user-avatar
habiken
2 năm trước
Kali trong tự nhiên là hỗn hợp của 2 đồng vị. Đồng vị thứ nhất A1 19K chiếm 93,3% số nguyên tử , đồng vị thứ 2 A2 19K có số notron hơn đồng vị thứ nhất là 2 . Nguyên tử khối trung bình của kali 39,134 . a) Tính số khối mỗi đồng vị b) Tính sô % A1 19K trong 23,567g K2O ( xem nguyên tử khối mỗi đồng vị có giá trị bằng số khối)
Thích Trả lời Chia sẻ

Các câu hỏi liên quan

40. Hellen was looking after a dog _______ in an accident.A. which leg had been broken B. whose leg had been broken C. its leg had been broken D. that leg had been broken 41. Ann_______ going for a walk, but no one else wanted to.A. admitted B. offered C. promised D. suggested 42. After_______ by the police, the man admitted_______ the car.A. being stopped/ stealing B. stopping/ stealingC. being stopped/ to steal D. stopping/ being stolen 43. I find it difficult to make a good _________ on this problem.A. want B. decision C. thought D. view 44. We didn’t ________ to the station in time to catch the train. A. reach B. arrive C. get D. lead 45. He last had his eyes _______ ten months ago. A. test B. testing C. tested D. to be tested 46. I hope you don’t mind _______ to come tonight. A. being asked B. asking C. we ask you D. you were asked 47. Waste paper can be recycled ________ . A. because it can be burnt B. instead of burningC. instead of being burnt D. so it can be burnt 48. Have a cup of tea, _______?A. do you B. will you C. won’t you D. don’t you 49. I was just _______ to go out when Peter phoned.A. used B. planned C. about D. around 50. The book provides students ________ useful tips to pass the coming exam.A. of B. about C. on D. with 51. I felt disappointed because I was ________ by the company I applied to.A. criticized B. rejected C. blamed D. forgotten 52. ________ he always did well on his English tests, his parents were not surprised that he got an A. A. Since B. Even though C. If D. Because of 53. You should pay attention ________ what the teacher said.A. of B. with C. in D. to 54. Solar energy doesn't cause________.A. pollution B. polluted C. pollute D. pollutant 55. Were you _________ of the regulation against smoking in this area ?A. capable B. aware C. involved D. interested 56. Tom was unware of the danger. He was not _________ of it.A. conscious B. knowledgeable C. sensitive D. sensible 57. – “This painting isn’t an original- It’s a copy.” – “_________”A. How do you know that? B. Why don’t you think so?C. What did you think of this painting? D. I don’t know what it means. 58. He has recently. _________ golf to provide himself with some relaxation.A. taken with B. taken over C. taken on D. taken up 59. The trade talks which had begun between the two countries were _________ when the war began.A. broken down B. broken in C. broken off D. broken out 60. – “You have been spending too much money lately” – “You’re right. I need to _________on my expenses”A. cut out B. cut up C. cut down D. cut away 61. Susan’s doctor insists ______ for a few days.A. that she is resting B. her resting C. that she rest D. her to rest 62. “I’d rather you______ home now.”A. going B. go C. gone D. went 63. Eight dollars ______the price of a movie these days.A. are B. is C. were D. am 64. ______ he arrived at the bus stop when the bus came. A. Hardly had B. No sooner had C. No longer has D. Not until had 65. I turn down the job______ the attractive salary.A. because B. because of C. although D. despite 66. He asked me______.A. since when I waited B. since when I am waiting C. how long I have been waiting D. how long I had been waiting 67. His parents never allowed him ______.A. to smoking B. smoking C. to smoke D. some smoke

Find the one choice that best completes the sentence 20. Nam said he was from Hai Phong, but he was _______from Ha Noi.A. may be B. possibly C. really D. preferably 21. If Lan _______, please tell her that I have gone to the bookshop.A. calls B. is calling C. called D. will call 22. Food and drinks _______at the reception.A. is served B. are served C. are serving D. is being served 23. Give her a telephone number to ring _______she gets lost.A. whether B. unless C. in case D. because 24. There’s no use _______to him. He never answers our letters. A. write B. to write C. written D. writing 25. Timson _______13 films and I think her latest is the best.A. made B. had made C. has made D. was making 26. – “Do you think your father will worry if we’re late?” – “Maybe we’d better _______him.”A. call B. be calling to C. to call D. will call 27. Tam _______last night when the telephone _______.A. slept / rang B. slept / was ringingC. was sleeping / rang D. was sleeping / was ringing 28. – “Would you like to go to the movie with me tonight?” – “_______”A. Yes, please. B. I’m sorry. I’d love to.C. No, thanks. D. Yes, I’d love to. 29. She spends most of her free time_______volunteer work.A. doing B. to do C. do D. for doing 30. She is wearing a _______dress.A. red new pretty B. pretty red new C. new pretty red D. pretty new red 31. Each of them_______ a different character.A. have B. has C. to have D. having 32. Do you often watch_______ programmes broadcasting on TV ? A. lively B. living C. alive D. live 33. He told me _______ the safe before he left.A. to remember to lock B. remember locking C. to remember locking D. remember to lock 34. The World Cup_______ every four years. A. is held B. has been C. is made D. is taken 35. The Blacks live in the house_______ the green doors.A. have B. with C. which D. has 36. I sent a card to congratulate Nam _______ winning the first prize in the English speaking contest.A. about B. for C. on D. of 37. _______ I had an umbrella, I got very wet in the rain.A. In spite of B. Despite C. Even though D. As long as 38. The fire alarm _______ and we all rushed out.A. went off B. turned out C. exploded D. A and C are correct. 39. Susan_______ her keys. She can’t find them anywhere. A. loses B. has lost C. lost D. has been lost 40. Hellen was looking after a dog _______ in an accident.A. which leg had been broken B. whose leg had been broken C. its leg had been broken D. that leg had been broken 41. Ann_______ going for a walk, but no one else wanted to.A. admitted B. offered C. promised D. suggested 42. After_______ by the police, the man admitted_______ the car.A. being stopped/ stealing B. stopping/ stealingC. being stopped/ to steal D. stopping/ being stolen 43. I find it difficult to make a good _________ on this problem.A. want B. decision C. thought D. view 44. We didn’t ________ to the station in time to catch the train. A. reach B. arrive C. get D. lead

2018 © Loga - Không Ngừng Sáng Tạo - Bùng Cháy Đam Mê
Loga Team