swmcl
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Hi,
This should be a fairly easy one for our chemists ...
I'm using a concentrate of 200g sodium carbonate per litre of distilled water as my stock solution.
When I add 0.25ml of this stock to 300ml of distilled water I get a pH of 10.75. Please see the following results:
0.25ml --> 10.75
0.5ml --> 10.87
0.75ml --> 10.94
1ml --> 10.99
1.25ml --> 11.00
1.5ml --> 11.03
1.75ml --> 11.06
2.0ml --> 11.06
3.0ml --> 11.06
My pH meter is a Chinese meter that I am fairly sure is drifting with ambient temperature. The gain is very variable. I do have buffer solutions to calibrate the meter just before I do the testing.
The distilled water started with a pH of around 7.2 and it dropped to around 5.6 pr 5.7 or so as I stirred the pH tester probe in the water. This is expected as the water is dissolving CO2 into carbonic acid.
My question is whether these results are representative to the process. Do they look right ? Is the graph that would be created atypical of this test ?
My subsidiary question would be, is there a carbonate that would produce a lower pH at a given concentration that would be commonly used in photography ? For example, say at 1ml per 100ml I'm getting a pH of 11.06 here, what carbonate would given me a pH of say 10.3 ?? I'm assuming potassium carbonate would give an even higher pH than sodium carbonate and am thinking there might be another product again to give me a lower pH.
Cheers,
Steve
This should be a fairly easy one for our chemists ...
I'm using a concentrate of 200g sodium carbonate per litre of distilled water as my stock solution.
When I add 0.25ml of this stock to 300ml of distilled water I get a pH of 10.75. Please see the following results:
0.25ml --> 10.75
0.5ml --> 10.87
0.75ml --> 10.94
1ml --> 10.99
1.25ml --> 11.00
1.5ml --> 11.03
1.75ml --> 11.06
2.0ml --> 11.06
3.0ml --> 11.06
My pH meter is a Chinese meter that I am fairly sure is drifting with ambient temperature. The gain is very variable. I do have buffer solutions to calibrate the meter just before I do the testing.
The distilled water started with a pH of around 7.2 and it dropped to around 5.6 pr 5.7 or so as I stirred the pH tester probe in the water. This is expected as the water is dissolving CO2 into carbonic acid.
My question is whether these results are representative to the process. Do they look right ? Is the graph that would be created atypical of this test ?
My subsidiary question would be, is there a carbonate that would produce a lower pH at a given concentration that would be commonly used in photography ? For example, say at 1ml per 100ml I'm getting a pH of 11.06 here, what carbonate would given me a pH of say 10.3 ?? I'm assuming potassium carbonate would give an even higher pH than sodium carbonate and am thinking there might be another product again to give me a lower pH.
Cheers,
Steve
