In going back through my notes, it was suggested for my mountain water (pH 5.3) to add 0.5 teaspoons of sodium acetate/ liter of water and just a little bit of acid.  For 5 liters of room temp water, I added 2.5 teaspoons of sodium acetate and 0.5 mL acetic acid.  That didn't do much and added an additional 1.5 mL for a total of 2 mL acetic acid.  70 mL later, I'm not getting it much below 5.  I can go back out and do more lowering but I don't trust whatever is going on.  The plastic bucket is a brand new one and by using my diabetic 1 mL syringes (they weigh out accurately), I'm not quite sure what else is happening. 

Comments

Wed, 03/23/2011 - 04:04

pjdoney (not verified)

Karren, you had a "general measurement" amount of 1 mL acetic acid/ 1 L water + 1 tablespoon sodium acetate.  Obviously my 70 mL of acetic acid is way out of line!

If a buffer is supposed to keep a solution at its pH, am I fighting the buffer in trying to lower the pH?  The small print instructions  of the pH test strip box (pH 4.0 - 7.0) says:

Dip in - read while still moist. 

Immerse in weakly-buffered solutions until there is no further color change (1 - 10 mins).

I am thinking that I need to start over with fresh water and add my acetic acid and take its pH.  Once I have that correct reading, then add the sodium acetate.

Wed, 03/23/2011 - 15:11

Karren K. Brito

Are you using a fresh pH test strip for each reading?  They are one use strips.

Tell me what kind of acetic acid you are using. Does it  have an odor?

I don't use a tablespoon of acetate, maybe 1/2 teaspoon for a large bath, but my water is very different from yours, starts at pH 8.

Addition of acid lowers pH.

Addition of acetate raises pH.

OK, assuming you are getting good readings, start again  and just add a 1/4 tsp of sodium acetate, then the acid. 

Yes, you are getting into the buffer range where the addition of acid/acetate has less effect but none the less you can adjust the pH; it just means that the response is no longer linear.

You can look at the table on Google docs and see what others have used.

Wed, 03/23/2011 - 15:19

pjdoney (not verified)

Yes, I am using a fresh pH test strip each time.  I am using 5% White vinegar and yes, it does have a smell!  I added 2.5 teaspoons sodium acetate (which did raise my pH up to 5.8 or so initially) thinkingsomething along the lines of a recipe.  If you are making 5 batches, a lot of the ingredients you multiply the amount by 5. 

For my "chemical" water I have this as the basic recipe:

1 L water   2- 3 gr Glauber   1 gr A. Set    0.5 tsp sodium acetate

Which of these should I multiply by 5?  Water obviously, sodium acetate - nope!

I'll have to wait until after math tutoring in a bit to try it again.  Thanks!

Wed, 03/23/2011 - 15:50

Karren K. Brito

I use approx. 50% acetic acid  and 1mL/L usually does it, but since you are using vinegar, max. 5% acetic acid I would expect to need 10mL/L, or 50ml for 5L so 70 mL is not outrageous with the large amount of acetate added.  Maybe you just gave up too soon.