Dodgy titration liquid

[E Tolle Senior Member Find all posts View Profile Close E Tolle]

OK...I have this other annoying problem.

I cannot seem to get my titration liquid correct !!

It always seem to be 3 points under the correct value and I cannot work out why

I use a scale capable of measuring to 0.01 gms.

I use deironised water, and I use the diggers NaOH of the shelf.

I mix up 10gms of NaOH in 100gms of water and then take 11gms of that and add it to 990gms of water.

How do I know that it is wrong ??? well I titrated 4 samples of oil and wrote down the values.....then I sent the samples to a friend of mine and he titrated them....his readings were around 3 above mine......so we did it all again ( including mixing new titration fluid) and we got exactly the same result.

I know his is correct because I have to add 6gms to my titration instead of 3gms per litre to get a conversion.....if I don't it doesn't happen.....so I'm out, not him.

How could this be ??

I was using metho to do the titrations with and I thought this might have been the problem.....so I got some IPA and this was better by a few points as the oil dissolved completely in the IPA....it didn't in the metho. But it is still out 3 points consistently, and it is making it a bit hard to accurately know where I am with the oil I'm using as it is all over the place FFA wise....

Any clues out there ???

[WesleyB Donating Member Find all posts View Profile Close WesleyB]

Re: Dodgy titration liquid

How pure is the Sodium Hydroxide that you're making the titrating solution with? Impure Sodium Hydroxide might account for part of it.

[geewizztoo Senior Member Find all posts View Profile Close geewizztoo]

Re: Dodgy titration liquid

The cause of your problem is that you're using weights for the liquid measurements instead of volume. We all know that 1ml of water = 1g, but when you make a strong caustic solution of 10g in 100g water (10% w/w), the density has increased and this rule no longer applies.

The titration solution we're aiming for is 1g in 1000ml of water (0.1% w/v). So this takes no account of the minute increase of density caused by adding the caustic. Whereas your method does - you're taking 11g of your (strong) first stage solution (You'd be better off taking 10ml and adding it to 990ml instead, if you can measure 10ml precisely).

The method I follow is:

Dissolve 10g of caustic in 1000ml of water (1% w/v).

Then take 100ml of this solution and add it to 900ml of water.

Also, I think you'll get greater accuracy if you use 1000ml for your first stage solution as the larger volumes are easier to measure.

Give it a try and see how you go.

[E Tolle Senior Member Find all posts View Profile Close E Tolle]

Re: Dodgy titration liquid

How pure is the Sodium Hydroxide that you're making the titrating solution with? Impure Sodium Hydroxide might account for part of it.

Wesley....the caustic I use is Diggers brand of the shelf at the supermarket.....I just tried to look up the MSDS on their site but it's not available (don't know how they can get away with that)....searching around I found several references to it at 98-99% ......I have used this stuff for years with no probs....maybe a brummy batch !!!

The cause of your problem is that you're using weights for the liquid measurements instead of volume. We all know that 1ml of water = 1g, but when you make a strong caustic solution of 10g in 100g water (10% w/w), the density has increased and this rule no longer applies.

The titration solution we're aiming for is 1g in 1000ml of water (0.1% w/v). So this takes no account of the minute increase of density caused by adding the caustic. Whereas your method does - you're taking 11g of your (strong) first stage solution (You'd be better off taking 10ml and adding it to 990ml instead, if you can measure 10ml precisely).

The method I follow is:

Dissolve 10g of caustic in 1000ml of water (1% w/v).

Then take 100ml of this solution and add it to 900ml of water.

Also, I think you'll get greater accuracy if you use 1000ml for your first stage solution as the larger volumes are easier to measure.

Give it a try and see how you go.

OK...thanks for that....I'll mix up some tonight and see what happens.......

my mate uses the same method yet we get different results.... !!!

[Tony From West Oz Vice Chairperson of WARFA Find all posts View Profile Close Tony From West Oz]

Re: Dodgy titration liquid

Degraded NaOH used to make the titration solution would give a higher titration than a titration made with more pure NaOH, but the catalyst portion (5 g/L) used in the batch would be low in active NaOH, despite the correct amount of active NaOH being available in the Titration amount. That could cause a problem with your batch, but you would be getting very high titrations in that case.
Are you both using distilled / de-ionised water for the titration fluid? Most water is slightly alkaline due to the chlorine in it.

Have you sent your titration fluid to your friend for him to try out? Have you tried using his Titration fluid?

I doubt that the differences in measurement of the Titration fluid using Mass Vs Volume would make such a difference, especially when E Tolle had made allowance for the increased density of the solution. In a worst case scenario, from those numbers, this would make less than 1% error in the titration measurement. The friend also uses this methodology, so the differences should be negligible between the 2.

Do you perform a "Blank Titration" before adding your oil to the indicator and Metho / IPA ?
If not, your indicator / solvent could be affecting the outcome of the titration.

I hope this helps,
Tony

[E Tolle Senior Member Find all posts View Profile Close E Tolle]

Re: Dodgy titration liquid

Wesley....the caustic I use is Diggers brand of the shelf at the supermarket.....I just tried to look up the MSDS on their site but it's not available (don't know how they can get away with that)....searching around I found several references to it at 98-99% ......I have used this stuff for years with no probs....maybe a brummy batch !!!




OK...thanks for that....I'll mix up some tonight and see what happens.......

my mate uses the same method yet we get different results.... !!!

Well.........I followed your method to the letter and was very carefull with my measurements.......and I still get the same result as before....albeit with a slightly lower reading. 14.8 instead of 15.

I even bought a fresh bottle of demineralised water and a new container of caustic.....

So....next I will get a different brand of caustic tomorrow and try bottled drinking water.

I never had this problem when I was over east and using tap water

[WesleyB Donating Member Find all posts View Profile Close WesleyB]

Re: Dodgy titration liquid

I called the USA division of Hach Company. I was told "Hach Pacific Australia" is in Australia. They sell, and probably will ship, Sodium Hydroxide in water for testing things. I think it is the 0.025 molar solution that I bought. It is an exact strength (no mistakes). Sodium hydroxide is 40 grams per mole, if I remember correctly. I might have bought the 0.05 molar solution, which can be diluted with distilled water to half strength, to get the proper strength for titration solution ie 1 gram in one litre of solution. Any way Hach Pacific Australia's phone number is 03 95 45 6229. One way to solve a problem is to throw a little money at it by buying chemicals that were mixed right, like NaOH titrating solution. Thanks

[WesleyB Donating Member Find all posts View Profile Close WesleyB]

Re: Dodgy titration liquid

I've arrived home and now I'm looking at my Hach Company Sodium Hydroxide Solution, 0.050 NORMAL, not molar. But in the case of Sodium Hydroxide solution molarity equals normality. I titrated corn oil with it and just multiplied the amount of solution I used by two, rather than dilute it to half strength, to get my titration number. A liter of this NaOH aqueous solution ought to last me a long time if I keep the cap on it so it doesn't absorb carbon dioxide from the air, that would pollute it.

[Captaincademan Senior Member Find all posts View Profile Close Captaincademan]

Re: Dodgy titration liquid

You need to minimise the variables. One easy way to minimise the errors associated with proportions of your titration fluid is to mix a big batch. I assume you can reasonably accurately measure 10 grams. Dissolve 10 grams in 10 litres of demineralised water. (i actually use rainwater) mixing a big batch seriousely reduces errors in measuring proportions. Just remember that you get all wound up in calculating how much catalyst to use down to the gram, but we rearely worry about measuring the oil quantity to the litre. And what temperature do you measure your oil volume at? I measure mine at 55'. It usually expands by at least 5 litres from cold. Then there is the errors associated with measurement of oil volume... My point is dont get your nickers in a knot over super precise measurements. I have found it is a pretty forgiing formular.

[geewizztoo Senior Member Find all posts View Profile Close geewizztoo]

Re: Dodgy titration liquid

I doubt that the differences in measurement of the Titration fluid using Mass Vs Volume would make such a difference, especially when E Tolle had made allowance for the increased density of the solution. In a worst case scenario, from those numbers, this would make less than 1% error in the titration measurement.

Gee Tony, you sound like Alan Jones talking about the small percentages of CO2 in the atmosphere not making any differenence. If you do the numbers and convert mass to volume of ETolle's strong solution (10/100 w/w) he's 0.5ml off. 9.5ml instead of 10ml which is 5% error. Splitting hairs?.... yes probably, so the most likely cause of errors in the accuracy of measuring small amounts. And as I said (& others), its a lot easier to make large volumes to minimise inaccuracies.

[E Tolle Senior Member Find all posts View Profile Close E Tolle]

Re: Dodgy titration liquid

Are you both using distilled / de-ionised water for the titration fluid? Most water is slightly alkaline due to the chlorine in it.

Yep...both use de-ironised water. He used different NAoH. Don't think that is the issue though !!!

Have you sent your titration fluid to your friend for him to try out? Have you tried using his Titration fluid?

No...not a bad idea....but we are on opposite sides if the country

Do you perform a "Blank Titration" before adding your oil to the indicator and Metho / IPA ?'t
If not, your indicator / solvent could be affecting the outcome of the titration.

Yep....I do the "blank" bit on every titration....I actually didn't do a few on purpose to see what the difference was...about 0.4 of a mm on the pipette.

I use the No2 pool indicator and have done for years with no issues....I even mixed up some turmeric indicator but that didn't make much difference.....this has me baffled, anyway I'll try different caustic and some bottled water as the tap water around here is full of calcium.

What I'm doing is adding 6 to my titration and doing a 1ltr conversion....if it doesn't convert I keep adding 1gm of NAoH mixed in a teaspoon of water till it converts...I've only been out 1 to 2 gms. That's on single stage.....it's not much help if I want to do a two stage conversion.

[Tony From West Oz Vice Chairperson of WARFA Find all posts View Profile Close Tony From West Oz]

Re: Dodgy titration liquid

It would be better to mix the NaOH with methanol than water, but that should not be the issue because you have processed according to standard procedures by the sounds of it (prior to adding more NaOH).
Don't bother trying retail bottled water, that could be as bad or worse than the tap water. De-ionised water is fine.

If you can send him your oil sample, then you should be able to send him your titration fluid sample. Does anyone know if it is considered weak enough to not require an aviation declaration?

Regards,

Tony

[E Tolle Senior Member Find all posts View Profile Close E Tolle]

Re: Dodgy titration liquid

OK....nailed it

I got some reochem caustic (the one in the blue bottle) and followed geewizzos method again, this time I just used bottled water as I forgot to get some more de-ironised water......and it worked.

I did three titrations of samples I sent to my mate and came up with almost the exact readings he did.....ranges were from 1.5, 15 and 18......I did another for good measure on some different oil that I know was 10.2 from converting a ltr sample and It read 10.2.....so I'm a happy boy as I can now proceed with confidence

I think the problem was with me though....not the chemicals !!!

Thanks for your help guy's.

Cheers

[Tony From West Oz Vice Chairperson of WARFA Find all posts View Profile Close Tony From West Oz]

Re: Dodgy titration liquid

Congratulations!

Did you work out what you did wrong?

Regards,
Tony

[E Tolle Senior Member Find all posts View Profile Close E Tolle]

Re: Dodgy titration liquid

Congratulations!

Did you work out what you did wrong?

Regards,
Tony

Errrmm...not really

I think that I might have only added 90mls of the 1st mix to 900mls of water last night....still not sure !!!

But.....I know the mix I made up that didn't work was correct to my mates method, so that has me confused.

What I should do is make up another batch using the Diggers caustic and use bottled water and see if that is any different.....I'll do it but not immediately !!

Anyway...I have some 18 titrating oil to convert now that I can measure the FFA's again......better get over to the other thread