种算法的主要思想是:越“重要”的网页,页面上的链接质量也越高,同时越容易被其它“重要”的网页链接,于是,算法完全利用网页之间互相链接的关系来计算网页的重要程度,将网页排序彻底变成一个数学问题,终于摆脱了访问量统计的框框。 

不过要强调的是,虽然PageRank是谷歌搜索结果排序的重要依据,谷歌也以此发家,但是它并不是全部依据——实际上,谷歌发展到现在,已同时用了数百种不同的算法来确定最终显示给用户的搜索结果顺序。

关于PageRank算法,下列说法错误的是()

A.PageRank算法提出了一种新的数学统计方法 

B.PageRank算法使谷歌在搜索引擎的竞争中脱颖而出 

C.PageRank算法改变了以网页访问量作为排序依据的传统想法 

D.PageRank算法能够更准确、更省力地统计出网页的访问量

题型:计算题

下列情境中,不适宜推行参与管理的是()

A.完成任务的时间比较紧迫

B.员工具备相应的智力、知识技术和沟通技巧

C.参与不会使员工和管理者的地位和权力受到威胁

D.组织文化支持员工的参与管理

题型:计算题

关于血吸虫病的发病机制,下列哪些说法是正确的?()

A.急性期是体液,细胞免疫的表现

B.慢性期属于迟发型变态反应

C.血吸虫病可获得完整免疫力

D.虫卵肉芽肿属假性结核

E.存在伴随免疫

题型:计算题

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