问题 问答题

实验室有一瓶硫酸废液,老师请小红同学设计方案测定该废液中硫酸的质量分数,小红同学先取一洁净的烧杯,称其质量为18.2克,然后向其中倒入一定量的废硫酸后称得其总质量为33.2克,之后,将一枚质量为10.8的铁钉(表面无锈)放入小烧杯中反应,待铁钉表面不再产生气泡为止,称得总重为43.9克.请回答下列问题:

(1)写出上述反应的方程式:______

(2)反应中产生的气体质量是______(克)

(3)计算该废液中硫酸的质量分数是多少(写出计算过程)

答案

(1)铁和硫酸反应生成硫酸亚铁和氢气,反应的方程式为:Fe+H2SO4═FeSO4+H2↑;故填:Fe+H2SO4═FeSO4+H2↑;

(2)完全反应后,容器中的物质的质量差,就是生成氢气的质量,氢气的质量为:33.2g+10.8g-43.9g=0.1g;故填:0.1g;

(2)设与铁反应的硫酸的质量为x,

烧杯中稀硫酸废液的质量为:33.2g-18.2g=15.0g

Fe+H2SO4═FeSO4+H2

98 2

x0.1g

98
x
=
2
0.1g

x=4.9g

该废液中硫酸的质量分数为:

4.9g
15.0g
×100%=32.7%

答:废液中硫酸的质量分数是32.7%.

填空题
填空题

For centuries people have been fighting over whether governments should allow trade between countries. There have been, and probably always will be, (1) to the argument. Some people argue that just (2) is best for both the country and the world. Others argue that trade with other countries (3) for some people to make a good living. Both sides are at least (4) .
International trade matters a lot. Its effects on (5) are enormous. Imagine a world in which your country (6) at all with other countries. Imagine what kind of job you would be (7) and what goods you could buy or not buy in such a world.
For the United States, for example, start by imagining that it lived without its (8) a year in imported oil, and cut back on its (9) because the remaining domestic oil and other energy sources were (10) . Producers and consumers in other parts of the economy would (11) if they were suddenly stripped of foreign-made goods like CD players and clothing. On the (12) side, suppose that Boeing could sell airplanes, and farmers could sell their crops, (13) the United States, and that U. S. universities could admit only (14) . In each case there are people who gain and people who lose from (15) international trade. In any case, less or more international trade will have (16) on your career as well as your life.
For years, American companies are often faced with the choice of buying (17) , which are expensive, and foreign-made goods, which are cheap. If the company buys American goods, it may (18) taxpayers by failing to keep prices low. But if it buys foreign goods, it may (19) the jobs of American workers. Recently, Congress has passed a law compelling American companies with government contracts to (20) domestic goods and services.

For centuries people have been fighting over whether governments should allow trade between countries. There have been, and probably always will be, (1) to the argument. Some people argue that just (2) is best for both the country and the world. Others argue that trade with other countries (3) for some people to make a good living. Both sides are at least (4) .
International trade matters a lot. Its effects on (5) are enormous. Imagine a world in which your country (6) at all with other countries. Imagine what kind of job you would be (7) and what goods you could buy or not buy in such a world.
For the United States, for example, start by imagining that it lived without its (8) a year in imported oil, and cut back on its (9) because the remaining domestic oil and other energy sources were (10) . Producers and consumers in other parts of the economy would (11) if they were suddenly stripped of foreign-made goods like CD players and clothing. On the (12) side, suppose that Boeing could sell airplanes, and farmers could sell their crops, (13) the United States, and that U. S. universities could admit only (14) . In each case there are people who gain and people who lose from (15) international trade. In any case, less or more international trade will have (16) on your career as well as your life.
For years, American companies are often faced with the choice of buying (17) , which are expensive, and foreign-made goods, which are cheap. If the company buys American goods, it may (18) taxpayers by failing to keep prices low. But if it buys foreign goods, it may (19) the jobs of American workers. Recently, Congress has passed a law compelling American companies with government contracts to (20) domestic goods and services.