Phenolphthalein Agar
- Labbie
- Posts: 3259
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Re: Phenolphthalein Agar
Good buy Milo, it's oh so handy.
Regards Labbie
Lab Manager/Lab Tech, mind reading etc etc
Now retired
Lab Manager/Lab Tech, mind reading etc etc
Now retired
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- Posts: 75
- Joined: 18 Aug 2021, 09:33
- Job Title: Labbie
- School: Wollongong High School
- State/Location: NSW
Re: Phenolphthalein Agar
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!
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!
Re: Phenolphthalein Agar
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.
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.
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- Posts: 1548
- Joined: 12 Mar 2013, 08:10
- Job Title: Labbie
- School: Wollondilly Anglican College
- Suburb: Tahmoor
- State/Location: NSW
Re: Phenolphthalein Agar
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 )labbassistant wrote: ↑25 Feb 2022, 10:37 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!
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
- Posts: 275
- Joined: 16 Feb 2021, 14:39
- Job Title: Lab Manager
- School: DET Secondary School
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Re: Phenolphthalein Agar
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
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Re: Phenolphthalein Agar
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
- KassH
- Posts: 68
- Joined: 16 Oct 2020, 10:14
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- School: SPC KMPSY
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Re: Phenolphthalein Agar
First time in charge of this one. How do you dispose of the agar once the students have finished?
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Re: Phenolphthalein Agar
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
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
- Posts: 68
- Joined: 16 Oct 2020, 10:14
- Job Title: Lab Tech
- School: SPC KMPSY
- State/Location: NSW
Re: Phenolphthalein Agar
Thanks Bigmack.
I was more worried about the phenolphthalein in it. Does anyone have an other way of doing this prac without using it?
I was more worried about the phenolphthalein in it. Does anyone have an other way of doing this prac without using it?
- Anna Z
- Posts: 275
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- School: DET Secondary School
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Re: Phenolphthalein Agar
if it's still solid, we throw it in the bin.
- cactus155
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Re: Phenolphthalein Agar
If you are worried place it in either NaOH (if its the clear one) or an acid (if its the pink one) as I believe the pH should be neutral or close to when the colour has changed to the opposite so pink to clear or clear to pink, drain and then throw in bin or just throw straight into bin
- KassH
- Posts: 68
- Joined: 16 Oct 2020, 10:14
- Job Title: Lab Tech
- School: SPC KMPSY
- State/Location: NSW
Re: Phenolphthalein Agar
Has anyone tried doing this one with a different indicator? I worry about giving the students the phenolphthalein and also the younger female teachers. They wear gloves but if we can eliminate the risk all together that would be better. Right?
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Re: Phenolphthalein Agar
Yes!
We made some with Bromothymol Blue, it was great! Southern Biological have a video showing how they do it, we ended up needing to add a little more sodium hydroxide than they did, but it came out great!
We gave 1M acetic acid but found 0.1M sulfuric was better
We made some with Bromothymol Blue, it was great! Southern Biological have a video showing how they do it, we ended up needing to add a little more sodium hydroxide than they did, but it came out great!
We gave 1M acetic acid but found 0.1M sulfuric was better
- KassH
- Posts: 68
- Joined: 16 Oct 2020, 10:14
- Job Title: Lab Tech
- School: SPC KMPSY
- State/Location: NSW
Re: Phenolphthalein Agar
Thank you labbassistant!!!
I knew there'd have to be a better option.
I found one video that used zucchini with liquid food dye but it just didn't cut it.
I knew there'd have to be a better option.
I found one video that used zucchini with liquid food dye but it just didn't cut it.
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- Posts: 1548
- Joined: 12 Mar 2013, 08:10
- Job Title: Labbie
- School: Wollondilly Anglican College
- Suburb: Tahmoor
- State/Location: NSW
Re: Phenolphthalein Agar
I have one teacher who prefers to use potato and iodine.