bromothymol blue solution
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Old 08-07-2011, 05:52 PM   #1
skmdmasud
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bromothymol blue solution


Hello,
i made bromothymol blue solution following this instruction

BTB can be prepared by mixing 0.1 g (a pinch) of bromothymol blue powder in 10 mL of a 4% solution of sodium hydroxide.
Add 20 mL of alcohol and dilute to 1 L with distilled water.
The solution should be deep blue.
If it is green, add sodium hydroxide solution drop by drop until the solution turns blue.

After making my solution it turned good blue. I was satisfied. After using it i found out that it dosent change colour even after i directly inject co2 in it.

I used few drops of lemon juice and it turned yellowish instantly so i figured out that my solution is very base.
I made 4% sodium hydroxide myself and I think I used a bit more than i was suppose to.

i still have around 1 liter of solution so how do i make it acidic so that i can use it to test my tank co2 level.

Thanks.
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Old 08-08-2011, 01:46 AM   #2
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I have never done this, but the instructions you give make it seem that the solution is ready to use only if you have titrated it so it just does change from green to blue. And, this doesn't seem quite correct to me either. My API pH test reagent, which is bromothymol blue solution, is not blue, it is yellow-orange. Perhaps you are supposed to titrate the test solution until it just turns yellow-orange.
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Old 08-08-2011, 04:02 AM   #3
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Ok.. I think i got your point and the instruction

If it is green, add sodium hydroxide solution drop by drop until the solution turns blue.

So what i need to do is make the solution just slight blue to blue making sure not to add too much of sodium hydroxide. May be i will dilute it in pure water and then add sodium hydroxide drop by drop.

Quote:
Hoppy
And, this doesn't seem quite correct to me either. My API pH test reagent, which is bromothymol blue solution, is not blue, it is yellow-orange. Perhaps you are supposed to titrate the test solution until it just turns yellow-orange.
what colour do you get when your CO2 is just right



from: http://aquatic-art.blogspot.com/2011...-aquarium.html

I think we have to make it to blue which means not enough CO2 so that as the co2 increases in the tank the colour of solution will also change.
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Old 08-08-2011, 05:24 AM   #4
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If you want to change the pH of the solution, you could add hydrochloric acid dropwise until it reaches the particular pH/color you're after. I'm with hoppy though, my indicator solution comes out of the bottle on the yellowish side.

The buffering capacity of the few mL of 4 KH solution in the drop checker should overwhelm the pH of a couple of drops as long as the drops are fairly close to neutral (i.e. greenish.) When you add the drops to the drop checker, it will turn blue because of the bicarbonate that you've put in there.

When you wrote that you injected CO2 into the solution and it didn't change color, did you mean that you injected directly into your indicator, or that you prepared a 4 KH buffer, put drops in, injected CO2 for a while, and nothing happened? If it was the first, I'm not terribly surprised, as it sounds like you made it fairly basic. If it was the second, could you have made an error in your buffer solution?
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Old 08-08-2011, 05:44 AM   #5
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Is 10 mL of a 4% solution of sodium hydroxide is the buffer solution.

I made everything according to the instruction and then injected CO2.

Do you add aquarium water to your indicator solution before putting it in drop checker? Because according to the diagram yellow or close to yellow means too much CO2.
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Old 08-08-2011, 06:19 AM   #6
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OK.. After some reading i think i am getting the picture or i may be wrong

THE DIFFERENCE
If you buy indicator solution then you need the 4 KH solution because the indicator solution is bromothymol in liquid form.

Where else i bought bromothymol powder which i think i can mix with alcohol to make a solution something like the API Product I THINK
And the sodium hydroxide 10ml 4% will make the 1 liter distilled water to 4kh

Anyone any idea.
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Old 08-08-2011, 01:12 PM   #7
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You can back titrate with HCL if you have it. More effective that lemon juice.


What you need to do is get indicator solution and then mix it WITH 4KH I think it'd be easier to just make a 4kh solution and then add indicator to it than make a solution with 4kh. As for what you're doing wrong I can't really say. Do you have any reference solutions? Try a 7.0 pH reference and a basic and acid reference and see if you can get a good scale going.

I'd personally just remake the solution....
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Old 08-08-2011, 01:37 PM   #8
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A 4%/1 molar solution of NaOH (which you presumably made by dissolving 40g NaOH to 1L total volume in distilled water, or some other equivalent ratio, right?) is going to be very basic (pH of 14.) Diluting 10mL of that into 1L of water will still give you a pretty basic solution (pH 12.) It will always be blue as you have found. It's not a buffer, it's a relatively strong base, at least in aquarium terms. It might also have unintended effects on the pH of the drop checker solution, once you've got that going.

The drop checker isn't filled with bromothymol blue indicator. You make a 4KH buffer that goes into the drop checker, then add one or two drops of bromothymol blue, just enough so that the color of the indicator is clear. Instructions for doing that are about 1/3rd of the way down this page.
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Old 08-09-2011, 02:04 AM   #9
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Thanks for the link. What I made is actually for school science fair not for aquarium use. Hopefully making the 4KH solution wont be difficult once i have a sensitive digital measuring tool.
My bromothymol blue is in powder form, How do i make it liquid. Or should i just pour a pinch in my 4kh solution directly.
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Old 08-09-2011, 02:40 AM   #10
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I think the bromothymol blue can only be dissolved in something like ethanol or some kind of alcohol. Just make a stock solution. The concentration I cannot tell you. I suggest just adding X amount then if you have a pH probe titrate it with HCL to like 6pH and then using several reference solutions build your own scale. Do you work in the lab? Because a little test bottle of premade bromo will last you a year or two and is only like 8 bucks. IMO if you're going to spend 2 hours making the solution you might as well get the premade lol.
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Old 08-09-2011, 02:57 AM   #11
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NOPE dont work in any Labs.

Pre made solutions are not available, in the chemist shop only powder is available that is why i bought it. The powder I have will last a life time.

I read somewhere that you can also put in bromothymol blue powder in your drop checker and it will change colour very accurately??
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Old 08-09-2011, 05:37 AM   #12
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I think I figured out what your instructions are for. I suspect you've got instructions for making a bromothymol blue staining solution for biological specimens. In that case you want the stain to remain blue, thus the very basic solution.

It appears that some versions of the indicator are water soluble (sold as the sodium salt of bromothymol blue) and all of them should be alcohol soluble to some degree. You might try simply dissolving a bit of the indicator in ethanol (even something like vodka ought to work.) It should be much easier to get a color change in that case.

ETA: You could try adding a tiny bit of the powder to the drop checker as well. Heck, it's worth a shot.
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Old 08-09-2011, 05:49 AM   #13
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No matter what you need a scale. You need several known pH substances like add a bit of HCL to water to a known H+ concentration to get your acid scale and then add a known amount of NaOH to another set of solution to get your basic scale. You need to know these numbers to know whether or not your solution means yellow-too much CO2, green ok, and blue too little or green- too much, blue wayy too little etc.
I think this is actually what you're looking for anyways here you go: http://www.csudh.edu/oliver/chemdata/ind-prep.htm

3',3" - Dibromothymolsulfonephthalein (Bromothymol Blue) 6.0 - 7.6 yel to bl 0.1 g in 16 ml 0.01 M NaOH + 234 ml water


so you need 1g in 160ml of .01 M NaOH ( .4g NaOH/L) in 2340ml of water.

Seems easy enough...and with about a half gallon it'll last you 3 life times in one gram lol. 4% NaOH is really basic. I think that was your problem. Also this is the exact same range of the API test kit.

When making the drop checker solution I just add to ~3-5ml of 4dKH reference solution 3-4 drops of indicator, mix it up and then use a pipette to deposit it into the drop checker and call it at that.
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Old 08-09-2011, 06:19 AM   #14
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DUDE, bromothymol blue is not blue, it is orange. IT TURNS BLUE when you put it into water that is 7.6 ph or higher, aka 4dkh solution. That is why the drop checker should be blue at first.
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Old 08-09-2011, 07:27 AM   #15
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Quote:
Originally Posted by skmdmasud View Post
Hello,
i made bromothymol blue solution following this instruction

BTB can be prepared by mixing 0.1 g (a pinch) of bromothymol blue powder in 10 mL of a 4% solution of sodium hydroxide.
Add 20 mL of alcohol and dilute to 1 L with distilled water.
The solution should be deep blue.
If it is green, add sodium hydroxide solution drop by drop until the solution turns blue.

After making my solution it turned good blue. I was satisfied. After using it i found out that it dosent change colour even after i directly inject co2 in it.

I used few drops of lemon juice and it turned yellowish instantly so i figured out that my solution is very base.
I made 4% sodium hydroxide myself and I think I used a bit more than i was suppose to.

i still have around 1 liter of solution so how do i make it acidic so that i can use it to test my tank co2 level.

Thanks.
All things done perfectly, it should be orange before you dilute it with 1 l of distilled water. After diluting with 1L distilled water it should be blue.
That 1l of distilled water is now your solution.
If when you add it to 1l it is not blue, then you have somehow messed it up, and then you make it more basic with sodium hydroxide.
I believe it will operate the opposite of some btb solutions, by turning from blue to orange instead of the other way around.
This mixture may be useless for our application.
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