NaOH for TA test... a question for the chemists.

[Chalkyt]

I have to confess that chemistry is my weak point, so I need the help of the chemically inclined. I hope the following isn't too confusing, but MY HEAD HURTS!!!

My Brewcraft Acid Test Kit has almost run out of Sodium Hydroxide (NaOH) 0.2N solution and the kit isn't available here any more. There is plenty of phenolphathlein indicator left (and I guess that indicator from the pool shop is the same if I need more). My plan is to make up some more NaOH solution using high grade NaOH beads from a reputable source since I can't find small quantities of NaOH solution (i.e. 2g NaOH in 250ml of distilled water, 4g in 500 ml, etc) . So far so good!

However, Jolicoeur suggests a simplified TA test using smaller test quantities to get more tests from the kit (see his book P182... using 2.68ml of juice, 3 drops of indicator and the number of mls of 0.2M NaOH x5 = g/L of malic acid).

Andrew Lea has a method using 0.1M NaOH with 6.7ml of juice and number of mls of NaOH to get g/L of malic acid.

I can't quite get my head around the difference between the 0.1M and 0.2M concentrations, and if it is important (probably is!). The Brewmaster Test Kit uses 15ml of sample (adjusted to 13.4 ml to convert from Tartaric Acid to Malic Acid equivalent as suggested by Jolicoeur), and this is 2 x the quantity sample suggested by Lea using 0.1M NaOH. I can see that there must be some consistency between the several methods given that 5x and 0.2 probably normalise them, but I can't figure it out.

So, can anyone who knows about this stuff tell me what is the best way to go, or if the methods all produce the same result. I am not too fussed about TA except it is good to know where it is in the range 5g/L - 7g/L. Unfortunately (for me) I have simply been doing the TA test on a "monkey see, monkey do" or "taste" basis and probably should understand it a bit better.

Thanks for any help.

 

[bracconiere]

i have no idea, but...i strugle with normality too.. it's not about molar weight per se but H+ donor and aceptors? i think?

so like sulphruic acid has two hydrogen doners...but HCl only one and that's the jist i get from normality compared to molecular weight?

 

[bracconiere]

i mean like NaOh has a molar weight of 40g's...water 18 or something...but NaOH only can take one H- atom? or something like that, my stupid ass is trying to help, because i want to help myself too!


which if 1 H- atom is 1 gram a 'mole' or normality....then a 40 gram mole of lye needs to be calculated to dilution in 18 gram a mole water? at 40 grams a mol weight? LOL

anyway that's my take on narmality so far, like mol weights, it's similar but how many H+, H- stuff there is by mol weight?

 

[CKuhns]

"I can't quite get my head around the difference between the 0.1M and 0.2M concentrations, and if it is important (probably is!)."

The way i understand it is it is important. ( kind of) Heres why. Others with more knowledge may need to correct these statements.

You must understand the concentration and volume of material being sampled to do the math and get your result.

If you know the actual concentration of naoh in solution 0.1m or 0.2 and adjust the sample volume accordingly what concentration you use doesnt really matter when using your x5 constant.

Except when you consider the following:
- You must have enough volume of each to be able to keep the ratio somewhat consistant between the sample volume and naoh to allow the phenolphathlein indicator to be observed when the acid is consumed / converted. (With that said you could do the math vs. using the constant x5 but to do that makes my head hurt.)
- Your distilled water solution carrying your noah at lower concentrations and smaller starting volume of sample may in fact add enough water by volume to dilute the sample. Skewing the result. Thus the reason for the differences in volume between the three examples provided. All at first glance appear to be based upon the naoh concentration. ( I didnt do the math to see how closely they match.)

Note:
- These titration tests when performed manually have a large amount of variability. As such are not very precise or accurate as we all see colors a bit differently. But for the home cider maker probably "good enough". Regardless, there must be enough volume to effectively evaluate the change. In my experience smaller volumes will be harder to see. Note - Some kits come with a color chart to help drive consistancy.
- I believe a more pecise result can be obtained by evaluating pH while performing the titration. At a pH of roughly 8.2 your acid will be consumed / converted by the naoh solution and your color indicator then works. ( I would have you validate that as my memory is not as good as it used to be.) But then again you probably need more volume to do so making it kind of counter to your objective.

I cant speak to the actual chemistry other than as simply stated above or even pretend to understand mol weights etc....

For others who are reading this feel free to correct any inacuracies.

Hope that helps and doesnt add more confusion.

 

[jerrylotto]

You can just as easily buy standard 2N NaOH solution from many reputable chemical companies. It's a standard concentration used for tritiometric measurement of an acid solution but I guess I'm curious why you're using tytometric methods at all. Just buy a cheap pH meter and be done with it!

 

[bracconiere]

malic acid has a mol weight of 134.09, and two carboxylic groups, so you'll need two mols of NaOH too nutrilize it...

naoh has a mol weight of 39.99


so if you're using an indicator that chages color when the malic acid is neutrilized. so like if there was 5g's of malic acid, then you'd see a color change from you're indicator after adding ~3g's of naoh?


you can figure it out in reverse...just like algebra. if KNOW how much NaOH you added, then you can solve for the malic acid.

and it's easier to weigh a dilute solution with a know conc. for presicion sake, because we're going to be dealing with mg's not grams?

 

[IslandLizard]

I can't quite get my head around the difference between the 0.1M and 0.2M concentrations

The 0.2M solution is 2x the concentration of the 0.1M one, containing 2x the amount of NaOH.
1M is 1 mole/liter.

For NAOH a 1N solution means 40g (1 mole) dissolved in water and the volume made to exactly 1 liter at 20°C.
0.1M would be 4g/l or 0.4g (400mg) per 100 ml.
0.2M would be 8g/l or 0.8g (800mg) per 100 ml.
Easy enough, right?

The bigger issue is sourcing 100% pure NaOH, as most contains some water (NaOH is highly hygroscopic) and/or Carbonate due to reaction with atmospheric CO2. It all depends how precise you want your estimates to be. For an off the cuff approximation, pretty much anything will work.

Moderator's Note:
Although this thread is on topic and A-OK being in the Cider forum, we could move it to the Brew Science forum to possibly get more input on the calculations, compounding, etc., although it seems fairly straightforward.
Let us know if you want it moved.

 

[bracconiere]

i was thinking of apple juice, and how there will be more then one acid present, with more then likely differing amounts of H+ donor groups...so if your trying to quantifiy something it's really tough to say it was all malic acid? and who know's how many g's there were of what?

Just buy a cheap pH meter and be done with it!

i'd have to agree with that comment..

 

[IslandLizard]

i was thinking of apple juice, and how there will be more then one acid present, with more then likely differing amounts of H+ donor groups...so if your trying to quantifiy something it's really tough to say it was all malic acid

I think he said the kit is measuring total acidity (TA), so yes, the total of H3O+ ions in the sample.

Jolicoeur suggests a simplified TA test using smaller test quantities to get more tests from the kit [...]

That makes sense, yes!

The only issue is, the error amount is the same, regardless of volume used. So there is a limit to how small a sample can be before the (measuring) error(s) becomes significant, skewing your test values or even invalidate them.
But if 0.2N is not too strong, yup, you'd only used half the reagent compared to the 0.1N solution.

 

[bracconiere]

so i just had fun doing this with orange juice...(i just so happened to have an unopened bottle of ph i never got to use, and thought...maybe i can work on my normality skills...

so i added 3g's NaOH to 58g's water....=0.05N? am i right on that?

it took adding 2g's of it to 41g's orange juice to turn it redish pink...so i get 0.1N for orange juice? it doesn't tell me how many mols of anything but i know that how many H+ donors there were right?

 

[bracconiere]

H3O+ ions in the sample

assuming they're all carboxylic acids?

 

[Kees]

It's really not that complicated at all.

This is all the chemistry that’s involved:

H+ + OH- --> H2O.

The number of mols or mmols tells you how many molecules or ions are involved. An ion being a molecule with an electrical charge: the + behind H and the - behind OH

A solution at pH =7 is called a neutral solution as there are no more H+ nor OH- ions in a neutral solution. This is a simplification of reality but good enough for the discussion of total acid.

So the number of mmols of OH- it takes to bring a solution to pH =7 equals the number of mmols of H+ that were neutralized. Cider makers assume that the total acidity of cider equals the amount of malic acid in the cider (another simplification of reality) . If yo do so the number of mmols of OH- needed to bring the juice to a pH of 7 equals the number of mmols of malic acid in the cider.

Mmol/mL can be converted to g/L if you prefer to work with grams instead of mols. Molecular weight of malic acid is 134,09 g/mol

 

[bracconiere]

It's really not that complicated at all.

This is all the chemistry that’s involved:

H+ + OH- --> H2O.

The number of mols or mmols tells you how many molecules or ions are involved. An ion being a molecule with an electrical charge: the + behind H and the - behind OH

A solution at pH =7 is called a neutral solution as there are no more H+ nor OH- ions in a neutral solution. This is a simplification of reality but good enough for the discussion of total acid.

So the number of mmols of OH- it takes to bring a solution to pH =7 equals the number of mmols of H+ that were neutralized. Cider makers assume that the total acidity of cider equals the amount of malic acid in the cider (another simplification of reality) . If yo do so the number of mmols of OH- needed to bring the juice to a pH of 7 equals the number of mmols of malic acid in the cider.

Mmol/mL can be converted to g/L if you prefer to work with grams instead of mols. Molecular weight of malic acid is 134,09 g/mol

it's a little bit more then that, i think?

There are other H+ accepting atoms other then just a OH, aren't there? and although a 1M solution of HCl would be 1N also, a solution of 1M sulphuric acid, would be a 2N solution?

just like a 1M solution of citric acid would be 3N? stuff like this is why i've always had trouble wrapping my head around normality....

but this thread is helping me out by leaps and bounds!

sorry @Chalkyt for using your thread....but you asked something that's haunted me for many, many, years....

 

[bracconiere]

but malic acid at 1M would be 2N, right?

so it would take 2M of lye, to neutrilize the two carboxylic groups? which would have to be calculated for....

and something like sodium carbonate would be an equal trade to neutrilize malic acid?

 

[passedpawn]

it's a little bit more then that, i think?

There are other H+ accepting atoms other then just a OH, aren't there? and although a 1M solution of HCl would be 1N also, a solution of 1M sulphuric acid, would be a 2N solution?

just like a 1M solution of citric acid would be 3N? stuff like this is why i've always had trouble wrapping my head around normality....

but this thread is helping me out by leaps and bounds!

sorry @Chalkyt for using your thread....but you asked something that's haunted me for many, many, years....

Sure, some acids contribute more than one H+, so their normality is > 1. And since all you care about are H+ (and OH-) in acid/base math, normality (N) makes more sense than molecular mass concentration (M). As long as you are clear which one you're referring to, it all works out fine. Obviously, with NaOH, HCl, and other compounds with one donor proton/ion, N=1 and normality = molarity

To the OP, I'd just get a pH meter and titrate NaOH until I saw the inflection point in the pH curve (at 7). From that you can determine the titratable acidity.

(warning: I'm not a chemist, just speaking out my backside as usual)

 

[Kees]

Malic acid is diprotic, that is correct. But the second H is only released at pH far above 7. So when caclulating total acid at pH ranges from 3 to 7 it can be considered monoprotic. That is how I understand it.

 

[bracconiere]

So when caclulating total acid at pH ranges from 3 to 7

i think i'm going to order a lb of malic, and f around with known solutions. see what math actually works...

 

[Chalkyt]

Thanks for all the feedback. I was happy to see that understanding the TA test made other peoples' heads hurt as well, so I don’t feel so alone! I now understand what I am doing a bit more thanks to the replies. It has been an interesting journey.

Anyhow, in the meanwhile I had enough NaOH left in the Kit to use Jolicoeur’s “el-cheapo” approach. And guess what, the colour change happened at around 7 g/L which is about where I expected it to be. The margin of error with Jolicoeur’s small quantities approach seems to work well enough to get a reasonable guide.

So, it means that I can cross check the test results against a known solution if I make up my own 0.2N NaOH. I should get the same result as the Jolicoeur test from the same juice if my home-made NaOH solution is indeed 0.2N. Unfortunately, it doesn’t seem possible to buy small quantities of NaOH solution here in Oz (the best I could find is 2.5L for $115… aargh!, but I can get small packets of powder/pearls from laboratory/food chemical suppliers, which I hope would be better quality than caustic soda from the supermarket.)

I am not really bothered about determining the precise TA, just an approximation so that I know how much Malic Acid to add as a starting point. I am not trying to replicate any particular style… with my cider, what you get is what you get from year to year.

In the past I have adjusted and balanced by taste (I get more Red Delicious apples than anything else, and these don’t make a very exciting cider unless some acid or different juice is added. Mind you, the RD cider is fine for a picnic or party type sparkling cider where people throw a few iceblocks into it anyway).

This year we had a lot of late summer rain so the RD apples are a bit waterlogged and down on flavour, and the Pomme de Neige and Granny Smith haven’t produced a lot of apples. Fortunately, Ballerina and Cox’s Orange Pippin have reasonable crops so I should get some complexity for my “better” cider. However, I do think that I will need to tinker with acid, hence the sudden interest measuring TA.

Thanks again for very enlightening responses to the post

 

[bracconiere]

Thanks for all the feedback. I was happy to see that understanding the TA test made other peoples' heads hurt as well, so I don’t feel so alone! I now understand what I am doing a bit more thanks to the replies. It has been an interesting journey.

Anyhow, in the meanwhile I had enough NaOH left in the Kit to use Jolicoeur’s “el-cheapo” approach. And guess what, the colour change happened at around 7 g/L which is about where I expected it to be. The margin of error with Jolicoeur’s small quantities approach seems to work well enough to get a reasonable guide.

So, it means that I can cross check the test results against a known solution if I make up my own 0.2N NaOH. I should get the same result as the Jolicoeur test from the same juice if my home-made NaOH solution is indeed 0.2N. Unfortunately, it doesn’t seem possible to buy small quantities of NaOH solution here in Oz (the best I could find is 2.5L for $115… aargh!, but I can get small packets of powder/pearls from laboratory/food chemical suppliers, which I hope would be better quality than caustic soda from the supermarket.)

I am not really bothered about determining the precise TA, just an approximation so that I know how much Malic Acid to add as a starting point. I am not trying to replicate any particular style… with my cider, what you get is what you get from year to year.

In the past I have adjusted and balanced by taste (I get more Red Delicious apples than anything else, and these don’t make a very exciting cider unless some acid or different juice is added. Mind you, the RD cider is fine for a picnic or party type sparkling cider where people throw a few iceblocks into it anyway).

This year we had a lot of late summer rain so the RD apples are a bit waterlogged and down on flavour, and the Pomme de Neige and Granny Smith haven’t produced a lot of apples. Fortunately, Ballerina and Cox’s Orange Pippin have reasonable crops so I should get some complexity for my “better” cider. However, I do think that I will need to tinker with acid, hence the sudden interest measuring TA.

Thanks again for very enlightening responses to the post

well, 0.2N would be the same as 0.2M for lye and you say it's easy to get and a Mol of lye is 39.99=~40g's...


so 8 grams in a liter?

and not to say eye patches don't look cool...but you do wear eye protection for this stuff right?

 

[bracconiere]

well i just did a bit of an experiment for my own learning....


i added 2g's citric acid (which has different pKa's for the carboxylics also...) added water up to 45g's, which i don't think is important...


then i added 3g's lye to 50g's water..(i just added a pinch of powder ph to the citric solution) added 22g's of the lye solution to turn it red...(and it did take stiring near the end, i think that's important to say)

here's the math i did which tells me the citric took 3 mols of lye to neutrilize, 1 mol of citric acid...

please if i'm doing this wrong, someone tell me! i'm just trying to learn?

edit: i just tried to check it with a digital ph meter, but i think i threw it away a bit ago....check it with litmus paper, as far as i can tell, ph is 9.5...(so might have over shoot, it is really dark, i think that last squirt from the eye dropper might have been a bit too much...but still G.E.)

but 21 g's of the lye solution is spot on...at 6/3=2g's citric acid....

edit #2: i'd suggest to the OP, buy a pound of malic it's only $13 here...f'around with it and your lye (wearing eye protection) and get a feel for it...

and molecular weight is just all the atoms added up and kinky stuff are carbons with two hydrogens when you're looking at fancy molecules...(if something kinky has two line then there's a missing hydrogen on one of the carbons...and if there's 3 lines...well....they're just drinking buddies)

edit #3: what i did was divide how many grams of lye i had in the 50g's of water...then calculated how many it took to neutrilize the citric acid...then calculated for a comparison to the mol weight of lye needed to neutriliz what i asstablished as a kown amount of citric acid....


Let me know if you think i should go into a field of education?

 

[passedpawn]

i have no idea, but...i strugle with normality too..

Very sigworthy, bracc.

 

[bracconiere]

Very sigworthy, bracc.

well according to your explanation...i'd just try and be normal, and use the 'normality scale! say well i've got 1 normal solution, and a 3 other normal people.....cram them together, and i'll have a neutral room?

 

[IslandLizard]

So, it means that I can cross check the test results against a known solution if I make up my own 0.2N NaOH. I should get the same result as the Jolicoeur test from the same juice if my home-made NaOH solution is indeed 0.2N.

If you can source a decently pure enough amount of NaOH, you can indeed calibrate that against the titration solution you're using now.

IOW, even if the NaOH is only 80% pure, for example, you'd start out making a somewhat stronger solution, then dilute it until it responds similarly as your "calibrated" 0.2N titration solution. You can get close enough for your purpose.

BTW, I just checked some pricing on standardized NaOH titration solutions, and it's indeed totally ridiculous. Also know that those will also slowly shift over time due to CO2 pickup from the air in the container headspace.

If you know someone who works at a lab or studies chemistry, they could probably set you up too. It's fairly simple to make/compound a calibrated titration solution.

This makes for a compelling case to post questions like this in our Brew Science forum, as members frequenting that forum can likely steer you in the right direction.

 

[Chalkyt]

Well, this is where it all ended up. Today I was preparing to to bottle some cider that I am using to see what difference different yeasts make. Part of this process was to check the TA.

I made up a new 250ml solution of NaOH using 2g of the pearls. Yes, they are small amounts and so a bit prone to quantity errors.

Anyhow it was about 10% out of whack when compared with the original test kit NaOH (which for the sake of the exercise I took as being correct). So, adding an extra 10% of distilled water to the new NaOH solution resulted in a TA that was acceptably close to the original solution result. Conveniently, I had some of the original juice that was measured at 5g/L. Using the Jolicoeur "el-chepo" approach, 1ml of the new solution was just on the cusp of the indicator changing colour so it also came up with "about" 5g/L... good enough for my purposes.

I guess that my future issue will be how to make up new solutions without a proper reference since comparing a "new" solution with and "old" solution that I have made up will invariably lead to error creep. So, I will keep watch for any proper test kit that appears.

 

[DuncB]

I've read through this thread and I'm wondering why you need to know Total acid. I'm obviously missing something you neutralise the acid in a sample of cider that is fermented using a known amount of base and therefore can work out the amount of Hydrogen ions. But then how do you use this information with your cider that you are about to bottle.
I feel like I've watched the whole movie and I've got no idea what happened.

Looking at it from another way couldn't you make up various solutions of Malic acid and measure the pH at those concentrations and then you wouldn't need to do all this dilute and convert, just read it off the chart.

I know there's an elephant in the room that I can't see.

 

[IslandLizard]

I made up a new 250ml solution of NaOH using 2g of the pearls.

How accurately did you measure those amounts? Much hinges on it for your TA analysis purposes.

A (small) scale that is accurate (resolves) at 0.01 gram is the minimum requirement for such endeavors, IMO. They're about $10-15 here in the U.S. (through Amazon, eBay, etc.). You could weigh up to 100 grams on those, and could be used for weighing solutions. The ones I've used are pretty accurate, a true marvel for the price, I must say.

A 100ml or 250ml volumetric or "measuring" flask would be handy, as it allows you to get very close to the standard 100 or 250ml volume, by filling up to the scribed calibration line in the long, narrow neck. Most are calibrated at 20°C, but double check.
When measuring watery substances, the bottom of the meniscus resting on the calibration line is standard practice.
https://en.wikipedia.org/wiki/Volumetric_flask
Although the mass (weight) remains the same, volume will change with temperature:
At 4°C (39.2°F) 1 gram of water has a volume of 1 ml.
At 25°C (77.0°F) 1 gram of water has a volume of 0.9970749 ml.
Keep this in mind when measuring volumes.

 

[bracconiere]

I guess that my future issue will be how to make up new solutions without a proper reference since comparing a "new" solution with and "old" solution that I have made up will invariably lead to error creep. So, I will keep watch for any proper test kit that appears.

use it on something you already know the conc of? so titrate something just for calibration purposes? if you titrate something you already know how much it 'should' be then you can solve for how much it took, then use that to solve for when the acid is the variable?

 

[IslandLizard]

use it on something you already know the conc of? so titrate something just for calibration purposes? if you titrate something you already know how much it 'should' be then you can solve for how much it took, then use that to solve for when the acid is the variable?

Yup, something like 5% (common household) vinegar, 10% Phosphoric Acid, or 88% Lactic Acid as sold to and used by brewers.
Or make your own by weighing out powdered Malic acid.

 

[bracconiere]

Yup, something like 5% (common household) vinegar, 10% Phosphoric Acid, or 88% Lactic Acid as sold to and used by brewers.
Or make your own by weighing out powdered Malic acid.

for that you'd have to understand normality though? because vinegar and lactic has an equal number of H+ per mol, and phosphoric 3?

and malic has 2 H+ ions?

https://www.nestgrp.com/protocols/trng/molarity.shtml

keep in mind the difference of the molarity, and normality... lye is equal, but you can tell some acids have 2-4 times the normality, and when doing math....it matters for a titration?


i really don't want to say what is closest to malic acid with 2 H+....might be too hard core, especially for some fermented apple juice? i have made great jams with it though, with homemade pectin i extracted from orange peels though! that was a fun project!

 

[bracconiere]

i just ordered this here in the states...when i get it i'll report on if i can prove the titration works, i'll try it with reasonable levels compared to the mg's you'd have in apple juice....like i'll add 0.5 gram to 500ml water, and see if it takes 0.29g's lye to neutralize as expected....and yes i will have to seriously dilute the lye to be that accurate....

https://www.ebay.com/itm/4024936416...37dT55NP19a1Mw/wRAZ42LzPzoYK|tkp:BFBM3q7b4JJg
to the OP if you're having trouble with 'molarity' and not normality...molarity is easy, just add up the atomic weight of the all the atoms in the molecule, then you know how many molcules are in a certain weight? based on something i forget what...

 

[bracconiere]

for the record

turns to this

for pictorial...that started with a mol mass of 134, before the sodium neutrilized it....and the magic stuff turns pink!

and this is where the sodium came from with a mol mass of 40 per 'molecule'....

 

[RPh_Guy]

The bigger issue is sourcing 100% pure NaOH, as most contains some water (NaOH is highly hygroscopic)

This point got lost in the discussion.

Making your own NaOH solution without standardizing it with KHP is an exercise in futility --- you will not get an accurate result because you cannot measure a known quantity of NaOH.

Potassium hydrogen phthalate (KHP) is not hygroscopic or volatile, so the amount can be accurately measured (unlike other acids being suggested above). If you can acquire some, I'll help you create a proper NaOH solution. Otherwise I wouldn't bother with testing TA using a bad NaOH solution.

adding an extra 10% of distilled water to the new NaOH solution resulted in a TA that was acceptably close to the original solution result.

This makes zero sense; one or both of your solutions are way off the mark.

 

[Chalkyt]

Thanks again for all the interest. At least this post has provided some entertainment during your "off' season. Ours has just started, and we had another big frost this morning, so time to start crushing apples.

Anyhow, to answer a couple of questions and ask some more...

The reason for the interest in TA (the elephant in the room?) was simply that I had just relied on adding acid to taste in the past and figured that it might be worthwhile knowing what the TA was. (Jolicoeur and Lea point out that pH and TA don't necessarily correlate). Mind you, the French guys in the video that sometime appears, where they shovel scungy looking apples into an ancient grungy press and quite happily quaff the result, don't seem to be bothered with such niceties as pH, TA, etc.

Yes, I did measure the NaOH pearls with a micro electronic scale. Yep, the quality and precision for the low price is amazing.

Overnight I was pondering about how to get the right concentration of NaOH, and a couple of the responses touch on this. Shoot me down if this is dumb, but could a 5g/L mix of distilled water and malic acid be used as a reference. Then use this to make up NaOH solution that get the right (i.e. 5g/L) test result. (since I started this reply another one came in which sort of shoots this idea down, but I thought I would leave it here anyway). I do have to say it is not all that important as going on taste works O.K. with my apples, measuring TA is just an interesting diversion, after all isn't making cider just about having fun, crushing, fermenting and enjoying the result . I don't wan to get sidelined by "analysis paralysis".

For example, I have about 5 litres of "store bought" juice left over from a yeast comparison that I was doing. So I plan making up some Graham's English Cider, just for fun (this is a great quaffer). It uses limes for acidity and rather than just do the "monkey see - monkey do" with the recipe, my curiosity wonders what the TA is before and after the limes. Not essential to know, but interesting... all part of "adding to the body of knowledge" as the academics say to justify their PhDs.

On the issue of accurately measuring liquids. Yes, I have always believed that measuring at the bottom of the meniscus is correct. But, would you believe that my French hydrometer instructions say the TOP!

Cheers!

 

[bracconiere]

Thanks again for all the interest.

Cheers!

this thread has helped me finally understand normality! thanks for being interested!

but for this titration, you just need to know how many molecules, or mols of lye it took. you can make a 0.3M solution, or a 0.5M solution...

but for your 0.008M solution of lye, did you weigh how many grams of it you added? i just realized that was missing from your post? because i get 0.008M lye...which in my head is irrelevant for this experiment...you've 2g's lye/250g's water.....so 0.008 gram of lye a gram of water...and malic acid will consume 0.016g's lye out of that solution? and malic acid has a molecular weight of 134g's?


so if you weigh how ever much of that 2/250=0.008, to a weighed sample of cider, and also weigh how much it takes to turn it pink.?

 

[bracconiere]

this a bit off-topic, but here is a quick guide for how to do a vitamin c titration...it's a classic junior high science lab thing...


https://www.thoughtco.com/vitamin-c-determination-by-iodine-titration-606322
it's how i learned...

 

[RPh_Guy]

but for your 0.008M solution of lye, did you weigh how many grams of it you added?

You cannot accurately measure NaOH using a scale because you don't know how much water it has absorbed from the air.

 

[bracconiere]

You cannot accurately measure NaOH using a scale because you don't know how much water it has absorbed from the air.

i'd think for a titration it would have to absorbe enough to be a paste? mol weight of water is only like 14g's a mol? so negligeable for this type of stuff?

 

[bracconiere]

for some reason i got curious....and looked it up on wiki pedia....this gave me a laugh...

solubility. in water...
418 g/L (0 °C)
1000 g/L (25 °C)[4]
3370 g/L (100 °C)


how the f would 1000g's add up to 1000g's in water?

edit: i think usually that sorta thing they just call miscible? i mean seriously, so a drop a water will dissolve in 1000g's lye big deal? but it's miscible in water?

 

[RPh_Guy]

negligeable for this type of stuff?

It's not negligible.

Perhaps the NaOH powder is 10% water. Maybe it's 20% water. Maybe more. You don't know. That's why it needs to be standardized against a known amount of acid (typically KHP). Otherwise the titration results will be inaccurate (falsely high) by a corresponding percentage.

As @IslandLizard mentioned, there's also an issue with the NaOH reacting with CO2 in the air, further decreasing the purity (even after it's been standardized). Freshness and air-tight storage conditions are important to maintain the proper NaOH solution concentration. You can't use old NaOH solutions to standardize new solutions.

I can address other questions after we make sure the answer to the OP's question is understood.

 

[bracconiere]

Hey! thought i'd update my malic acid showed up today! just got done shoveling 2 TONs of gravel so the science was a welcome smile! (not that i didn't have fun shoveling the gravel too, but it was a different kinda fun )


so i whipped my mg scale out and added 136mg's malic acid to 224g's water....for with the glass a total of 546g's weight....(i think the water is irrelevant here?)


i added 590mg's Lye to 100g's water....it took 14 grams of the lye water to turn the malic water pink....which if my math is right, here it is...

somebody said just 1 mol of lye but this would indicate maybe i'm not as stupid as typing makes me out to be thinking 3 mols of lye?


edit: in conclusion, you don't need smarty pants making a pre made kit, it's pretty easy!