Bài 4 :                              

                              \(n_{H2}=\dfrac{V_{H2}}{22,4}=\dfrac{3,36}{22,4}=0,15\left(mol\right)\)

Pt :                         \(2Al+3H_2SO_4\rightarrow Al_2\left(SO_4\right)_3+3H_2|\)

                                 2           3                     1              3

                               0,1        0,15                 0,05        0,15

  a)                            \(n_{Al}=\dfrac{0,15.2}{3}=0,1\left(mol\right)\)

                                       ⇒ \(m_{Al}=n_{Al}.M_{Al}\)

                                                   = 0,1 . 27

                                                   = 2,7 (g)

                                      \(m_{Cu}=10-2,7=7,3\left(g\right)\)

                              ⁰/₀Al = \(\dfrac{m_{Al}.100}{m_{hh}}=\dfrac{2,7.100}{10}=27\)⁰/₀

                            ⁰/₀Cu = \(\dfrac{m_{Cu}.100}{m_{hh}}=\dfrac{7,3.100}{10}=13\)⁰/₀

b)                           \(n_{Al2\left(SO4\right)3}=\dfrac{0,15.1}{3}=0,05\left(mol\right)\)

                             ⇒ \(m_{Al2\left(SO4\right)3}=n_{Al2\left(SO4\right)3.}M_{Al2\left(SO4\right)3}\)

                                                  = 0,05 . 342

                                                   = 17,1 (g)

                                     \(n_{H2SO4}=\dfrac{0,1.3}{2}=0,15\left(mol\right)\)

                                      ⇒ \(m_{H2SO4}=n_{H2SO4}.M_{H2SO4}\)

                                                        = 0,15 .98

                                                        = 14,7 (g)

              \(C_{H2SO4}=\dfrac{m_{ct}.100}{m_{dd}}\Rightarrow m_{dd}=\dfrac{m_{ct}.100}{C}=\)\(\dfrac{14,7.100}{15}=98\left(g\right)\)

                m_{dung dịch sau phản ứng} = (m_Al + m_Cu) + m_H2SO4 - m_H2

                                                    = 10 + 98 - (0,15 . 2)

                                                     =107,7 (g)

                       \(C_{Al2\left(SO4\right)3}=\dfrac{m_{ct}.100}{m_{dd}}=\dfrac{17,1.100}{107,7}=15,88\)⁰/₀

 Chúc bạn học tốt

a)

b) Ta có :

Góc tới = \(90^o-40^o=50^o\)

Góc phản xạ = góc tới nên => góc phản xạ = 50^o = góc tới

Góc tạo bởi tia tới và tia phản xạ : \(50^o+50^o=100^o\)

Góc tạo bởi tia phản xạ và mặt gương :\(90^o-50^o=40^o\)

Bạn tự làm nốt nhé ⚠

D

D

D

D 

21.D

22.D

a: Xét ΔABC có MN//BC

nên AM/AB=AN/AC

=>AN/4=1,2/3=4/10

hay AN=1,6(cm)

b: BC=5cm

Xét ΔABC có AD là phân giác

nên BD/AB=CD/AC
=>BD/3=CD/4

Áp dụng tính chất của dãy tỉ số bằng nhau, ta được:

\(\dfrac{BD}{3}=\dfrac{CD}{4}=\dfrac{BD+CD}{3+4}=\dfrac{5}{7}\)

Do đó: BD=15/7(cm); CD=20/7(cm)

khu vực giờ gốc nằm trên đường kinh tuyến gốc 

Khu vực giờ gốc ở Kinh tuyến gốc ,( ở Luân Đôn )

Chọn C

1 Yesterday was cooler than today

2 Salim is the most beautiful in her team

3 His house is the highest in my city

4 No one in her class is as intelligent as Lan

5 BJ is one of the greatest tennis players in the world

1. Yesterday was colder than today.

2. Salim is the most beautiful in her team.

3. His house is the highest house in my city.

4.No one in her class is more intelligent than Lan

8. BJ isthe greatest tennis player in the world.

1) Yesterday was colder than today.

2) Salim is the most beautiful in her team.

3) His house is the highest house in my city.

4) No one in my class is more intelligent than Lan.

5) BJ is one of the greatest tennis players in the world.

Enviroment is neccessary thing for this life. Enviroment is the air we breath, the water people drink and is everything they need for their life. But now the most important thing for the life is being polluted. This pollution affects the health of all living things. Air is damaged by lorry fumes and car, and power stations create acid rain which can destroys entire lakes and forests. When fossil fuels: gas, oil and coal are burned to provide energy for cooking, lighting etc. they form polluting gases. Not only on land but also in the sea, oils spills pollute sea water and kill marine life; chemical waste from sewage works and factories, and artificial fertilisers from farmland, pollute river water, spreading disease, and killing wildlife. Everything is being caused by human’s existence. Humans create rubbish! Each household produces about one tonne of rubbish each year! Most of this is taken away by dustmen and burned in incinerators or buried in enormous landfill sites – both of these actions can be dangerous for our environment.

But only people can change and solve it. Pollution could be prevented by all thing we do each day. First people can use recycled paper to save trees. Second try to avoid using plas. It is hard to recycle. People should refuse to use carrier bags. If people can not avoid buying plas bags, they should use re-use plas bags many times. Finally people must take their old clothes to charity shops. People also should save energy to protect environment. Switching off all electric things when they are not in use, walk or use a bicycle instead of car for short trips, keep healthy life and  keep clean atmosphere.

Keep clean environment isn’t only all ways are mentioned before but also to protect natural resources. That is the way to conserver wild life. First we need to conserve the old forest, rainforest, build more safari and national park, and plant more trees to make place to live for wild animals. Second we need to prohibit hunters who hunt animals too many out of the law allowance.

Finally, we now know that enviroment is the most important thing for life and we know how to protect and use it scientifically. Everyday we invent and find more and more way to protect enviroment. I hope that in the future the earth will be cleaner.