a) PTHH : \(H_2+CuO-t^o->Cu+H_2O\)  

Có : \(m_{CR\left(giảm\right)}=m_{O\left(lay.di\right)}=20-16,8=3,2\left(g\right)\)

=> \(n_{O\left(lay.di\right)}=\frac{3,2}{16}=0,2\left(mol\right)\)

BT Oxi : \(n_{O\left(lay,di\right)}=n_{CuO\left(bi.khu\right)}=0,2\left(mol\right)\)

=> \(n_{Cu\left(spu\right)}=n_{CuO\left(bi.khu\right)}=0,2\left(mol\right)\)

=> \(\hept{\begin{cases}m_{Cu}=0,2\cdot64=12,8\left(g\right)\\m_{CuO}=16,8-12,8=4\left(g\right)\end{cases}}\)

b) \(n_{H_2}=\frac{5,67}{22,4}=0,253125\left(mol\right)\)

    \(n_{CuO}=\frac{20}{80}=0,25\left(mol\right)\)

Ta thấy : \(0,253125>0,25\left(mol\right)\) => theo pthh, ta sẽ tính theo số mol của CuO

=> Theo lí thuyết, \(n_{CuO\left(bi.khu\right)}=0,25\left(mol\right)\), mà thực tế \(n_{CuO\left(bi.khu\right)}=0,2\left(mol\right)\)

=> \(H\%=\frac{0,2}{0,25}\cdot100\%=80\%\)

\(M:Cu\)

\(A:CuO\)

\(B:CuSO_4\)

\(C:CuSO_4\)

\(D:CuSO_4\)

\(E:CuSO_4\cdot5H_2O\)

PTHH : \(2Cu+O_2-t^o->2CuO\)

              \(CuO+H_2SO_4-->CuSO_4+H_2O\)

Ta có : \(n_{Fe2O3}=\frac{m}{M}=\frac{16}{160}=0,1\)

PTHH phản ứng : Fe₂O₃ + H₂ -----> Fe + H₂O

=> Cân bằng PTHH : Fe₂O₃ + 3H₂ -----> 2Fe + 3H₂O

Tỉ lệ hệ số chất tham    1      :   3        :    2     :   3

gia và sản phẩm        0,1         0,3          0,2    :  0,3 

                                   mol        mol      mol         mol

=>  VH₂ \(=n.22,4=0,3.22,4=6,72\left(l\right)\)                                                                   

=> m_Fe = n.M = 0,2 . 56 = 11,2 (g)

1) Định luật bảo toàn khối lượng: trong phản ứng hóa học, tổng khối lượng các chất đã tham gia phản ứng bằng tổng khối lượng các sản phẩm tạo thành. 

2) a) Ta có: \(SO_4\)có hóa trị là \(2\).

Gọi \(a\)là hóa trị của \(A\)trong \(ASO_4\).

Khi đó, theo quy tắc hóa trị: \(1a=1.2\Leftrightarrow a=2\).

Vậy trong công thức \(ASO_4\), \(A\)thể hiện hóa trị \(2\).

b) \(n_{Cu}=\frac{12,8}{64}=0,2\left(mol\right)\)

\(n_A=n_{Cu}=0,2\left(mol\right)\)

\(M_A=4,8\div0,2=24\left(đvC\right)\)

Suy ra \(A\)là \(Mg\).

em nơi chị thương chị giao bài khó vcn

\(1,d_{\frac{N_2}{CO_2}}=\frac{28}{44}\approx0,634\)

\(d_{\frac{N_2}{K^2}}=\frac{28}{29}\approx0,966\)

\(2,M_{Na_2SO_4}=142\left(g/mol\right)\)

\(\%Na=\frac{2.23}{142}.100\%\approx32,39\%\)

\(\%S=\frac{32}{142}.100\%\approx22,54\%\)

\(\%O=100\%-\%Na-\%S=45,07\%\)

\(3,n_{Na}=\frac{3.10^{24}}{6.10^{23}}=5\left(mol\right)\)

\(m_{Na}=5.23=115\left(g\right)\)

chịu mới học lớp 5 sao biết

\(nFe=\frac{m}{M}\)   

\(=\frac{42}{56}\)   

\(=0,75\left(mol\right)\)    

Vậy chọn đáp án D 

* một số câu trực tiếp gián tiếp mình chưa học nên không làm được nhé 

18. The Browns (have) ________is having____________ dinner at the moment.

19. He (live) _________has lived___________ in Hanoi for 20 years.

20. Alexander Graham Bell (invent) ______invented_______ the telephone many years ago.

21. She (be) _____is_____ very ill now. She (not go) ______hasn't gone______ to school since Monday.

22. + _____Have_____ you (be) ____been______ to Phong Nha before?

+ Yes. I (spend) ____spent______ my holiday there last summer.

23. I must go now. I (phone) _____phoned___ you when I (arrive) ____was arriving__________ there.

24. When I last (see) ____saw______ them, they ( work) _____were working______ in a factory in Hanoi.

25. Ba's teacher (give) ____gave______ him a lot of homework last week.

26. Tom hopes he (meet) ________will meet__ many interesting people when he goes to Hanoi next month.

27. Mai and her friends (walk) __________are walking__________ to school now.

28. They (go) ______went____ to Sao Mai Movie Theater last night.

29. She (not see) _________hasn't seen___________ that film before.

30. My mother was waiting for me when I (come) ________came______ home.

31. Ann and Susan (cook) ___________were cooking__________ dinner when Martin arrived home.

32. The light (go) ______was going________ out while we were having dinner.

33. + What _____were_____ you (do) ______doing________ at this time yesterday?

+ I (play) ____________was playing_________ games on the computer.

34. Tom! Turn off the TV. You (always watch) _________always watch___________ TV.

35. Lan often (do) ____does______ her homework carefully.

36. This is the first time Hoa (meet) __________has met__________ Tim's family.

38. Yesterday (be) ______was____ a beautiful day. The Sun (shine) _______was shining_____________ brightly when we (leave) _______left_______ home.

40. Listen! Mai (play) ________is playing____________ the piano in her room.

41. + What kind of music __do__________ you (lik e) ___lik e_______ ?

+ I pop music.

42. In summer, the Sun usually (shine) _________shines_________ brightly.

43. I (not finish) ___________haven't finished____________ reading the novel you lent me yet.

44. Julia (write) _____________is writing___________ an email to her boy friend now.

45. Jack (not meet) ______________didn't meet_________ Tom the last time he came to America.

I. Chia động từ trong ngoặc cho đúng thì (Give correct tenses of the verbs)

1. Mary (be) ___________has been_________ seriously ill since last night.

2. They sometimes (go) _________go___________ school by bus.

3. How long _____have_____ you (study) ____studied______ English?

- I (study) _______have studied_____________ it for 7 years.

4. We last (see) ________saw_____ them last Sunday.

5. I (not meet) _______haven't met_____________ him since he moved to Hanoi.

6. Now they (play) _________are playing___________ happily in the school yard.

7. We (not finish) ___________haven't finished_________ our exercises yet.

8. My friend said he (be) _____will be_____ working in Hanoi then.

9. Mr. David (just buy) ________just has bought____________ a new house.

10. They (build) _________will build___________ a new hospital in my neighborhood next month.

11. It (not rain) __________hasn't rained__________ since the beginning of this month.

13. We (begin) _____began_______ to learn English three years ago. Now we (learn) __________________ for 3 years. ( xem lại đề)

14. _____Have_____ you ever (be) ____been______ to Ho Chi Minh City?

15. The telephone (ring) ___rang_______ when we (watch) _____were watching______ television last night.

16. Mrs Hoa (teach) _____taught____ English in this school since she (leave) ___has left___ the university.

17. Look! That car (run) ______is running___________ very fast.

* Một số câu trực tiếp gián tiếp mình chưa học nên không làm được, cậu tự làm nhé :

1. Mary (be) _________has been__________ seriously ill since last night.

2. They sometimes (go) _________go___________ school by bus.

3. How long ____have______ you (study) _____studied_____ English?

- I (study) ___________have studied_________ it for 7 years.

4. We last (see) _______saw______ them last Sunday.

5. I (not meet) _________haven't met___________ him since he moved to Hanoi.

6. Now they (play) __________are playing__________ happily in the school yard.

7. We (not finish) _________haven't finished___________ our exercises yet.

9. Mr. David (just buy) __________just has bought__________ a new house.

10. They (build) __________will buid__________ a new hospital in my neighborhood next month.

11. It (not rain) ________hasn't rained____________ since the beginning of this month.

14. ________Have__ you ever (be) _____been_____ to Ho Chi Minh City?

15. The telephone (ring) ____rang______ when we (watch) ______were watching_____ television last night.

16. Mrs Hoa (teach) ____taught_____ English in this school since she (leave) ___has left___ the university.

17. Look! That car (run) ______is running___________ very fast.

18. The Browns (have) ________is having____________ dinner at the moment.

19. He (live) _________has lived___________ in Hanoi for 20 years.

20. Alexander Graham Bell (invent) ______invented_______ the telephone many years ago.

21. She (be) _____is_____ very ill now. She (not go) ______hasn't gone______ to school since Monday.

22. + _____Have_____ you (be) ____been______ to Phong Nha before?

+ Yes. I (spend) ____spent______ my holiday there last summer.

23. I must go now. I (phone) _____phoned___ you when I (arrive) ____was arriving__________ there.

24. When I last (see) ____saw______ them, they ( work) _____were working______ in a factory in Hanoi.

25. Ba's teacher (give) ____gave______ him a lot of homework last week.

26. Tom hopes he (meet) ________will meet__ many interesting people when he goes to Hanoi next month.

27. Mai and her friends (walk) __________are walking__________ to school now.

28. They (go) ______went____ to Sao Mai Movie Theater last night.

29. She (not see) _________hasn't seen___________ that film before.

30. My mother was waiting for me when I (come) ________came______ home.

31. Ann and Susan (cook) ___________were cooking__________ dinner when Martin arrived home.

32. The light (go) ______was going________ out while we were having dinner.

33. + What _____were_____ you (do) ______doing________ at this time yesterday?

+ I (play) ____________was playing_________ games on the computer.

34. Tom! Turn off the TV. You (always watch) _________always watch___________ TV.

35. Lan often (do) ____does______ her homework carefully.

36. This is the first time Hoa (meet) __________has met__________ Tim's family.

38. Yesterday (be) ______was____ a beautiful day. The Sun (shine) _______was shining_____________ brightly when we (leave) _______left_______ home.

40. Listen! Mai (play) ________is playing____________ the piano in her room.

41. + What kind of music __do__________ you (lik e) ___lik e_______ ?

+ I pop music.

42. In summer, the Sun usually (shine) _________shines_________ brightly.

43. I (not finish) ___________haven't finished____________ reading the novel you lent me yet.

44. Julia (write) _____________is writing___________ an email to her boy friend now.

45. Jack (not meet) ______________didn't meet_________ Tom the last time he came to America.

+) Oxit chứa 50% khối lượng oxi :

Gọi công thức hóa học của oxit là \(M_xO_y\) (x,y nguyên dương tối giản)

Ta có : \(\frac{16y}{M_M\cdot x+16y}\cdot100\%=50\%\)

=> \(32y=M_M\cdot x+16y\)

=> \(M_M=8\cdot\frac{2y}{x}\)

Ta có bảng sau : 

=> oxit cần tìm là SO₂

=> \(M_{SO_2}=32+16\cdot2=64\) (g/mol)

+) Oxit chứa 60% khối lượng oxi :

Gọi công thức của oxit chứa 60% khối lượng oxi là \(M_aO_b\) (a,b nguyên dương tối giản)

Ta có : \(\frac{16b}{M_M\cdot a+16b}\cdot100\%=60\%\)

=> \(16b=0,6M_M\cdot a+9,6b\)

=> \(M_M=\frac{16}{3}\cdot\frac{2y}{x}\) 

Ta có bảng sau : 

=> oxit cần tìm là SO₃

=> \(M_{SO_3}=32+16\cdot3=80\)(g/mol)

 Postscript : khi tìm đc ngto là lưu huỳnh, có thể lắp xuống dưới để tìm cthh của oxit còn lại, có vẻ như thế sẽ dễ hơn