"Acidic Solutions and Alkaline Solutions" Initial Acids, Bases and Salts PPT Courseware 2

"Acidic Solutions and Alkaline Solutions" Initial Acids, Bases and Salts PPT Courseware 2

[Association and Enlightenment]

In daily life, we often feel this fact:

Tea and soda water have a bitter taste; vinegar and yogurt have a sour taste; sugar water has a sweet taste; wine has a spicy taste, etc.

Different foods have different tastes, and the taste of food can be confirmed by tasting. The sourness and bitterness are related to the acidity and alkalinity of the solution.

But chemicals cannot be tasted, so how to test the acidity and alkalinity of the solution?

To test the acidity and alkalinity of a solution, acid-base indicators are usually used. Purple litmus test solution and colorless phenolphthalein test solution are commonly used.

1. Acidic solution and alkaline solution

Experimental exploration

Put a few drops of white vinegar, salt water, sucrose water, sodium hydroxide solution, dilute hydrochloric acid, ammonium chloride solution, sodium carbonate solution, and lime water into a small test tube (or the holes of the white drip plate), and then add each drop 1-2 drops of purple litmus test solution to observe the phenomenon of the solution

Experimental results:

1. White vinegar, dilute hydrochloric acid, ammonium chloride solution, etc. can make the purple litmus test solution turn red, but the colorless phenolphthalein test solution does not change color. These solutions are acidic solutions

2. Sodium hydroxide solution, sodium carbonate solution, lime water, etc. can turn purple litmus test solution blue and colorless phenolphthalein test solution red. These solutions are alkaline solutions.

Salt water, sucrose water, etc. cannot change the color of the purple litmus test solution, nor can they change the color of the colorless phenolphthalein test solution. They are neutral solutions.

Summarize:

1. Purple litmus test solution turns red when exposed to acid, turns blue when exposed to alkali, and remains purple in neutral solution.

2. The colorless phenolphthalein test solution does not change color when exposed to acid, but turns red when exposed to alkali. It remains colorless in neutral solution.

Give it a try: you can do it!

1. Which of the following solutions will turn red when dropped into colorless phenolphthalein test solution ( )

A. Tap water B. Salt water

C. Hydrochloric acid D. Clarified lime water

2. Which of the following common substances in life can make purple litmus test solution turn red ( )

A. White vinegar B. Salt water C. Lime water D. Soapy water

3. Add phenolphthalein test solution dropwise to a certain solution. If the solution does not change, then the solution must be certain ( )

A is a neutral solution B is an acidic solution

C is an alkaline solution D is not an alkaline solution

2. Expression of solution acidity and alkalinity—PH

The pH value of an acidic solution is <7. The stronger the acidity, the smaller the pH.

The pH value of an alkaline solution is >7. The stronger the alkalinity, the greater the pH.

The pH value of neutral solution = 7 (such as the pH value of NaCl solution and Na2SO4 solution = 7)

3. Understand the significance of solution pH

1. Many reactions in chemical production must be carried out in a certain pH solution.

2. Crops are generally suitable for growing in soil with a pH of 7 or close to 7.

3. Measuring the pH of rainwater can help you understand air pollution.

4. Measuring the pH of liquids in the human body or eliminated can help understand the health status of the human body.

【Classroom Exercise】

【Question 1】The pH of a certain solution=3, then the solution ( )

A. Acidic B. Alkaline C. Neutral D. Unable to determine

[Question 2] It is known that the approximate pH of apple juice is 2.9~3.3. If purple litmus test solution is dropped into the apple juice, the color displayed is ( )

A. Colorless B. Red C. Blue D. Purple

[Question 3] Which of the following pH indicates the most acidic solution ( )

A. PH=14 B. PH=7 C. PH=1 D. PH=0

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