Question

Recently, I've been told that similar pH shift (of about 0.5 units) was observed with 20 times NPS solution as well.

In case of NPS the authors provide the following recipe for the 20 times solution:
H2O 900 ml,
(NH4)2SO4 66 g,
KH2PO4 136 g,
Na2HPO4 142 g. with expected pH to be about 6.75.

Why is that?

Answer 1

The pH shift observed in the 20 times NPS solution is due to the presence of basic compounds in the solution.

Step-by-step explanation:

The pH shift observed in the 20 times NPS solution is due to the presence of (NH4)2SO4, KH2PO4, and Na2HPO4 in the solution. These compounds can act as either acids or bases when dissolved in water, and their presence can affect the overall pH of the solution.

In this case, the (NH4)2SO4, KH2PO4, and Na2HPO4 in the solution are all basic compounds. When dissolved in water, they release hydroxide ions (OH-) which increase the pH of the solution.

The combination of these basic compounds in the 20 times NPS solution results in a pH of about 6.75.