Isoamyl acetate là một ester có mùi hương ngọt ngào, dễ chịu tương tự mùi chuối chí...

Isoamyl acetate là một ester có mùi hương ngọt ngào, dễ chịu tương tự mùi chuối chí...">

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Cô Phương Thảo

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4 tháng 4 - olm

Isoamyl acetate là một ester có mùi hương ngọt ngào, dễ chịu tương tự mùi chuối chín nên được sử dụng phổ biến trong ngành công nghiệp thực phẩm, nước hoa và mỹ phẩm. Để điều chế isoamylic acetate, người ta trộn 2,2 gam isoamylic alcohol với 2,2 gam acetic acid, thêm 10 ml H₂SO₄ đặc rồi tiến hành phản ứng ester hóa. Sau phản ứng, thu được m gam ester. Biết isoamylic có công thức hóa học như sau:

a. Viết phương trình phản ứng.

b. Tính giá trị của m, biết hiệu suất của phản ứng ester hóa là 70%.

#Hỏi cộng đồng OLM #Tiếng anh lớp 11

Chim Đâm Kim

4 tháng 4

OoO

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Chim Đâm Kim

4 tháng 4

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Đỗ Khánh Ly

14 tháng 8 2021 - olm

Choose the best answer in each sentence below by circling it. 1. You are late. If you …… a few minutes earlier, you …… him. A. came / would meet B. had come / would have met C. come / will meet D. had come / would meet2. “Can I borrow your car for this evening?”“Sure, but Nora’s using it right now. If she …… it back in time, you’re welcome to borrow it.” A. brings B....

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Choose the best answer in each sentence below by circling it.

1. You are late. If you …… a few minutes earlier, you …… him.

A. came / would meet B. had come / would have met

C. come / will meet D. had come / would meet

2. “Can I borrow your car for this evening?”

“Sure, but Nora’s using it right now. If she …… it back in time, you’re welcome to borrow it.”

A. brings B. would bring C. will bring D. brought

3. We’re going to lose this game …… the team doesn’t start playing better soon.

A. if B. unless C. although D. whereas

4. If I …… somebody else, I’d like to be a film star.

A. could be B. would be C. become D. must be

5. If he had told me the truth, I …… him.

A. would have not punished B. would not have punished

C. would not punish D. will not punish

6. If they had not given me advice, I …… again.

A. would have failed B. would fail C. would have been failed D. wouldn’t fail

7. …… immediately, I will call a policeman.

A. Unless you leave B. If you leave C. If you didn’t leave D. Unless you left

8. Bill …… more photographs if he …… more film.

A. would have taken / had had B. would have taken / had

C. would take / has had D. would take / had had

9. If there …… no floods last year, the crop …… better.

A. had been / would have been B. were / would be

C. had / would have been D. was / would have been

10. Had you told me that this was going to happen, I …… it.

A. would never have believed B. don’t believe

C. hadn’t believed D. can’t believe

11. If someone …… into the store, smile and say, “May I help you?”

A. comes B. came C. come D. could come

12. If I had a chance to do creative work, I …… happy working in an office.

A. would be B. will be C. would have D. will feel

13. If they …… soon, I’m not going to wait.

A. don’t come B. won’t come C. hadn’t come D. didn’t come

14. If I …… hungry, I …… something. But I am not hungry now.

A were / would eat B. had been / would have eaten

C. had been / would eat D. were / would have eaten

15. You won’t pass the examination …… you study more.

A. unless B. as C. if D. whether

16. I’m playing tennis tomorrow …… it’s raining.

A. unless B. if C. as long as D. provided

17. Tell him to ring me if you …… him.

A. see B. saw C. have seen D. had seen

18. Unless she ……, she’ll be late.

A. hurries B. didn’t hurry C. hurried D. doesn’t hurry

19. Would George be angry if I …… his bicycle without asking?

A. took B. take C. had taken D. would take

20. I …… you a postcard while I was on holiday if I …… your address.

A. would have sent / had had B. would have sent / had

C. would send / had D. would send / had had

21. …… still my friend if I were put in prison?

A. Would you be B. Will you be C. Would you D. Would you are

22. If anybody …… any question, please ask me after class.

A. has B. have C. don’t have D. doesn’t have

23. If I weren’t working for an accounting firm, I …… in a bank.

A. would be working B. will work C. have worked D. work

24. He said, “…… watch TV all the evening if you wish.”

A. You may B. You have to C. You need to D. You should

25. If he ……, please tell me.

A. comes B. won’t come C. will come D. come

#Hỏi cộng đồng OLM #Tiếng anh lớp 11

Nguyễn Thuỳ Dương

14 tháng 8 2021

Theo em nghĩ thì là C vì You thì ko thể dùng had đc.

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Tuan Phuong

14 tháng 8 2021

sao nhiều thế. Ai mà trả lời nổi

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Mai Thị Tuyết Anh

2 tháng 10 2021 - olm

Read the passage below and choose the best answer (A, B, C or D) to each question.The nuclear family, consisting of a mother, father, and their children f may be more an American ideal than an American reality. Of course, the so-called traditional American family was always more varied than we had been led to believe, reflecting the very different racial, ethnic, class, and religious customs among different American groups.The most recent government statistics reveal that only about one third...

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Read the passage below and choose the best answer (A, B, C or D) to each question.

The nuclear family, consisting of a mother, father, and their children f may be more an American ideal than an American reality. Of course, the so-called traditional American family was always more varied than we had been led to believe, reflecting the very different racial, ethnic, class, and religious customs among different American groups.

The most recent government statistics reveal that only about one third of all current American families fit the traditional mold and another third consists of married couples who either have no children or have none still living at home. Of the final one third, about 20 percent of the total number of American households are single people, usually women over sixty-five years of age. A small percentage, about 3 percent of the total, consists of unmarried people who choose to live together; and the rest, about 7 percent, are single, usually divorced parents, with at least one child.

1. With what topic is the passage mainly concerned?

A. The traditional American family.

B. The nuclear family.

C. The ideal family.

D. The current American family

2. The author implies that...................

A. there has always been a wide variety of family arrangements in the United States

B. racial, ethnic, and religious groups have preserved the traditional family structure

C. the ideal American family is the best structure

D. fewer married couples are having children

3. Who generally constitutes a one-person household?

A. A single in his twenties.

B. A single woman in her late sixties.

C. An elderly man.

D. A divorced woman,

4. According to the passage, married couples whose children have grown or who have no children represent...................

A. 7 percent of households

B. 20 percent of households

C. 33, 3 percent of households

D. 3 percent of households

5. The word "current" in line 7 is closest in meaning to...................

A. present B. contemporary

C. now D. modern

#Hỏi cộng đồng OLM #Tiếng anh lớp 11

Lê Nguyễn Hải An

2 tháng 10 2021

1.A

2.D

3.B

4.D

5.A

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Nguyễn Xuân Quý

2 tháng 10 2021

Hello

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Ngô Phương

Admin VIP

14 tháng 11 2023 - olm

Câu hỏi hay

Write a proposal for a welcome event

#Hỏi cộng đồng OLM #Tiếng anh lớp 11

Ngô Phương

Admin VIP

14 tháng 11 2023 - olm

Câu hỏi hay

Write an essay about the advantages and disadvantages of living in a smart city

#Hỏi cộng đồng OLM #Tiếng anh lớp 11

Nguyễn Hoàng Minh

26 tháng 11 2023

Living in a smart city brings many benefits and disadvantages. In this article, I will present some pros and cons of living in a smart city.

The first advantage of living in a smart city is convenience. Information and communications technology is integrated into urban systems, helping to provide public services more effectively. For example, through mobile applications, people can easily search for information about transportation, destinations, and entertainment activities. Furthermore, the smart traffic system helps reduce congestion and save travel time.

Another advantage of smart cities is energy saving and environmental protection. Advanced technologies are applied to manage and use resources effectively. For example, automatic lighting and temperature regulation in buildings help save energy. In addition, the use of smart public transport and self-driving cars helps reduce polluting emissions.

However, living in a smart city also has disadvantages. One of them is the issue of information security. With the widespread use of information technology, the risk of personal information insecurity and privacy violations increases. This requires strong security measures to ensure the safety of people's personal data.

Another drawback of smart cities is their dependence on technology. If technology systems fail or are attacked, public services could be disrupted. This poses challenges for maintaining stability and ensuring security of smart cities.

In short, living in a smart city brings many benefits such as convenience and energy savings. However, it is also necessary to pay attention to information security issues and dependence on technology. To make the most of the advantages and minimize the disadvantages, smart investment and management from city managers is needed.

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