Science Buddies: "Ask an Expert"

Hi there!

For a project of mine I need the alkalinity of water in ppm. I didn't think it to be too hard but when I needed to do the actual calculation my brain just stopped and now I pretty much stuck.

What I got is this:
A pH of 5.

That's it. I know alkalinity can be calculated using the pOH (which in this case would be 9) and I know it isn't that hard of a calculation but I am just stuck

Please help?

Hello and thank you for your question,

The measurement of pH and alkalinity can be correlated, but you cannot derive it just by knowing the pH. The pH of a solution is indicative of how strong an acid is (related to the concentration of H+ ions in solution), while the alkalinity is a measure of water's buffering capacity (the concentration of ions that resist pH changes, such as carbonate ions).

In order to measure the alkalinity, you can do a titration experiment in a lab that ultimately allows you to express alkalinity in terms of CaCO3 in mg/L, which can be converted to ppm. See the website below, it gives some helpful information on alkalinity and pH:

http://dnr.wi.gov/regulations/labcert/d ... enchem.pdf

Let us know if you will have to do further experiments (such as the titration experiment above), and we can help you on the setup.

Best of luck!