pH and Salt test on pncSi
We have been wondering about the reason for discoloration for a while. This could be due to the pH of the solution or the concentration of the salts in the solution. To narrow down our vision on this, first we tried using solutions with different pH values ranging from 4 to 9 in room temperature. The solution was made using NaOH and HCl. The problem with this experiment was that the pH changed with time. This might be due to the deionised water used or evaporation or carbon dioxide absorption. Nothing conclusive could be derived out of this.
Next, we used NaCl solution (1M) in different buffers (pH=4, 7 & 10).
Buffer A (pH=4): Potassium hydrogen phthalate
Buffer B (pH=7): Disodium hydrogen phosphate + Potassium dihydrogen phosphate
Buffer C (pH=10): Sodium carbonate + Sodium bicarbonate
Over a period of 20 hours, the samples in the solution with pH=10 were completely discolored, whereas others didn’t. The discoloration started after 2 hours.
Further, the solution with the salt (1M NaCl) was observed to start discoloring at a later stage (after 4 hours) in comparison to the one w/o salt ( after 2 hours).
One more thing, the buffer with pH=10 has bicarbonate in it and we know that bicarbonate is bad for the membranes. So, the discoloration might be because of the pH which is controlled by the salt concentration (salt with hydrogen in it).
So, at high pH, salt actually helps keep the membranes stable? None of these results indicate that there is an issue with sodium bicarbonate – it really looks like pure pH to me. Please prove me wrong if you think there is something special about bicarbonate…
Are the pH 4 and pH 7 samples still being run to see how long they last?
What was the problem with the NaOH and HCl solutions? Why did the pH change over time? Is something growing or dissolving or something. DI is not the issue, unless you are at pH 7. Certainly a strong acid or base should have a stable pH. HOw much did the pH wander and in which direction?
Yes, thats what it looks like. I’ll try doing further experiments to prove that bicarbonate is not the actual culprit. We need to have a solution with high pH w/o using bicarbonate or any other salt w/o hydrogen in it.
We have tried doing this earlier but the pH changes with time. In case of the NaOH and HCl solutions, the pH drifted towards 6-7 after 8 hours.This is being repeated again and hope something conclusive comes out.
The samples are still there in the pH 4 and 7 and have not discolored after over a week.