Calculating pH from number of drops of acid demand reagent?

[JamesW]

Acid demand to reduce pH to 7.5 — 1 drop

What is your pH sample size?

 

[JoyfulNoise]

What is your pH sample size?

For R-0005 the acid demand test is done on the pH side of the large comparator block so the water sample volume is 44mL

 

[JamesW]

For R-0005 the acid demand test is done on the pH side of the large comparator block so the water sample volume is 44mL

Is that what they are using?

 

[JoyfulNoise]

Is that what they are using?

I assume so.

The R-0015 acid demand drops use the midget comparator which is roughly 4.5mL sample size. Since the chart is the same no matter which test reagent you use, I’d assume the R-0015 is one tenth (roughly) the strength of the R-0005.

 

[SoDel]

Yes, 44 ml

 

[mgtfp]

So, using the 0015 acid demand test with the large comparator could improve the resolution of the method, but needed an adjustment of the table. With a factor of 10, that wouldn't be too hard.

 

[JamesW]

I assume so.

We need to know for sure.

If they are using a smaller volume, then that will throw off the results.

 

[mgtfp]

We need to know for sure.

If they are using a smaller volume, then that will throw off the results.

I guess that could be relatively easily checked, at least with the precision required here. Just check if 10 drops of 0015 in a 44ml sample result in the same pH change as 1 drop of 0005. Or 20 or 30 drops of 0014 with 2 or 3 drops of 0005.

Either with a pH-meter or by having two 44ml samples with R-0004 indicator next two each other (use the comparator to measure the right quantity and pour it into another tube or even just a glass like a 100ml wine tasting glass - ideally use two identical tubes/glasses). That allows direct comparison of the colour changes.

 

[SoDel]

Could we just dilute the R-0005 with a measured ratio of distilled water? Say 10:1, or even more?

 

[mgtfp]

I guess, for the method to actually get used by non-nerds it shouldn't involve diluting reagents. And nerds like us will probably just buy a pH-meter and move on to the fridge with the cold beverages.