indicators

[RosalieM]

Hi All,
I'm needing to make up some more indicators. Some of my recipes say to use ethanol (eg for phenolphthalein and methyl red). Does metho do the job just as well? It is far cheaper and easier to order...
Rosalie

[Mother]

Hi Rosalie
I use metho for the indicators you mentioned,haven't had any problems
Cheers
Mother

[Whspa]

I also use metho.

Carol

[RosalieM]

Thanks - this is the first time I've had to make them up as there was already quite a supply when I started working here. I'll go with the metho then!

[RosalieM]

Today I actually had time to start making up my indicators... but when I got to Litmus, I found that 10g in 500ml water (which is what my recipe says) isn't dissolving. I had it on the hotplate/magnetic stirrer for ages, then I added extra water to make it up to almost 1L but it still hasn't dissolved! Does anyone have a different recipe? I just looked it up in the catalogue because 10g almost finished the jar and it is about $45 for 25g so I don't want to waste it by getting it wrong!

I also had trouble dissolving bromothymol blue in water (5g in 500ml), so I ended up filtering it out. Then I came across another recipe while looking for the litmus one which said 1g in 1L. What do other people use?

Rosalie

[cheltie]

Hi Rosalie,
I just checked my recipes.
Litmus says boil 10gms in 500mls distilled water. Stand until powder settles and filter.
I guess this is similiar to yours.
My Bromothymol blue recipe says only 0.1g in a litre of distilled water. If green add .4% NaOH a drop at a time until it turns blue.
Don't know if this helps.
Helen

[Marjan]

Hi Rosalie;
I got both recipes from The Laboratory Manual. it says you need to filter them both at the end as they wouldn't dissolved 100%.
Litmus indicator:
Boil 10g of litmus in distilled water. Make up to 1L and allow to cool. filter
Bromothymol blue:
Dissolve 0.4g bromothymol blue in 200mL ethanol, make up to 1L with distilled water. filter
I made them up afew weeks ago and worked well.
Hope these would help.
Cheers
Marjan

[Whspa]

I boil 5g of litmus in a litre of water, let it stand, then filter it. The litmus granules don't really dissolve, but the water turns a deep blue - which is what you want.
I make up bromothymol blue 0.4g per liter of 20% ethanol (metho).

These recipes come from the "Manual for School Assistants Working in Science".

Hope this helps.

Carol

[RosalieM]

Thank you! I guess my instructions were misssing the 'filter' step... Not to worry - hopefully they all indicate what they are supposed to by the time I finish with them!
Rosalie