1. Chemical Reactions

2. What are we going to learn about?
Acids and Bases, and the pH scale
Exothermic vs. Endothermic reactions
Reduction vs. Oxidation

3. Acids and Bases Acids and Bases are two different types of chemicals.
Almost all liquids are either an acid or base
Whether a liquid is an acid or base depends on the type of ions that are in it.
Acids have a lot of hydrogen (H+) ions
Bases have a lot of hydroxide (OH-) ions

4. The pH Scale The pH scale measures how acidic or basic a liquid is.
Another word for basic is alkaline
All liquids have a specific pH that ranges from 0 to 14
From 0 to 7 are acids, with 0 being the strongest acid
From 7 to 14 are bases, with 14 being the strongest base.
If a liquid has a pH of 7, it is neutral
Example: water

5. How is the pH of an Acid or Base determined?
Litmus test – a simple pH indicator made by scientists
A litmus test is simply a dry strip of paper that changes color when dipped into a liquid.
It changes color according to how acidic or basic the liquid is
Based on the color change, pH can be determined
Cabbage juice – a natural pH indicator
Cabbage juice is purple and changes color when combined with an acid or base
When combined with an acid, it turns pinkish-purple
When combined with a base, it turns greenish-blue
Base on the color change, pH can be determined
This is what we will be doing in one of our experiments!

6. More about Acids and Bases and the pH scale
Acids with a low pH of around 1 are very reactive and can be dangerous
The same is true for bases of a pH near 13
There are many acids and bases in nature and in our bodies.
Our stomach’s use hydrochloric acid to help digest food and kill bacteria to help keep us from getting sick.
Our body is full of different proteins, which are all made of smaller molecules called amino acids

7. Interesting Facts about Acids and Bases
Acids taste sour
Bases taste bitter
Acids and bases can be combined to help neutralize each other
QUESTION:
if an acidic solution were combined with a basic solution to become completely neutral, what would the pH be?
(think about water. Is water neutral? What is water’s pH?)

8. Exothermic vs endothermic reactions
today we experiment with exothermic and endothermic reactions!

9. Exothermic vs. endothermic reactions
Sometimes chemical reactions between two or more substances give off or take in energy, often in the form of heat
Exothermic reaction -- gives off heat
Example: lighting a match
When a match is lit, fire is produced, which gives off heat
Endothermic reaction – absorbs heat
Example: photosynthesis in plant leaves
Absorb sunlight to produce energy for the plant

10. Reduction vs oxidation
In chemistry, there are reduction reactions and oxidation reactions.
Reduction reactions are reactions in which an atom or compound gains electrons, Example:
F2 + 2 electrons(e-)  2F—
Here, F2 is gains two electrons
Oxidation reactions are reactions in which a compound loses electrons, Example:
H2  2H+ + 2 electrons (e-)
Here, H2 loses two electrons
Together, oxidation and reduction reactions make up what is called a redox reaction, which is a reaction in which atoms either lose or gain electrons

11. Reduction vs. oxidation
Example of oxidation and reduction:
Rusting
Iron rusts because surrounding oxygen steals electrons from the iron, which produces a compound called iron oxide, or rust
So, if the oxygen steals (gains) electrons from iron during this process, then is oxygen reduced or oxidized?
What about iron?
Many oxidative reactions are exothermic, which means what?
Today we will study reduction and oxidation by experimenting with steel wool and vinegar