In doing some research online, it looks like alkalinity can be determined by titration with any strong acid. However, being a water chemistry novice I'm having difficulty in determining the proper method to do so. What I think I understand: a measured sample is dosed with a volume of acid of known strength to a specific endpoint pH (~4.4). What I do not know/understand: what other parameters must be identified WRT the acid strength and what formula would be used to calculate alkalinity when using lactic acid? I have 88% lactic acid on hand and was hoping to be able to use it and my MW102 to perform a home alkalinity test. Any advice would be greatly appreciated. Thanks.
Titration with 88% Lactic to Calculate Alkalinity?
- Thread starter carvetop
- Start date
Help Support Homebrew Talk - Beer, Wine, Mead, & Cider Brewing Discussion Forum:
You are spot on WRT the process for determining alkalinity but note that the end point pH depends on the ISO if you are using their procedure or your choice if you are using AWWA's. IOW it doesn't matter as long as you specify what the end point pH is. It is usually between 4.3 and 4.5.
The other thing you need to know is the strength of the acid in mEq/L (miliequivalents per liter). The problem with lactic acid is that it's strength depends on the end point titration pH The strength of 88% w/w lactic acid is 8.66 mEq/L (written 8.66 N) at pH 4.3, 9.15 N at pH 4.4 and 9.55 N at pH 4.5. For this reason perhaps lactic isn't the best choice (it's not really a strong acid) but it is doable. The strengths above are calculated assuming that you have exactly 88% lactic acid and you probably don't. What you actually have is what you actually have.
In an actual titration 100 mL is generally considered a convenient sample size to work with and with 0.1 L of sample 0.1 N acid means that the alkalinity is numerically equal to the number of mL it takes to get that 0.1 L from whatever pH it comes out of the tap at to the end point pH. In the US we multiply the mEq/L by 50 and call the result alkalinity in ppm as CaCO3.
88% lactic acid is way too strong (this is a separate meaning for 'strong' as it refers her to concentration) for your titration. But of course you can dilute down to 0.1 N with DI water and go from there. This, of course, involves measurement of dilution water and small amounts of acid of unknown (precisely) strength. So what you do is 'standardize' your dilute acid against something whose strength is exactly known. The only thing like that you are going to find in the LHBS is the 0.2 N NaOH that they sell for vintners use in determining titratable acidity of their wine musts. You can also buy 10% phosphoric acid at an LHBS which is about 1 N. It isn't of constant strength over pH either but is more so than lactic acid so that may be a better choice. You could dilute it 10:1 with DI water and standardize with the NaOH. There is a big problem with NaOH, however, and that is that it sucks CO2 out of the air thus reducing its strength the longer it is exposed to air.
It is far, far less trouble, IMO, to buy a bottle of 0.1 N sulfuric acid (constant normality over the end point range) from Hach for about $12 (IIRC) and not have to do any dilution or standardization. Pay them to do that for you!
Pop over to http://www.wetnewf.org/pdfs/measuring-alkalinity.html to read more about how to measure alkalinity.
Now lets ask the fundamental question: "Why do you want to measure the alkalinity of your water?" The real answer to that is so that you will know how much acid you will need to add to your mash or sparge in order to overcome that alkalinity. You can, of course, titrate a volume of your water to mash pH end point using your lactic acid. Use a syringe or eyedropper to dispense. If you want to mash to pH 5.4 add drops of 88% lactic acid to a gallon until it's pH reaches 5.4. The result is your alkalinity to pH 5.4 (your choice of endpoint) in units of drops/gallon. You don't really care how that relates to mEq/L, ppm as CaCO3, dH or any other unit as when you go to treat you water for brewing then you simply multiply the drops/gal by the volume in gal and add that many drops.
The other thing you need to know is the strength of the acid in mEq/L (miliequivalents per liter). The problem with lactic acid is that it's strength depends on the end point titration pH The strength of 88% w/w lactic acid is 8.66 mEq/L (written 8.66 N) at pH 4.3, 9.15 N at pH 4.4 and 9.55 N at pH 4.5. For this reason perhaps lactic isn't the best choice (it's not really a strong acid) but it is doable. The strengths above are calculated assuming that you have exactly 88% lactic acid and you probably don't. What you actually have is what you actually have.
In an actual titration 100 mL is generally considered a convenient sample size to work with and with 0.1 L of sample 0.1 N acid means that the alkalinity is numerically equal to the number of mL it takes to get that 0.1 L from whatever pH it comes out of the tap at to the end point pH. In the US we multiply the mEq/L by 50 and call the result alkalinity in ppm as CaCO3.
88% lactic acid is way too strong (this is a separate meaning for 'strong' as it refers her to concentration) for your titration. But of course you can dilute down to 0.1 N with DI water and go from there. This, of course, involves measurement of dilution water and small amounts of acid of unknown (precisely) strength. So what you do is 'standardize' your dilute acid against something whose strength is exactly known. The only thing like that you are going to find in the LHBS is the 0.2 N NaOH that they sell for vintners use in determining titratable acidity of their wine musts. You can also buy 10% phosphoric acid at an LHBS which is about 1 N. It isn't of constant strength over pH either but is more so than lactic acid so that may be a better choice. You could dilute it 10:1 with DI water and standardize with the NaOH. There is a big problem with NaOH, however, and that is that it sucks CO2 out of the air thus reducing its strength the longer it is exposed to air.
It is far, far less trouble, IMO, to buy a bottle of 0.1 N sulfuric acid (constant normality over the end point range) from Hach for about $12 (IIRC) and not have to do any dilution or standardization. Pay them to do that for you!
Pop over to http://www.wetnewf.org/pdfs/measuring-alkalinity.html to read more about how to measure alkalinity.
Now lets ask the fundamental question: "Why do you want to measure the alkalinity of your water?" The real answer to that is so that you will know how much acid you will need to add to your mash or sparge in order to overcome that alkalinity. You can, of course, titrate a volume of your water to mash pH end point using your lactic acid. Use a syringe or eyedropper to dispense. If you want to mash to pH 5.4 add drops of 88% lactic acid to a gallon until it's pH reaches 5.4. The result is your alkalinity to pH 5.4 (your choice of endpoint) in units of drops/gallon. You don't really care how that relates to mEq/L, ppm as CaCO3, dH or any other unit as when you go to treat you water for brewing then you simply multiply the drops/gal by the volume in gal and add that many drops.
Thank you very much for the information, AJ. Very helpful. Your last statement regarding a simple titration of brewing liquor to an endpoint; how is the buffering capacity of the grain bill taken into account? Or isn't it when using this method? Clearly, my understanding of the chemistry involved could use some help.
It isn't if you just do the water. It is if you make a test mash including the grains you intend to use. Making a mash or test mash is simply, in effect, measuring the alkalinity of the mash to the desired pH. You can also handle the grains by titrating them separately and combining their alkalinities (which can be negative in the case of a high kilned malt or sauermalz) with that of the water. This is a lot of work and we are hoping to be able to convince maltsters that they ought to do these titrations as part of their batch analyses. With good malt data you can predict mash pH to a couple hundredths.
I recently ran a few titrations on my tap water to bring the pH to 5.5 as indicated by Sierra Nevada et al. I like the ease and repeatability of this method for treating brewing liquor and, for the few pale beers I've brewed using this technique, I'm pleased.
