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Hi All,

I need to make some phenolphthalein agar sheets 0.5cm, 1cm and 2cm thick. I have tried to do a search but it does not seem to work. Does anyone have a method?

Sharls

Boil 2.5 L water, Add when water is boiling 50g agar, when mixed take off heat. Add 1/2 teaspoonful of Phenolphthalein powder, Add a few drops of 2m Sodium hydroxide, until it turns a deep pink in colour.

Pour into your containers, and pop in fridge.

Or 1.5 L Water and 40g agar with 1/2 teaspoonful of phenolphthalein powder.

Freezing causes moisture to leak out leaving cracks and wrinkles, so only store in the fridge.

Thanks Sue that's great!
Sharls

I have used the recipe which is in "The Laboratory" manual by B.Dungey which every lab technician should have at their fingertips. However I use 20g of agar per litre of distilled water to make a firmer usable agar.
20g agar
4g sodium hydroxide (solid)
1 litre distilled water
Dissolve sodium hydroxide in 100ml water. Bring rest of water to the boil but add agar just before the water boils to stop lumps from developing. Stir the water constantly while you add agar slowly. Make sure that the agar has a clear quality before taking off the boil. Cool the agar to somewhere between 60 degrees and 40 degrees centigrade depending on which recipe you are following (I sometimes can't wait that long) and add the sodium hydroxide solution. Then add phenolphthalein indicator drop by drop until it turns a deep pink. Or simply add 10ml of indicator and be done with the fiddling. Add more if deeper colour required.
I would also discuss with the teacher who is doing the prac that it would be far better for the students to cut their own blocks of agar to size as part of their prac. This means that you will only have to make up a number of large 1 litre takeaway containers of agar roughly 2cm in depth. Make allowances if you have a bottom that is not flat. Definitely prepare one or two days beforehand so that the agar can be handled without breaking. Store in fridge so the ants or other vermin don't eat it. Use gloves when handling.
Lots of luck, Lyn.

If you do a search for 'agar revisited' you will find another thread on this topic

I agree with Lyn. I use my "the laboratory" constantly
Have a nice day
lada

Thanks Lyn, that is a great method. I will have to try a get a hol of 'The laboratory'.
Sharls

I too, use the Laboratory as a bible and have made the phenolphthalein agar to their recipe. The only thing I do differently is that I add 1g phenolphthalein powder after the sodium hydroxide which gives a more than adequate pink and the results of the experiment is always good. Saves a lot of time mucking around than with drop by drop and it has worked each time I have done it now.

Regards,
Lou.

Hi Sharls, Just check the Southern Biological online catalogue. They have a revised edition and it's about $64-$65. Worth badgering your head of department to get one in. Downside is that you might have to keep it under lock and key so that the science teachers won't spirit it away. It does have really useful information in it.
Lyn.

Hi Sharls
I use a receipe like Sue's but have put in up to 80g agar in 2.5L water. Maybe my agar is old but the one time I put 50g in it didn't set. I was trying to save agar because I lost the first batch when the 3L beaker broke at the base - what a mess - it was like a wave that froze -you should have seen the drawer handles! I had to reheat the second batch and add more agar .Third time lucky that day.
Sue G

Hi all

Someone must have been reading my mind today. I was panicking because I couldn't find my recipe so I thought I would ask and low and behold there it was.

I don't write on this site because I know so little about Science but to every body that does contribute I thank you from the bottom of my heart for all the information and practical assistance you all give me. I am learning a lot and feel more confidant just knowing there is someone on the computer.

Thanks all

Cindy

PS I also don't know how to get rid of the smilies. I'm not really drunk

Hi Cindy,
I'm like you,unwilling to say much because I can't say a lot with confidence! But I learn something every day and certainly pay homage to those who have experience and share their knowledge. Adam did a great thing when he started this site.
By the way, Happy Birthday to "rae" and "Cactus 155" - 21 again?
Lou.