"The Composition of Water" Water in Nature PPT Courseware 3

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"The Composition of Water" Water in Nature PPT Courseware 3

Create situations to introduce new lessons

According to the ancient understanding of water, metal, wood, water, fire, and earth are the basic material elements that constitute all things. Water is one of them, which cannot be decomposed into new substances.

For a long time, water was considered an element. It was not until the end of the 18th century that people finally understood the composition of water through experimental research on the formation and decomposition of water.

The study of hydrogen combustion experiments was the beginning of people's understanding of the composition of water. Let’s learn about hydrogen first.

1. Hydrogen:

1. Physical properties: colorless, odorless, poorly soluble gas with a density smaller than air.

2. Chemical properties: flammability (produces light blue flame)

Literal expression: Hydrogen + Oxygen----Water

3. Purity testing method: Therefore, the purity of hydrogen must be tested before igniting hydrogen.

With the mouth of the test tube facing down, block the mouth of the test tube with your thumb, move it closer to the flame of the alcohol lamp, and remove your thumb to light it. If you hear a small sound, it means the hydrogen is pure, and if there is a sharp popping sound, it means the hydrogen is impure.

Think about it: What would happen if you ignited impure hydrogen mixed with air?

Hydrogen mixed with a certain amount of air or oxygen will explode when exposed to an open flame.

2. The composition of water - electrolysis water experiment

1. Experimental phenomena:

(1) Bubbles are generated on both electrodes;

(2) The volume ratio of gas generated on the positive and negative electrodes is 1�2;

(3) The gas produced by the positive electrode can make the burning wood sticks burn more vigorously, and the gas produced by the negative electrode can burn.

2. Experimental conclusion:

(1) Water is energized to generate hydrogen and oxygen;

(2) Water is composed of hydrogen and oxygen elements.

3. Things to note:

(1) A small amount of sodium sulfate or sodium hydroxide can be added to the water to enhance conductivity;

(2) The power source used for electrolyzing water is direct current;

(3) The two electrodes produce gases: positive oxygen and negative hydrogen (thinking about my father)

Positive one and negative two ( V positive : V negative = 1�2 = V oxygen : V hydrogen )

Interactive in class

1. Which of the following statements about the phenomenon of hydrogen burning in air is incorrect ( )

A. Produce light blue flame

B. Release a lot of heat

C. The product is water

D. Cover a small beaker above the flame, and small droplets appear on the inner wall of the beaker

2. The picture on the right is a simple device for electrolyzing water. Try to answer:

(1) Judge according to the picture:

A is _________qi; B is _________qi;

C is the ________ pole; D is the ________ pole.

(2) In order to enhance the conductivity of water, _________ should be added to the water.

(3) The gas produced in the test tube connected to the negative electrode can ________ and produce a ________-colored flame, which proves that it is _________ gas. The volume ratio of the gases at the positive and negative poles is: _________.

(4) The literal expression of this reaction is: ____________________; it is a _________ reaction.

3. Elements and compounds

1. Compounds: Pure substances composed of different elements are called compounds.

Examples: water (H2O), carbon dioxide (CO2), potassium permanganate (KMnO4)

2. Oxide: A compound composed of two elements, one of which is oxygen is called an oxide.

Example: H2O, CO2, CO

3. Elemental substance: A pure substance composed of the same elements is called an elemental substance.

Examples: Hydrogen (H2), Nitrogen (N2), Oxygen (O2)

Note: A substance containing only one element may be a simple substance or a mixture, but it must not be a compound.

Class summary

1. Water is composed of hydrogen and oxygen elements

2.Elements are pure substances composed of the same elements

3. Compounds are pure substances composed of different elements

4. A compound composed of two elements, one of which is oxygen is called an oxide

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Update Time: 2024-11-18

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

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