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问题 实验题

某化学兴趣小组在学习“硫酸盐的某些性质和用途”中，进行了如下实验探究：

【实验一】检验(NH4)2Fe(SO4)2·6H2O溶液中含有的阳离子。

（1）在下表中写出操作步骤和实验现象：

限选试剂：新制氯水、1mol/LH2SO4溶液、0.1mol/L KSCN溶液、NaOH浓溶液、浓盐酸、1mol/LNa2CO3溶液

操 作 步 骤实验现象结 论
步骤I：取少量待检液于试管中，        

                                    。

                     

                     

溶液中含有Fe2+
步骤II：取少量待检液于试管中，        

                                     。

                     

                     

溶液中含有NH4＋
 

【实验二】用KHSO4制取H2O2并测其质量分数：

查阅资料得知：工业上用电解KHSO4饱和溶液可制取一定浓度的H2O2。兴趣小组进行下列实验测定H2O2的质量分数。已知：2MnO4－+5H2O2+6H＋= 2Mn2＋+8H2O+5O2↑

操作①：取5.00 mL H2O2溶液(密度为1.00 g/mL)置于锥形瓶中加水稀释，再加稀硫酸酸化；

操作②：用0.1000 mol/L KMnO4溶液滴定；

操作③：用同样方法滴定，四次消耗KMnO4溶液的体积分别为20.00 mL、19.98 mL、20.02 mL、22.00 mL。

回答下列问题：

（2）操作②中，开始滴入KMnO4溶液时反应速率很慢，随着KMnO4溶液滴入反应速率显著加快，最有可能的原因______________________。

（3）滴定时盛装KMnO4溶液应选取的仪器是       （填序号）。

A．50mL酸式滴定管　                B．50mL碱式滴定管 　

C．25mL酸式滴定管　                D．25mL碱式滴定管

（4）在上述实验中，下列操作会造成测定结果偏高的有         （填序号）。

A．锥形瓶用待测液润洗

B．量取 H2O2溶液的滴定管用蒸馏水洗净，未用H2O2溶液润洗  

C．滴定速度过快，又未摇匀，停止滴定后发现紫红色褪去

D．滴定前读数时平视，滴定终点读数时仰视

（5）分析数据，计算H2O2溶液中溶质的质量百分含量为___________（保留三位有效数字）。

答案

（共17分）

（1）（每空2分，共8分）

操作步骤实验现象
先滴加几滴0.1mol/L KSCN溶液，再滴加适量的新制氯水，振荡开始时无明显现象；然后溶液呈(血)红色 
滴加适量的NaOH浓溶液，加热，将蘸有浓盐酸的玻璃棒靠近试管口。 (溶液中产生气泡，管口) 产生白烟
 

（2）反应中生成的 Mn2＋具有催化作用  (2分) 

（3）C  (2分)；  （4） AD  (2分)；   （5）3.40% （3分）

题目分析：（1）从题给试剂和铁离子、亚铁离子的性质设计步骤I的方案，亚铁离子具有还原性，遇KSCN溶液不变红，新制氯水可以将亚铁离子氧化，生成的铁离子遇KSCN溶液变红，因此取少量待测溶液于试管中，先滴加几滴0.1mol/L KSCN溶液，再滴加适量的新制氯水，振荡，开始时无明显现象，然后溶液呈红色，说明溶液中含有Fe2+；根据铵根离子的性质设计步骤II的方案，铵根离子与强碱溶液混合加热时生成氨气，氨气与氯化氢气体混合时产生大量的白烟，氨气可用蘸有浓盐酸的玻璃棒检验，因此取少量待测溶液于试管中，滴加适量NaOH浓溶液，加热，将蘸有浓盐酸的玻璃棒靠近试管口，若溶液中产生气泡、管口产生白烟，说明溶液中含有NH4+；（2）根据外界条件对反应速率的影响规律，刚滴定时浓度最大，反应速率慢，说明不能用浓度、压强解释，由于该反应的反应热未知，也不宜用温度解释，排除之后只有用催化剂解释反应速率先慢后快的原因，即反应中生成的 Mn2＋具有催化作用；（3）酸性高锰酸钾溶液具有腐蚀橡胶中碳碳双键的性质，因此只能用酸式滴定管盛装高锰酸钾溶液，由于每次滴定都消耗20mL酸性高锰酸钾溶液，25mL规格的酸式滴定管最接近20mL，可以减少误差，因此C选项正确；（4）锥形瓶用待测液润洗，就会使消耗的酸性高锰酸钾溶液体积增大，导致测定结果偏大，故A选项错正确；量取双氧水的滴定管未润洗，其中的蒸馏水能稀释加入的双氧水，就会使消耗的酸性高锰酸钾溶液体积减小，导致测定结果偏低，故B选项错误；滴定速率过快，未摇匀，停止滴定后紫红色褪去，说明消耗高锰酸钾溶液偏少，导致测定结果偏低，故C选项错误；滴定管上小刻度在上，大刻度在下，二者之差就是消耗标准酸性高锰酸钾溶液的体积，若前读数正确，仰视导致后读数偏大，就会使消耗酸性高锰酸钾溶液体积增大，导致测定结果偏高，故D选项正确；（5）先处理酸性高锰酸钾溶液体积的数据，将异常数据（22.00mL）舍去；再用正常数据求酸性高锰酸钾溶液的平均体积，即(20.00+19.98+20.02)mL/3=20.00mL；然后计算每次滴定消耗高锰酸钾或高锰酸根离子的物质的量，即n(MnO4－)=c•V=0.1000mol/L×20.00×10—3L；由于反应2MnO4－+5H2O2+6H＋= 2Mn2＋+8H2O+5O2↑中过氧化氢与高锰酸根离子的系数之比等于物质的量之比，则5.00mL待测液中n(H2O2)=5n(MnO4－)/2=0.1000mol/L×20.00×10—3L×5/2；接着根据m=n•M求过氧化氢的质量、m=ρ•V 求双氧水溶液的质量，即前者为0.1000mol/L×20.00×10—3L×5/2×34g/mol，后者为1.00g/mL×5.00mL；最后根据溶质的质量除以溶液的质量求溶质的质量分数，即（0.1000mol/L×20.00×10—3L×5/2×34g/mol）/（1.00g/mL×5.00mL）×100%=3.40%（保留三位有效数字）。

填空题


A
PASSAGE 1: According to US Trade Representative Robert B. Zoellick, the ambitious US proposal for worldwide zero tariffs is comprehensive, and would benefit both developed and developing nations.
The proposal, said Zoellick, when combined with the far-reaching US agricultural reform proposal submitted to the WTO in July, would eliminate tariffs on the nearly ＄6 trillion in annual world goods trade, lifting the economic fortunes of workers, families, businesses, and consumers.
"Our proposal would turn every corner store in America into a duty-free shop for working families," said Zoellick. "This historic proposal would benefit the average American family with an extra ＄1,600 a year, while also removing high foreign tariff barriers on more than ＄670 billion in US industrial and consumer goods exports. Globally, tariff-free trade could help lift millions of people in developing countries out of poverty."
"President Bush believes that American workers, farmers, ranchers and businesses must have more than just the ability to compete globally, they must also have the opportunity to do so," said US Commerce Secretary Don Evans. "This proposal says that ’no one wins unless we all win’ and ensures a level playing field for America’s goods and ingenuity to compete fairly around the world."
B
PASSAGE 2: The US proposal envisions a two-step approach to eliminating tariffs on a full-range of consumer and industrial goods ranging from women’s shoes, to tractors, to children’s toys.
First, WTO members would be required to cut and harmonize their tariffs in the five year period from 2005 to 2010. Specifically, WTO members would eliminate all tariffs at or below 5 percent by 2010, cut all other tariffs through a "tariff equalizer" formula to less than 8 percent by 2010, and eliminate tariffs in certain highly traded industry sectors as soon as possible, but not later than 2010.
Next, all WTO members would make equal annual cuts in remaining tariffs between 2010 and 2015. These cuts would result in zero tariffs.
The proposal also calls for a separate program to identify and eliminate non-tariff barriers, which would run on a parallel track with the negotiations on industrial tariffs. The US will put forward an initial list of such barriers in January of 2003.
C
PASSAGE 3: According to the Office of US Trade Representative (USTR), eliminating US tariffs would significantly benefit US families and consumers through lower import taxes and a more competitive economy. Hidden import taxes cost American consumers ＄18 billion in 2001, alone. USTR contends that duty-free trade would eliminate these hidden costs and lower prices for consumers. While this proposal would offer substantial benefits to all Americans, it would particularly help low-income families. A recent study by the Progressive Policy Institute found that cutting US import taxes especially benefits single-parent, low-income families, who typically pay a higher proportion of their income on import taxes than other households. A study done by the University of Michigan found that the US economy would expand by ＄95 billion as a result of tariff-free trade--contributing to job-creation and higher wages. The University of Michigan study also revealed: The elimination of industrial tariffs by other countries could increase US exports by ＄83 billion annually highly-traded goods exports, such as chemicals, paper, and scientific equipment, which are targeted in the US proposal for total tariff elimination, account for 60 percent of all US exports.
Estimates by the World Bank project that tariff-free global trade would result in a worldwide income gain of ＄832 billion from trade in all goods including agriculture, of which ＄539 billion (65 percent) would flow to developing countries. Representing an income increase of about ＄544 for a family of four, the World Bank estimates that free trade in goods and services could help lift 300 million people out of poverty-- a number greater than the entire population of the United States.
D
PASSAGE 4: The reduction and elimination of tariffs on consumer and industrial goods is a component of the WTO negotiations launched in Doha, Qatar in 2001 to be completed by January 1, 2005.
Throughout the year, United States leadership has continued to spur momentum on the Doha Development Agenda in the WTO:
·On July 1, the United States announced proposals for liberalizing global trade in services, designed to remove foreign barriers in areas such as financial services, telecommunications, and environmental services.
·On August 9, the United States submitted a proposal to expand transparency and public access to World Trade Organization dispute settlement proceedings. The proposal would open WTO dispute settlement proceedings to the public for the first time and give greater public access to briefs and panel reports.
·On October 17, the United States submitted a paper highlighting the importance of strengthening transparency and due process in the application of trade remedies (antidumping, subsidies, and safeguard actions). It addresses the basic concepts and principles of the trade remedy rules against unfair trade, and the importance of tackling the trade-distorting practices that are frequently the root causes of unfair trade. The US also submitted a paper presenting a number of ideas and recommendations for addressing trade- and market-distorting practices in the steel sector.
·the US will propose tariff-cutting in two phases71. ______
·how a duty-free world would help US consumers 72. ______
·the proposal could averagely save a US family ＄1,600 a year73. ______
·the US will submit an initial list of non-tariff barriers 74. ______
·the procedure of the tariff-free proposal arranged through the whole year 75. ______
·tariff-free world trade could help lift millions of people out of 76. ______
poverty in the world 77. ______
·the US put forward a paper about reasons of unfair trade78. ______
·the US has called on the WTO to eliminate all tariffs on consumer 79. ______
and industrial goods worldwide80. ______
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