Australia's Science Forum

The biology teachers want to try the reverse of the normal phenolph agar prac by using agar made with HCl and the students putting NaOH to look at surface area.

Has anyone done it this way? I was just thinking of using the same amount of HCl as I would normally use of NaOH.

Worth a try, but will it set?

That was my thought smiley. The HCl may denature the agar and not allow it to set?!

Hi All
Jazz helped me out with a recipe. Make up agar, add the phenolphthalein as usual. If it is pink add a few drops of HCl until clear.

I've tried this and it worked fine, even with the addition of a few drops of acid, all has set properly.

Thanks Jazz!