含n g硝酸的稀溶液恰好和m g铁粉完全反应若有
g HNO3被还原成NO，n:m可能
A．1:1
B．2:1
C．3:1
D．9:2
CD
此题可以用极限法求解。假设一，铁粉刚好完全消耗干净，只能还原n/4g硝酸，那就有方程表达：Fe+4HNO3=Fe（NO3）3+NO↑+2H2O，理清关系有：Fe～NO，可看出被氧化的铁粉与被还原的硝酸（根据元素守恒）具有相同的物质的量，于是有计算式m/56=n÷4÷63由此推出n:m=9:2
假设二，铁粉过量，硝酸被完全消耗，甚至连三价铁离子也被铁单质全部还原成亚铁离子。在这种情况下，根据氧化还原反应电子得失守恒，mg铁粉提供电子总物质的量为m÷56×2=m/28mol，而硝酸得到的电子为，n÷4÷63×3=n/84mol。m/28=n/84，所以n:m=3:1
答案应该是CD。
In the following passage, there are 20 blanks representing words that are missing from the context. Below the passage, each blank has 4 choices marked by letter A, B, C and D respectively. There is only ONE right answer. Blacken the corresponding letter as required on your Machine-scoring ANSWER SHEET.
| How many of us would temp for three years while we waited for the perfect job Not many of us, perhaps. But Wentworth Miller, the "Prison Break" star, said he chose to wait even longer time (91) he found the right job. "Actually I think it might have been three or four years until I was lucky enough to get guest (92) on TV shows," said Miller, 34, who rose to international stardom (93) to "Prison Break" in 2006. That kind of patience and p will was portrayed in "Prison Break". Miller (94) engineering wizard Michael Scofield, who tries everything to break out of a Chicago (95) with his brother. Miller said he was fond of his character, (97) he said "exists in shades of grey". Miller comes from a (97) of teachers. He said he didn’t seem fated for a career in the arts, (98) his passion for acting. After (99) from Princeton with an English degree, he moved (100) his parents’ request to Los Angeles to look for a stable life. He started (101) in a little company that made television movies. This (102) simply faxing, filing, walking the boss’ dog and going to the store for the boss’ lunch. Every weekend during the summer, Miller (103) go to the office (104) he didn’t have air-conditioning. "I would hang (105) in the conference room and set up camp and rob the company kitchen," recalled Miller. (106) , Miller realized he still had questions about his choice. He decided to quit. But the boss said he was making a mistake and offered him a well-paid assistant position. "I eventually (107) that if I did the corporate job, it would be great if I was successful, but I would always wonder about the (108) . If I did the acting and was successful, I would never wonder (109) that job," he explained. He quit and temped (110) many people in the entertainment industry. |
A．implied
B．held
C．meant
D．demonstrated