Hi all,
Welcome back to a new year!
Can any one shed some light on this one? It seems that our Phenolphthalein solution goes milky. It seems alright in the dropper bottle, but if put into a clean dry beaker, within a few minutes it goes milky white. Is this normal? One of my Year 7 teachers wanted a few drops of "Clear" phenolphthalein in the bottom of a beaker for a "Chemical Magic" trick, but when he went to use it, it was no longer clear! Our Senior Chem teacher has been having trouble with it in his titrations also. Any ideas?
Regards
Ian
Phenolphthalein problems?
Phenolphthalein problems
Hi Ian,
our recipe for this indicator is:
2 grams of phelolphthalein dissolved in 600mL ethanol.
Made up to 1 litre with distilled water and filtered if needed.
As most of the solution is alcohol, it evaporates readily and can leave a white ppt.
Maybe make it a little weaker for that experiment??
~Robyn
our recipe for this indicator is:
2 grams of phelolphthalein dissolved in 600mL ethanol.
Made up to 1 litre with distilled water and filtered if needed.
As most of the solution is alcohol, it evaporates readily and can leave a white ppt.
Maybe make it a little weaker for that experiment??
~Robyn
phenolphthalein problems
Sorry,
also Ian, when we do this experiment, we roll only a drop or two of the indicator around in the beaker so the cloudiness is less obvious until it has to react.
hope this helps,
~Robyn
also Ian, when we do this experiment, we roll only a drop or two of the indicator around in the beaker so the cloudiness is less obvious until it has to react.
hope this helps,
~Robyn
Preparation of Phenolphthalein
Hi All,
There is a way to avoid the white opaque colour you get when you use Phenolphthalein, but I will address Ian's problem first.
The Ethanol is evaporating upon additions of the Phenolphthalein (PP) due to the PP being exposed to warm conditions and when you spread this over a large surface area eg, Beaker it evaps more rapidly.
1. To avoid this it is ideal to make the solution up in water first, YES water first we all know that PP is Insoluble in water but some does dissolve and it is this process which causes the PP to become "wet".
I make a 1% solution which is more than enough to give a change in colour, and when this is used in titrations the Ethanol does not interfere with the final pH, (As ethanol will change pH if there is a high content present).
Make quantities up only as you need them and carry on with the following steps.
2. A magnetic stirrer makes the mixing much more efficient, as this keeps the PP and water in interaction with each other. After around 5 Minutes of stirring, begin to add Ethanol to allow the PP to just dissolve. (here, you have now reached the solubility constant of the PP). Add NO MORE PP and just allow the mixture to stir for a further 5 minutes. This will allow the Ethanol to absorb water which it naturally does, and continue with the next step.
3. Now add to the mixture a further 100mL of Ethanol to make sure this will dissolve any PP that may try to drop out of solution upon storage.
Including the 100mL Ethanol addition at the end allow the total volume to be the required volume to give you the 1% w/v needed.
This will serve you well for many indicator uses.
(The interaction of the water is important to the PP and Ethanol as you can see as this wets the whole solution and allows for minimal evaporation as the moisture content of Ethanol has increased).
But the method ri has outlined would also be suitable for your needs.
Hope this adds to your repertoire of Preparation steps.
Cheers,
Robb.....
There is a way to avoid the white opaque colour you get when you use Phenolphthalein, but I will address Ian's problem first.
The Ethanol is evaporating upon additions of the Phenolphthalein (PP) due to the PP being exposed to warm conditions and when you spread this over a large surface area eg, Beaker it evaps more rapidly.
1. To avoid this it is ideal to make the solution up in water first, YES water first we all know that PP is Insoluble in water but some does dissolve and it is this process which causes the PP to become "wet".
I make a 1% solution which is more than enough to give a change in colour, and when this is used in titrations the Ethanol does not interfere with the final pH, (As ethanol will change pH if there is a high content present).
Make quantities up only as you need them and carry on with the following steps.
2. A magnetic stirrer makes the mixing much more efficient, as this keeps the PP and water in interaction with each other. After around 5 Minutes of stirring, begin to add Ethanol to allow the PP to just dissolve. (here, you have now reached the solubility constant of the PP). Add NO MORE PP and just allow the mixture to stir for a further 5 minutes. This will allow the Ethanol to absorb water which it naturally does, and continue with the next step.
3. Now add to the mixture a further 100mL of Ethanol to make sure this will dissolve any PP that may try to drop out of solution upon storage.
Including the 100mL Ethanol addition at the end allow the total volume to be the required volume to give you the 1% w/v needed.
This will serve you well for many indicator uses.
(The interaction of the water is important to the PP and Ethanol as you can see as this wets the whole solution and allows for minimal evaporation as the moisture content of Ethanol has increased).
But the method ri has outlined would also be suitable for your needs.
Hope this adds to your repertoire of Preparation steps.
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 **
Phenolphthalein
Hi Ian,
Let me know how you get on with the prep.
Cheers,
Robb.....
Let me know how you get on with the prep.
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 **
