Acids and Bases

Acids

An acid is a substance that increases the concentration of H+ (H3O+) ions in a solution. For the most part, an acid has a sour taste, it turns blue litmus paper red, it turns methyl orange solution red, it reacts with carbonates and bicarbonates, it is neutralized by bases, and it reacts with metals. There is also something called an Arrhenius acid which is a substance that increases the concentration of OH- when it is dissolved in water. This concept is helpful because it describes the acid-base properties of substances in water, but it is limited to aqueous solutions and bases are limited only to those that produce hydroxide ions.  A Bronsted-Lowry acid makes the substance a proton donor. This concept is helpful because it can be applied to reactions between two substances and it is not limited to water, but it only covers reactions involving H+ transfers. A Lewis acid is a substance that donates electrons to form a covalent bond. This structure is helpful because it can be applied to reactions between two substances and is not limited to water, but it only covers reactions involving electron transfers except H+ transfers.

Bases

A base is a chemical substance that decreases H+ concentration in aqueous solution or that increases OH- concentration in solution. Usually bases taste bitter, they are slippery, they turn red litmus paper blue, they turn colorless phenolphthalein pink, they neutralize acids, they may react with some metal salts, and they may react with carbon dioxide. An Arrhenius base is a substance that increases the concentration of OH-. This concept is helpful because it describes the acid-base properties of substances in water, but it is limited to aqueous solutions and bases are limited only to those that produce hydroxide ions. A Bronsted-Lowry base makes the substance a proton acceptor. This concept is helpful because it can be applied to reactions between two substances and it is not limited to water, but it only covers reactions involving H+ transfers. A Lewis base is a substance that donates electrons to form a covalent bond. This structure is helpful because it can be applied to reactions between two substances and is not limited to water, but it only covers reactions involving electron transfers except H+ transfers.

Where they fall on the pH scale

First off, pH is the measurement in which the amounts of hydronium ion concentration that an aqueous solution contains is measured. The pH scale ranges from 1 to 14, 1 being the most acidic and 14 being the most basic. Halfway through the scale is the number 7 and the 7th pH unit represents a neutral state. Acidity is represented by a pH under 7 and alkalinity (or basicity) is represented by anything over a pH of 7. There is also something called pOH which is the measure of hydroxide ion concentration in a solution. It is kind of like the opposite oh pH because as pH increases the pOH decreases. This means acids with a low pH have a high pOH while bases have a high pH and a low pOH.

Catalysts

A catalyst is a substance that increases the rate of a chemical reaction but it is not consumed during the reaction. A catalyst provides an alternate reaction pathway with lower activation energy and is not a reaction or product.  It is represented above the arrow in between the reactants and products. Catalysts increase the reaction rate by holding molecules in proper orientation, or they form temporary reaction intermediates with reactant molecules, or they weaken or break reactant bonds, increasing activity. There are homogeneous catalysts (catalyst in the same phase as as the reactants in a chemical reaction) and heterogeneous catalyst that is in a different phase than the reactants in a chemical reaction).

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