Fe + H2SO4 -> FeSO4 + H2

 1           1                 1            1

A là: FeSO4

B là: H2

nFe = 2,8/56 = 0,05 mol => nH2SO4 = 0,05 mol

mFeSO4 = 0,05 x (56+32+64) = 7,6 gam 

VH2 = 0,05 x 22,4 = 1,12 lit

Fe + 2HCl -> FeCl2 + H2

 1        2               1         1

nH2 = 2,24/22,4 = 0,1 mol => nFe = 0,1 mol

mFe = 0,1 x 56 = 5,6 (gam)

mFe phản ứng = 5,6 x 90% = 5,04 (gam)

UNIT:  PHRASAL VERBS

EX 1: Choose the best answer.

1. Could you ______ a moment while I see if Peter is in his office?

A. Get on well      B. get on         C. hold on          D. stand on

2. Extension 286? I’ll ______ .

A. Put you through   B. get you through    C. come you through   D. break into you

4. Jack and Linda ______ last week. They just weren’t happy together.

A. Broke up (tan vỡ)    B. broke into  C. finished off  D. ended up

5. I’m ______ Tom’s address. Do you know it?

A. Looking on    B. finding out   C. looking for      D. getting for

6. “Who ______ out that tie for you?” No one. I choose it myself.”

A. bought           B. brought       C. turned       D. picked

7. If we don’t do something now, the birds are going to ______ soon.

A. Die of            B. die with        C. die out              D. die on

8. If you really want to lose weight, you need to ______ eating desserts.

A. Give away         B. give up       C. put off              D. take off

 9. I had to ______ her request for a loan. Her credit was just not good enough

A. Turn on      B. turn off       C. turn down         D. turn into

10. I need to_______ from work and take a holiday.

A. Go away          B. get away          C. relax on          D. run on

11. It ______ to be a beatiful night tonight!

A. Turned into       B. turned out   C. turned on      D. turned off

12. I want you to _______ every bad word you’ve said about my brother.

A. Take back         B. say again      C. take off            D. give off

13. When I was turning out my cupboard I ______ this photograph of my uncle

A. Came over       B. came round    C. came across    D. came into

14. He ______ in German, but moved to the US at the age of 18.

A. Brought to          B. grew up   C. turned off             D. went to

15. He _got into_ the club on recommendation from his friend Jack.

Số mol SO3 cần thân vào là x (mol)

Ta có: SO3 + H2O -> H2SO4

             x          x

mH2SO4 tạo thành là: 98x (gam)

mH2SO4 22,5% là: 500 x 22,5% = 112,5 (gam)

-> (98x + 112,5). 100/80x + 500 = 42,5

-> x = 1,5625

mSO3 = 1,5625 x 80 = 125 (gam)

9x² - 30x + 225 = 0

Δ' = (-15)² - 9.225

Δ' = 225 - 2025

Δ' = -1800 < 0

=> phương trình vô nghiệm

cj ơi e hỏi chút....trước vòng này còn có vòng nào nữa ạ?