Phenolphthalein Agar

[Milo]

Indeed it does. I ended up buying a new microwave for us last week! Now I just need to make sure nobody uses it for their lunch...

[Labbie]

Good one Milo, is it in the prep room? We had a sign on the door of microwave, Needs deep cleaning if used for food.

[Milo]

Yes it's in the prep room, which directly adjoins the Science office. For now I've just written on it in texta, need to get around to making a sign.

[emma.hunt]

Hey,

So I've got this agar from 3-4 weeks ago. It's been stored in the fridge uncovered and has cracked and come away from the edges as you can see.
How do you all store yours for the next time someone wants to do this?
Is it past saving now?

Thanks

[Merilyn1]

Wrap it up in a few layers of cling wrap. This will help although I've never had to keep it longer than a few weeks.

[RosalieL]

Hi Emma,
It doesn't really last long. I do remember when I needed to keep some for later that if you keep putting phenolphthalein on top it helps to keep the colour and stops it drying out but I don't remember how long you can continue this. I don't remember keeping it for more than a few days to a week.
Rosalie

[Milo]

If you remelt it and put it in a bottle it will last until next year!

[Labbie]

WOW, milo, how do you melt it, water bath?

[Merilyn1]

The microwave when no one is looking??
(Actually - I probably wouldn't put this in the microwave with the chemicals it contains).

[Milo]

As documented in this thread I bought a microwave solely for use in Science prac prep! Whenever I have to deal with agar I feel very appreciative that I have it.

[Labbie]

Good buy Milo, it's oh so handy.

[labbassistant]

Hey,
So in the past when I've made the agar, it looks set but the bottom layer seems to crumble and not set properly.
We usually let it set overnight out of the fridge, then the next day in the fridge. (2 days for colour to develop well and set)

Should I put it straight in the fridge or keep it out?

Thanks!

[superbug]

Hi
Did you add too much agar? was it boiling enough to dissolve all the gelatine and mixed well when you added in the cold water to the final volume.
i also made some 2 days ago myself.
I place in unitrays and let it sit until it is cool enough to place in fridge. i wrap in gladwrap first and place them all in fridge ready for use.
it has kept in the fridge for a few months with no loss of colour.

[Merilyn1]

Hey,
So in the past when I've made the agar, it looks set but the bottom layer seems to crumble and not set properly.
We usually let it set overnight out of the fridge, then the next day in the fridge. (2 days for colour to develop well and set)

Should I put it straight in the fridge or keep it out?

Thanks!

I would guess the agar hadn't dissolved properly. Could be that you have had the heat too high to start with which can make it go lumpy (bit like making white sauce )
It will set out of the fridge and in fact can lose its colour a bit if it is cold. Usually best to bring it to room temperature.

[Anna Z]

We made up a huge batch this week, cooled on the bench then in the fridge. Love how the pink fades and then as it comes to room temp again it goes a nice pink. Fun stuff to play with, beakers are crap to wash . Oh and I found out, don't be tempted to add the hydroxide before you have a beautiful smooth agar..... it goes black

[Merilyn1]

Yeah, let it cool to below 60 deg before adding anything. I had to chuck my NaOH in at about 70 - went a bright yellow, so was just heavy handed with the phenolphthalein. All good

[bigmack]

Oh and I found out, don't be tempted to add the hydroxide before you have a beautiful smooth agar..... it goes black

Haa , thanks Anna . First time I made it that happened to me .Wasn't sure why .
It certainly is an art making this stuff .

[KassH]

First time in charge of this one. How do you dispose of the agar once the students have finished?

[bigmack]

Stuff they haven't used can be remelted and reused .

Stuff they have used ,I just poor it down the drain ( finger in the plug hole ). It has nothing growing on it so doesn't need to be Autoclaved

[KassH]

Thanks Bigmack.
I was more worried about the phenolphthalein in it. Does anyone have an other way of doing this prac without using it?