Testing Alkalynity - Green to Red

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C

casedit

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Jul 29, 2009
18
Hi - i'm trying to get used to the method for the TA test.. When i have the water sample in the tube and u add the green drops, now your sample is green.. ok. Now, you add the red drops one at a time while stirring at the same time until the solution turns red. My question is, is it when your sample first turns red, because if I stop stirring at that point it goes back to green, or is it only when you first see red during stirs?

So in otherwords, mine turned to red at 8 drops or so (80ppm i think then), but if I stop stirring it immediately goes back to green... should I keep adding until it stays Red??

thanks!!
 
you do it until it stops changing color. you should go one drop past that. so it will be red, then a brighter red, then no change on the next drop. so you don't count the last drop in your total.
you haven't finished it yet.
 
The basic rule is:
If you add a drop, and you can see something changes, you aren't done.
If you add a drop, and you don't see anything change, you're done.

If it's turning red and then going back to green, well that's a change, and you aren't done.
--paulr
 
Thanks, but thats still not quite what i'm asking... since the test says to do this all WHILE stirring... is it when it stays red only WHILE stirring, or if you stop stirring it stays red as well?
 
I think it says swirl to mix each time you add a drop. once the drop is mixed in a second or two, you're done swirling.
the reagent you're adding will turn the green sample red. it will do that on every single drop. but it takes a bunch of drops (depending on the TA level of course) to make the whole thing permanently change color.
 
Not sure which instructions you're looking at... the TF-100 instructions, and the instructions from my Taylor kit, and my own instructions (see link in my sig) all say "swirl to mix" after each drop; you're not constantly stirring. So you add a drop, swirl (a few seconds) to mix, then stop and look at the color.

If you're using a mechanical stirrer, I have no experience with those, but it still seems odd that it would look red while stirring and green when not.
--paulr
 
I'm using leslie's top of the line kit, i believe it is very similar to the TF-100. It states add the red drops while stirring. Every other drop type it states add drops then stir, but for TA it says WHILE stirring... so thats where my confusion was. When I got to 8 drops it would turn red while stirring, but when I stopped it would turn green...
 
You should be swirlling the entire time. You are looking for the color change to be stable for several seconds while swirlling. Often the color will change for an instant and then go back, that doesn't count. Nor does it matter what happens after you are done, as long as the color stays stable for several seconds and an additional drop does not change it further, swirlling the entire time, you are done.
 

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In all titration tests the swiriling should be continuous as you add the drops. This is why a magetic stirrer is such a good investment, particularly for the CH test where you need to swirl for 20-30 seconds between drops.
 
Hmph. My Taylor Trouble-Shooter DPD instructions for TA says "After each drop, count and swirl to mix..." if it oughta be continuous, they should say so.

Good to know there's still stuff to learn about test methodology. Time for another revision of the one-page instruction sheet!
--paulr
 
PaulR said:
Hmph. My Taylor Trouble-Shooter DPD instructions for TA says "After each drop, count and swirl to mix..." if it oughta be continuous, they should say so.

Good to know there's still stuff to learn about test methodology. Time for another revision of the one-page instruction sheet!
--paulr
Click to expand...
After each drop, count and swirl to mix until color changes from green to red. is the instruction in question from the K-1004. You want to count after each drop and make sure it is mixed before adding the next one but if you keep the containier swirling what you add the drops that is exactly what you accomplish.
 
heh, I think you just like to shake tests ;) strange-blobs-in-ch-test-vial-t15297.html

no shaking allowed except for cya though!
should-i-switch-t13145.html
waterbear said:
NONE of the titration tests should be shaken. the tube should be swirled or you could invest in a magnetic stirrer. The pH/OTO test (comparator tube) should not be shaken either. Cap both sides after adding the reagents and turn it over three or four times.

The only test that should be shaken is the CYA test. Shake for about 30 seconds, let it sit a few minutes, then give it a quick shake again before dispensing into the view tube.
Click to expand...
 
anonapersona said:
Can I put the cap on and shake it? I know it mixes well that way, but I do worry about the tiny bit that may escape as I open the cap again and again.
Click to expand...
NO becuase it can change the results. (See my sig, that's for you! :wink: ) You are actually doing a titration to a specific pH in this test and if you shake you can outgas CO2 which will lower the pH of your sample and lead you to think that your TA is lower than it actually is.
The ONLY test that can be shaken (and should be) is the CYA test. Even the pH and OTO tests should not be shaken. They should be capped and inverted about 3 times to miix.
 

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