<PRE><B>Question 258174</B>
The pH scale is logarithmic and as a result, each whole pH value below 7 is ten times more acidic than the next higher value. For example, pH 4 is ten times more acidic than pH 5 and 100 times (10 times 10) more acidic than pH 6. 
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The concentrations of hydrogen ions and indirectly hydroxide ions are given by a pH number. pH is defined as the negative logarithm of the hydrogen ion concentration. The equation is:

pH = - log [H+] 
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Example: If an acid has an H+ concentration of 0.0001 M, find the pH.
Solution:
First convert the number to exponential notation, find the log, then solve the pH equation.

H+ = 0.0001M = 10-4; log of 10-4 = -4;

pH = - log [ H+] = - log (10-4) = - (-4) = +4 = pH

The purpose of the negative sign in the log definition is to give a
positive pH value.
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The PH of coffee = 5
The PH of orange juice = 4</PRE>