acid testing using a PH meter Question

[blackfin1]

I am in the process of making a blueberry wine and I have been acid testing using the PH meter. I followed the directions to the tee, and I noticed that when I added 1ml of sodium hydroxide I get to 8.9 or a bit higher on the ph meter. So I am assuming I multiply 1 to .75 and I end up with an acidity of .75. is this correct or am I doing something wrong. I am trying to get to an acidity of .6. SO, I added 1/4 tsp of bicarbonate to bring down the acid.

Can someone give me some input on this?

Thanks,
Sal

 

[ibglowin]

The end point for TA is 8.2 not 8.9

What was your sample size?

What is the normality of your NAOH?

What instructions did you follow?

 

[blackfin1]

Mike, I realize the end point should be 8.2 but I kept over shooting that number. I used the instructions on the site, "measuring acidity with PH meter.
My sample size was 10ml, I then added .5ml of hydroxide until the meter reached 8.2 but like I said I kept overshooting it. I added .5ml then .1 at a time and found that I put about .9 to 1.0ml of solution. SO I calculated .75 x 1 and of course got .75. Is that correct.

thanks,
Sal

 

[ibglowin]

What is the strength (Normality) of your NaOH?

 

[blackfin1]

Mike all I see is a .2 N what ever that means. Is this the strenght, I purchased at Midwest supplies. Does this change the formula or should I just purchase the .1N.

Thanks,

Sal

 

[ibglowin]

Yes,

That is the strength of your NaOH.

The formula for 10ML sample size is the amount of NaOH added times (0.75)

The problem with using 0.2N NaOH is it is so strong that you don't need to add very much and one drop can put you way over making it hard to get to 8.2

Your calculation is right, I just think your not getting a very accurate number as you keep going over 8.2 almost to 9.0

Go slow, one drop at a time and swirl well between drops. Sneak up on it slowly.

 

[blackfin1]

THank for the advice. I contacted Midwest supplies and complained about selling me the .2N NaOH and they told me to dilute it with distilled water by 1/2. So if I use 10ML I would have to use 5ml NaOh with 5Ml water and that should do it.

Heck, I just ordered two bottles of the .1N NaOH why put up with the hastle of diluting.

THanks Again,
Sal

 

[ibglowin]

Do not mess with diluting unless you have a very accurate ball flask and a graduated cylinder. Its cheap enough to just order some 0.1N. Keep the 0.2N on hand. You never know when you will need it.

 

[blackfin1]

Good Advice,
Thanks,
Sal