"The Composition of Water" The Source of Life - Water PPT Courseware 2

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"The Composition of Water" The Source of Life - Water PPT Courseware 2

1. Hydrogen

1. Physical properties: Colorless, odorless gas, insoluble in water, less dense than air

2. Chemical properties: flammability

Hydrogen purification and combustion

Observe the experiment carefully and record the experimental phenomena

Hydrogen purity test

Properties of Hydrogen (Combustion)

Observe and think:

[Experiment 2: Synthesis of Water]

(1) What do you guess the products of hydrogen combustion might be?

How to verify the products of hydrogen combustion?

(2) What experimental phenomena did you observe from the video?

(3) Can you infer the constituent elements of water based on the fact that hydrogen burns to form water?

The flammability of hydrogen

Phenomenon: Pure hydrogen burns quietly in the air, producing a light blue flame. Water mist appears on the inner wall of the beaker. The hand touching the beaker can feel hot (heat is released).

Hydrogen purity test

Collect a test tube of hydrogen, plug the mouth of the test tube with your thumb, move the mouth of the tube downward toward the flame, and ignite it. A sharp popping sound indicates that the hydrogen is impure; a slight popping sound indicates that the hydrogen is purer.

Note: The purity of flammable gases must be checked before burning to avoid explosion.

2. Determine the composition of water by electrolyzing water:

1. Experimental device: (as shown in the picture)

2. Experimental phenomena:

There are bubbles on both electrodes. After a period of time, the volume ratio of gas collected in test tube 1 and test tube 2 is approximately 1:2.

3. Test gas:

Use a wooden stick with sparks to test the gas in test tube 1 (connected to the positive electrode) and find that the wooden stick re-ignites, indicating that it is oxygen; when the gas in test tube 2 (connected to the positive electrode) is close to the flame, the gas can burn and the flame will appear light blue. It means hydrogen gas.

4 Conclusion:

(1) Positive oxygen and negative hydrogen, volume ratio: hydrogen 2 oxygen 1

(2) Water is composed of hydrogen and oxygen elements, and the atomic number ratio is 2:1. The chemical formula of water is H2O

extension

1. Water is composed of hydrogen and oxygen elements

2. Each water molecule is made of:

Made of two hydrogen atoms and one oxygen atom

3. The experiment of electrolyzing water further proves that the essence of chemical reaction is:

The splitting of molecules and the recombination of atoms

Two questions about electrolyzed water:

1. Dilute sulfuric acid or sodium hydroxide is usually added in experiments to enhance the conductivity of the solution.

2. The reason why the gas generated by the negative electrode is usually twice that of the positive electrode is:

(1) Hydrogen is more difficult to dissolve in water than oxygen

(2) Oxygen is more active than hydrogen, and part of the oxygen reacts with the electrode

important concepts

(1) Single substance

a pure substance composed of an element

Such as: hydrogen H2 oxygen O2

Nitrogen N2 Carbon C Sulfur S Iron Fe, etc.

(2) Compounds

pure substance composed of various elements

Such as: water H2O carbon dioxide CO2

Phosphorus pentoxide P2O5 Sulfur dioxide SO2

Iron tetroxide Fe3O4

Hydrogen chloride HCl Potassium chloride KCl

Potassium permanganate KMnO4 Potassium chlorate KClO3, etc.

(3) Oxides:

Composed of two elements, one of which is a compound of oxygen

Such as: water H2O carbon dioxide CO2

Phosphorus pentoxide P2O5 Sulfur dioxide SO2

Iron tetroxide Fe3O4

practice

1. In winter, iron water pipes are easy to freeze and crack. The main reason is ( )

A. Iron pipes expand and contract with heat and cold

B. Iron pipe heat shrinks and cold expands

C. Liquid water is denser than ice, and water expands when it freezes.

D. Ice is denser than liquid water

2. Water decomposes into hydrogen and oxygen under the action of direct current. Explain ( )

A. Water is composed of hydrogen and oxygen

B. Water is composed of hydrogen and oxygen elements

C. There is hydrogen and oxygen in water

D． Mix hydrogen and oxygen thoroughly to get water

3. Pure water is ( )

A. Colorless, odorless, tasteless liquid

B. Elemental substance C. Compound D. mixture

Deepen your understanding:

The basis for dividing substances into pure substances and mixtures: the types of constituent substances

The basis for dividing purity into elements and compounds: the types of constituent elements

Differences and connections between elements and compounds:

1. Pure substances can be divided into elements and compounds according to the number of constituent elements.

2. Pure substances composed of the same kind of elements are called simple substances. The concept contains two elements: pure substances and the same kind of elements, which are remembered as "one thing and one element". For example: oxygen, phosphorus, copper, etc.

3. Pure substances composed of different elements are called compounds. There are also two elements: pure matter and different elements, which are recorded as "one thing with many elements". For example: water, potassium permanganate, etc.

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Update Time: 2024-10-17

This template belongs to Chemistry courseware Cantonese Education Edition Ninth Grade Chemistry Volume 1 industry PPT template

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