Chemical Reactions

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

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

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

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!

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

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?)

Exothermic vs endothermic reactions https://www.youtube.com/watch?v=yvyHVA1Ww_M today we experiment with exothermic and endothermic reactions!

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

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

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