Ethanol in Universal Indicator Solution

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bigmack
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Joined: 15 Dec 2015, 10:49
Job Title: Lab Assistant
State/Location: NSW

Ethanol in Universal Indicator Solution

Post by 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
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Re: Ethanol in Universal Indicator Solution

Post by 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! :D

(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
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Job Title: Lab Assistant
State/Location: NSW

Re: Ethanol in Universal Indicator Solution

Post by bigmack »

Thanks Merilyn
yeah I was wondering because denatured is way cheaper to buy and I didn't want to waste my precious
Merilyn1 wrote: 05 Nov 2018, 13:13 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 :crazy:
Merilyn1 wrote: 05 Nov 2018, 13:13You 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! :D
Haa ...no flies on you Merilyn :D ....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 8) ...Hmmm not sure if schools can do that though
Merilyn1 wrote: 05 Nov 2018, 13:13 ........ I guess no one is going to want that much Ethanol though)
It's drinking grade :cheesy:
Merilyn1
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Joined: 12 Mar 2013, 08:10
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School: Wollondilly Anglican College
Suburb: Tahmoor
State/Location: NSW

Re: Ethanol in Universal Indicator Solution

Post by 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.
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Labbie
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Re: Ethanol in Universal Indicator Solution

Post by Labbie »

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

Lab Manager/Lab Tech, mind reading etc etc
Now retired :wub:
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fibreweb
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Re: Ethanol in Universal Indicator Solution

Post by 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
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Re: Ethanol in Universal Indicator Solution

Post by carolyn miller »

I use Methylated spirits and don't have a problem, or haven't so far... :D
bigmack
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State/Location: NSW

Re: Ethanol in Universal Indicator Solution

Post by bigmack »

carolyn miller wrote: 21 Nov 2018, 08:45 I use Methylated spirits and don't have a problem, or haven't so far... :D
Thanks for the glimmer of hope Carolyn .
I just made up some more last week , but this time I used Metho , It's OK still so I'm feeling confident .
fibreweb wrote: 21 Nov 2018, 08:43 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.
That happened to me fibreweb , but I had used Absolute Ethanol . It was maybe 6 months later and only happened once :-?

Now what was interesting is that the instructions say to adjust colour to green with 0.05M NaOH drop by drop .
Now I don't know if that is a typo , but both times I have made it I've put in about 100 drops and realized that there is something screwy going on . I ended up with more like 30 drops of 1M NaOH before switching to 0.1M .

Anyone else find this ? incidentally I'm using distilled water, not tap water and making a 2 litre batch.
Sunvalley
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Joined: 03 Feb 2017, 08:43
State/Location: NSW

Re: Ethanol in Universal Indicator Solution

Post by Sunvalley »

metho works for us. Just the regular coles brand. Ive had no problems with it changing colour and yes i adjust with 1M it takes to much other wise. I usually just give it a squirt while its on a stirrer with a flea and keep adding a few drops until it stays green. We've had it stored that way for months. I make up 2 L at a time on metho
Thymol Blue 0.10g
Methyl Red 0.25g
Phenophthalein 2.00g
Bromothymol Blue 1.00g
A lot easier volumes to manage.
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