"Preparing Oxygen" Air Around Us PPT Courseware 5

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"Preparing Oxygen" Air Around Us PPT Courseware 5

Background information on raw material preparation

1. Hydrogen peroxide (H2O2)

Commonly known as hydrogen peroxide, colorless liquid. The disinfectant water used in homes and hospitals is its 3% solution, which is also a commonly used disinfectant. The concentrated solution will slowly decompose into water and oxygen at room temperature. If mixed with manganese dioxide (MnO2), the decomposition will be greatly reduced.

Speed ​​up the reaction and release oxygen (O2) quickly.

2. Potassium permanganate (KMnO4)

Commonly known as gray manganese oxygen or PP powder, it has purple-black crystals and its solution is purple-red. It is a commonly used disinfectant. It decomposes quickly when heated and releases oxygen (O2).

3. Potassium chlorate (KClO3)

White crystal, melting point is 368℃, decomposes to release oxygen (O2) at 400℃.

4. Mercury oxide (HgO)

Red powder, commonly known as the Three Immortals. It decomposes into mercury vapor and oxygen when heated to 500°C. (Mercury vapor is poisonous!)

Catalyst characteristics:

1. Change: Change the chemical reaction rate of other substances

Two constants: the mass and chemical properties remain unchanged before and after the chemical reaction.

Oxygen collection method

The method of collecting the gas is determined by its physical properties.

(1) Oxygen is not easily soluble in water:

Answer: It can be collected by drainage method.

(2) The density of oxygen (1.43) is greater than that of air (1.29):

Answer: It can be collected using the upward air exhaust method.

How to check the air tightness of the device?

Put one end of the conduit mouth of the device into the water, and then hold the wall of the container tightly with both hands. The temperature of the palms is high, causing the air in the bottle to heat up and expand, and the bubbles are discharged through the conduit mouth. After the palms are removed, the gas shrinks due to cold, causing a water column in the conduit. rise. this phenomenon

It shows that the system does not leak, otherwise it leaks.

1. Use the outer flame of the alcohol lamp to heat the drug part, and preheat the test tube before heating.

2. The medicine should be laid flat on the bottom of the test tube and heated evenly.

3. The iron clamp should be clamped 1/3 away from the mouth of the test tube.

4. Place a small ball of cotton at the mouth of the test tube to prevent potassium permanganate powder from entering the tube during heating.

5. Just slightly expose the rubber stopper of the catheter in the test tube to facilitate gas discharge.

6. The mouth of the test tube is slightly tilted downwards

Some solid reagents tend to produce water vapor when heated. The mouth of the test tube is slightly tilted downward to prevent condensed water from flowing back to the bottom of the hot test tube and exploding the test tube.

7. When collecting by drainage method, the conduit can be extended to the mouth of the bottle. Collecting can only be done when continuous and uniform bubbles appear at the mouth of the conduit (the air that just comes out is heated and expanded air, which will make the collected gas impure)

Summary: Gas Collection Device

Select based on:

Whether the gas is easily soluble in water or reacts with water

Is the density of a gas greater or less dense than air?

Does the gas react with components in the air?

Principles for selecting substance preparation plans:

Economical raw materials; simple and safe operation; product pollution-free

So use hydrogen peroxide: no heating, simple operation, energy saving

[Example 1] Nitric oxide (NO) is a colorless gas at room temperature. It is difficult to dissolve in water and is slightly denser than air. It can react quickly with oxygen in the air to form reddish-brown nitrogen dioxide (NO2 )gas. To collect a bottle of nitric oxide gas in the laboratory, the method that should be used is ( )

A. Use drainage method

B. Use the upward air exhaust method

C. Use drainage method or upward air exhaust method

D. Use the downward air exhaust method

[Example 2] Which of the following changes is a decomposition reaction ( )

A. Separate oxygen and nitrogen from the air

B. Heating potassium permanganate to produce oxygen

C. Red phosphorus burns in oxygen to form phosphorus pentoxide

D. Candles burn in oxygen to produce carbon dioxide and water

[Analysis] A decomposition reaction is a chemical reaction in which one substance produces two or more substances. From this it is not difficult to judge that B is a decomposition reaction.

【Answer】B

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Update Time: 2024-10-06

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

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