# bromothymol blue solution



## Hoppy (Dec 24, 2005)

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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## skmdmasud (Nov 23, 2009)

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.




> 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/2011/02/drop-checker-in-planted-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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## jasonpatterson (Apr 15, 2011)

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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## skmdmasud (Nov 23, 2009)

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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## skmdmasud (Nov 23, 2009)

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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## Jeffww (Aug 6, 2010)

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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## jasonpatterson (Apr 15, 2011)

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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## skmdmasud (Nov 23, 2009)

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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## Jeffww (Aug 6, 2010)

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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## skmdmasud (Nov 23, 2009)

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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## jasonpatterson (Apr 15, 2011)

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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## Jeffww (Aug 6, 2010)

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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## btimmer92 (Mar 12, 2011)

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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## Chlorophile (Aug 2, 2011)

skmdmasud said:


> 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. _
> ...


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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## skmdmasud (Nov 23, 2009)

Hello 

jeffww i was feeling very hopeless but now i have hope



> 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


looks simple only need a high precision scale or can convert it to lets say 2 liter to make the values larger. *16 ml 0.01 M <--(is this mole) NaOH 


*jasonpatterson


> 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.


OK if i make 4kh solution and add btb powder and if it disolves then does that mean i am good to go...

does alcohol changes ph because yesterday i added good amount of pure alcohol in my solution in a test tube but the colour did not change the test tube just got cold lol:red_mouth i guess due to alcohol evaporation

Thanks and Regards.


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## Jeffww (Aug 6, 2010)

Alcohol is generally neutral. It may be slightly basic it may also be slightly acid depending on your alcohol but you can count on it being close enough to 7. That M is molar solution so it's mol/L. And since NaOH has a molar mass of 40. A 40g/1L solution is 1M. .1M is 4g/L and .01M is .4g/L.


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## skmdmasud (Nov 23, 2009)

Thanks Guys:bounce:
I think i am in the right direction this time. I will let you know my results.

Regards
Masud.


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## Jeffww (Aug 6, 2010)

So how runs the stream?


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## skmdmasud (Nov 23, 2009)

Hello
I am about to make my solution using using 4 times the original to keep this more accurate.
So here it goes... 
original formula --> 0.1 g in 16 ml 0.01 M NaOH + 234 ml water

4 times the original formula --> 0.4 g in 64 ml 0.04 M NaOH + 936 ml water

or

4 times the original formula --> 0.4 g in 64 ml 0.01 M NaOH + 936 ml water

which 4 times the original formula is correct? I have a feeling that 0.01 M NaOH is correct.
Regards. :icon_surp


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## Malakian (Aug 23, 2014)

Sorry for ressurecting a dead thread, but it never had a definite anserw, and might help others googling the same. Anywho, I'm studying to become a chemist, and just happen to have aquariums as my hobby too. So I wanted to make some Bromothymol blue (BTB) indicator, as I have it readily available and it was for a school project.

The issue that OP was having, is that he is making a BTB solution. For our use we need a BTB indicator. There is a difference. Comercial pH test is usually 0.04% BTB indicator, but I want 0.1%. As it makes no difference in readings, just make the color stronger.

When making a indicator you just use a solvent and the BTB, no NaOH. And since BTB is not very soluable in water, we have to use alcohol. 50% v/w or higher ethanol or isopropyl alcohol will work. This will make a dark green indicator that will work just as API pH test.

The reason API and some others are yellow/orange in the bottle is that they use Sodium Bromothymol Blue, which is soluable in water. This is for shipping reasons, alcohol is flammable and there is a ton of regulations when transporting flammable products. And I'm guessing they use some acid to inhibit bacterial/fungal growth in the bottle, lowering the pH. Hence the yellow. Since we use alcohol, we don't need perservatives. As a side note, you can use alcohol with Sodium BTB too without perservatives.

So say you want to mix 0.1% BTB indicator, 100ml:
0.1g BTB in a measuring container, add solvent (alcohol) to 100ml mark.

Or if you want just like commercial 0.04%:
0.04g in 100ml.


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## skmdmasud (Nov 23, 2009)

Thanks. It been a while since I have been into aquarium. I am planning to start planned tank soon and hopefully I will make it this time perfectly using your formula.


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