"Several Common Acids and Bases" Initial Acids, Bases and Salts PPT Courseware

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"Several Common Acids and Bases" Initial Acids, Bases and Salts PPT Courseware

Review before class

1. What kind of compound is called a base?

Compounds in which all cations produced during ionization are H+ are called bases.

2. Which of the following compounds are bases?

NaOH KOH Ca(OH)2 Ba(OH)2

Mg(OH)2 Cu2(OH)2CO3 H2O

CaO CuO Cu(OH)2 KNO3 NaCl

Bases include: NaOH KOH Ca(OH)2 Ba(OH)2 Mg(OH)2 Cu(OH)2

1. Sodium hydroxide

Sodium hydroxide is highly corrosive to skin, paper, fabrics, etc., so be very careful when using it!

Sodium hydroxide is a white solid, commonly known as caustic soda, caustic soda or caustic soda.

If you accidentally get lye on your skin, rinse with plenty of water and then apply boric acid solution.

Sodium hydroxide properties research experiment

Experiment 1: Put a small piece of oil-stained copper piece into the test tube, then add a small amount of sodium hydroxide solution, heat the test tube over the flame of an alcohol lamp, and observe the changes on the surface of the copper piece.

Sodium hydroxide can be used to remove oil stains from metal surfaces. The main ingredient in the cleaners used in the kitchen is sodium hydroxide.

Experiment 2: Put a little solid sodium hydroxide in a watch glass, expose it to the air for a period of time, and observe the changes that occur.

Sodium hydroxide easily absorbs water vapor from the air, making the surface moist and gradually dissolving. This phenomenon is called deliquescence.

Deterioration of sodium hydroxide

After Xiao Ming prepared a sodium hydroxide solution with a certain solute mass fraction using sodium hydroxide solid placed in an open door, he took part of the solution and added dilute hydrochloric acid dropwise to it. The result was that gas was generated; after testing, the gas was CO2. Please think and Answer the following questions.

1. Please tell me how Xiao Ming detected that the gas was CO2 gas.

2. What substances react with acids to generate CO2 gas? So we guess, what substances are present in the solid sodium hydroxide placed in the open?

3. Why is there sodium carbonate solid in the sodium hydroxide solid placed in the open?

Reason: Sodium hydroxide reacts with CO2 in the air to form sodium carbonate and water.

Can solid sodium hydroxide be exposed to the air for a long time? Why?

No, because if solid sodium hydroxide is exposed to the air for a long time, it will deliquesce and deteriorate.

2. Calcium hydroxide

Calcium hydroxide [Ca(OH)2]

1. Calcium hydroxide is a white solid, commonly known as slaked lime or slaked lime

2. Calcium hydroxide is slightly soluble in water, and its aqueous solution is clear lime water

3. The solubility of calcium hydroxide decreases as the temperature increases.

4. Calcium hydroxide is also corrosive, so please pay attention to safety when using it.

Contact with reality

1. How should substances such as sodium hydroxide and calcium hydroxide be stored in the laboratory? Why?

Substances such as sodium hydroxide and calcium hydroxide should be kept sealed in the laboratory, otherwise they will react with carbon dioxide in the air and deteriorate.

2. When Xiao Ming passed by a construction site, he found a layer of white film-like substance on the surface of lime water. What is this substance? How did it form? Can you write the chemical equation for its formation?

This white film is calcium carbonate, which is generated by the reaction between calcium hydroxide and carbon dioxide in the air. The chemical equation is: Ca(OH)2 + CO2 =CaCO3 ↓ + H2O

【Think about it】

1. When CO2 is passed into the NaOH solution, no obvious phenomenon occurs, and it is difficult to judge whether the NaOH solution reacts with CO2.

⑴How can we know whether the response has occurred?

Answer: As shown in the picture, pour a small amount of concentrated sodium hydroxide solution into a soft plastic bottle filled with CO2, close the cap tightly, and shake. If the plastic bottle becomes flat, it means that CO2 can react with the sodium hydroxide solution. .

(2) The common principles underlying the above experimental design are:

Answer: React gas into liquid to reduce the air pressure in the container.

(3) If some students question and think that the above experimental design does not rule out the hypothesis that CO2 may be dissolved in NaOH solution, how can you further design experiments to prove that a chemical reaction between CO2 and NaOH must have occurred?

Answer: Take the reaction solution and add dilute hydrochloric acid dropwise, bubbles will appear.

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Update Time: 2024-08-06

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