Science Buddies: "Ask an Expert"

Hi!
I'm doing a project for ocean acidification for my science class, based on the "Swimming In Acid" experiment posted on this website. I haven't started yet and I expect to this weekend. However, I had a few questions to ask first. 1) how can I control for other variables/ error? 2) What is the point of calibration liquids in the material list? 3) to make my "control group" which is our current ocean ph of 8.1 could I just use distilled tap water and put vinegar in it till it hits a ph of 8.1?
thanks!

Moderator note: I moved your post from "Careers" to "Life, Earth, and Social Sciences" since the experts in this forum have more experience with this topic. Also, I removed your duplicate post. Thanks!

That's a good choice for a science project! Acidification of sea water could destroy the whole ecosystem by killing off the tiniest creatures which feed the next largest, and the next largest, and so on, up to the big fish.

In answer to your questions:

1. Controlling for other variables?
I don't know what 'other' variables you are referring to. As long as you keep your control variables the same for each run, then there should be no problem. The one variable that you can't control is the room temperature, but keeping all the jars in the same area at least exposes them all to the same temperature fluctuations. I would recommend getting a cheap digital thermometer and putting it with the jars and recording the temperature at several times during the day to find out how much it fluctuates. Cooler temperatures might slow down the dissolving of the shells in the acidic seawater. By reading the temperature every day at the same time, you will be able to say how it changed over the duration of the experiment.

2. The calibration solutions are guaranteed to have a specific pH and they are used to make sure your pH meter is reading correctly. The electrode that a pH meter uses to measure hydrogen ion concentration can vary over time, so it is necessary to check it to make sure the pH on the meter corresponds to the pH of the solution--and to do that, you need solutions that have been prepared so that their pH is accurately known.

3. Adjusting pH of control seawater to 8.1
Dissolve the InstantOcean salts in distilled water and measure the pH after all the crystals have dissolved. If it is above 8.1 add a small amount of vinegar and measure again until the pH comes down to 8.1. If it is below 8.1, add a bit more InstantOcean until it reaches 8.1.

If you have more questions, let me know. It is much better to ask than make an error that might ruin the experiment.

Sybee