The pH scale is a standard measurement system used to indicate acidity with lower numbers and basicity with higher numbers. Pure water has a pH of 7, which is what we tend to think of as “neutral”.
—Log Proton Concentration [pH]
|Substance||[H+] concentration||scientific notation||pH|
|lemon juice||0.01 mol/L||1x10–2||2|
|black coffee||0.00001 mol/L||1x10–5||5|
|pure H2O||0.0000001 mol/L||1x10–7||7|
|human blood||0.00000004 mol/L||1x10–7.4||7.4|
|sea water||0.00000001 mol/L||1x10–8||8|
|baking soda||0.000000000316227766 mol/L||1x10–9.5||9.5|
[H+] from pH
What if you know the pH of a substance, and want to know how that translates to proton concentration?
Knowing this, you can simply plug in your pH as your Y value, allowing X to represent your proton concentration.
Using pure water (pH=7), let’s first take the log positive by shifting the negative to the other side of the equation:
Having done, that, we can simply follow the “if log X = Y, then X = 10Y” logic:
Thus, having run the calculation in reverse, we know that if pure water has a pH of 7, then its proton concentration must be 1x10-7 M.
Another way to calculate pH, which is especially useful for buffer solutions: