Standardizing NaOH and HCL

I am not sure whay you mean?

Do you mean that if you take the pH of your solution it shoudl read 12 on teh pH meter if it is correct?

Yeah, you coudl do this, butin practice pH meters are not precise enough to do that. (Precision in chemisty is the ability of the technique to determine the EXACT value). Standardization with potassium hydrogen phthalate is the simplest method for accurate determinization of the true concentration of Sodium hydroxide.

the reason for this is that crystaline sodium hydroxide is highly hygroscopic. It picks up water from the air very easily. So it is difficult to determine if you really have the measured amount of NaOH.

Now with all that being said, as home winemakers you really do not need to be that accurate. The types of errors you will see maybe on the order of 0.05% TA or so and will really not make a huge difference in your wine.

Thanx for your reply Droopy.

That is what I meant as far as reading the concentration of NaOH with a pH meter. And the inaccuracy of such a procedure is what I suspected, though in practice, it does seem to be fairly feasible with a resolution of two decimals on a meter.

I don't make up solutions from crystals, namely because of what you stated about the hygroscopic properties, and partly because I don't trust my ability to weigh things that accurately. Instead, I purchase

And finally, I'm not a homewinemaker. Not much beyond that, but do produce over 10k gallons professionally.

regards,

clyde

p.s. I use to post to this group frequently, and at that time there were other professionals here including many that where as qualified as professionals, but our ISP dropped the usenet account. Google use to be a hassle to use, but seems be acting well now!?

I would look into standardization with KHP then. Basically yuou bake the kHP in a warm oven to dry it out. Weigh it out, take it up into solution and titrate it with your NaOH solution. Then you can calculate your NaOH concentration. It is a proceedure used in college chemistry classes so you should be able to find the exact proceedure on google.

The problem is your 1 N NaOH solution will go bad just as easily as your 0.1 N solution. As far as water to use, deionized water should be fine but you have to degas it before use. To degas all you need to do is boil the water for 5-10 min. Alternately you can vacuum degas it. You have to do that to get rid of any CO2 dissolved in the water. (the CO2 is what degrades NaOH, they combine to form bicarbonates).

I can't remember off the top of my head but there is some other thing - potassium phtalate maybe? - that's used to standardize AFAIK. Iverson talks about it in his book.

BUT - why wouldn't this work - make a solution of say 10g TA in 1L distilled water and titrate that. The error from 10g/L TA should give the adjustment to the measured TA value in wine with this solution, no? Or does it matter that one solution is water and the other wine?

Pp

The following procedure published by vinquiry, using HCL, is the one I've been using for years;

For the few months that it resides on my shelf, 1N NaOH is plenty stable. I always standardize after making up the various concentrations, so I'm quite certain of this. Yesterday I ran across data on the net for the pH levels of the various concentrations, and they seemed to be predictable with the readings I was getting from the above procedures. Just made me wonder.

And, for he record, this concentration of NaOH (0.01) is being used for an A/O test, so the results are a bit more important to me than those for TA.

thanx again for your comments,

clyde

Potassium hydrogen phthalate is what you're thinking of. The reasons it's used as an acid standard are: (1) It has a very low % of reactive (titrable) hydrogen, (2) It's easily prepared in high purity, (3) It's very stable.

Using tartaric acid as a standard for determining the titer of your NaOH is probably good enough - at least for TA measurements. It won't give you "gnat's ass" accuracy, but you really don't need that for most practical winemaking purposes.

Tom S

Mainly because that isn't a very precise method. In fact, it's barely in the ballpark.

I'd guess that 0.05N and 0.015N NaOH solutions are pretty close to that same pH, so the slope of the pH meter's response between them would be quite shallow, despite the swing being a ±50% deviation from the norm.

Your pH meter would have to be a lot more sensitive, displaying accurately and at a much higher resolution, _repeatably and constantly_, than it is capable of doing to be useful in this fashion.

Tom S

Hey,

does nyone but me find that their potassium hydrogen phthalate gets pretty moldy pretty quickly? I've started storing it in the fridge--how do other people store theirs?

Thanks!

-- Dave

Thanx Droopy; TomS,

I supsected as much. My readings must have just been lucky.... I didn't really check many different concentrations.

clyde

Baking at ~250°F for an hour or so (to drive off water and kill any mold spores) and keeping it in a tightly sealed glass bottle should stop that problem.

Tom S

No, no, sorry. I mean the *solution* gets cloudy pretty quickly, not the powder.

Dave

Yeah standardization with HCl would work, but it is far from analytical in the sense of being highly precise.

Moldy?

That is weird. I have always seenit stored on the shelf and have never seen any go bad.

I have seen bottles of this stuff sitting around on shelves for upwards of 30 years (not personally seen, but have seen bottles that old).

If yours is gettng moldy, you should store it in a drier location....of find a different supplier.

KHP is not normally used in liquid form as a standard - probably at least partially for that very reason, but mainly because the titer will shift somewhat with age/use, thereby reducing its value as a precise standard.

Best to use the dry powder for standardizing.

Tom S