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Discussion Starter · #4 ·
>>>Hoppy
Bill,
What is your estimated error range for these solutions? 4 +/-? dKH. <<<

The lab certified alkalinity standard pretty much speaks for itself.
The sodium carbonate at 99.5 % purity so you could have a .5 % error.
If the baking soda is 97% pure you might get a 3% error.

From what I have read the typical error of an alkalinity titration test kit is 5 -10% so I don't think you would see the error of the standard anyway.

This method of making standard is not something new. The use of sodium bicarbonate to make an alkalinity standard it general procedure for water testing agency's and the lab certified alkalinity standard is what is used by the EPA when testing water.
 

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Discussion Starter · #5 ·
>>>oblongshrimp
interesting thing to sell <<<

There was so much misinformation out there as how to make a KH standard that I would have been glad to just buy a bottle of it and be done with it instead of having to do so much research.

I thought others may feel the same way so here it is.

I did post a new thread today in the general forum that tells you how to make your own KH standard if you want to.

Bill
 

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I agree with you just thought it was a interested (good) idea :)

So how do you measure how much to add to each bottle? That is likely your largest source of error
 

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Discussion Starter · #7 ·
>>>oblongshrimp
I agree with you just thought it was a interested (good) idea

So how do you measure how much to add to each bottle? That is likely your largest source of error <<<


The lab certified alkalinity standard is just a calculated dilution. The larger the sample size from the carbonates the less degree for error.

Thanks,
Bill
 

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>>>Hoppy
Bill,
What is your estimated error range for these solutions? 4 +/-? dKH. <<<

The lab certified alkalinity standard pretty much speaks for itself.
The sodium carbonate at 99.5 % purity so you could have a .5 % error.
If the baking soda is 97% pure you might get a 3% error.

From what I have read the typical error of an alkalinity titration test kit is 5 -10% so I don't think you would see the error of the standard anyway.
Don't forget the additive effect of the dilution glassware. In your How-to post you advocate graduated cylinders - that probably adds 1% error for each time you use one (50 ml diluted to 500ml = 2%). You could reduce the error greatly using volumetric glassware (pipet and flask) for the dilutions.

The accuracy of an alkalinity test kit is not really the issue - since these solutions are intended for use in drop-checkers. The indicator color change is determined by pH which is determined by the ratio of dissolved CO2 and HCO3- in the solution. The use of the 4dkH solution and the kH indicator is based on the calculation of 30ppm CO2 at or below the color change pH. If the concentration of bicarbonate is less, the CO2 concentration will be less when the color changes.

Are you adding any preservative to the solutions to prevent mold/bacterial growth once it is opened?
 

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"Are you adding any preservative to the solutions to prevent mold/bacterial growth once it is opened"

I doubt there will be much growth in a solution of distilled water and baking soda. That said, once can simply refridgerate one's stock solutions.

Keith
 

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Discussion Starter · #10 ·
Hi Kevin,

>>>Don't forget the additive effect of the dilution glassware. In your How-to post you advocate graduated cylinders - that probably adds 1% error for each time you use one (50 ml diluted to 500ml = 2%). You could reduce the error greatly using volumetric glassware (pipet and flask) for the dilutions.<<<

I have a 1000 ml, 500 ml, 50 ml volumetric flask, a 25 ml meausring pipet and a 1 ml pipet that I use to make the KH Standards.

You bring up a good point, a couple of reasons that I decided to list graduated cylinders as the measuring device was because they were cheaper, easier to buy in a local market and the fact that you could pick what mls you needed instead of having to have a flask for each meausrement of liquid.

I should probably edit it "how to" some telling the correct way to read the meniscus, that would help a little as far as accuracy goes.

I tought if someone was more concerned about accuracy than that they would probably buy a premade standard.

>>>>Are you adding any preservative to the solutions to prevent mold/bacterial growth once it is opened?<<<<

No, I haven't added any preservative to the standard.

Do you have any suggestions on a preservative?

Bill
 

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Please, don't add anything to the KH standard solutions except the source of carbonates. Remember, that is the whole reason for using such standards. Once we introduce another substance there is a chance that the KH/pH/CO2 relationship will not be accurate. Inorganic solutions are not likely to grow molds, etc. in them in any case - what would such critters find to eat? You could drink one of these standard solutions and think it was totally pure water.
 

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Discussion Starter · #12 ·
I keep deionized water in 5 gallon buckets for my reef tank (it's only a 29g tank). I had a bucket of deionized water left in my garage in Texas for a couple of months during the summer and it never had any mold in it.

I wasn't planning on adding anything to the KH Standard but I was interested in what Kevin had to say. I looked at his profile and it said he was a chemistry professor.

Bill
 

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"I should probably edit it "how to" some telling the correct way to read the meniscus,"

Or - if someone has a decent scale - you could weight the water. For the purposes of this exercise, water is 1 gm per ml. The stock solutions would be so close as to be identical.

Keith
 

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I keep deionized water in 5 gallon buckets for my reef tank (it's only a 29g tank). I had a bucket of deionized water left in my garage in Texas for a couple of months during the summer and it never had any mold in it.

I wasn't planning on adding anything to the KH Standard but I was interested in what Kevin had to say. I looked at his profile and it said he was a chemistry professor.

Bill
Yep, Chemistry - not biology though. My thought was regarding the shelf life - it would seem 500ml would last a long time if you only need it for one or two drop checkers - replacing once a month or so.

I often use ammonium acetate solutions for my work and they get growth of mold within a few days - yes, that is more organic, but also quite acidic which should retard growth. The convenient solution I have found is to add 5% methanol to the ammonium acetate solution. I agree with Hoppy though - methanol wouldn't work here as it would alter the pH.

Another example: I had a small vial of gasoline for a lab course. It actually grew a mold on the surface of the gas within a year!

Maybe a preservative isn't needed - I was asking out of curiosity more than anything.
 

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Discussion Starter · #15 ·
>>>Or - if someone has a decent scale - you could weight the water. For the purposes of this exercise, water is 1 gm per ml. The stock solutions would be so close as to be identical.<<<

I'm using a few class A volumetric flask, as far as I know that the most accurate way to measure volume of water.

Bill
 
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