"Air" The air around us PPT courseware 2

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"Air" The air around us PPT courseware 2

2. Composition of air

1. The contribution of French chemist Lavoisier

Lavoisier experimentally concluded that air is composed of oxygen and nitrogen

The device used by Lavoisier to study the composition of air

2. Determine the oxygen content in the air

Experimental phenomena:

1. Red phosphorus burns, producing a large amount of white smoke and releasing heat;

2. Wait until the burning stops and after cooling, the water level in the bottle will rise by about 1/5 of the volume.

Experimental conclusion: Oxygen accounts for about 1/5 of the total volume of air.

think about it

1. According to the experimental phenomenon, what are the properties of the remaining gas in the analysis bottle?

Answer: It is a colorless gas, accounting for about 4/5 of the total volume of air. It cannot burn or support combustion; it cannot be dissolved in water.

2. Can the "large amount of white smoke" generated after the combustion of red phosphorus be called "large amount of white mist"?

Answer: No, smoke is solid particles; fog is small droplets.

3. In the experiment, if the volume of entering water is less than 1/5 of the total volume of the gas collecting bottle, what will be the reason?

Answer: (1) The amount of red phosphorus is insufficient;

(2) The device is leaking;

(3) Some water remains in the pipe and does not enter the gas collecting bottle

(4) After the red phosphorus is extinguished, the clamp is opened before it cools to room temperature;

practice

Answer questions as requested:

① Add a small amount of water to the gas collecting bottle ② Check the air tightness of the device

③Put enough red phosphorus into the burning spoon and tighten the water-stop clamp

④Ignite the red phosphorus, put it into the gas collecting bottle and tighten the rubber stopper

⑤Open the water stopper after the gas bottle has cooled down

(1) The literal expression of the reaction in step ④ is __________;

(2) The phenomenon observed after opening the water stop clamp in step ⑤ is __________;

(3) This experiment concluded that the composition of air is __________;

(4) The properties of the remaining gas in this experiment are __________;

(5) After the experiment, the water in the gas collecting bottle is less than 1/5. The reason for the error may be __________;

Class exercises

1. Calculated by volume, the most abundant gas in the air is ( )

A oxygen B nitrogen

C carbon dioxide D rare gas

2. The volume of oxygen in 100 liters of air is approximately ( )

A 78 liters B 78% C 21 liters D 21%

3. The volume ratio of oxygen to nitrogen in the air is approximately ( )

A 4:1 B 1:4 C 1:5 D 5:1

4. In human history, the earliest scientist to experimentally prove that air is composed of oxygen and nitrogen was ( )

A. Scheler b. Lavoisier C． Dalton d. Priestley

3. Air is a precious resource:

1. Oxygen was once called “nourishing qi”

(1) Supply breathing

(2) Support burning

2. Properties and uses of nitrogen

physical properties

Colorless, odorless gas. Insoluble in water and low melting point. Density: 1.251g/L

chemical properties

Cannot burn Cannot support combustion (inactive)

3. Rare gases

(1) Rare gases are the general name for helium, neon, argon, krypton, xenon and other gases

(2) Rare gases are colorless, odorless, and very inactive chemically.

(3) Purpose: protective gas, electric light source laser technology, low temperature anesthesia

5. Pure substances and mixtures

(1) Pure substance: composed of a substance with fixed properties

Such as: N2, O2, CO2, P, P2O5, H2O

(2) Mixture:

It is composed of two or more substances. There is no chemical reaction between the components and they maintain their original properties.

Such as: air, sea water, river water, mineral water, beverages, etc.

Pure substances can be represented by special chemical symbols. For example, nitrogen, oxygen, and carbon dioxide can be represented as N2, O2, CO2, etc. respectively.

(3) Each substance in the mixture maintains its own properties.

For example: Nitrogen, oxygen, carbon dioxide, etc. in the air all maintain their respective properties.

Class exercises

1. Which of the following substances is pure ( )

A A rare gas separated from the air

Part B frozen distilled water

C salt water

D 75% medicinal alcohol

2. Among the following groups of substances, the former is a single substance and the latter is a mixture ( )

A. Nitrogen Distilled water B. iron ore salt water

C. Hydrogen CaCO3 D． carbon dioxide air

3. Which of the following water is a pure substance ( )

A mineral water B tap water C river water D ice-floating water

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Update Time: 2024-11-15

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

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