Lesson 17-19

Lesson 17

In lesson 17 we learned that an indicator is molecular substance that changes color when it comes into contact with an acid or a base.

Acids and bases are corrosive. When pH is 7 it is neutral or pure water. Below 7 is an acid and above 7 is a base. This is a picture of the pH scale.

These pH solutions are classified by their colors you can observe. Acids and bases change the color of indicators.

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Practice Problem

3. It means that the substance is neutral. 

Lesson 18

In lesson 18 we learned about cabbage juice and its indicator colors. Cabbage Juice: Pink=acidic, Green=basic, Purple=neutral. Substances that add H+ (just one proton) to a solution are acids. Bases are substances that add OH- to a solution. Substances that don't add H+ or OH- to the solution are neutral.

The definitions of acids and bases has changed over time.

• Arrhenius Definition: An acid is any substance that adds hydrogen ion to solution. A base is any substance that adds hydroxide ion to a solution.
• Brønsted-Lowry Definition- An acid is a proton donor. A base is a proton acceptor.

The products of a reaction is always called a conjugate.

(Red) Base + Acid --> Conjugate Acid + Conjugate Base

(Purple) Acid + Base --> Conjugate Acid + Conjugate Base

Strong acids and strong bases dissociate completely into ions, while weak acids do not.

Practice Problem
1. A base is a substance that adds a OH- ion to a substance and an acid is a substance that adds a H+ ion to a substance. 

Lesson 19

Lesson 19 talked more about the pH scale. The pH scale is a logarithmic scale the describes the concentration of H+ ions. pH is related to H+ by the formula: pH=-log[H+] Water dissociates into H+ and OH- ions. Below is a picture of the pH scale and examples of substances that fit into each pH level.

[H+][OH-]=1.0x10^-14

Practice Problem
3A. 4
3B. 12

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