Compounds Substances that are chemically formed They have physical and chemical properties that are different from the elements that make them up. They are formed as the result of a chemical reaction.
Hydrogen (an explosive gas) and oxygen (an explosive gas) combine to form the compound water (a harmless liquid). Here, the hydrogen gas in the zeppelin SS Hindenburg reacts with oxygen in the air to make water. Source: Photo courtesy of the US Navy, http://commons.wikimedia.org/wiki/File:Hindenburg_burning.jpg. http://commons.wikimedia.org/wiki/File:Hindenburg_burning.jpg
Acids and Bases Acids and bases are special classes of compounds that exhibit common chemical properties.
Acids and Bases Acids and Bases can be helpful or harmful. Acids and bases can be weak, some or strong. YOU MUST ALWAYS BE CAREFUL WHEN WORKING WITH ANY CHEMICALS!
Characteristics of Acids Have a sour taste They have Hydrogen atoms which have given up their electron, making them positive ions. (H+) They turn blue litmus paper red They react with metals to release Hydrogen gas. http://www.youtube.com/watch?v=PqUOGc6P05c
What is an ion? An ion is an atom that has lost or gained an electron giving it a positive (+) or negative (-) charge. 3 protons (+) and 3 electrons (-) = neutral charge Atoms don’t like having a non full outer shell, so this atom will give away its one valence electron making it 3+ and 2- for an overall 1+ charge, making it a positive ion.
USES OF ACIDS Citric acid and ascorbic acid (Vitamin C) are found in orange juice Carbonic acid and phosphoric acid give a “bite” to soft drinks Acids in your stomach aid in digestion Sulfuric acid is the most widely used industrial acid in the world. It is used in making metals, paper, paints, and fertilizers.
Characteristics of Bases Have a bitter taste (never taste an unknown!) They feel slippery They have Hydroxide (OH) compounds which have taken on an electron, making them negative ions. (OH-) They turn red litmus paper blue They do not react with metals.
Uses of Bases Bases are used in soaps (remember, bases are slippery) Bases are used to make paper, in oven cleaners, and to unclog drains Ammonia is a base and is used in many household cleaners
Detecting Acids and Bases You can detect an acid using an indicator. INDICATOR - A substance that changes color in the presence of an acid or a base.
INDICATORS Litmus paper is an indicator An acid turns blue litmus paper red A base turns red litmus paper blue Universal test papers can identify acids and bases Cabbage juice can also be used as an indicator. The juice should turn pink in acidic solutions, and green/blue/yellow in basic solutions.
How do we measure the strength of an acid or base? Use the pH (Powers of Hydrogen) scale
pH scale Acids and Bases are ranked on a pH scale. 0-6.9 = acids, lots of H+ ions 7.1-14 = bases, lots of OH- ions
Lots of H+ = Acid, Lots of OH- = Base. What happens if you have a perfect balance of H+ and OH-? HOH Or H 2 O Water!
Pure Water (H 2 O) is a perfect balance of the H+ ions and OH- ions Pure water is a 7 on the pH scale, it is called Neutral
Practice Acid/Base experiments http://www.kidsknowit.com/interactive-educational-movies/free-online- movies.php?movie=Acids%20And%20Bases http://www.bgfl.org/bgfl/custom/resources_ftp/client_ftp/ks3 /science/acids/ http://www.youtube.com/watch?v=ujkuW-0cpNw Magic tricks with Acids and Bases