"The Composition of Water" Water in Nature PPT Courseware 10

"The Composition of Water" Water in Nature PPT Courseware 10

1. Physical properties of hydrogen

1. Hydrogen is a colorless and odorless gas at room temperature.

2. Hydrogen is the gas with the smallest density under the same conditions.

3. Hydrogen is extremely difficult to dissolve in water

2. Chemical Properties of Hydrogen

Hydrogen's chemical properties are relatively stable at room temperature. Ignite hydrogen and it will burn.

1. Ignite pure hydrogen at the mouth of the conduit with a pointed mouth, and then cover a cold and dry beaker over the flame (as shown in the picture)

2. The chemical reaction principle of hydrogen burning in air or oxygen

3. Explosion experiment of igniting impure hydrogen mixed with air

It has been experimentally determined that when the volume of hydrogen mixed in the air is 4.0% to 74.2% of the total volume, it will explode when ignited. This volume fraction range is called the explosion limit of hydrogen.

4. Method for testing the purity of hydrogen:

Use the drainage method to collect hydrogen in a test tube, block the mouth of the inverted test tube with your thumb, move it close to the flame, and remove your thumb to ignite it. If you hear a sharp popping sound, it means the hydrogen is impure. If the sound is very small, it means the hydrogen is purer.

If the hydrogen gas is collected using the downward air exhaust method, and it is found to be impure and needs to be re-tested, the test tube opening should be blocked with your thumb for a while, and then the hydrogen gas should be collected. Why?

(Prevent the hydrogen flame in the test tube from igniting the hydrogen in the device or even causing an explosion)

3. Physical properties of water

1. Water is a colorless, odorless and transparent liquid.

2. The freezing point of water is 0℃ and the boiling point is 100℃.

3. The maximum density at 4℃ is 1g/ml. (minimum distance between molecules)

4. Composition of water

1. Research: Experiment of electrolyzing water: (passing direct current)

In order to enhance the conductivity of water, an appropriate amount of sodium sulfate or sodium hydroxide can be added to the water.

2. Phenomenon:

① Bubbles are produced on both the positive and negative electrodes

②The ratio of the gas volumes generated on the positive and negative electrodes is 1:2

③The gas generated on the positive electrode can re-ignite the wood strips with Mars (O2)

The gas generated on the negative electrode can burn (H2)

Experimental results:

1. Water is composed of hydrogen and oxygen elements

2. Water is energized to generate hydrogen and oxygen

Further prove the essence of chemical reactions through the experiment of electrolyzing water

3. In chemical reactions, molecules can be divided, but atoms cannot be divided and can only be recombined.

4. The types of elements remain unchanged before and after the chemical reaction

5. Elements and compounds

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

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

Oxide: A compound composed of two elements, one of which is oxygen (such as H2O, CO2, CO)

2. Elemental substance: A pure substance composed of the same element is called an elemental substance.

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

Use your brain

1.Pure water is ( )

A.Oxide B.Element

C. Compound D. Mixture

2. Water is ( )

A. Colorless, transparent liquid containing impurities

B. Composed of hydrogen molecules and oxygen molecules

C. Consists of 2 hydrogen molecules and 1 oxygen atom

D. Compounds made of water molecules

3. Electrolysis of water generates hydrogen and oxygen. The incorrect statement is ( )

A. During the process of electrolyzing water, hydrogen atoms and oxygen atoms cannot be separated again.

B. Electrolysis of water is a decomposition reaction

C. Water originally contains hydrogen and oxygen, but when it is heated, the hydrogen and oxygen are released.

D. When electrolyzing water, water molecules are destroyed

Teaching summary:

1. Understand the physical and chemical properties of hydrogen

2. Master the testing methods of hydrogen

3. Understand the composition of water and electrolysis water experiment

4. Understand and distinguish between elements and compounds

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