问题 计算题

(1)(2分)维生素A的化学式为C20H30O,能维持人体正常的视觉反应。回答下列问题:①一个维生素A分子共含有          个原子。

②维生素A 中C、H、O元素的质量比为                

(2)(4分)在科学家眼里,二氧化碳是可以利用的重要资源。在一定条件下,二氧化碳和金属钠反应可以制金刚石〖CO2+4Na一定条件C(金刚石)+2Na2O〗。请计算92g金属钠理论上可制得含碳96%的金刚石的质量是多少g?(最后结果保留一位小数)

答案

(1)(2分)①51 ②120︰15︰8

(2)

题目分析:解:(1)由维生素A的化学式C20H30O可知:

① 一个维生素A分子共含有20+30+1=51个原子;

② ②维生素A 中C、H、O元素的质量比为12×20:1×30:16=120︰15︰8。

(2)解:设92g金属钠理论上可制得含碳96%的金刚石的质量为x

CO2+4NaC(金刚石)+2Na2O

92          12

92g        x

92:12=92g:x

x=12g

可制得含碳96%的金刚石的质量:12g÷96%=12.5g

答:可制得含碳96%的金刚石的质量为12.5g

点评:根据化学式和化学方程式计算是中考必考题型,化合物中各元素的质量比等于各元素相对原子质量与原子个数乘积的比。根据化学方程式计算,要注意解题的步骤,设、写、找、列、解、答。

完形填空

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第二节: 完形填空(共20小题;每小题1分,满分20分)

阅读下面短文,掌握其大意,然后从36—55各题所给的四个选项(A、B、C和D)中,选出最佳选项。

I think we should try to find a happy memory, something to lift us up on those unpleasant days. I'm saying this because I think I just found mine!

I had some work in Glasgow then. I was on a really  36  schedule, which meant I would have no time for myself all day. I was having one of those days, the train was completely  37  and the conversation going on around me seemed to be particularly  38  . Besides, I had a bit of a headache.   _39   quickly across the station hall, I fished some  40  from my pocket. There was usually someone at the exit   41   The Big Issue ( a magazine that helps homeless folk earn a living).

_42  the crowd parted ways at the bottom of the hall, I saw someone selling the

Big Issue. She really looked like she'd been sleeping  43  . Her clothes were  44  and she obviously hadn't had a scrub up (擦洗) for quite a while.

As I  45   the exit, I saw that she was  46  from side to side. At first I thought maybe she was trying to keep  47  against the biting wind. But she wasn't, she was moving in time to a  48 . I couldn’t hear her, but I could see her lips moving.

When I got closer, I saw a white  49  hanging from her elbow and noticed that she had sunken eyes. She was  50 , dirty and living on tile streets. I came closer and through the  51  of the traffic I heard her  52  the immortal (不朽的)line, "... and I think to myself, what a wonderful world!"

I bought her last magazine for twice what I'd originally  53  . She thanked me, then she  54_     her belongings and went tapping off along the pavement – still singing!

So, I have my happy  55  for the day. And I think it will stay with me a long, long time.

36. A. enjoyable            B. relaxing           C. tight              D. tiring

37. A. crowded             B. delayed           C. loaded            D. crashed

38. A. moving             B. interesting          C. pleasing           D. meaningless

39. A. Crawling            B. Walking           C. Wandering        D. Searching

40. A. cigarettes           B. sweets             C. change             D. paper

41. A. selling               B. buying            C. collecting          D. delivering

42. A. With                B. Since             C. Until             D. As

43. A. comfortably          B. rough             C. soundly           D. anxiously

44. A. ragged              B. costly             C. tidy               D. fashionable

45. A. left                 B. passed            C. approached        D. examined

46. A. jumping             B. climbing           C. rolling             D. rocking

47. A. active                B. energetic         C. warm             D. awake

48. A. dance              B. tune              C. step                D. sound

49. A. issue                B. arm              C. stick               D. log

50. A. deaf                B. lame              C. mad              D. blind

51. A. noise                B. music             C. voice               D. whistle

52. A. recite               B. compose           C. read              D. sing

53. A. expected            B. charged           C. intended          D. organized

54. A. picked up            B. throw away        C. put down           D. hid away

55. A. decision             B. memory           C. program          D. design

名词解释 简答题