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آموزشی درسی و کمک درسی
هر مطلبی که بشه آموزش داد

بازديد : 507 مرتبه
تاريخ : پنجشنبه 20 اسفند 1389

  1-Don’t ask for another book until You …… this one.

1) finish              2) finished                     3) had finished               4) will finish

    2-Afshin’s father wants him to get home before it …….. dark.

1)got                             2) gets              3) getting                                  4) will get

    3-“Let’s get off”

“Don’t be in a hurry. You shouldn’t get off the train before it “…….…”

1) stops                    2) stopped              3) will be stopped                      4) will stop

 4- At this moment I ……….we have a good chance of victory.

1) feel                        2) am feeling                 3)  felt                          4) am felt

 5- Mr. Smith …..to his office in his car every morning.

1) went                         2) goes                    3) is going                         4)go

 6- In autumn the trees …..their leaves.

1)are losing                   2) are lost                     3) lose                      4) have lost

  7- “Is he studying now?”

      “No, he is not. He …….in the afternoon.”

1) doesn’t study             2) not study                   3) study                         4) don’t study

 8- The child always cries when her mother ……out of the house.

1)went                          2) had gone                   3) goes                             4) will go

 9- “Doesn’t Mehdi want to sell his car?”  “Yes , He…………”

1)does                          2) doesn’t                     3) sells                          4) wants

  10- “Who can pass the exam?”     “Every body unless they ……..hard enough”

    1) don’t work                        2) work                         3) worked              4) won’t work

 11-“Will you pay for my lunch today?” “Not unless you ……..to pay for mine tomorrow.”

1)promise                      2) promised                   3) will promise               4) would promise

 12-“Are you usually awake at mid night?”

       “No, I ……..until midnight.”

1) am never staying up                                        2) never stay up

3) never stayed up                                             4) might never stay up

 13-“ How long are you going to stay?”      “I’ll wait for him until he …..”

1) comes back                                       2) has come back

3) is going to come back                        4) will come back

 14- At the moment he ………to be getting better.

1) has seemed               2) seems                       3) seemed                     4) had seemed

15- I ….cook my own meal .

1)often does                  2) often have to          3)have to often           4)have often

 16- I see that you ……. your new suit today.

1) are wearing               2) were wearing            3) are worn                   4)be were worn

  17- “Does she still live in Tehran?”        “yes , she ….”.

1) is living there still                               2) is still living there

3) still is there living                               4) there is still living

  18- Look! That boy …..to break the window.

1) tries                          2) is trying                    3) tried                          4) is tried

 19- “ Is the class busy?”          “Yes , the student are ……. pronunciation.”

1) practice                    2) practiced          3) practices                      4) practicing

  20- Just now he ….. his dinner but he says he’ll see you when he’s finished.

1)has had              2) was having                3) is having                        4) had

21- Many countries …..to solve such problems nowadays.

1) are trying                  2) will try                      3) tried                          4) try

 22- Listen! The telephone……

1) ring                           2) rings                 3) are ringing                 4) is ringing

  23- They ……to the radio at present.

1) listen                    2) are listening               3) have listened                  4) is listening

 24- Listen! Someone …… upstairs.

1) walks               2) was walking              3) walked                         4) is walking

    25- “Has he ever been here before?”

        “No , he says that he …….tomorrow.”

1)would came               2) was walking              3) walked                       4) is walking

26- Be quiet or you will wake father up, he……..

1)slept                          2) sleeps                   3) is sleeping                 4) can sleep

  27- My great grand father …….. a new house nowadays.

1) builds               2) is building                  3)had built                        4) built

 28- Mehdi can’t have the newspaper now because his aunt…….it

1) reads                     2) has read                    3) is reading                  4)will read

 29- I think he …..his supper at the moment.

1) has                           2) having                       3)is having                   4) had

 30- For the time being he …..in Shiraz.

1) is studying                 2) will study      3) studied                                  4) studies

31- “Do you like Dr Irani’s new book?”    “Yes , it’s the best book he……….”.

1) is ever writing           2) has ever written          3) had ever written        4)was ever writin

  32- “Has anybody called today?”

        “The telephone has not rung…. I came”.

1) before                                   2) for                            3) since                        4) until

  33- I ……to the cinema since last month.

1)didn’t go                    2) hadn’t gone   3) haven’t gone             4) wouldn’t go

  34- Since the beginning of the term, we ……a lot of time on tenses.

1) are spending              2) have spent    3) spend                         4) will spend

  35- I ….him so angry.

1)never have seen         2)have never seen         3)am never seeing          4)never am seeing

  36- He ….those jobs since he started work five years ago.

1) was having                2) has had                     3) would have had          4) had had

  37- Since when ……….absent from class?

1) is he                  2) was he                      3) has he been               4) had he been

  38- I wonder how Ali’s trip was. I don’t know. I haven’t seen him……..

1) since he arrived         2) until he arrived    3) when he arrived   4) by the time he arrived

39- “Do you still work at the library?”     “Oh , no I …there for the last two months.”

1) don’t work                2) didn’t work      3) haven’t worked      4) won’t have worked

  40- I knew everything about the mysterious letter, but up to now I ….to anybody about it.

1) didn’t speak              2) won’t speak  3) haven’t spoken                      4) wouldn’t speak

  41- Poor mummy …….the dishes in the kitchen for an hour and there are still plenty of them unwashed.

1) washes           2) washed                     3) is washing                 4) has been washin

42- A: Please call John and tell him we can’t go to visit him today.

        B: But , he …..for us since this morning.

1) was waiting               2) is waiting          3) has been waiting        4) will been waiting

 43- Teacher : you look hot, Mary?

        Mary: I ….all the way to school to be on time.

1) am running                2) had run                     3) would run          4) have been running

 44-  “ I can’t decide on which color to buy”

         “You ….for ages, I can’t wait for ever”

1)would hesitate      2) are hesitating             3) hesitating               4) have been hesitating

    45- The patients ……in hospital since 8 o’clock.

1)were waiting              2) have been waited      3)are waiting     4)have been waiting

   46- She …for an hour, and she isn’t tired yet.

1) talks                  2) has talked                 3)have built                   4) has been talking

 47- The workers …..that bridge for over a year, but it is not finished yet.

1) are building               2) built              3) have built      4) have been building

48- The children playing volleyball over there ..since half past eight.

1) are playing                2) have been playing      3) had been playing        4) had played

 49- My friend Parviz …..on this difficult problem since 8 o’clock.

1) has been working                              2) had been working

3) is working                                         4) was working

  50- I ……. Mr. Duke because he speaks so fast.

1) never will understand                                     2) never understood

3) have never understood                                   4) has never understood

ادامه مطلب...
بازديد : 231 مرتبه
تاريخ : پنجشنبه 19 فروردين 1390

 

 

1

كلمات ناقص را بطور كامل بازنويسي كنيد.

A.B.They said that in fut-re they will watch only cerata-n programs.

C.D.The police r-alized that the man was telling a li- .

E.F.Di-ner times were more relaxed without the pres-ure of TV.

G.H.Some of the inf-rmation which goes into the bra-n is forgotten.

I.J.Several interesting ob-ervations were r-ported.

K.L.Psychol-gists believe that forgtting dosen t take place at an even p-ce.

M.N.My brother is very po-erful.He has gotten medals rec-ntly.

O.P.I can t recal-  his name.It does not st-ck in my mind.

2

با استفاده از كلمات داده شده جملات زير را كامل نماييد.(يك كلمه اضافي است)

( ashamed of – details – average – education – struggle – rubbish – programs – painful - memory)

1.They cleaned the house and took …………. away from their house.

2.The …………… of students in this class is 15.

3.Family members …………… on choosing different channels.

4.Ali is ………….. showing his bad marks to his mother.

5.Some people have photographic ………… .

6. I like watching TV ………….. at night.

7.They think that …………. is not an end but a means to an end.

8.Do you know all the ………… about the accident? – Yes , I do    

3

شكل صحيح كلمه هاي داخل پرانتز را در جاي خالي بنويسيد.

 

9.Last night I had only …………. Soup. (water )

10.She ………… me to dinner yesterday. (invite)

11.Preparing this food is not as ……….as it may seem.(easy)

12.What do you …………. think about this problem? (real)

13.He could not ………….. how computer works. (explain)

14.He likes walking in such a …………. night. (rain)

4

جملات زير را با نوشتن كلمه اي مناسب از اطلاعات خود كامل كنيد.

15.Our television doesn’t t work. So we bought a new television ………….. .

16.Driving on snow – covered streets isn’t safe. It is very …………. .

17.This man cannot see. He is ………. .

18.A person who is watching TV is a TV …………. .

19.The ability to remember things is called ………… .

20.Her mother didn’t t …………. her to go out, because she had an exam. 

5

گزينه صحيح را از ميان پاسخهاي داده شده انتخاب كنيد.

21. “What dose she say?” “ I don t know what ……….. .”

a)she said            b)does she say            c)she says          d)did she say                       

22.It is important for him ………… that tall tree.

a)to climb                  b) climb                 c)climbing                 d)climbs

23.I can give you the book  if you look …………. it carefully.

a)about                      b)after                    c) up                          d)for

24.He doesn’t t enjoy …………. in this part of the river.

a)swim                      b)swimming           c)to swim                  d)swims

25.Look at the cloudy sky.It …………. Soon.

a)was raining            b)is going to rain    c)has rained              d)rained

26.”Did you turn off the CD player?” “-Yes ,I turned ……….. .

a)it off                       b)off it                    c)off them                d)them off

6

با توجه به تصوير به سوالات زير پاسخ دهيد.

27.What is Maryam going to do ?                                   

 

 

 

 

28.what has made Ali tired?

 

 

 

7

بر اساس جمله ي داده شده جمله ناقص را كامل كنيد.

29.”Where can she find her pen?”

“ I don t know …………………………….. .”

30.Finding a job is important for him.

It …………………………………………... .

8

با هر گروه از كلمات زير يك جمله بنويسيد.

31.smoking – stopped – last year – my father.

32.monkeys – are – afraid – they – of.

9

كدام كلمه از نظر تلفظ S با بقيه متفاوت است؟

33.A)a)mixes            b) taxies           c)dishes          d)matches

33.B)a)coughs          b)cars               c)dolls            d)dogs

ادامه مطلب...
ارسال توسط من و تو |دسته:| امتياز : 3 | 1 2 3 4 5 6|نمونه,سوال,سوم,نظری, نمونه سوال سوم نظری,
بازديد : 420 مرتبه
تاريخ : شنبه 21 فروردين 1390

In the Name of Allah

English 1-Lesson 2

Full Name:

 

A-Fill in the blanks with the given words. There is one extra word:(4)

 

necessary, hot , climb , cloudy , should , monkey , little , easily , take

 

1-Their radio doesn’t work .They ……………buy a new one.

2-The …………… has a coconut in his hand.

3-The tree is very tall. I can’t ……………. it.

4-It is fun to watch …………….. children play.

5- The tea is very …………… I can’t drink it.

6-He’ll …………….  an exam tomorrow.

7-She can learn ……………….. She is a clever student.

8-Food and water are ………………….to man.

 

B-Complete the following sentences with your own words.(2)

 

9-The ……………..of a …………….. coconut is brown.

10-Funny things are the things that make us ………………….

11-The child is …………………. He should drink something.

 

C-Find the meaning of the underlined words in the right column and write them in the brackets. (2)

 

12-Farmers raise plants and vegetables.(                    )                                a)like

13-The cows are eating grass in the field(                       )                             b)a piece of land

14-Farmhands help farmers .(                )                                                       c)grow

15-The cat climbed to the top of the tree.(                  )                                 d)clever

                                                                                                                        e) went up

                                                                                                                        f)also

D-Choose the correct answer:(2)

 

16-Mina ……………………some flowers  and gave them to the old woman.

 a)looked                     b)picked                      c)talked                       d)walked

 

17-The glass fell and ……………………..

a)ate                b)broke                       c)thought                     d)bought

18-Give me some food because I’m very …………………

a)hungry                      b)clever                       c)thirsty                       d)careful

19-A ………………….. often works in a field.

a)baker                        b)butcher                    c)farmer                      d)doctor

 

E-Read the following sentences and choose the best answers.(2)

 

20-Flowers are beautiful. Don’t pick them .These two sentences mean that…………………. a)flowers shouldn’t pick you.

b)you shouldn’t pick beautiful flowers .

c)you have beautiful flowers in your hands.

d)you don’t like beautiful flowers.

 

21-The monkey knows that a green coconut must stay on the tree longer. This sentence means that the monkey  …………………….

a)drops the green coconuts down the tree.

b)picks the green coconuts

c)doesn’t know the brown coconuts

d)doesn’t pick green coconuts

 

F-Put the following words in the correct order.(2)

22-animals , full , of , wild , the jungle , is , .

…………………………………………………………………………

23-house , the post , my , far from , office , isn’t , .

………………………………………………………………………..

G-Grammar: Choose the correct answer .(1)

 

24-“How far  ……………. to the nearest  hospital?”  “I don’t know.”

a)is there                     b)is it                           c)are there                  d)are they

25-I think …………………….. easy to learn English.

a)there is                     b)there are                  c)they are                    d)it is

 

 

H-Language Functions: Find the answers for the following questions in column B and put the letters in brackets.(3)

                    A                                                             B

26-Where is she from?(           )                                a-She is 25.

27-Does she live in a hotel?(            )                       b-She is a nurse.

28-Can she speak Arabic?(          )                           c-No, she can’t.

29-When did she arrive here?(        )                      d-She is Mrs. Alavi.

30-Who is that woman?(       )                                 e-Yes, she can.

31-How old is she?(      )                                          f-Yes, she likes Iran.

                                                                                  g-She is from France.

                                                                                  h-Yes, she does.

                                                                                  i-She arrived here on Saturday.

 

I-Spelling :Write the complete form of the following words in front of the numbers given.(2)

He  r _ des on the back of the farmer’s  bic _ _ le.

You know that a ripe or _ _ ge  is  bet _ er than a green one.

32- ……………    33-………………   34- …………………..  35- ……………………

 

ادامه مطلب...
ارسال توسط من و تو |دسته:| امتياز : 3 | 1 2 3 4 5 6|نمونه,سوال,درس,دوم,اول,نظری, نمونه سوال درس دوم اول نظری,
بازديد : 352 مرتبه
تاريخ : پنجشنبه 26 فروردين 1390

 

 so – such – too – Enough  

   1- Watching television…………. .

1) I fell asleep                           2) the light went out

3) my father came in                 4) it fell down

                 2- Peter was feeling sick. He called a doctor.

     In other words “,….sick. Peter called a doctor.”

1) fell                2) feeling                      3) having felt                 4) to feel

                  3-yesterday ……….the whole morning the young boys went home happily.

1) swimming                 2) having swum                         3) swam                       4) to swim

                4- “George was reading a story. He fell asleep.” “…a story. George fell asleep.”

1) Read                        2) Having read              3) Reading                    4) To read

                5- Leaving the house……… .

1) we met him                                   2) it began to rain

3) the room was cleaned                        4) a car passed by

                6- This morning……………there , I found Ali sick.

1) arrive                                    2) to arrive                    3) arrived                      4) arriving

             7- ………her approach , Ali ran away.

1) seeing                                   2) to see                       3) see               4) saw

            8- Asking my friend a question………… .

1)                he did not know the answer to my question.

2)                he said that he wanted to ask me question first.

3)                I saw a man running fast across the street.

4)                the question did not appear interesting to him.

             9- Walking along the street…………..

1) Ahmad ran into a close friend             2) it started to rain heavily

3) the street was very crowded              4) there was a terrible car accident

            10- Buying my son a story book,…… .

1)                I realized that I had read it years ago.

2)                it seemed very interesting and amusing.

3)                my son seemed quite happy and satisfied.

4)                the shopkeeper recommended two more books.

         11- Did Susan leave the room after turning off the light?

Yes, ………the light, she left the room.

1) turned off                  2) to turn off                 3) turning off     4) having turned off

       12-At 11:00 ……..,we left the cinema.

1) having been finished              2) the film having finished

3) finishing the film                                4) Being finished

       13- Having ……..a hotel, we looked for somewhere to have dinner.

1) find               2) finding                      3) finds                         4) found

     14- “We had spent nearly all our money, so we couldn’t afford to stay in a hotel” Actually……nearly all our money, we couldn’t afford to stay in a hotel.

1) spending                   2) being spent                3) having spent              4) had spent

             15- “she finished her work. Then she went home”. It means that………her work , she went home.

1) to finish                     2) finishing                3) having finished            4) have to finished

             16- Ahmad has enough ….to carry the heavy box.

1) strong                        2) strength                3) strongly                     4) strengthen

     17- Our English teacher does not speak fast. I can understand him.

1)                Our English teacher speaks slowly enough for me to understand him.

2)                Our English teacher speaks enough slowly for me to understand him.

3)                Our English teacher speaks too slowly for me to understand him

4)                Our English teacher doesn’t speak very slowly for me to understand him

        18- Amir is six years now. He will be …to go to school next year.

1) too old          2) old enough                3) too young      4) young enough

    19- You’re …….to know things better than my son.

1) old enough                2) much older    3) too old                      4) very old

              20- Mother: Stand on the chair and fix the lamp, please.

        Ali: Oh mother. I’m …..to reach the ceiling.

1) so tall                        2) tall enough    3) too all                       4) too strong

   21- The rope wasn’t ….to pull the car to the safe side.

1) so strong that           2) strong enough               3) such strong             4) too strong

       22- Please drive more slowly. We have ….time to get to the airport in time.

1) too                2) enough                      3) very              4) so

        23- I think if I will give him some advice that would be a mistake. He is …..for, himself.

1) enough old to decide              2) so old to decide

3) old enough to decide              4) old he decides

   24- Why don’t you ask Peter to keep the accounts?

He doesn’t have …….experience to do that.

1) enough                      2) too                3) so                 4) as

    25- Is there …..bread for all the sandwiches we have to make?

1) so many                    2) too                3) enough                      4) such as

         26- They worked so hard that they were ……..tired to eat their supper.

1) much                                    2) enough                      3) too                4) very ]

   27- A physics problem is usually ………difficult for a six year old student to solve.

1) so                             2) enough                      3) too                            4) much

          28- “ Can he drive us to the airport?”

“No, his car is …..small to take us all”

1) too                            2) such             3) much                        4) more

     29- I can’t put this bag in the picnic basket.

It’s ……big to go in.

1) so                             2) such                         3) too                4) very

          30- Some stars are ….far away to be seen without a telescope.

1) so                             2) such                         3) too                4) very

      31- He was ……..excited to think wisely.

1) very                          2) too                            3) such                         4) so

      32- He was ……clever to throw himself out of the window.

1) much                                   2) so                             3) such                         4) too

          33- Are you sure that he will take us in his own car?

        No, his car is ……small to hold eight people.

1) so                             2) such                         3) much                        4) too

        34- “Would you like to play tennis tonight”

“ No, I’m …….tired to do anything tonight”

1) so                             2) such                         3) much                        4) too

       35- Ahmad was ………out of breath that he couldn’t speak at first.

1) such                                     2) as                             3) so                             4) very

    36- The weather was……..lovely that you could hardly stop playing.

1)so                              2) such                         3) too                            4)such as

      37- The teacher was ……..tired that she could not continue teaching.

1) so                             2) such                         3) too                4) very

     38- Ali drives………..carelessly that he usually has one accident each week.

1) so                             2) more                         3) very              4) much

    39- The temperature has really risen today.

Yes, it is………. I can’t work.

1) to hot                                    2) so hot that     3) very hot                    4) really hot

      40- He looked ….that I thought I had better take him to the hospital.

1) to be so frightened                             2) with such a fright

3) with such fright                                 4) so frightened

  41- I couldn’t sleep last nigh. That’s why I feel …..sleepy that I can’t stay awake any longer.

1) too                            2) so                             3) enough                      4) much

     42- It is ….that I’d like to go on a picnic.

1) such a lovely day                               2) a lovely a day

3) so lovely day                                                 4) too lovely a day

   43- There are………….interesting stories that I can’t stop reading them.

1) such an                     2) such as                     3) such                         4) so

  44- It was …..that we all were frightened.

1) such a terrible storm  2) too terrible  storm      3) so terrible storm        4) so terribly storm

       45- “Are you going to watch T.V tonight?”

“ I have ……work that I cannot watch it”

1) so many                    2) so much                    3) too many                   4) too much

       46- The examination was ……difficult one that I couldn’t do it.

1) so                             2) such                         3) so much                    4) such as

     47- It was……….an expensive car that nobody could buy it.

1) such                                     2) so                             3) too                4) very

       48- Please type the letter more carefully, you’re making……..mistakes.

1)too many                    2) too much                   3) enough                      4) too

   49- There were ……..questions on the test that I couldn’t finish it in time.

1) as much                    2) so many                    3) so much                    4) too many

    50- The problem was difficult for Maryam. She couldn’t do it.

1)                The problem was too difficult for Maryam to do

2)                The problem was difficult for Maryam not to do

3)                The problem was too difficult for Maryam not to do

4)                The problem was not difficult enough for Maryam not to do.

 

 

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این نمونه سوال برای دانش آموزان سال اول راهنمایی  تا پایان درس ۶  طراحی شده   است .

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 دانش آموزان عزیز نمونه سوالات تستی سال سوم راهنمایی    برای شرکت در مدارس نمونه  طراحی شده است

لطفا برای دانلود این نمونه سوال    اینجارا کلیک کنید

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simple present

 

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1- تیل چیست و استفاده از آن در این آزمایش چه مزیتی نسبت به بشر دارد؟

 

*وسیله ی ساده ای است که به سهولت قابل دسترسی است.لوله ی تیل به نحوی طراحی شده است،

که وقتی در آن روغن میریزیم و لوله را گرم میکنیم در آن تبادل گرمایی صورت میگیرد به نحوی که توزیع دما،

در سراسر روغن داخل لوله یکنواخت می شود.

 

 

2- چرا نمیتوان از نمونه ای که یکبار دمای ذوب آن اندازه گیری شده است برای

اندازه گیری مجدد دمای ذوب استفاده کرد؟

 

*وقتی یک جسم جامد به دمای ذوب خود برسد، ساختار اولیه اش تغییر میکند؛

در نتیجه در مرتبه دوم دمای ذوب متفاوتی از دمای ذوب اولیه خواهیم داشت.

 

 

3- چرا بجای نقطه ذوب، اصطلاح دمای ذوب را بکار میبریم؟

 

*در اکثر مواد بجای نقطه ذوب، از گستره دمایی که در آن ماده شروع به ذوب شدن میکند تا دمایی که بطور کامل

ذوب میشود را مد نظر قرار میدهند؛ به همین دلیل اصطلاح دمای ذوب بکار میرود.

 

 

 

4- یک دانشجو دمای ذوب ماده دارای ناخالصی شن را 130-118 درجه سانتی گراد بدست آورد، در حالیکه

دمای ذوب ماده خالص 123-121 درجه سانتی گراد گزارش شده است! این پدیده را چگونه توجیح میکنید؟

 

*ناخالصی موجب زیاد شدن گستره دمای ذوب میشود؛ تبلور مجدد یک ترکیب ناخالص موجب خالص شدن آن

و در نتیجه کاهش گستره دمای ذوب میگردد.

 

 

آزمایش دمای جوش

 

1- علت خروج حباب ها از لوله موئین در روش میکرو چیست؟

 

*با افزایش دما، کم کم مایع به فاز بخار میرود و همین امر سبب افزایش فشار بخار روی سطح مایع میگردد؛

در نتیجه فشار وارد بر سطح مایع بیشتر از فشار گاز درون لوله موئین خواهد شد، به همین دلیل بتدریج هوای

درون لوله موئین با ایجاد حباب خارج میشود.

 

2- چرا پس از خروج مکرر حباب هیتر را خاموش میکنیم؟

 

*چون این حالت نشانگر محلول ابر گرم شده است، یعنی دمای ماده بیشتر از دمای جوش است بنابراین

 هیتر را خاموش میکنیم تا دما پائین بیاید و بتوانیم دمای جوش را اندازه گیری کینم.

 

- محلول ابر گرم شده را تعریف کنید؟

 

*محلولی است که در آن، فشار کمتر از فشار جو و دما بیشتر از دمای جوش است اما ماده هنوز نجوشیده است.

 

 

آزمایش تبلور مجدد

 

1- چرا به این روش، تبلور مجدد میگویند؟

 

*وقتی ماده به صورت جامد باشد، سپس آن را در حلالی حل کرده و مجددا آن را به صورت بلور رسوب گیری کنند،

تبلور مجدد مینامند.

 

1- تبلور با رسوب گیری چه تفاوت هایی دارد؟

 

*تبلور فرآیندی کند و انتخابی است، اما رسوب گیری سریع و غیر گزینشی است.

 

 

2- چرا برای تبلور باید از حلالی استفاده کرد که دمای جوش آن کوچکتر از دمای

ذوب ماده خالص باشد؟

 

*در غیر اینصورت ماده متبلور، مجددا ذوب شده و ایجاد امولسیون کرده و در نهایت

روغنی شدن رخ میدهد.

 

3-  چرا برای بدست آوردن بلور خالص در مرحله آخر قیف بوخنر استفاده میشود؟

 

*تبلور فرآیندی کند است؛ از قیف بوخنر برای تسریع عمل تبلور استفاده میشود.

 

 

آزمایش استخراج کافئین از چای

 

1- چرا از آب به عنوان حلا اول استفاده شده است؟

 

*آب دمای جوش بالایی دارد و باعث استخراج کافئین از نسوج گیاهی میود.

 

2- چرا از حلال دومی، مانند CH2 CL2 و... استفاده میشود؟

 

*تا کافئین را که یک ترکیب آلی ست، در خورد حل کرده و از طرف دیگر به علت

دمای جوش پائین تبخیر آن نیز راحت تر صورت گیرد.

 

3-برای استخراج کافئین، اضافه کردن نمک Na2 CO3 مناسب تر است یا Na CL؟ و چرا؟

 

 

Na CL؛ زیرا Na2 CO3 یک گونه بازی است و کافئین هم حالت بازی دارد، و از آنجا که دو گونه هم سان

از یکدیگر فرار میکنند، Na CL برای این کار بهتر است.

 

آزمایش تقطیر

 

1- چرا مایع داخل بالن باید بین یک سوم تا دو سوم حجم بالن باشد؟

 

*چون اگر کم باشد، فشار کافی برای تقطیر فراهم نمیشود، و اگر زیاد باشد

سر ریز میشود.

 

2-چرا بهتر است، که قبل از پایان یافتن همه مایع داخل بالت تقطیر را قطع کرد؟

 

*چون مواد تـــه ظرف غیر فرارند و خارج نمیشوند و باقی مانده به تـــه ظرف میچسبد.

 

3- چرا مایعات تقطیر شده قبل از ثبات دمایی را دور میریزیم و این مواد چه میباشند؟

 

*چون این مایعات دارای ناخالصی هستند و ممکن است غیر فرار باشند.

 

4- چرا در تقطیر از سیستم کاملا بسته استفاده نمیشود؟

 

*چون باعث انفجار میگردد.

 

5-علت اضافه کردن سنگ جوش به بالن چیست؟

 

*به منظور توزیع یکنواخت گرما و جلوگیری از پریدن مایع است.

 

6- آزئوتروپ چیست؟

 

*به دو ماده که باهم در یک دما بجوش می آیند، آزئوتروپ میگویند. آزئوتروپ به

معنای همسان جوش یا هم جوش میباشد؛ به این معنی که وقتی محلول به نقطه آزئوتروپ میرسد در فشار ثابت و غلظت ثابت آنقدر در نقطه آزئوتروپ میماند

تا به بخار هم غلظت با خود تبدیل شود.ادامه مطلب...
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