ACIDS AND BASES

ACIDS AND BASES
Scientists use something called the pH scale to measure how acidic or basic a liquid is. Although there may be many types of ions in a solution, pH focuses on concentrations of hydrogen ions (H+) and hydroxide ions (OH-). The scale goes from values very close to 0 through 14. Distilled water is 7 (right in the middle). Acids are found between a number very close to 0 and 7. Bases are from 7 to 14. Most of the liquids you fmd every day have a pH near 7. They are either a little below or a little above that mark. When you start looking at the pH of chemicals, the numbers go to the extremes. If you ever go into a chemistry lab, you could find solutions with a pH o( 1 and others with a pH of 14. There are also very stong acids with pH values below one such as battery acid. Bases with pH values near 14 include drain cleaner and sodium hydroxide (NaOH). Those -chemIcals are very dangerous.
NAMES TO KNOW
Here are a couple of definitions
Acid: A solution that has an excess ofH+ ions. It comes from the Latin word acidus that means "sharp" or "sour".
Base: A solution that has an excess ofOH- ions. Another word for base is alkali.
Aqueous: A solution that is mainly water. Think about the word aquarium. AQUA means water.
Strong Acid: An acid that has a very low pH (0-4).
Strong Base: A base that has a very high pH (10-14).
Weak Acid: An acid that only partially ionizes in an aqueous solution. That means not every molecule breaks apart. They usually have a pH close to 7 (3-6).
Weak Base: A base that only partially ionizes in an aqueous solution. That means not every molecule breaks apart. They usually have a pH close to 7 (8-10).
Neutral: A solution that has a pH of 7. It is neither ecidic nor basic.
Acids are compounds that break into hydrogen (H+) ions and another compound when placed in an aqueous solution. Bases are compounds that break up into hydroxide (OH-) ions and another compound when placed in an aqueous solution.
If you have an ionic compound and you put it in water, it will break apart into two ions. If one of those ions is H+, the solution is acidic. If one of the ions is OH-, the solutions is basic.
That pH scale we talked about is actually a measure of the number of H+ ions in a solution. If there are a lot of H+ ions, the pH is very low. If there are a lot of OH- ions, that means the nmber of H+ ions is very low, so the pH is high.
Catalysts
A catalyst is a substance that will change the rate of a reaction. A catalyst is often used to make a reaction go faster. The catalyst itself does not take part in the reaction as a reactant. It is not changed by the reaction, it is not used up during the reaction. It is still there in the same form when the reaction is complete. A catalyst is usually a transition metal, a transition metal oxide or an enzyme in living cells. An exception is aluminium oxide, used in the cracking of hydrocarbons. A substance which works well as a catalyst for one reaction might not work well as a catalyst for a different reaction.
How does a catalyst work?
A catalyst works by providing a convenient surface for the reaction to occur. The reacting particles gather on the catalyst surface and
1) collide more frequently with each other
2) more of the collisions result in a reaction between particles because the catalyst can lower the activation energy for the reaction.
A catalyst is often used as a powder, so that it has a bigger surface area per gram.