Below is a description of a single scientific experiment. It shows us how iron reacts (反应) with air and with water. Aim: To find out if iron rusts(生锈) (a) in dry air; (b) in water that has no air in it (air-free water) ; (c) in ordinary water. Materials: Some clean iron nails (铁钉) ; test tubes(试管); test tube holder; cotton wool; oil; Bunsen burner. | |
Iron in dry air Method (1) Put some iron nails at the bottom of a test tube. (2) Push some cotton wool down the tube. (3) Leave the tube for one week. Result After one week, the nails have not rusted. Conclusion Iron does not rust in dry air. | (4) Add some oil to the water. (This will keep air out of the water.) (5) Leave the tube for one week. Result The nails do not rust in the tube with air-free water. Conculsion Iron does not rust in air-free water. |
Iron in ordinary water Method (1) Half –fill a test tube with water and add two or three clean nails. (2) Leave the tube for one week. Result The nails rust in the tube with ordinary water. Conclusion Iron rusts in ordinary water. (238 words) | |
Iron in air-free water Method (1) Half-fill a test tube with water. (2) Boil the water for three minutes. (This makes sure there is no air in the water.) (3) Put two or three clean nails in the water. | |
1.In the first part of the experiment the cotton wool is most probably used to ____.
A. keep the air dry B. keep the tube wet
C. make the nails rust D. keep the tube clean
2.What are necessary steps to make sure the water in the tube is air-free?
① Leave half a tube of water in it.
② Boil the water for some time.
③ Put some clean iron nails in the tube.
④ Add some oil to the water.
A. ①② B. ①③ C. ②③ D. ②④
3.We can conclude from the experiment that only ____ makes iron rusty.
A. dry air B. cotton wool
C. ordinary water D. air-free water
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Trees are one of the oldest plants of our earth．Just like us，trees change a lot when they grow. At one to three years old，young trees learn how to protect themselves. For example，many trees grow thorns (刺) to tell animals not to go near. Most young trees have large, deep green leaves so that they can catch enough sunlight and change it into their food and energy.
When trees are 4 years old，they begin to grow very fast and become strong enough to face challenges (挑战) in life.
At the age of l5，trees become young adults. They grow more slowly and begin to grow flowers and fruit.
It is not until the trees are 20 to 25 years old that they become real adults．The trees reach their largest sizes. Adult trees give us many things such as oxygen (氧气) and natural beauty. If we give them good care，they will go on to live healthily for many years．
As time goes on，trees begin to grow older and older and even die．At this time，they still have their important place in nature．In many ways，the life of trees is like our own life experience.
Enjoy every minute of the life of the trees and take care of them!
Title: The 1. of trees | ||
2. | Growing | Things they can do |
1～3 | Growing thorns； Having large, deep green leaves | Learn to protect themselves； 3. enough sunlight and change it into their food and energy |
4 | Growing very fast； Becoming strong enough | Face challenges in life |
15 | Becoming young adults； Growing more 4. | Grow flowers and fruit |
20～25 | Becoming real adults； Reaching their largest sizes | Give people many things 5. oxygen and natural beauty |