题干

为了测定某品牌小苏打样品中碳酸氢钠的质量分数,兴趣小组进行了如图所示的实验(假设该样品中只含有氯化钠一种杂质).请计算:

(1)生成CO2气体的质量;

(2)样品中碳酸氢钠的质量分数.

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答案(点此获取答案解析)

解:(1)生成二氧化碳的质量为:10g+100g+100g﹣205.6g=4.4g; (2)设碳酸氢钠的质量为xNaHCO3+HCl=NaCl+H2O+CO2↑84 44x 4.4g

同类题1

任务型阅读

Quiet Virtue: The Conscientious

    The everyday signs of conscientiousness (认真尽责)—being punctual, careful in doing work, self-disciplined, and scrupulous (一丝不苟的) in attending to responsibilities—are typical characteristics of the model organizational citizen, the people who keep things running as they should. They follow the rules, help out, and are concerned about the people they work with. It's the conscientious worker who helps newcomers or updates people who return after an absence, who gets to work on time and never abuses sick leaves, who always gets things done on deadline.

    Conscientiousness is a key to success in any field. In studies of job performance, outstanding effectiveness for almost all jobs, from semi-skilled labor to sales and management, depends on conscientiousness. It is particularly important for outstanding performance in jobs at the lower levels of an organization: the secretary whose message taking is perfect, the delivery truck driver who is always on time.

    Among sales representatives for a large American car manufacturer, those who were most conscientious had the largest volume of sales. Conscientiousness also offers a buffer (缓冲) against the threat of job loss in today's constantly changing market, because employees with this quality are among the most valued. For the sales representatives, their level of conscientiousness mattered almost as much as their sales in determining who stayed on.

    There is an air around highly conscientious people that makes them seem even better than they actually are. Their reputation for dependability influences managers' evaluations of their work, giving them higher evaluations than objective measures of their performance would predict.

    But conscientiousness in the absence of social skills can lead to problems. Since conscientious people demand so much of themselves, they can hold other people to their own standards, and so be overly judgmental when others don't show the same high levels of model behavior. Factory workers in Great Britain and the United States who were extremely conscientious, for example, tended to criticize co-workers even about failures that seemed unimportant to those they criticized, which damaged their relationships.

    When conscientiousness takes the form of living up to expectations, it can discourage creativity. In creative professions like art or advertising, openness to wild ideas and spontaneity (自发性) are scarce and in demand. Success in such occupations calls for a balance, however; without enough conscientiousness to follow through, people become mere dreamers, with nothing to show for their imaginativeness.

同类题2

The values of artistic works, according to cultural relativism(相对主义), are simply reflections of local social and economic conditions. Such a view, however, fails to explain the ability of some works of art to excite the human mind across cultures and through centuries.

              History has witnessed the endless productions of Shakespearean plays in every major language of the world. It is never rare to find that Mozart packs Japanese concert halls, as Japanese painter Hiroshige does Paris galleries, Unique works of this kind are different from today’s popular art, even if they began as works of popular art. They have set themselves apart in their timeless appeal and will probably be enjoyed for centuries into the future.

               In a 1757 essay, the philosopher David Hume argued that because“the general principles of taste are uniform(不变的) in human nature,”the value of some works of art might be essentially permanent. He observed that Homer was still admired after two thousand years. Works of this type, he believed, spoke to deep and unvarying features of human nature and could continue to exist over centuries.

               Now researchers are applying scientific methods to the study of the universality of art. For example, evolutionary psychology is being used by literary scholars to explain the long-lasting themes and plot devices in fiction. The structures of musical pieces are now open to experimental analysis as never before. Research findings seem to indicate that the creation by a great artist is as permanent an achievement as the discovery by a great scientist.