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For quite a while, I have been doing pH adjustment with baking powder because using baking powder requires little precision to get bubble juice into the desired pH range.

On SBF, the Soap Bubble Fanciers Yahoo Group, Megan reported some problems getting pH adjusted with baking soda and citric acid. When I did some follow-up measurments, I was puzzled. My results were nothing like Megan's BUT they were also nothing like what I expected.

Theory tells us that 1.3 parts baking soda to 1 part citric acid should yield a complete reaction that will be more or less pH neutral (not quite because the C02 can dissolve in water and lower the pH). Megan had to add much more baking soda than predicted to get the pH over 7. I. I found the same thing.

The 2:1 baking soda:citric acid ratio that we recomended until now will yield a much too acidic mix using the baking soda and citric acid that I have now.

There are a few questions that need to be resolved: is the problem due to some sort of degradation of the baking soda or perhaps impurities. When the 2:1 ratio was suggested, this was before it was understood that pH adjustment was the main reason for the benefit, and we were all following the recommendation of Alan McKay who had much success with that ratio -- and most of us found that it worked well for us, too. I didn't have a pH meter at the time.

So, I don't know if my current strange results are due to my baking soda being different than it was.

Another interesting thing is that I have noticed that Dawn Pro's pH measures lower (about 8.4) when measured pure than when diluted 25:1 with distilled water (whose pH was about 5.5). The distilled water/detergent mix measured 9.0! I am no chemist and hope that one will explain why the pH of the detergent/water mix goes up when water with a low pH is added to the detergent.

Here is a little test that I am hoping a number of people will perform so that we can get a sense of how general my results are. I will share my results once we get some more data.

Here is the worksheet and methodology.

Early July Exploration

The initial impetus for this re-exploration of baking soda/citric acid ratios was based on a posting to SBF, the Soap Bubble Fanciers Yahoo Group by Megan. She noted a few anomalies when mixing a batch of juice. Around the same time, someone else was reporting very different anomalies. I figured it was time to re-explore -- as the last time that I did pH studies was a few years ago -- mostly before we shifted to the dilute solution that we use now. (As an aside, those dilute solutions are primarily possible because of the pH adjustments -- there have been numerous confirmations that without the pH adjustments, bubble juice based on Dawn and its relatives don't work nearly as well in our favored dilution range).

Since Megan noticed a much larger than expected pH drop, we set up the following experiment to see if our initial 2:1 baking soda:citric acid recommendation (which we picked up from legend Alan McKay) was the wrong ratio. Perhaps more baking soda was needed since the pH drop was so much larger than expected.

This test was intended to see what ratio was needed to achieve a final pH in the mid 7's.

Rick Findley and I performed these tests.

What we found was that when using baking soda and citric acid together, you get a much higher (but, in retrospect, understandable) pH drop than expected. However, that low pH is temporary. It is due to excess carbon dioxide most of which does not stay in solution. It takes a lot more baking soda than you would think to counteract that acidity. If you add baking soda to neutralize the acidity while the solution is still supersaturated, you end up raising the alkalinity too much -- and once the excess C02 has outgassed (which can take anywhere from 1 to several days depeneding on the ambient temperature) you end up with a much higher pH than desired.

We did a follow-up with a 4:1 baking soda/citric acid ratio. What we found was that while the pH immediately after mixing was below 7 -- the pH would climb to close to 9 over a couple of days. In cool temperatures it took a few days. In hot temperatures, it happened over night.

One surprise was the discovery that a 25:1 water:dawn solution with either tap or distilled water has a pH of 9.0 which surprised us since undiluted Dawn has a pH of about 8.4 and distilled water has a pH of 5.5.

MORE TO COME! After these tests, I went on to perform some tests that are still ongoing. The short take away of those tests -- which I will publish when they are done -- seems to be this: C02 by itself can drop the pH well below 6 (using nothing but water, compressed C02, and detergent) but as the excess C02 comes out of solution (a process that can take more than a week), the pH rises and stabilizes at a pH higher than our desired target. Baking powder seems to result in a much more stable pH in the desired target as long as you add it once all the ingredients are present. My speculation is either that baking powder is not designed to be pH-neutral or that the dry acid reacts so slowly with the water and baking soda (found in the baking powder) that you end up with a somewhat buffered solution. It is possible that not all baking powder will behave this way. More study is needed. 2:1 baking soda:citric acid gets things into the target zone for several days, but the pH appears to stabilize at a pH higher than our preferred range. We will try the class 1.3:1 to see if that will result in a better pH. Given the similarity between 2:1 bs/ca and simple carbonation in terms of the final pH -- our suspicion is that 2:1 is a fairly neutral ratio and that 1.3:1 (the predicted neutral ratio) may be slightly acid heavy which might result in a better long-term pH. But, we have not tested that yet.

The other very important pH-related study that needs to be done is whether the pH is the only important factor or if there is a difference in performance between juice that use different methods of adjustment.

PH EXPLORATION WORKSHEET (early july)

Perform with both tap water and also distilled water.

Water type:

Water pH:

Detergent type:

Detergent pH (optional):

Baking Soda brand:

When opened:

Detergent type: Measure into your container:

250 grams (ml) water

measured pH: add and stir till mixed

10 ml detergent

measured pH of mixture:

IMPORTANT! Measurement note: all powders must be packed/tamped and leveled.

Make sure to stir until the powder is completely dissolved after each addition!

add 1/4 tsp citric acid. measured pH:

add 1/2 tsp baking soda. measured pH:

add 1/2 tsp baking soda. measured pH:

add 1/2 tsp baking soda. measured pH:

add 1/2 tsp baking soda. measured pH:

add 1/2 tsp baking soda. measured pH:

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