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Testing the Accuracy of pH Reagent Drops

August 13, 2011 | Alkaline Water
Today Susan, at Alkaline Water Plus, is going to compare pH drops with the results of pH tested with a calibrated pH meter. First of all, we want to ensure that the pH drops test accurately. Then secondly, since we sell two different sizes of the pH drops we are curious if both sizes are equally accurate.

Hypothesis

It is also predicted that the pH drops will be pretty accurate in their ability to show the pH of various levels of ionized water. The smaller bottle is predicted to be slightly more accurate than the larger bottle, because the larger bottle is less popular and probably sits on the shelf longer…therefore is not as fresh.
We will see what happens.

Conclusion

So, it looks like the smaller bottle was more accurate than the larger bottle of pH reagent drops. However, the larger bottle was not too far off. I noticed while doing this test that the color chart that comes with the bigger bottle was slightly different than the color chart that comes with the smaller bottle. The color that the water turned was about the same color with both bottles of pH reagent drops. It is misleading though the slight color differences in the charts. The color chart for the smaller bottle of pH reagent drops is definitely more accurate.

Chemical makeup of pH Reagent Drops:

Ethanol- This is another name for alcohol. It is found in alcoholic beverages and is used as a fuel and also as a solvent. In this case, pH reagent drops, it is used as a solvent.

Phenolphtalein- This is a chemical compound made up of carbon, hydrogen, and oxygen. It does not dissolve in water but will dissolve in alcohols. This compound when mixed in strongly acidic solutions turns orange. When it is mixed in acid or near neutral solutions it is colorless. When mixed in basic solutions it turns pink or fuchsia. When it is mixed in strongly basic solutions it is colorless.

Methyl Red- This is an indicator dye that turns red in acidic solutions. It is red below pH 4.4, yellow in pH above 6.2, and orange between 4.4 and 6.2 pH.

Bromothymol Blue- This is another indicator for weak acids and bases. It is yellow below 6.0 pH, blue above 7.6 pH, and green between 6.0 and 7.6 pH.

Note: Do not drink this solution or get in your eyes or on your skin. This solution is combustible so keep away from heat, flames, or fire.

pH Testing Paper

As you can deduce, the mixture of these three color indicators which change with the different pH levels is what causes the pH reagent drops to have their different colors. That is what the handy color chart that comes with the pH reagent drops is for, so you don’t have to figure out what color it should be based on the color indicators used.

The pH testing paper, on the other hand, probably only uses one of the above chemical pH indicators. My best guess is that it uses bromothymol blue because it goes from yellow to shades of green to shades of blue. The reason why you wouldn’t use the pH test paper for testing your water is because it only tests from a pH of 5.5 to 8.0. So above and below those pH levels it would not be able to accurately test the water. This is great, however, for testing saliva because it’s right in the range that the saliva should be. It also allows for a more precise color chart.

pH Meter

Some people wonder if they should get a pH meter or just rely on the drops. PH meters are usually as reliable as pH reagent drops, but they are expensive and require extra work to keep them calibrated and clean. As long as the pH drops are stored in room temperature and out of direct sunlight, they should be accurate for at least 2 years.

Definitions

Reagent:

-a substance or compound that is added to a system in order to bring about a chemical reaction or is added to see if a reaction occurs-wikipedia

-a substance that, because of the reactions it causes, is used in analysis and synthesis-dictionary.com

This video is included to demonstrate how cabbage juice can be used as a pH indicator. This is a great home-experiment that anyone could do.

pH:

-This stands for potential Hydrogen. This is the ability to attract hydrogen ions. Acidic molecules have a low ability to attract hydrogen ions and alkaline has a high ability to attract hydrogen ions. But in laments terms it is the measurement of acid or alkaline. Zero is very acidic, seven is neutral, and fourteen is very alkaline. Also this system of measurement is logarithmic, meaning that a pH of 6 is 10 times more acidic than 7(neutral) and a pH of 8 is 10 times more alkaline than 7.

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