Before we begin it is important to know the difference between pH and pOH. If you forgot the difference click here! If you understand them lets move on!
Molarity
It is also important that we also go over molarity:
- Molarity is the measure of concentration and is usually used in acids, alkali's and other solutions
- Molarity is measured in concentration- the amount of solute in a solution which is measured in moles
- [H+] means the concentration of hydrogen ions and [OH-] is the concentration of hydroxide ions. This is because the square brackets mean concentration and the definition of molarity (M) is concentration
So how do we calculate pH, pOH, [H+] and [OH-]?
Lets do some examples so we can get comfortable with these equations....
*If needed use the calculator below
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If a solution has a pH of 3 what is the [H+]?
1. The first thing to do would be to see which equation fits in best with the question asked
1. The first thing to do would be to see which equation fits in best with the question asked
- Here we are looking for [H+] so the best equation would [H+]= 2nd log (-pH) since we already have the value of pH
- Here we have pH so we would plug 3 into the equation for pH
- The equation would look like this: [H+]=2nd log (-3)
- In this cause the answer should be 0.001M
If a solution has a pOH of 9 what is the [OH-]?
1. The first thing to do would be to see which equation fits in best with the question asked
1. The first thing to do would be to see which equation fits in best with the question asked
- In this case since we are looking for the [OH-] the best equation to used would be [OH-]= 2nd log (-pOH) since we already have pOH
- Here we have pOH so we would plug in 9 into the equation for pOH
- The equation would look like this: [OH-]=2nd log (-9)
- The answer should be 1X10-9