Topic 2 Chemistry is an experiment-based science

Topic 2

Chemistry is a science based on experiments

Chemistry is a science based on experiments, and many major chemical discoveries and research results are obtained through experiments.

You may be surprised to say that the predecessor of the chemical laboratory was the workshop of the ancient alchemists and alchemists. Alchemists wanted to obtain the medicine of immortality through alchemy, and alchemists tried to use the " philosopher's stone" to turn ordinary metals into gold and silver. They invented many experimental equipment and some methods of separating substances, such as filtration, steaming stuffing, etc. At the same time, they also accumulated a lot of chemical knowledge and made contributions to the development of chemistry as a science.

Experiments are an important way to learn chemistry. Through experiments and the observation, recording and analysis of experimental phenomena, the principles of chemistry can be discovered and verified, the methods of scientific inquiry can be learned, and new chemical knowledge can be acquired.

Let us learn the method of scientific inquiry in the experiment together.

1. Exploration of Candles and Their Burning

Candles are made of paraffin and cotton wicks. Using all the senses except taste, observe as much as possible the three stages of a candle before it is lit, while it is burning, and after it is extinguished. You can follow the steps suggested below for experimental observation, and you can also add or change some experimental observation contents.

(1) Before lighting, observe the color, state, shape, hardness of the candle, and smell the smell, etc. Use a knife to cut a piece of paraffin from a candle, put it in water, observe whether it dissolves in water, whether it floats on the water or sinks to the bottom, and judge whether the density of paraffin is small or large compared with that of water.

(2) Light the candle and observe the burning candle carefully. What happens when the candle burns? How many layers does the flame have? Which layer is the brightest? Which layer is the darkest?

Take a matchstick, hold one end and quickly put it flat into the flame , take it out after about 1s , and guess which part of the flame has the highest temperature and which part the lowest temperature.

Take a dry beaker and a beaker whose inner wall is moistened with clarified lime water respectively, and put them over the flame successively, and carefully observe what happens on the beaker wall. Guess what substance is formed when the candle burns.

(3) Extinguish the candle and observe what happens when the candle is extinguished. Use a match to light the white smoke generated when the candle is just extinguished , can the candle be re-burned??

The inquiry activities on candles and their burning reflect the following characteristics of chemistry learning:

(1)Focus on the properties of matter. For example, the physical properties of paraffin wax, such as color, state, smell, hardness, density, melting point, etc.; chemical properties such as whether paraffin wax can burn, and whether the combustion products can make clarified lime water turbid.

(2)Watch for changes in matter. For example, physical changes such as melting of paraffin when heated; phenomena such as luminescence and heat release during combustion, and chemical changes such as the formation of carbon dioxide and water.

(3)Focus on the process of material change and the interpretation and discussion of the results. Systematically and carefully observe and describe the phenomena of substances before, during and after changes, instead of focusing on a certain property or change of substances in isolation, and draw reliable conclusions through the thinking process of comparison and analysis .

2. Research on the air inhaled and exhaled by the human body

What is the difference between inhaled air and exhaled air

The following information can be used as a reference when we conduct scientific research; we can also obtain more information by inquiring about relevant information and verify it through experiments to draw correct conclusions.

(1) Carbon dioxide can turn clarified lime water into white turbid liquid. In the following experiments, the more white turbid matter, the more carbon dioxide in the gas.

(2)Oxygen can re-ignite the sticks with sparks, and the more the sticks burn, the more oxygen they have.

(3)Carbon dioxide can extinguish a burning stick.

(4)Air is mainly composed of nitrogen and oxygen, and also contains carbon dioxide and water vapor.

In the experiment, we will mainly observe the oxygen, carbon dioxide,

Changes in water vapor content.

Step 1 Take two empty air collecting bottles and cover the mouth of the bottles with a glass piece , so that the two bottles of air samples are collected.

Step 2 Take another two gas collecting bottles and fill them with water respectively, Figure i_i3 air sample

And cover a small part of the mouth of the bottle with a glass piece, and then push the glass piece to

Cover the mouth of the bottle completely, and put the bottle full of water upside down together with the glass piece in the sinko Carefully insert the drinking tube into the gas collecting bottle, and slowly blow air into the gas collecting bottle, until the gas collecting bottle is full of exhaled gas. Immediately cover the mouth of the gas collecting bottle with a glass piece under water, then take out the gas collecting bottle and put it on the experiment table . Collect another vial of exhaled breath in the same way.

Step3 Insert the burning wooden strips into the air sample and the exhaled gas sample respectively , observe and record the phenomenon.

Step 4 Add the same number of drops of clarified lime water to a bottle of air sample and a bottle of exhaled gas sample, shake, observe and record the phenomenon.

Step 5 Take two pieces of dry glass or lenses, breathe on one of them , and compare and observe the phenomena that occur on the two pieces of glass or lenses.

Through the above experiments, what preliminary conclusions can you draw by comparing the amount of carbon dioxide, oxygen, and water vapor contained in the air inhaled by the human body and the gas exhaled by the human body?

After studying this topic, you should know

1.From daily life, we can often find some questions worth exploring. These questions can be explored through experiments and other means, and valuable conclusions can be obtained through the analysis of experimental phenomena.

2.When conducting chemical inquiry activities, under the guidance of the teacher, the questions and the purpose of the inquiry should be clarified, attention should be paid to the properties and changes of substances, and the phenomena of substances before, during and after changes should be carefully observed, recorded truthfully, and compared and analyzed , in order to draw reliable conclusions, and finally fill in the report carefully.