Australia's Science Forum

Does any one have the recipe for making up Universal Indicator. Its years since I have made any up, but can not find that recipe.

Thank you

Hi Sue

From 'The Laboratory' - page 143

0.025g Thymol Blue
0.0625g Methyl Red
0.5g phenolphthalein
0.25g bromothymol blue
500ml ethanol
Dissolve the 4 stains in the ethanol. Solution should be green in colour(neutral) If becessary, adjust using 0.05M sodium hydroxide drop by drop until a green colour appears.

Have fun!
Julie

Hi Sue,
I know it spoils the fun of making it up yourself, but Q-Stores sell a 500mL bottle of UI for around $37, as do Science Supply Australia, (similar price).
regards
Ian

Yes I must agree. I made up my own universal indicator once, not long after I started working in Science. Then when I discovered an easier source at a reasonable price (after all, we don't use all that much in our small school), I decided that making your own is a waste of time. Just buy it in. Much easier!!
Julie

Sue,
Omega Scientific in S.A. sell 500ml bottles for $23.20 (incl. GST) if you're interested.
Cheers,
Lisa

Hi All,

Keep in mind that Universal Indicator is not a generic indicator. It can be made from different types of Synthetic Indicators, so not all recipes will be identical. The excellent thing about the preparation of Uni indicators is that you can be very selective about what you put in them to match what you need.

One good tip I have not shared until now is to make a HIGH pH Uni Indicator solution and a LOW pH Uni Indicator solution. These two solutions can replace or work with RED and BLUE Litmus Paper.

Cheers,

Robb.....

I just discovered an inconsistency in a batch of Universal Indicator I made up compared to the bottle of commercially available indicator.
For Environmental Science (First Period) the class was doing some soil testing on different soils from around the school and we ran out of some of the indicator I made (all the results were around pH 6.5) including some soil samples the Assistant Principal who was running class bought in from home.

So I used the commercial one for another class (Third Period) and one of the Assistant Principals Soil Samples gave a reading of pH about 2.5-3, I was in the class room and was asked what was happening, I didn't know.

So today I tested both a sample of the indicator I made up and some the commercial one with:

Vinegar - both showed a pH of 3-4
2M HCl - both showed a pH of 2-3
Sodium Bicarb. Solution - Commercial showed a pH of 9-9.5, made up solution pH of 7-7.5
1M NaOH - Commercial showed a pH of 9.5-10.5; made up solution pH of 7-7.5

I would have to assume that the made solution was the problem here and so the results of the soil tests would have to be incorrect. Also this may sound like a stupid question but when you buy commercial Universal Indicator Solution do you use it straight or do you dilute it first?

Thanks
Andrew

I have always used it neat, now you have me questioning it too,
This is what I love about this site, there is always something else to learn, and learning from peers is the best way, I think!
cheers Lisa

Once it was printed on the label, dilute to 5 parts or something like that to 3 parts water. But not any more. We also just use it straight fromt the bottle.

HELP!!!!!!!!!

I have a problem with the universal indicator that I made up this morning. I have made it up a gazillion times before with no problems

Following the instructions I added the four indicators to 500 mls ethanol and then added 500ml de-ionised water. This usually send to solution a red/brown colour, about pH 5 and then I add NaOH 0.1M drop by drop until I get the green colour that I need.

This time as i added my de-ionised water it turned blue immediatly about pH8. Upon further investigation it turns out my de-ionised water for some reason now has a pH of 8 itself where it is more often around the 6.5 mark. So I can understand what happened.

What I done know is if I can add something to get it back to the right colour, and whether what I add will affect it's accuracy? I tried a small amount in a beaker with .05M HCl but it jumped straight back to pH about 4.

Has anyone come across this problem before? Should I try a weaker acid like acetic acid in a small bit to see what happens?

I'm only back at work for 3 hours each day as my leg gets better so haven't got a lot of time to keep fiddling until I get it right.

With the cost of ethanol and the indicators I am loath to throw out the 1L of solution if I don't have to. We go through over 4 litres of universal indicator a year so at $37 for 500 ml buying it made up isn't an option.

Any suggestions?

Wendy

Hi Sue
I buy universal indicator- much easier than making ,as you have to have 4 different ingredients on hand. However I did find a recipe for you.

Dissolve in 500mls of ethanol all of the following:

0.025g thymol blue
0.0625g methyl red
o.5g phenolphthalein
0.25g bromthymol blue
Dilute this solution to 1 litre with distilled water.
Add drops of 0.05M of sodium hydroxide until green colour appears.
And there you have it!!!!!
Hopes this helps you.
Cheers
Mother

That's the recipe I used and when I added the distilled/de-ionised water it went straight to dark blue!!!!!!

I know my water has a pH of over 8 so tomorrow I will investigate why. I've bought some distilled water from the supermarket to try again if I can't salvage the lot I made.

Wendy

Hi Wendy
Let us know how it turns out,would you??
Have a good day!!!
Mother

Hi Wendy

I have had very high pH readings for my tapwater lately, too, and it's really unusual because our tap water has always been really pure and neutral, to the point where I used to feel I was wasting my time distilling it. My chemistry teacher is thinking about approaching the local council and asking them about the water supply. So far it's a mystery.

Julie

I realised this morning I had accidentally used Bromophenol Blue instead of Bromothymol Blue but I still think the high pH of the water had a lot to do with it.

Today I discarded the solution and started again ,this time with a bottle of purchased distilled water ph 7. It worked beautifully.

Our resin in the de-ioniser is over 12 months old so maybe I need to replace it.

Wendy

I have always made our Universal Indicator as we use so much of it. I also substitute Methylated Spirits for the Ethanol, as one time I ran out of Ethanol, and the Metho worked just as well, for us anyway. Of course, it made the stuff cheap as chips.

I agree Dime; I also make our own and we do use about 2-3 litres each term. I think it is fun to make, and I also have tried metho and it seems to work just fine. I use the recipe in the "Laboratory" book too.

I used Metho one time and after a few weeks the indicator went brownish agoin and I needed to add a few more drops of NaOH to get it back to green.

Wendy

I think it depends on how much NaOH you put in. After making on Ethanol many years ago, it reverted to red a few weeks later. And as you say, just had to add some more NaOH and voila! So I make sure it is a strong green to stop it reverting.

I used to make up my own too... Was Ok for Juniors - and cheap!
BUT - we now have some teachers of senior classes who didn't like the home-made one because the colours weren't exactly the same as the Colour Card... they were close, but not close enough....


So - now I purchase it ready made ...all that fun i used to have...sigh ...