Acid Rain and Aquatic Life

[s100126]

My son is working on the experiment to look at how acid rain affects aquatic plants. He set up the experiment according to the project outlined in Science Buddies. Initially, he added drops of vinegar to 3 of the containers of distilled water to make them more acidic. (0 drops in Container 1, 1 drop in Container 2, 2 drops in Container 3, and 3 drops in Container 4) But he was unable to measure any difference in the pH of the containers of water using the pH test strips we bought. We bought the Hydrion pH Indicator Strips that measure from 5.0 - 9.0, by the way.

Based on some of the comments from other students who tried this experiment, he added more vinegar to containers 2, 3, and 4. Specifically, he added 25 ml vinegar to Container 2, 50 ml to Container 3, and 100 ml to Container 4. This allowed him to measure a difference in the pH of the various containers. After that, he added 10 duckweek plants to each container and began observing how they fared.

One problem he has encountered is in measuring the pH of the distilled water (without any vinegar). It measures 5.0 on the test strips that we have. I googled "pH of distilled water" and Google said the pH should be 7. This is well within the range of the test strips we have, but it isn't measuring 7. Any ideas why that is the case?

Also, my son set up a second set of containers with the same conditions as the first 4 (1 L water and 0 ml, 25 ml, 50 ml, and 100 ml of vinegar added). Then he put a single 6 inch segment of hornwort plants in each of those. The experiment in Science Buddies calls for snails, but my son wanted to try something else. He has been making notes about the color and appearance of the hornwort in his lab notebook, and will measure it again at the end of the experiment. But other than that, do you have any ideas for how to quantify how the hornwort is doing under the experimental conditions?

[MadelineB]

Hello and welcome to Science Buddies!
One interesting way to "quantify" the effects on the hornwort would be to take photos of each hornwort. These photos would add some interest to your project display. The measurements might also provide a quantitative response, if the measurements change with time and the experimental conditions. You could also weigh each hornwort piece and compare the change in weight for each experimental condition.

You could also create a qualitative score, like 0 to 4, with 0 being no change and 4 being the worst effect. Be careful with these qualitative scores since it won't make sense to calculate a mean or median, since the "change" between say a score of 0 and a score of 1 won't be the same as the "change" between a score of 3 and a score of 4.

Here's a link to the Science Buddies project guide for measuring plant growth. This might give you more ideas:
https://www.sciencebuddies.org/science- ... ant-growth

Be sure to let us know how your experiment turns out and let us know if you have more questions!