Phenolphthalein Agar

[Tina]

Hi Estelle
After my previous failures trying something similar I would try a new batch. but then you cont have much time for a new batch either. But then again, you might have more luck than me. Actually, you are probably doing that prac right now. Did it work?
cheers
Tina

[noona]

Hi All
I just made some yesterday in Ice cream containers they very well thatns for the tip
Have a grat break and I hope the Easter Bunny comes to ALL

[estelle]

Hi all,
Yes it still worked after reheating the mix.
I ended up having enough for probably 5 classes. The bio teacher forgot to tell me he only needed enough for 4 groups and then he ended up having bio students away on an excursion and having to "babysit" year 10 in the same class so didn't even get to use 4 lots.
He wants to run it again next term. I am contemplating wrapping the left over up in glad wrap, putting it in the fridge and testing it next term with H2SO4, if it still works he gets it again!!
Estelle

[rae]

Hi Estelle,

I had mine for at least 3 weeks in the fridge after we had used it and the colour was stll fantastic and the gel was even better than when it was fresh so I think it would be fine to keep in the fridge over the holidays. Its only 2 weeks afterall.

Lorrae

[merilyn]

Hi all

I'm a real newbie at this - only been a labbie for a couple of months, so would appreciate some help.

I was asked to prepare some phenolphthalein agar. I used the "recipe" from "The Laboratory" by B. Dungey, which said to use 18g agar, 4g sodium hydroxide and 1 litre of distilled water, and to add the phenolp. until the agar turned a deep pink. Not being sure what "deep pink" is, I added the phenolp. until it didn't seem to be making any difference to the colour. It was pink, but probably not what it should have been. After leaving it to set, the colour appeared much paler than before. The instructions said to leave it a few days as the colour would develop better. but time restraints did not allow for this - it was made less than 24 hours before using. The result was that the students found it difficult to notice any colour change when added to acid.

One of the teachers suggested that the phenolphthalein may have been old, or diluted. Any other suggestions?

Where is it best to store it? Should it be in the fridge?

[Labbie]

Hi Welcome to chemtalk, I have merged the post's for you. So you can read all the great information on Phenolphthalein. Do hope it helps.

[RosalieM]

Hi Merilyn and welcome to labbie land I have used that recipe before and found that more phenolphthalein is needed than it indicates. You just keep adding it until it is quite dark. Don't do it drop by drop, either. It will take you forever! I usually do about 50ml (dropper bottle full) and probably a second one squirt by squirt.

[Ocker]

Aw bugger it! throw the second 50ml bottle in as well!!!!!

[rae]

Hi Merilyn and welcome.

I hope you find this site as invaluable as the rest of us do. Not only for useful information but for venting and laughing and sanity.

Anyway I have an extra strong bottle of phenolphthalein that I use to colour the gel and I also leave it overnight with a layer of phenolphthalein over the top this soakes in and helps maintain the colour.

Lorrae

[Ian]

Welcome to ChemTalk Merilyn!
I read your post yesterday morning, and got a PM from you yesterday afternoon but did not quite twig that they were both from the same "Merilyn" I guess that makes my high recommendations to you about ChemTalk a bit redundant as you are already here!. Welcome aboard! I will have to tell you some of MY Agar stories at some time. (I could write a book, I'm sure!)

Cheers
Ian

[Loopy]

Hi Merilyn! Welcome!
I use 1g of phenolthalein powder for my phenolthalein agar and have never had any problems with colour.
Hope this might help you...

[lada]

I have used a very small amount of powdered phenolphthalein. It works really well and does not dilute the agar mix.
Good luck
Lada

[Lab]

Thanks everyone for their answers and suggestions. Every year I make this and until this year when I was told to use gelatine to set it with the agar it as been a dismal failure. So I look forward to trying the receipe next year. Love this site.

[Ocker]

Yeah! I tried jelly once because of the cost of Agar, as you state "dismal" then I tried Guar gum, that was worse, it might cost a bomb but there is no substitute

[merilyn]

Thanks, everyone, for your tips and advice. I just hope I remember all this for next time! Being new, I feel pretty bad when things don't go to plan. Next time I'm not sure of something I'll be checking here first.

[estelle]

Just letting you know that I kept the leftover phenolthalein agar in the fridge over the holidays wrapped well in gladwrap and we used it in the biology class yesterday with success.
I tried it before sending it out to class just in case, but the reaction in the sulfuric worked just fine.
Saved me wasting it and saved me having to make more.
Estelle

[vlclabbie]

Cool Estelle! Will remember that - I put mine in the fridge in their containers but they must have some air leaks..... will wrap em up next time!

[rae]

Hi Just revisiting an old topic with a new question.

We always have heaps of gel left over. Has anyone tried keeping the gel for any length of time? I was thinking of giving it a go!!

[Ian]

I use the dropper bottle trays with the dividers still in. I run a knife blade around the edge before I tip the cubes out, as I would with a jelly mould . I get ready made cubes that can be left as 3cm cubes or cut down in halves or thirds, etc

regards
Ian

[RosalieM]

I have kept the normal agar in the fridge in flasks with parafilm sealing it for quite some time. I think if you kept the phenolphthalein one it would be ok but keep in as air tight as possible and not ready made in the trays. I did try that once and it just dried out too quickly.