"The Composition of Water" Water in Nature PPT Courseware 8

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"The Composition of Water" Water in Nature PPT Courseware 8

1. Hydrogen

1.Physical properties

2. Chemical properties (flammability)

Pure hydrogen: Pure hydrogen burns quietly in the air, producing a light blue flame and releasing heat;

Impure hydrogen (mixed with air or oxygen): Will explode in contact with open flame.

Essence: Hydrogen reacts with oxygen in the air.

3.Pure test

Method: Use a small test tube to collect a test tube of hydrogen, use your thumb to block the test tube mouth, with the mouth of the test tube pointing downwards, move it closer to the flame of the alcohol lamp, remove your thumb to ignite it, if you hear a sharp popping sound, it indicates that the hydrogen is impure and the sound is very small. It means gas calibration.

By watching the experiment, think about whether any new substances are generated during the above process?

Can you write text expressions?

2. The composition of water

1. Experimental phenomenon: Bubbles are generated on both poles connected to the power supply, and the volume ratio of gas in the glass tube connected to the positive and negative poles is about 1:2.

2. Gas test: Use a wooden stick with sparks to check the gas generated by the positive electrode. If the wooden stick re-ignites, it means that the gas is oxygen; use a burning wooden stick to check the gas generated by the negative electrode. The gas can burn and the flame will be light blue. Explain that the gas is hydrogen.

3.Experimental conclusion:

(1) Water generates hydrogen and oxygen under the condition of electricity.

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

(3) Each water molecule is composed of 2 hydrogen atoms and 1 oxygen atom.

(4) This experiment also verified that in chemical changes, molecules can be divided into atoms, but atoms cannot be divided further.

Elemental: A pure substance composed of the same elements.

Compound: A pure substance composed of different elements.

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

practice

1. The picture below is a device designed by a student: use a large plastic bottle to cut off the bottom of the bottle, leaving a section of the bottle mouth about 8cm to 10cm, and fit a rubber stopper to tighten the bottle mouth from the inside out. The A and B poles are made of straightened chrome-plated paper clips, and the wires are connected by the exposed part of the plug. Try to answer:

(1) The power supply used is ______ electricity. From the figure, we can see that terminal A is the ______ pole.

(2) When the A-end is connected to the test tube, the gas obtained is ______, which can be tested by ______.

(3) If the volume of gas in the test tube connected to end B is 8 mL, then the volume of gas in the test tube connected to end A is ______.

2. Please indicate which of the following substances are pure substances and which are mixtures, elements or compounds?

(1) Air (2) Oxygen (3) Tap water

(4) Nitrogen (5) Rare gases (6) Seawater

(7) Sulfur dioxide (8) Phosphorus pentoxide

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Update Time: 2024-11-19

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