Saved Bookmarks
| 1. |
Explain pH scale and pH. |
|
Answer» Solution :pH Scale Hydronium ion concentration in molarity is more conveniently expressed on a logarithmic scale known as the pH scale. Defination of pH : pH of a solution is defined as the magnitude of the negative power to which 10 must be raised to express the activities of `H^+` ion (`a_H +`) concentration. Activities a have no unit `a_H + = [H^+] "mol L"^(-1)` This definition of pH is written as following. `pH=-LOG a_H +` ....(Eq.-i) `=-log [[H^+]/("mol L"^(-1))] [ THEREFORE a_H + = [H^+] / "mol L"^(-1)]` If mol `L^(-1)` = 1 So, pH=-log `[H^+]` ...(Eq.-ii) The pH scale is only for dilute solution in which pH method is suitable for solution whose concentration of `[H^+]` is less than 1 M. The CHANGE with temperature the variations in pH with temperature are so SMALL that we often ignore it. It should be noted that as the pH scale is logarithmic a change in pH by just one unit also means change in `[H^+]` by a factor of 10, e.g. `[H^+]=1xx10^(-2)` So, pH=2 and `[H^+]=1xx10^(-3)` =0.001 So, pH=3 |
|