Ethanol in Universal Indicator Solution

[bigmack]

Hi all .

Just made a batch of Universal indicator ( pH4-10 )
0.025g thymol blue
0.0625g methyl red
0.5g phenolphthalein
0.25g bromothymol blue
500ml ethyl alcohol (ethanol)

adjust to green with sodium hydroxide dropper

I used Absolute Ethanol as we have a 20 liter drum of it but I was wondering can it be made with denatured Ethanol or Methylated spirits ?

[Merilyn1]

Denatured would be fine, but not sure on the metho. You're keen, I buy the UI ready-made.
Why do you have 20L? You got a still going - that's right you do, the one from the beer shop! And you told us it was for water, yeah sure Richard!

(Actually, I had a 20L drum of metho here when I started. I'm not sure who it belonged to. My coordinator was quite sure we hadn't bought it. Maintenance were happy to take it off my hands and I got back a truck load of space in my flammables cabinet. I guess no one is going to want that much Ethanol though)

[bigmack]

Thanks Merilyn
yeah I was wondering because denatured is way cheaper to buy and I didn't want to waste my precious

Why do you have 20L?

It has always been in the flammables cupboard . There's only 15 odd litres left in it now .
Stuffs worth an arm and a leg so no way am I giving it up

You got a still going - that's right you do, the one from the beer shop! And you told us it was for water, yeah sure Richard!

Haa ...no flies on you Merilyn ....unfortunately those airstills are good for about 50% ABV from a typical 10% ABV fermentation so not quite Lab grade . LOL , infact there's no way I'd drink that stuff either .Now setting up a reflux still might be the go ...Hmmm not sure if schools can do that though

........ I guess no one is going to want that much Ethanol though)

It's drinking grade

[Merilyn1]

Denatured is just ethanol with stuff added to it to make it taste bad. So, not for drinking! But otherwise, as far as I know, it's interchangeable for what we do.

[Labbie]

You two just crack me up, go Bigmack & Merilyn we need this on a Monday

[fibreweb]

We go through over 4 litres of Universal indicator each year so I make my own rather than purchasing.
Many years ago the lab assistant that I worked with ( that was back when there was one full time labby and one .8, now there is just me) decided to use Metho instead to cut costs.
She got the correct green colour with the NaOH but within days the solution had turned brown/red again and more drops of NaOH were needed to get it green again. This kept on happening.
I always use denatured alcohol and have streamlined the procedure by making up 500 stock solution bottles of the 4 indicators and then when I need to make more universal indicator I use 125 mls of each of the stock solutions then add distilled water to make up to 1Litre.
The recipes are
Thymol Blue; 0.1gm in 500 Ethanol
Methyl Red: 0.25 gm in 500 ml Ethanol
Phenolphthalein: 2gm in 500 ml Ethanol
Bromothymol Blue: 1gm in 500 mls Ethanol

The bottles then have the following instructions on their labels
"To make universal indicator from stock bottles add 125 mls of each of the 4 solutions into a 1 litre beaker
*Thymol Blue
*Methyl Red
*Phenolphthalein
*Bromothymol Blue
Add 500 mls distilled water.
If necessary adjust the colour to neutral green by adding 0.05 NaOH drop by drop.
They also state how many gms of the indicator is in 125 mls.

[carolyn miller]

I use Methylated spirits and don't have a problem, or haven't so far...