a. Vì NaCl ko phản ứng với HCl

\(n_{CO_2}=\dfrac{0.448}{22,4}=0,02\left(mol\right)\)

PTHH : Na₂CO₃ + 2HCl -> 2NaCl + CO₂ + H₂O

                 0,02        0,04       0,04      0,02

\(C_{M\left(HCl\right)}=\dfrac{0.04}{0,02}=2\left(M\right)\)

b. \(m_{NaCl}=0,04.58,5=2,34\left(g\right)\)

\(m_{Na_2CO_3}=0,02.106=2,12\left(g\right)\)

\(\Rightarrow\) m muối sau phản ứng là : \(\left(5-2,12\right)+2,34=5,22\left(g\right)\)

c. \(\%m_{Na_2CO_3}=\dfrac{2.12}{5}.100=42,4\%\)

\(\%m_{NaCl}=100\%-42,4\%=57,6\%\)

Bài 6 :

a. \(\sqrt{\dfrac{a}{3}}\) có nghĩa khi \(\dfrac{a}{3}\ge0\Leftrightarrow a\ge0\)

b. \(\sqrt{-5a}\) có nghĩa khi \(-5a\ge0\Leftrightarrow a\le0\)

c. \(\sqrt{4-a}\) có nghĩa khi \(4-a\ge0\Leftrightarrow a\le4\)

d. \(\sqrt{3a+7}\) có nghĩa khi \(3a+7\ge0\Leftrightarrow a\ge-\dfrac{7}{3}\)

a. \(n_P=\dfrac{3.72}{31}=0,12\left(mol\right)\)

\(n_{O_2}=\dfrac{4.032}{22,4}=0,18\left(mol\right)\)

PTHH : 4P + 5O₂ --t^o---> 2P₂O₅

              0,12                      0,06

Ta thấy : \(\dfrac{0.12}{4}< \dfrac{0.18}{5}\) => P đủ , O₂ dư

b. \(m_{P_2O_5}=0,06.142=8,52\left(g\right)\)

c. PTHH : P₂O₅ + 3H₂O -> 2H₃PO₄

                  0,6                    0,12

Cho H₃PO₄ vào quỳ tìm sẽ làm cho quỳ tím hóa đỏ

\(C_M=\dfrac{0.12}{0,3}=0,4\left(M\right)\)

1, D

2, C

3, D

4, A

5, B

6, A

7, C

8, C

9, B

\(\dfrac{1}{\sqrt{3}-\sqrt{5}}=\dfrac{\sqrt{3}+\sqrt{5}}{3-5}=-\dfrac{\sqrt{3}+\sqrt{5}}{2}\)

66, Despite feeling tired, Sue stayed up late talking to Jill.

67, It was such a hot day that  we had lunch outside in the garden. 

68, I started working for this company ten years ago.

69, I wish I had finished my homework last night.

70, I'm interested in reading scientific books.

1, The sun sets in the west every evening. 

2, My brother likes making model cars.

3, Do Trang and Minh play basketball everyday after school?

4, They enjoy collecting stamps.

5, The flight from Ho Chi Minh City doesn't arrive at 10:30. 

6, This river runs through my home town.

7, Our science teacher starts our lessons at  p.m on Fridays.

8, My drawing class starts at  a.m and finishes at  a.m every Saturday.

9, They make the models at weekend.

10.  She goes to judo club every weekend.

Không rõ thời gian viết chỉ biết rằng văn bản "Tôi đi học" được in trong tập "Quê mẹ" xuất bản năm 1941.

1, My  singing lessons are always fun.

2, There is a chess competition in June .  (thừa chữ sometimes??)

3, Kiera never enjoys her  music lessons .

4, We often go shopping in the holidays.

không gì ạ:3