I prepared a bottle of "50%" citric acid solution using a suggested method of filling a bottle halfway by volume then filling the rest with water. I filled a bottle (4 fl. oz) with citric acid powder to the top after weighing it empty, weighing it full, and subtracting the empty weight. The powder weighed 114 grams. I put 57 grams of citric acid powder back into the bottle, filled it with water, and dissolved the powder into the solution - the bottle remained full to the top.
I weighed it again and subtracted the empty bottle weight. The solution then weighed 147 grams, so subtracting the 57 g weight of the citric acid powder, the weight of the water that had filled the remaining space in the bottle was 90 grams, so this solution was approx. 38.8% citric acid by weight, quite a departure from 50%. I subtracted 57 from 90, and added 33 g of citric acid powder to the mix, then refilled the bottle and weighed it. After subtracting the bottle weight, it then weighed approx. 154 grams, or about 7 grams more than the 38.8% solution.
I also weighed equal volumes of citric acid powder and distilled water, and found that with the small grained powder I'm using (NOW brand) the powder weighs approx. 90% of what the same volume of water does. So mixing a batch by equal volumes will result in an approx. 47.4%, by weight, solution.
I intend to do further work testing activation with different percentage solutions and testing for the amounts of chlorine dioxide present over time in an activated solution in water. But that's for another day (week?).
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