Presentation on theme: "Properties of Matter Investigation 4. Acids and Bases An acid is a compound that releases hydrogen ions in water. The word “acid” comes form the Latin."— Presentation transcript:
Acids and Bases An acid is a compound that releases hydrogen ions in water. The word “acid” comes form the Latin word acidus, which means sour. When you think of an acid, you might a picture a scary smoking liquid eating away at a piece of metal. Some acids do react that way, but many acids are much more common and safer.
Common Acids Grapefruit, lemons, and vinegar taste sour because they contain acids.
Acids All acids contain hydrogen atoms. Hydrogen atoms are neutral, that is they have equal numbers of positive and negative charges. When some elements combine, atoms of one element can lose negative charges to atoms of the other element. That leaves the atoms of one element with more negative charges and atoms and the other element with more positive charges. These charged atoms are called ions. When an acid compound is added to water, the acid dissolves in water to form an acid solution that contains hydrogen ions.
Acids cont. The more hydrogen ions the acid releases when it dissolves in water, the stronger the acid is. Strong acids burn your skin and are poisonous. They react quickly with many metals, releasing hydrogen gas. Weak acids give foods the sour, sharp taste that you find in vinegar, soda water, spinach, apples, limes and lemons.
Acids cont. Your stomach contains an acid that dissolves your food. If you eat too many pickles or other sour foods, the acid can become too strong, giving you a “sour” stomach.
Bases A base is a compound that releases hydroxide ions when dissolved in water. Just as with acids and hydrogen ions, the more hydroxide ions that are released into the water as a base dissolves, the stronger the base is. Bases taste bitter and feel slippery.
Common Bases Soap is made from a base. Weak bases are found in baking soda and some antacids. Strong bases are often found in cleaning products, such as ammonia.
The pH Scale Because acids and bases can be very dangerous, you shouldn’t touch them or taste them. So how do you know if something is an acid or a base? A simple test using litmus paper can tell you if a substance is an acid or a base. Litmus paper is a paper that changes color when it contacts acids or bases.
Litmus Paper If you place a strip of blue litmus paper into an acid, the paper changes to a pink or red color. In a base, pink litmus paper changes to blue.
pH Litmus paper shows whether you have an acid or a base but doesn’t show how strong the acid or base is. The strength of an acid or a base is measured using a set of numbers from 0-14. This set of numbers is called the pH scale. The strongest acids are found at the low end of the pH scale. For example, if a compound has a pH of 1, it is a very strong acid.
pH continued As the pH number increases, the strength of the acid becomes weaker. An acid with a pH of 3 is weaker than an acid with a pH of 1. A solution with a pH of 7—halfway between 0 and 14– is neutral. Substances with pHs beyond 7 are bases. The higher the number, the stronger the base.
Indicators Litmus paper can’t tell you how strong an acid or a base is, but certain other substances called indicators, can. Indicators are substances that change color at a certain range of the pH scale. Some indicators change color many times as the pH of the solution changes. For example, red cabbage juice can change from red to green to greenish yellow as the pH changes.
Effects of pH Changes The pH of soil, rivers, lakes, and even rain is very important to life on Earth. Many of the plant foods that you eat grow well in soil with a pH range between,5 and 7 which is slightly acidic. Some of the acid gets into the soil as plants decay and acid forms. Rain washes the acid into the soil. This process keeps the soil slightly acidic.
Effects of pH Changes cont. Farmers also add materials to the soil to keep its pH in the correct range. In dry areas, the soil tends to be basic, and very few plants grow.
What can be done to change substances that are too acidic or basic? Plain water is a neutral substance. When an acid reacts with a base, water is always one of the products. The other product depends on which acid and base you combine.
Neutralization Neutralization is a process in which an acid and a base react to produce a salt and water. The kind of salt produced depends on the acid and base that reacted with each other. Sodium chloride is only one of the salts that can be formed during neutralization.
Review What is pH? What are acids? What are bases? What is neutralization? What are some effects of pH changes?