Because measured pH values usually have no fundamental significance, when reporting pH values it is essential to describe how the values were obtained so that others can reproduce them. When this description is absent, others reproducing the work can usually will make differing assumptions or measuring operations, which can lead to different results.
We have seen this problem many times on this Forum. Suppose one reports that a reaction or separation is best accomplished by preparing a buffer by adding XX grams of component A and YY grams of component B.
There is no ambiguity in reproducing this buffer and it can be reproduced with great precision. An operational pH of this buffer can be measured and reported, but is this value more useful than the buffer recipe? Bill Tindall. Ph and weight. Tindall ,for me , it seems that you are missing some thing. Your balance may be very accurate in weighing, but still there is some thing hidden there when you try to connect weight of the salt to Ph meter.
Ph meter depends on the activity of hydrogen. But then how many? Even a small variation in weight may vary your hydrogen ion concentration if try to calculate it using avagadro s number. I thik this is what actually makes difference.
Basic solutions have high hydroxide concentrations and lower hydronium concentrations. In pure water, the concentration of hydronium ions equals that of hydroxide ions. Another equation can be used that relates the concentrations of hydronium and hydroxide concentrations.
The ionization of strong acids and strong bases in dilute aqueous solutions essentially go to completion. In aqueous solutions of strong acids and strong bases, the self-ionization of water only occurs to a small extent.
Since it only occurs to a small extent, the self-ionization of water is an insignificant source of hydronium and hydroxide ions. Knowing this, we can say in calculating hydronium concentration in an aqueous solution of a strong acid that the strong acid is the main source of hydronium ions.
We can also say that in calculating hydroxide concentration in an aqueous solution of a strong base that the strong base is the main source of hydroxide ions. Yet the actual ionic strength of a typical buffer is not zero.
This effect for your buffer is not likely to be large unless your buffer was fairly concentrated. Some tables provide a practical pK a value, which attempts to correct for this effect. So what i have to make sure of is my preparation and not to make a fairly concwntrated buffer. But how concwntrated are we takling about and where can i find the practical pka values? Sign up to join this community. The best answers are voted up and rise to the top.
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