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hello i was just wondering if anybody had the receipe for agar with sodium hydroxide and phenolphthalein for a diffusion prac thanx

G'day Lee
I've found this one works great!
23g Agar powder, 565ml of 0.1M Sodium Hydroxide solution, heat to simmer an add tiny (TINY!) amount of powdered phenolphthalein to make a deep pink. Makes anough for 565mls or 3 marg. containers to a depth of 1, 2 & 3cm. We make trays and require 2400ml a time!
Hope this helps you.

Regards
Richard

That is on page 136 in "The Laboratory - a science reference and preparation manual for schools"

Preparation: 18g agar
4g sodium hydroxide
1 litre distilled water
phenolphthalein indicator

1. Dissolve the sodium hydroxide in approximately 100ml of the water.
2. Boil the remaining wter and add the agar, stirring constantly.
3. Allow cooling until temperature is below 60°C. Add sodium hydroxide solution, stirring constantly.
4. Add the phenolphthalein indicator drop by drop, again stirring constantly, until the agar is a DEEP PINK colour.
5. Pour into a shallow dish to a depth of 10 to 20 mm and allow to set.
NOTE: If made a couple of days before using, the blocks will develop a better colour.

Procedure:
1. Cut agar into appropriate sized blocks. (e.g., cut a 20x10x10mm block)
Halve the block to form two 10x10x10 blocks
Keep one and halve the other to form two 10x10x5 blocks
Keep one and halve the other to form two 10x5x5 blocks.
Keep one and halve the other to form two 5x5x5 blocks
Keep one and hallve the other to form a 5x5x2.5 block
e.g., Include a sphere or a pyramid with the rectangular blocks.
2. Add blocks to a beaker of 0.1M sulphuric acid; largest first, noting the time.
3. Time how long it takes for the different sized blocks to cecolourise.
4. Work ouot surface area to volume ratio for each block, and relate this to the time taken for each block to decolourise.

Good luck with it.
Sue

Agar 18g,sodium hydroxide 4g dissolved in a little water, phenolthalein solution 2ml,
boil 1l of distilled water and add the agar , as per normal agar making, cool 40 C dissolve sodium hydroxide in this solution and add phelpthalein indicator drop by drop until solution turns a deep pink. Pour into containers and allow to set.

use 0.1m sulphuric acid

from STAV Biology reference manual

A great big thankyou for helping us with the agar receipe you guys are great