Home water testing (alkalinity)

[dstar26t]

Is there an accurate way to titrate a sample of my house water with an acid to a certain endpoint using a pH meter in order to calculate alkalinity? My Ward Labs reports have varied from 33-54ppm. I'm trying to minimize the amount of acid used in the sparge water so measuring the alkalinity at home would be nice. I may have everything I need at home already so I'm trying to avoid buying a test kit like Lamotte's.

I found this procedure but I have Lactic and Phosphoric acids already. Is there a way to modify that procedure for the different acids? I remember reading that Ward uses 4.4 pH as the endpoint. Should I?

While we're at it, is there a procedure to test for hardness, Cl and SO4 at home as well that is full proof for color blindness?

Nate

 

[mabrungard]

Sure, if you have a pH meter and can measure the fine additions of acid, you certainly can use that procedure or one from USGS to calculate alkalinity. The question on end point is nebulous. There are sources that suggest end points between 4.3 and 4.5. Using 4.4 seems a reasonable compromise to me.

Since many home tests are colormetric, I don't know what to tell you with regard to color-blindness. AJ has experience with this and could probably guide you better than me.

 

[dstar26t]

Thanks Martin.

I just remembered I have some Sulfuric acid at home already but not Sodium Carbonate. Can I store Sodium Carbonate in water and measure the gravity to get the concentration so I don't have to bake it and cool it in a desiccator? Kind of like how I store my CaCl2 now?

Is a 1mL Sibata Mohr Class A pipette fine enough?

 

[ajdelange]

Theoretically any strong or relatively (to carbonic) acid can be used. It is simply a matter of calibrating it against CaCO3 but for accuracy and convenience it is hard to beat 0.1 N sulfuric acid sold specifically for this purpose by Hach and others. Let them worry the metrology stuff.

As for hardness tests for the color blind - I have always found the alkalinity test color change easier to see than the hardness tests but it will depend on your flavor of color blindness. There are hardness tests which detect color change with a spectrophotometer.

Sulfate is checked by precipitating barium sulfate with the scattering measured by nephelometer or photometer. LaMotte (I think) has a test in which a Secci disk is lowered into the test tube.

 

[dstar26t]

Thanks AJ

Ha, looks like I can make Sodium Carbonate from Baking Soda.
Any thoughts on making a stock solution in water and measuring the concentration by specific gravity?

Pretty neat that I can possibly measure the alkalinity of my water at home with materials and tools I already have for brewing.

 

[ajdelange]

Yes, you could make sodium carbonate from sodium bicarbonate but it would require the use of pure lye which is ver difficult to measure out because it is deliquescent. I guess you could rely on pH. At pH > 12.38 more than 99% of the bicarb would have converted to carbonate. Measurement of high pH values is complicated by 'sodium error' and you must know how your electrode responds to this in order to correct for it.

Then you would have to measure the density of the resultant solution and compare to a table which you can probably find somewhere on the Internet.

So why not just standardize with bicarbonate rather than bringing lye and density measurement into it? It's pretty easy to compute the alkalinity of a mole (84g) of sodium bicarbonate to any end point pH. I'm not going to do that on my cell phone but could show you how to do it in a day or two or you could figure it out fr the Palmer book (use the bicarbonate charge curve).

 

[dstar26t]

Don't worry about it AJ. I had to place an order at cynmar and added some Sodium Carbonate to it.

 

[ajdelange]

Cynmar has 0.1 N H2SO4 for $10.47/L. Add this to 100 ml of your water until end point pH is reached. Alkalinity is the number of ml you used. No need to standardize. Cynmar (or really their supplier) does this for you.

 

[dstar26t]

I like the sound of that. Thanks!

Why does the procedure I linked in the first post have you standardize a .02N Solution of H2SO4 then? Less likely to overshoot?

 

[ajdelange]

0.1 N acid is handy because if you use it to test an 0.1 L sample the alkalinity, in mEq/L, is simply the number of cc used. You read the buret and you are finished. This is great in most of the rest of the world as they measure alkalinity in mEq/L. Here in the States you have to multiply by 50 to get ppm as CaCO3.

The size of the sample and the strength of the acid are arbitrary. If the water's alkalinity is 2 mEq/L (50 ppm as CaCO3) each liter will contain 2 mEq alkalinity and require 2 mEq acid to 'neutralize'. An 0.1 L sample would require 0.2 mEq and it doesn't matter whether that comes from 2 mL of 0.1N acid or 10 mL of 0.02 N acid. Insert either 2 and 0.1 or 10 and 0.02 into the formula in the procedure to which you linked and you will get the same answer.

Clearly the more dilute acid requires more acid volume and will give you better 'precision' but not better accuracy unless you use a more accurate buret.

 

[dstar26t]

Just a heads up for anyone who wants to order acids like this from Cynmar...they require a business address and paperwork showing your business's Federal Employer Identification Number for shipping. They wouldn't ship to my house.

 

[ajdelange]

That's your government protecting you from terrorists. Don't you feel safer now you know? Cynmar wouldn't sell me sodium bicarbonate without all that paperwork. They used to be a good friend to brewers.

AFAIK Hach still sells this stuff (it's 0.1 N for heavens sake!) to anyone. I just got a liter of it recently but then I've had an account with them for years which, I believe, they may think is a commercial account tied to my previous employer. Can't hurt to try though. Just go to the website and order the stuff.

 

[stoneBriar]

This thread sparked my interest so I tried a titration. I had some certified N/50 H2SO4 (.02N). That 50 should seem familiar as it's what we use to convert equivalents to ppm. I calibrated my pH meter, weighed out 100g of water and titrated to pH 4.3. That took 4.15 mL. If I'm mathin' right that's 41.5 Alkalinity as CaCO3 yes? Titration graph below. This didn't take much time at all. I may start doing this on brew day.

 

[ajdelange]

Yep.
(4.15 mL) (N/50)*(1000/100) = 0.83 mEq/L
(4.15 mL) (N/50)*(1000/100)*50 = 41.5 ppm as CaCO3

Compare the shape of the curve to the charge on carbo graph (turned on its side) in Palmer's book if you have it.

Nit, of which you are probably aware: normalcy is equivalents per liter so the sample is measured by volume. For tap water the difference between 100 g of water and 100 mL of water is negligable.

 

[ajdelange]

PS: you might want to look at
http://www.wetnewf.org/pdfs/measuring-alkalinity.html
for some further details on alkalinity measurement.

 

[stoneBriar]

Yep.
(4.15 mL) (N/50)*(1000/100) = 2.075 mEq/L
(4.15 mL) (N/50)*(1000/100)*50 = 41.5 ppm as CaCO3

Compare the shape of the curve to the charge on carbo graph (turned on its side) in Palmer's book if you have it.

Nit, of which you are probably aware: normalcy is equivalents per liter so the sample is measured by volume. For tap water the difference between 100 g of water and 100 mL of water is negligable.

Not sure I understand how you got 2.075; can you explain that? Based on my math 4.15 mL of .02N acid is 0.083 mmoles of protons. Doesn't that mean that I added 0.83 mEq of acid per L? Was that just a typo?

Yes I to the second part about volumes and weight. We have a LOT of gear for working with small volumes (10-100µL) but in the ~100mL range I had to chose between a crappy beaker and a 4 decimal place balance. I should have grabbed the temp of the water and compensated for the density

 

[ajdelange]

Not sure I understand how you got 2.075; can you explain that?

Mental prestidigitation! I divided by .02 when I should have multiplied by 0.02. Fixed it in the post.

 

[dstar26t]

So for Hardness testing, how does the following procedure look:

Take a 100mL room temp water sample and buffer with NaOH to 10.1 pH

Add Eriochrome Black-T indicator (how much?). Sample will turn Red.

Titrate with 0.01 M EDTA until sample turns blue

#mL of EDTA used x 10 = Total Hardness.

To get permanent hardness, can I just test a boiled water sample?

 

[dstar26t]

Any thoughts on my previous post?

 

[ajdelange]

So for Hardness testing, how does the following procedure look:

This is indeed the drift of the complexometric test for hardness but there are a few twists.

Take a 100mL room temp water sample and buffer with NaOH to 10.1 pH

Add Eriochrome Black-T indicator (how much?). Sample will turn Red.

The buffer will turn red if there is magnesium present. For this reason the buffer contains complexometrically neutral magnesium/EDTA complex. When added to sample calcium in it preferentially complexes with EDTA releasing the Mg++ which complexes with the indicator to give the red color. As additional EDTA is added during the titration any extra calcium is picked up followed by the Mg++ and then when all the Mg++ is chelated the solution turns blue. So just plain old NaOH isn't a very good buffer for this purpose (it isn't much of a buffer anyway - it's a strong base). Standard Methods for the Analysis of Water and Waste Water give recipes for suitable buffers and you can find them on the web as well.

Titrate with 0.01 M EDTA until sample turns blue

For decent accuracy the EDTA solution must be standardized against a standard strength calcium solution. You can, of course, forgo standardization at the cost of the implied improvement in accuracy.

#mL of EDTA used x 10 = Total Hardness.

Though EDTA is hexadentate one mole of it only apparently chelates 1 mol (2mEq) of calcium or magnesium. Thus a 0.01 M solution is 0.02 N and a mL of it chelates 0.02 mEq. Thus each mL used in the titration of 0.1 L of sample indicates the presence of 0.02/0.1 = 0.2 mEq or 10 ppm as CaCO3 so yes, it looks as if 10 is the right multiplier.

As a consequence of all the above and because there are better indicators that Eriochrome Black T and because we usually want to know not only total hardness but calcium and magnesium hardness individually I think it would be a great deal simpler to buy a kit and let the manufacturer worry about the standardization, the buffer, the indicator(s) and so on.

To get permanent hardness, can I just test a boiled water sample?

No, because boiling does not drop all the temporary hardness. The usual way to get permanent hardness is to subtract the alkalinity from the total hardness. This obviously only works when total hardness is greater than alkalinity. But then when it isn't there is no permanent hardness.