题目

将6.8g含杂质的锌粒，加入到盛有50.0g过量的稀硫酸的烧杯中（杂质不溶于水，也不与稀硫酸反应），充分反应后，称得烧杯内物质的总质量为56.6g．试计算： （1）生成氢气的质量． （2）锌粒中所含锌的质量分数（精确到0.1%）． 答案：【考点】根据化学反应方程式的计算． 【分析】锌与稀硫酸反应生成硫酸锌，同时放出氢气；根据质量守恒定律，实验前后烧杯中物质的质量差即为反应放出氢气的质量；而利用锌和稀硫酸反应的方程式依据氢气的质量可以求出反应的锌的质量进行解答． 【解答】解：（1）根据质量守恒定律，生成氢Recently in the hope of earning both money and social experience, I became a door-trw door salesman.   I once read a saying. “If somebody wants something of yours, you will be treated as warmly as spring, but if they don’t you may be treated as coldly as winter.” You may consider this an exaggeration (夸张), but if you are a salesman, it is clearly correct.    You would never have found it to be so true if you hadn’t been a salesman. You needn’t stand doubtful looks and unfriendly comments; you needn’t listen to something completely wrong and nod to say that it was quite right, you needn’t worry about being refused time after time; you needn’t always keep patience and a smile; you needn’t repeat the same sentences over and over again; you needn’t talk to somebody you dislike ....   I did this work for a month, then I decided to give it up; Apart from the reasons above, I found I was paying too much attention to the job and thus sacrificing my study time. The latest test result proved that my grades were getting worse.   Even worse, I hadn’t enough time to join my classmates in college activities. Some times 1 felt lonely and unhappy because of both my study and my part-time job. Now I don’t think it is worth doing such a thing for even though I was earning money it came at great cost.   Newspapers and magazines often publish stories about excellent students who do part-time work while also keeping high scores in class. But according to my experience, park-time work can have some strong negative influences on study.   Most students don’t view the relationship between study and work correctly. In my opinion, if it isn’t a must for financial reasons, students should be careful about taking up a part-time job. 1. From the text, we can tell that the writer is _____.       A. an unemployed man                  B. a middle-school student   C. a college student                    D. a door-to-door salesman 2.Which of the following words has the closest meaning to the underlined word “sacrificing”?    A. Losing            B. Wasting        C. Using              D. Getting 3.The writer thought_____.   A. doing a part-time job was unnecessary  B. part-time jobs had good effect upon study  C. it was hard to deal with the relationship between study and work  D .part-time jobs would be good for every college student 4.What would be the best title for the text _____.  A. Part-time Jobs Are Useful             B. Part-time Jobs Can Cost Dear  C. Students Shouldn’t Take Part-time Jobs  D. Part-time Jobs Are Important to Many Students