#2 - Checking the quality of distilled water
Started: 22nd July 2011
Using Universal Indicator to check water pH
As an exercise, I decided to test the quality of my distilled water (both from my home-made apparatus and from the commercial water distiller) by checking the pH of the output water.
The Universal Indicator will change colour depending on the solutions pH value, like this:
The Universal Indicator will change colour depending on the solutions pH value, like this:
I decided to test three samples of water; domestic tap water, distilled water from my home-made apparatus, and the distilled water from my new commercial water distiller; the results are shown below:
Sample 5 (far right) is domestic tap water. The green colour indicates a pH value of around 7 - Neutral which is what I'd expected.
Sample 1 is a sample of water from the commercial water distiller. It's showing a pH value in the range 5 to 6; slightly acidic which was supprising.
Sample 4 is a sample of water from the home made distiller, and it's showing a pH value in the range 4 to 5; even more acidic.
Since all the equipment was clean, I was fairly sure no contamination had managed to get into anything, and I’d washed each test tube out in a sample of the water before re-filling the tube and adding the Universal Indicator; just to make sure.
The only thing I could think of, is that something in the atmosphere had been absorbed by the water during the distillation process; Carbon Dioxide.
Another test tube was filled with each sample of distilled water, and Universal Indicator added; again, the same acidic pH values were shown. However, these tubes were gently boiled over a spirit burner flame. Slowly, as the Carbon Dioxide was boiled off from the solution, the pH value started to move back towards neutral.
Sample 2 shows the boiled sample of water from the commercial distiller, and sample 3 shows the boiled sample from home-made apparatus. Both are now showing closer to netrul and if I’d carried on with the boiling process both samples would have eventually read pH 7 once all the Carbon Dioxide have been boiled off.
During the distillation process, the following occurred:
H20 + C02 = H2CO3 – This is Carbonic acid
Carbon Dioxide is soluble in water, and must have been dissolved as the water vapour condensed back into water.
I’ve now filled a small stoppered reagent bottle with boiled distilled water and labelled it as pH7 in case I require it in my experiments.
Sample 1 is a sample of water from the commercial water distiller. It's showing a pH value in the range 5 to 6; slightly acidic which was supprising.
Sample 4 is a sample of water from the home made distiller, and it's showing a pH value in the range 4 to 5; even more acidic.
Since all the equipment was clean, I was fairly sure no contamination had managed to get into anything, and I’d washed each test tube out in a sample of the water before re-filling the tube and adding the Universal Indicator; just to make sure.
The only thing I could think of, is that something in the atmosphere had been absorbed by the water during the distillation process; Carbon Dioxide.
Another test tube was filled with each sample of distilled water, and Universal Indicator added; again, the same acidic pH values were shown. However, these tubes were gently boiled over a spirit burner flame. Slowly, as the Carbon Dioxide was boiled off from the solution, the pH value started to move back towards neutral.
Sample 2 shows the boiled sample of water from the commercial distiller, and sample 3 shows the boiled sample from home-made apparatus. Both are now showing closer to netrul and if I’d carried on with the boiling process both samples would have eventually read pH 7 once all the Carbon Dioxide have been boiled off.
During the distillation process, the following occurred:
H20 + C02 = H2CO3 – This is Carbonic acid
Carbon Dioxide is soluble in water, and must have been dissolved as the water vapour condensed back into water.
I’ve now filled a small stoppered reagent bottle with boiled distilled water and labelled it as pH7 in case I require it in my experiments.