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问题 选择题

下列实验能达到预期目的的是

编号实验内容实验目的
A取两只试管，分别加入4ml 0.01mol/L KMnO4酸性溶液，然后向一只试管中加入0.1mol/L H2C2O4溶液2ml，向另一只试管中加入0.1mol/L H2C2O4溶液4ml，记录褪色时间。可以证明H2C2O4浓度越大反应速率越快。
B向1ml 0.2mol/L NaOH溶液中滴入2滴0.1mol/L MgCl2溶液，产生白色沉淀后，再滴加2滴0.1mol/L FeCl3溶液，又生成红褐色沉淀。可以证明在相同温度下，溶解度Mg(OH)2＞Fe(OH)3
C测定等物质的量浓度的Na2SO3与Na2CO3溶液的pH，后者较大。证明了非金属性S＞C
D向含有酚酞的Na2CO3溶液中加入少量BaCl2固体，溶液红色会变浅。可以证明Na2CO3溶液中存在水解平衡。
 

答案

答案：D

题目分析：A、两只试管中草酸的浓度几乎是相同的，所以不能证明H2C2O4浓度越大反应速率越快，A不正确；B、由于氢氧化钠在和氯化镁溶液反应时氢氧化钠过量，所以再加入氯化铁时一定产生红褐色氢氧化铁沉淀，所以不能证明在相同温度下溶解度Mg(OH)2＞Fe(OH)3，B不正确；S元素的最高价是＋6价，因此应该测定等物质的量浓度的Na2SO4与Na2CO3溶液的pH，如果后者较大可以证明非金属性S＞C，C不正确；D、向含有酚酞的Na2CO3溶液中加入少量BaCl2固体，溶液红色会变浅，这说明溶液中OH－浓度降低，这是由于碳酸钠与氯化钡反应生成了碳酸钡沉淀，从而抑制了CO32－的水解，溶液的碱性降低，D正确，答案选D。

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活髓切断术的适应证和手术方法。
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For more than two centuries, American’s colleges and universities have been the backbone of the country’s progress. They have educated the technical, managerial, (1) and provided generation after generation of national leaders. Today educators from around the globe are turning to U. S. institutions of higher learning (2) . They are apt to find many reasons for the excellence of American universities, but (3) stand out as watersheds:
Education (4) : In 1862 Congress enacted the Land-Grant College Act, which essentially extended the opportunity of higher education (5) , including such disenfranchised groups as women and minorities. Each state was permitted to sell large tracts of (6) and use the proceeds to endow at least one public college.
(7) : Over the years, the decentralization and diversity of the America’s colleges and universities have promoted competition for students and resources. Competitive pressure first arose (8) . The academy’s impact really grew after World War II, when (9) commissioned by President Roosevelt argued that it was the federal government’s responsibility to (10) for basic research. Instead of being centralized in government laboratories, scientific research (11) in American universities and generated increasing investment. It also gave graduate students research opportunities and helped (12) far and wide, to the benefit of industry, medicine and society as a whole.
(13) : The end of the World War II saw passage of the Servicemen’s Readjustment Act of 1944. The law, which provided for (14) for returning veterans, made an already democratic higher-education system accessible in ways that were (15) in Europe, opening the doors of the best universities to men and women who had (16) of going to college.
(17) : The creation of federal loan guarantees and subsidy programs, as well as outright grants for college students brought (18) to higher education and further helped to democratize access. Since its founding (19) , the Federal Family Education Loan Program has funded more than 74 million student loans worth more than (20) .
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