Co-Authored by James W. Webb* and Otis Rothenberger*
*Department of Chemistry, Illinois State University, Normal, IL 61790
If you walk through the water aisle of a grocery store, you will find a plethora of specialized waters – e.g. smart water, infused water, flavored water, and alkaline water. In this article, we will look at the properties of alkaline water. Basically (yikes!), alkaline water has an elevated pH (generally greater than 9). There are all sorts of beneficial claims of alkaline water such as improving metabolism, increasing energy, and slowing ageing1, but none of these claims have been proven2. Alkaline water is manufactured by forming a buffer solution with an alkaline pH. The pH can be increased by electrolysis or by adding basic salts such as K2HPO4. Neutral salts are also added for taste. In electrolysis, the hydroxyl ion is formed at the cathode: 2H2O(l) +2e- → H2(g) + OH-.
What happens in the stomach when alkaline water is consumed? In his 2022 blog post, Can Alkaline Water Change Body pH?,3 Tom Kuntzleman showed that various brands of alkaline water are almost immediately acidified when added to stomach acid. Another way to show the effect of adding acid to alkaline water is to do a pH titration. Normally, a pH titration would be done with a strong acid, but in this demonstration, we will add vinegar drop wise to the alkaline water sample. Vinegar contains 5% acetic acid which is a weak acid. The titration will help us to compare the buffer capacities of the water samples. The buffer capacity is defined as the ability of the solution to resist changes in pH4.
alkaline water
12 ounce samples of alkaline water
Universal Indicator
250 mL beakers
pH strips or pH meter
12 ounce plastic cups
The demonstration is set up by adding 250 mL of each water sample to a 12 ounce cup followed by 15 drops of Universal Indicator (U.I.). The brands of alkaline water and their properties are shown in Table I. Alternatively, teachers may choose to have small groups complete the investigation and share their results with the class.
Table 1: Properties of the water samples tested
| Water | Description | Ingredients |
Initial pH (pH meter) |
| Essentia |
purified by reverse osmosis |
|
9.8 |
| Hannaford | local brand |
|
9.9 |
| Smart Water |
With antioxidant vapor distilled water |
|
10.2 |
| Well Water | from author's (JWW) well | 7.8 |
Figure 1. pH after adding vinegar drop wise to water samples
The initial pH of the alkaline waters shows that they have pH’s between 9 and 10 as advertised on the bottles. The well water has a slightly basic pH due to the natural bicarbonate present in the water.
Figure 1 shows the change in pH as vinegar is added drop wise to each sample. Clearly, not all alkaline water samples are the same. The Smart Water brand gives up its buffer capacity easily after two drops of vinegar, and the local brand gives up its buffer capacity after the third drop of vinegar.
Why does it take about four drops of vinegar to acidify the Essentia brand? The ingredients listed in Table 1 indicate that this brand contains NaHCO3 and K2HPO4. Both are basic salts; however, K2HPO4 is more basic requiring more acid to neutralize. Tom Kuntzleman discussed this difference in his article3.
Why does the well water require so much vinegar to acidify it? In fact, it required about 20 drops of vinegar to bring its pH to 4. As noted above, this well water sample contains natural bicarbonate compared to the other brands that have added bicarbonate. Clearly, the well water has a much higher buffer capacity.
Conclusion
This activity is a good opportunity to test products using readily available materials. It shows that not all alkaline waters are the same. However, why would you buy alkaline water in the first place, considering its questionable value, and that a 12 oz serving cost between 50 and 90 cents.
Suggestions for further study
- Test other alkaline water brands that may be locally available.
- Test municipally treated water and well water if it is available.
- If Universal Indicator is not available (it can be purchased from Amazon), perform the test with the red cabbage indicator5.
- Try making water with a pH of 9 using a basic salt, such as sodium bicarbonate (NaHCO3, also known as baking powder) or sodium carbonate (Na2CO3, also known as washing soda). Explain any differences.
Citations
- https://www.webmd.com/diet/what-is-alkaline-water
- https://www.mcgill.ca/oss/article/controversial-science-news-quackery/alkaline-water-nonsense
- Kuntzleman, Tom, Can Alkaline Water Change Body pH?, May 5, 2022.
- https://en.wikipedia.org/wiki/Buffer_solution
- Shakhashiri, B.Z. Chemical Demonstrations, Volume 3; UW press, 2011; 52.
This demonstration / activity requires limited time to set up materials.
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