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Acids and Bases pH Calculations pH scale. pH Scale Created to express acidity as a more simple number than molarity. pH stands for “power” of the hydrogen.

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Presentation on theme: "Acids and Bases pH Calculations pH scale. pH Scale Created to express acidity as a more simple number than molarity. pH stands for “power” of the hydrogen."— Presentation transcript:

1 Acids and Bases pH Calculations pH scale

2 pH Scale Created to express acidity as a more simple number than molarity. pH stands for “power” of the hydrogen ion concentration. pH = - log [H + ] If... [H+] = 1 x 10 -7 then pH = 7 (neutral) [H+] = 1 x 10 -3 then pH = 3 (acid) [H+] = 1 x 10 -10 then pH = 10 (base) It is based on a logarithmic scale which has a base power of 10. –A pH of 1 differs from a pH of 2 by a factor of 10.

3 How to calculate pH…. What is the pH of a solution with a [H + ] = 4.2 x 10 -10 M? pH= -log [H + ] = -log (4.2 x 10 -10 ) = 9.38 Enter into calculator like this or, Enter 4.2 x 10 -10 in calculator and hit log button, then remove (-) sign.

4 To find the [H + ] from pH [H + ] = 10 -pH Determine the [H + ] of a solution with a pH = 6.35. [H + ] = 10 -pH [H + ] = 10 -6.35 [H + ] = 4.47 x 10 -7 M Find the “log” button on your calculator Above this button it should say “10 x ” You can use the 2 nd key and this button to “un-log” the pH. But, remember to put the (-) sign on the pH first!!

5 pOH We can also express the [OH-] as pOH pOH = -log [OH-] pOH stands for the “power of the hydroxide ion.” pOH<7 is basic pOH=7 is neutral pOH>7 acidic

6 pH and pOH together pH + pOH =14 What is the pH of a solution which has a pOH of 11.2 ? Is this solution acidic or basic? pH + 11.2 = 14 pH = 2.8 So, the solution is acidic.

7 What is the pH of a solution with a [OH-] = 4.0 x 10 –11 M? Step 1: Find pOH pOH = -log[OH-] = -log (4.0 x 10 -11 ) = 10.40 Step 2: Find pH using pH + pOH = 14 pH + 10.40 = 14 pH = 3.60


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