Hi all,
Can anybody advise me? I have attempted to mix up some Cresol Red pH indicator according to the proportions of 0.5g to a litre of 20% Ethanol (scaled down to the quantity I needed). However, I can not get the powder to completely dissolve. Possibly about 40-50% remains in the bottom of the beaker. I had a similar problem with Methyl Red last week. Is there a trick that I have missed?
Regards,
Ian
Cresol Red Indicator?
Cresol Red Indicator
Hi Ian,
When mixing the Cresol Red try to use a Magnetic Stirrer. This way you can get the maximum amount to dissolve.. as you have found not all will. Then simply filter the whole solution as you need this for obvious reasons then bottle this and the clear solution is ready to be use as the desired indicator.
Keep in mind that some impurities lay within Indicators which cannot be helped, and the best way to resolve this is to filter the liquid.
Hope this is added to your repertoire.
Cheers,
Robb........
When mixing the Cresol Red try to use a Magnetic Stirrer. This way you can get the maximum amount to dissolve.. as you have found not all will. Then simply filter the whole solution as you need this for obvious reasons then bottle this and the clear solution is ready to be use as the desired indicator.
Keep in mind that some impurities lay within Indicators which cannot be helped, and the best way to resolve this is to filter the liquid.
Hope this is added to your repertoire.
Cheers,
Robb........
Dr Robert Crosdale. MRACI. NSS. NSSA. NASA.
Ph.D (Chem), Post Grad Ph.D (Physics), M.Ed, B.Sc (Hons), Dip. Appl. Sc. (Chem)
Lake Munmorah High School.
University of New England.
University of New South Wales.
University of Newcastle.
To understand the Universe from our perspective, we need to look towards our own backyard first for answers.
** AD ASTRA PER ASPERA - SEMPER EXPLORO **
Ph.D (Chem), Post Grad Ph.D (Physics), M.Ed, B.Sc (Hons), Dip. Appl. Sc. (Chem)
Lake Munmorah High School.
University of New England.
University of New South Wales.
University of Newcastle.
To understand the Universe from our perspective, we need to look towards our own backyard first for answers.
** AD ASTRA PER ASPERA - SEMPER EXPLORO **
-
Ian
- Posts: 575
- Joined: 16 Oct 2006, 10:00
- Job Title: Lab Assistant
- School: Macarthur Anglican School
- Suburb: Cobbitty
- State/Location: NSW
Thanks Rob.
I filtered it as you suggestedl. Then I popped the filter paper and filtrate into a beaker and added a few mls of ethanol to see what would happen. It disolved well in pure ethanol!
Perhaps, next time, I should add the powder to the ethanol, and then add the water, rather than to make up the 20% Ethanol and then try to disolve the powder in it as I did this time (???) Would there be a problem in doing it that way?
regards
Ian
I filtered it as you suggestedl. Then I popped the filter paper and filtrate into a beaker and added a few mls of ethanol to see what would happen. It disolved well in pure ethanol!
Perhaps, next time, I should add the powder to the ethanol, and then add the water, rather than to make up the 20% Ethanol and then try to disolve the powder in it as I did this time (???) Would there be a problem in doing it that way?
regards
Ian
Cresol Red Indicator
Hi Ian,
The best technique to use is the process you have suggested. Dissolving the Cresol Red in Ethanol (EtOH) first. The problem with using water and EtOH mixture is that the Cresol Red then becomes hydroscopic, hence the EtOH struggles to dissolve the Cresol Red and you are left with small quantities of undissolved Cresol Red.
If you were to dissolve the Cresol Red into the EtOH first, then mix this solution with water, I suggest you do that by adding small volumes of water with constant stirring, until you get to the desired volume, to prevent any Cresol Red from dropping out.
This has worked well in the past, but on occasions there will be times where filtering will certainly be needed. This is fine to do and will not interfere with what the Cresol indicator will be used for.
Thanks Ian,
Robb........
The best technique to use is the process you have suggested. Dissolving the Cresol Red in Ethanol (EtOH) first. The problem with using water and EtOH mixture is that the Cresol Red then becomes hydroscopic, hence the EtOH struggles to dissolve the Cresol Red and you are left with small quantities of undissolved Cresol Red.
If you were to dissolve the Cresol Red into the EtOH first, then mix this solution with water, I suggest you do that by adding small volumes of water with constant stirring, until you get to the desired volume, to prevent any Cresol Red from dropping out.
This has worked well in the past, but on occasions there will be times where filtering will certainly be needed. This is fine to do and will not interfere with what the Cresol indicator will be used for.
Thanks Ian,
Robb........
Dr Robert Crosdale. MRACI. NSS. NSSA. NASA.
Ph.D (Chem), Post Grad Ph.D (Physics), M.Ed, B.Sc (Hons), Dip. Appl. Sc. (Chem)
Lake Munmorah High School.
University of New England.
University of New South Wales.
University of Newcastle.
To understand the Universe from our perspective, we need to look towards our own backyard first for answers.
** AD ASTRA PER ASPERA - SEMPER EXPLORO **
Ph.D (Chem), Post Grad Ph.D (Physics), M.Ed, B.Sc (Hons), Dip. Appl. Sc. (Chem)
Lake Munmorah High School.
University of New England.
University of New South Wales.
University of Newcastle.
To understand the Universe from our perspective, we need to look towards our own backyard first for answers.
** AD ASTRA PER ASPERA - SEMPER EXPLORO **
