Science Buddies: "Ask an Expert"

Hello,

Could you please explain why in the 'Swimming in Acid" test procedures section where you add the drops of vinegar to the seawater to adjust the pH, the instructions then say to ' Wait for a few minutes and then measure the pH of the solution with the pH meter'? Why is it necessary to wait a few minutes? Is there a scientific explanation for this? Is it to allow time for the pH to metabolize into carbon dioxide?

Also, a judge asked me about Acid Base Equilibrium and how it applies to this project, but I didn't know the answer. Would you be able to explain Acid Base Equilibrium to me in case I get asked this question again?

Thank you for your help.

Hi,

Acid-base equilibria are pretty complicated, especially in a situation like seawater where there are multiple components (carbonate, bicarbonate, calcium, magnesium, etc.). I found one source that explains it in a nontechnical way that should help you to understand what’s going on: http://www.google.com/url?sa=t&rct=j&q= ... Wc&cad=rja

As to scientifically why the instructions on Swimming in Acid say to wait after adding acetic acid [vinegar] before taking the pH measurement--the answer is that an equilibrium reaction such as this does take a finite amount of time to come to its final point. If you measure the pH before this happens then the reading won’t be accurate.

If you are curious you could test this by putting the pH probe in your seawater, adding the vinegar and then recording the pH every 30 seconds or so until it stops changing. Then you will know exactly how long it takes for the equilibrium to be established.

I hope this helps and I’m glad you were curious enough to want to know the answer for next time. If you have further questions, just ask us.

Scibee

I think it would be very beneficial for your own understanding and even for your final experiment to do as Scibee suggested regarding taking pH measurements every 30 seconds after adding the vinegar. This way you can further understand your experiment and allow you to speak in depth if you are asked another question by a judge. It can also help others understand the importance of reaction times and how it contributes to your experiment in particular. It will not take very long and it would help make a more thorough experiment!

Lily