Diluting Question?

Please help.
I need voor making a Stopbad a 28% acetic acid. I can only get a 25% solution. When I use the criss-cross method I get a minus 3? See below;

25..................................28

..................28..................

0...................................-3

And now I'am confused what to do.

If I need 120ml of 28% acetic acid what will be the the amount when I use the 25% diluted solution?
I divide the 120 by 25 en add this with 28?
That makes (120/25)*28=134.4ml.
Is that the right way to do??

Thanks

That seems right to me.

The "important" thing is to get the same amount of CH3COOH - acetic acid.

On the other hand I doubt the difference between 120ml 28% acetic acid and 120ml 25% acetic acid will have any practical consequence.

Whenever I use a "real" stop bath, I put half a 25g bag of citric acid in about a liter of water. Close enough for practical use...

If you have 25% instead of 28% then you amount you need to use is multiplied by 28/25 = 1.12 i.e. 12% more than you would normally use.

However, as Ole said, I'm sure it would make no difference.


Steve.

Ole and Steve,
Thanks for your quick reply.