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The pH is a measure of the concentration of hydrogen ions in a solution. A solution with a high concentration of hydrogen ions is acidic. A solution with a low amount of hydrogen ions is basic, or also known as alkaline. Hydrogen ions, also known as hydronium, are written shorthand as H+ or H3O+.  Know the pH scale. The pH scale is usually presented from 0 to 14. The lower the number, the more acidic the solution. The higher the number, the more basic the solution. For example, orange juice would have a pH of 2 because it is quite acidic. In contrast, bleach has a pH of 12 as it is quite basic. Numbers in the middle of the scale are neutral, such as water, with a pH of 7. One level of pH is a 10x difference. For example, when comparing pH 7 to pH 6, pH 6 is ten times more acidic than pH 7. Furthermore, pH 6 would be 100 times more acidic than pH 8. The pH scale is calculated by a negative logarithm. A negative logarithm of base b is simply how many times a number must be divided by b to reach 1. The pH equation can be seen as follows: pH = -log10[H3O+].  The equation can sometimes be seen as pH = -log10[H+]. Know that whether the equation has H3O+ or H+, they are the same. It is not vital to have a firm understanding of what a negative log is to calculate pH. Most calculators used at high school and post secondary level will have a log button. Concentration is the number of particles of a compound in a solution relative to the volume of the same solution. For pH, you have to use molar concentration for the formula to work out. Molar concentration, which is also called molarity, denotes the number of moles of dissolved compound per liter of solution. Its units are moles per liter (mol/L), also called molar (M). If you’re using a solution in a lab, the concentration will be written on the bottle. When working on your chemistry homework, the concentration will usually be given to you.

Summary:
Know what pH actually is. Define pH in an equation. Understand concentration.