"Acidity and Alkalinity of Solutions" Common Acids, Alkalis, and Salts PPT Courseware 4

Description

"Acidity and Alkalinity of Solutions" Common Acids, Alkalis, and Salts PPT Courseware 4

Knowledge review

Knowledge point 1: Distinguish between acidic solution and alkaline solution

To determine the acidity or alkalinity of a solution, use _____________.

Substances such as litmus and phenolphthalein that can react with acid or alkali solutions to display different colors are called _____________.

【Notice】

① When the indicator encounters an acidic solution or an alkaline solution, it is the indicator that changes color, not the acidic solution or alkaline solution;

②According to the color change of the indicator, the acidity and alkalinity of the solution can be judged, but it cannot be determined that the solution must be acid or alkaline. Because some salt solutions may be acidic or alkaline, such as Na2CO3 solution, which may be alkaline.

Knowledge point 2: Test the acidity and alkalinity of the solution

People use _______ to express the acidity and alkalinity of a solution.

When pH=7, the solution is ____

When pH<7, the solution is ____

When pH>7, the solution is ____

The more acidic a solution is, pH____; the more alkaline a solution, pH_____.

pH measurement method: Place a small piece of pH test paper on the ________, dip the test liquid into the _________, drop it on the test paper, and compare the color of the test paper with ___________.

【Notice】

① When measuring the pH of a solution with pH test paper, the pH test paper cannot be wetted with water;

②Do not put the pH test paper directly into the sample solution to be tested, as it will contaminate the reagent.

Example analysis

►Type 1 Acid-base indicator

Proposition perspective: Test students’ mastery of acid-base indicators

Example 1 A solution that can turn colorless phenolphthalein test solution red can turn purple litmus test solution ( )

A.turn into red B.turn into colorless

C.turns blue D.does not change color

[Analysis] The solution that can turn phenolphthalein test solution red is alkaline, and the alkaline solution can turn litmus test solution blue. So choose C

[Variation question] After learning about acid-base indicators, classmate Xiaohong tried to make her own indicator using purple cabbage. She put the chopped purple cabbage into a glass, added _____ to soak it, and filtered the soaked juice with gauze to get a homemade indicator. This indicator turns blue when exposed to lime water and red when exposed to hydrochloric acid. Put a small amount of white vinegar into a glass and add a few drops of homemade indicator to develop ____ color.

[Method Instructions] In addition to the commonly used litmus and phenolphthalein solutions, acid-base indicators can also be replaced by plant juices.

[Analysis] Pigments are generally not easily soluble in water but easily soluble in alcohol, so alcohol should be added for soaking. The homemade acid-base indicator made with purple cabbage turns blue when exposed to lime water and red when exposed to hydrochloric acid. Both white vinegar and hydrochloric acid are acidic, so add a few drops of the homemade indicator to the white vinegar and the indicator should appear red.

►Type 2: pH and pH

Proposition perspective: Test students’ understanding of the acidity and alkalinity of solutions

Example 2 The following substances are dissolved in water, and the pH of the resulting solution is less than 7 ( )

A． CaO B． NaCl

C. K2SO4 D． CO2

[Analysis] Carbon dioxide dissolves in water and reacts with water to form carbonic acid. Carbonic acid is an acid, and its aqueous solution is acidic. So choose D

[Variation question] A classmate measured the pH of some food and daily necessities at home. The results are as shown in the figure:

The following statement is correct ()

A． Vinegar can remove the astringency of preserved eggs

B． Toothpaste is a neutral substance

C. Soy sauce is alkaline and can turn phenolphthalein red

D． People with excessive stomach acid should eat more grapes

[Analysis] To answer this question correctly, you must understand the relationship between the pH and acidity and alkalinity of the solution.

A. The pH of vinegar is 3, which is an acidic solution. The pH of preserved eggs is 10, which is alkaline. Neutralizing the acid and alkali can remove the astringent taste, so option A is correct. B. The pH of toothpaste is 9, which is an alkaline substance. Option B is wrong; C. Soy sauce has pH=5, which is an acidic substance and cannot change the color of phenolphthalein, so option C is wrong;

D. The pH of grapes is 4, which is an acidic substance. People with excessive stomach acid should not eat more, so option D is wrong; so choose A.

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"Acidity and Alkalinity of Solutions" Common Acids, Alkalis, and Salts PPT Courseware Learning Objectives 1. Learn to use two indicators, litmus and phenolphthalein, to test the acidity and alkalinity of solutions. 2. Understand the relationship between the acidity and alkalinity of a solution and the pH of the solution, and be able to use pH test paper to quantitatively measure the pH of the solution. 3..

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Update Time: 2024-09-26

This template belongs to Chemistry courseware Cantonese Education Edition Ninth Grade Chemistry Volume 2 industry PPT template

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