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General Chemistry - Acids and Bases

The Bronsted and Lowry’s definition of an acid is any species that donates a proton when it dissociates in a solution. The Bronsted and Lowry’s definition of a base is any species that accepts a proton in solution. Lewis defined a base as an electron pair donor and an acid as an electron pair acceptor. Every Bronsted-Lowry acid has a matching Bronsted-Lowry base. Every Bronsted-Lowry base has a matching Bronsted-Lowry acid, and the matching pairs are called conjugates. 

pH and pOH 

Rule number 18: 
pH equals negative logarithm of the hydrogen ion concentration. pOH equals negative logarithm of the hydroxide ion concentration. To find the pH of a solution, we take the exponent of the hydrogen concentration and change its sign, then subtract to the log of the coefficient from the exponent. Since the log of the coefficient is always less than one, the pH is always between the negative log of the exponent and 1 less than that value. 

Water Solubility Constant 

Rule number 19: 
Kw is the solubility constant for water, and it is equal to the hydrogen concentration times the hydroxide ion concentration. Kw is equal to 1x10-14. If we now take the log of each concentration, we get pH plus pOH equals 14. 

Acids in solution have low pH values and high pOH values. Bases in solution have high pH values and low pOH values. Because pH and pOH add up to 14, the pH scale varies from 0 to 14. Neutral solutions have a pH of 7. Anything higher than that is on the basic side and anything lower than that is on the acidic side.