"The Composition of Water" Water in Nature PPT Courseware 5

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"The Composition of Water" Water in Nature PPT Courseware 5

The true identity of water was revealed for the first time (mid-18th century)

Priestley, a British chemist, often liked to perform magic tricks for his friends: he took an "empty" bottle, shook it in front of his friends a few times, and then quickly moved a lit candle close to the bottle. . With a sound of "pop!", a long tongue of flame spit out from the mouth of the bottle, but it immediately went out again...

It turned out that the magician had already filled the bottle with colorless "combustible air" (hydrogen and air). When mixed and ignited, they make a loud noise.

At first, Priestley just performed magic tricks for his friends. But he didn't realize that after doing the magic, there was a mysterious "guest" in the bottle. Finally one day, Priestley found a lot of water droplets on the bottle wall!

Water is also considered an element

In 1781, Priestley told Cavendish of his discovery.

Cavendish conducted experiments with various proportions of "combustible air" and air mixtures, confirmed Priestley's findings, and concluded that the resulting liquid was water.

After the oxygen element was confirmed, Cavendish replaced air with pure oxygen, thereby confirming that 2 volumes of "combustible gas" and 1 volume of oxygen were exactly combined to form water.

However, devout believers in the "phlogiston theory" still believe that water is an element and have not given a correct explanation of the composition of water.

learning target

Understand the composition of water, understand and experience the process and methods of human understanding of the composition of water;

Able to distinguish elements, compounds and oxides based on their elemental composition, and classify common substances.

1. What does water consist of?

The combustion experiment of hydrogen was the beginning of people's understanding of the composition of water

1. Study the combustion of hydrogen (read textbook page 79)

fill in the blank

1. Physical properties

Usually, hydrogen is a ____-colored, ____-stinky ____ body with a density ____ higher than that of air and is ____ soluble in water.

2. The combustion of hydrogen

Pure hydrogen burns in air to produce __________ flame; ____________ heat; _________ appears on the inner wall of the beaker.

Hydrogen mixed with a certain amount of ______ or ______ will ________ when exposed to an open flame. Therefore, you must _________ before igniting hydrogen.

Determining the composition of water by electrolyzing water

2. Experimental phenomena:

(1) Bubbles are generated on both electrodes

(2) After a period of time, the volume ratio of gas generated by the positive electrode and the negative electrode is approximately 1:2.

3. Test gas:

The gas produced by the positive electrode can re-ignite the wood strips with sparks, indicating that it is oxygen

When the gas produced by the negative electrode is close to the flame, it will burn and the flame will turn light blue, indicating that it is hydrogen.

Class exercises

The picture on the right is a diagram of the experimental device for splitting water by electricity. Try to answer the following questions:

1. A small amount of sodium hydroxide or sulfuric acid is often added to electrolyzed water for the purpose of __________________.

2. According to the figure, it can be seen that the gas collected in test tube A is _______, and the gas collected in test tube B is _______.

3. The method to test the gas in test tube A is ____________________

4. The method to test the gas in test tube B is_______________

5. Through the experiment of electrolyzing water, the conclusion can be drawn: the electrolysis of water produces hydrogen and oxygen, and water is composed of hydrogen and oxygen elements.

6． Decide whether the following statements are correct:

(1) Hydrogen and oxygen can be obtained by electrolysis of water, so water contains hydrogen and oxygen. ( )

(2) Water can evaporate into hydrogen and oxygen. ( )

(3) Water molecules are destroyed during water electrolysis. ( )

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Update Time: 2024-11-22

This template belongs to Chemistry courseware People's Education Press Ninth Grade Chemistry Volume 1 industry PPT template

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