Litmus ??

[merilyn]

I need everyone's help on this one. A teacher has ordered a whole range of indicators for a Year 12 Chemistry prac. One ordered is "Litmus". When I've gone to the cupboard I've found bottles labelled "litmus solution". When I looked in the book "The Laboratory", there are separate recipes for Litmus Indicator and Litmus Solution. I've got no idea what is contained in these bottles of mystery. The liquid contained is a purplish colour, almost indigo. Given the rest of the prec request, I'm assuming he needs the indicator.

Any ideas? Do the terms Litmus Indicator and Litmus Solution ever get interchanged?

As there isn't that much left, only about 100mL, I'm thinking of disposing of it and starting again - with more specific labelling!

Thanks, in advance.

M.

[RosalieM]

It should be ok. Turns red in acid, turns blue in base. You can get litmus paper which is either red or blue. test your solution that you have there already made up. don't start again! They will only need a few drops each so 100ml should be plenty (unless it is a really big class!) but just check it works first.

[dime]

It is a bit of a pest to make as well, in that you have to filter the boiled solution. This is fine as long as you're not in a hurry to make it. But it doesn't go off. Only made it twice in 18 years.

[Ian]

Hi Merilyn,
I would go the "Litmus Indicator". The "Litmus Solution" is in the section of the book dealing with "Culture Mediums", so I am guessing it is for some kind of Litmus Agar concoction. Besides, the Litmus Indicator looks a lot easier to make.
I have had staff ask for both Red Litmus indicator as well as Blue Litmus indicator. I just add a drop or two of HCl to the Blue stuff and it goes red.

Don't throw away the old stuff if it still works. Test it by adding a drop to some acid and a drop to some base and checking that they change colour (red and blue, respectively) The recipe in "The Laboratory" suggests using 10g to make up 1 Litre of indicator, but you won't need that. about 1/4 of that!

Cheers
Ian

[merilyn]

Thanks guys.
When I checked it, it definitely goes red with acid, and kind of went bluer with a base, but not a great change. When I really looked at quantities there wasn't as much as I first thought. So it looks like I will be making more in the not too distant future.

(Ian - I thought too, that the indicator looked far easier! It was the labelling here that got me confused. I figured I'd only need to make about 200 -250mL in total; I've got 10 x 25mL dropper bottles. I'm thinking of making up a new batch, given the blue not being very distinct. I won't throw away the old stuff just yet, I'll wait and see how much "fun" I have making up the new. It's for Year 12, so I'll try to get it right.)

[smeee]

Hi Chemtalk gurus
I have had a query on how to make up red litmus.
In my experience I have only ever heard of red litmus paper not actually the solution.
Any ideas ??

[sunray18]

silly but I thought
WHY? WHY BOTHER?
then I thought well make up litmus solution with the normal blue litmus powder and add acid to make it red....

[lada]

Merilyn,
do not expect radical change in basic solution. It is light purple blue rather than just blue.
So even fresh solution will not give you dramatic change.
Lada

[Ian]

silly but I thought
WHY? WHY BOTHER?
then I thought well make up litmus solution with the normal blue litmus powder and add acid to make it red....

That's what I did. My Red Litmus solution is just blue Litmus Solution with a dash of HCl added until it goes red. It works for me!

Oh, Lada: Merilyn is no longer with us . She got a job in private industry and has deserted our ranks. (Their gain, but our loss)
Cheers
Ian

[lada]

Thanks, Ian,
I do feel stupid after looking at the date!!!
Anyway, I wish her all the best and crawl into my little prep room.
Lada

[Ian]

Thanks, Ian,
I wish her all the best and crawl into my little prep room.
Lada

Hey Lada, Don't hide away in that Prep Room too long. We need you out here helping the rest of us!

All the best
Ian