Talk:Phenolphthalein

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How can one have a pH of less than zero? A pH of zero (also physically impossible) would mean that the concentration of H+ ions is 100%. A pH of less than zero would mean the concentration of H+ ions is more than 100%.MarkDoc704 17:33, 25 July 2007 (UTC)

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[edit] Comments

This page is badly formatted in MSIE, and I have no idea how to correct the "colorless" bit in the box for MSIE and Opera. It works in Firefox, but the long vertical image causes problems there.. 218.102.71.159 10:47, 28 November 2005 (UTC)

There isn't any info about what pH the indicator returns back to clear in highly basic conditions (ie when the concentration of "Phenolphthalein(OH)3-" is highest). Any reason for this?


Not sure about the coding problems - it seems to show up fine in Opera 9b2 for me.

As for the pH of changing back to colorless - I did some experiments the other day and found that the maximum absorption (i.e. when the solution is the most pink) occurs around pH 12 or so. I didn't need any more accuracy than that, but at least it'll give you a starting point.

Hope this helps.

Zxian 18:29, 24 May 2006 (UTC)


The chart in the body of the article appears to say that phenolphthalein is only pink between pH 8.2 and pH 10.0. Isn't this misleading if the maximum absorption is above pH 10?

The chart directly contradicts the box in the upper right hand corner which says that phenolphthalein is pink above pH 10.0.

9 Feb 2007

[edit] Error!

Why is the melting point listed as higher than the boiling point? —The preceding unsigned comment was added by 74.64.65.118 (talk) 16:40, 18 February 2007 (UTC).

[edit] Structure for In

Does anyone know exactly what this is (i.e. the form present below pH 0) - as it leaves rather a hole in the article. 86.148.60.205 19:54, 2 March 2007 (UTC)

[edit] Laxative Use

A quick note (this is not really article material): James Outlaw, PhD (a chemistry professor I know) tells me that there are two reasons for keeping the indicator (phenolphthalein) present all of their labs' pure ethanol. First, it is handy to have so you aren't required to add it later for any acid/base titration. However, the second reason is related to its medical uses. By adding the indicator to otherwise pure drinking alcohol, the ethanol is rendered undesirable to drink, as the phenolphthalein would cause severe diarrhea. Josh3580 14:31, 5 March 2007 (UTC)


[edit] Uses - Construction

I know phenolphthalein is used in construction materials testing (for roadways especially), to test for the presence of stabilizing agents in soils, such as lime, cement, or fly-ash, because it picks up the presence of Calcium ions or CaO, or something similar. However, i'm not familiar with the chemistry of it, can someone more knowledgeable add it to the 'uses' section in the article?Foij00 21:06, 11 May 2007 (UTC)

[edit] Response to Error!

Error! Why is the melting point listed as higher than the boiling point? —The preceding unsigned comment was added by 74.64.65.118 (talk) 16:40, 18 February 2007 (UTC).

Chemfinder has the same information listed, I'm guessing it just got copied from there.

The CRC lists the mp as 262.5 C and does not list a boiling point. I will try to fix this.

2003. CRC Handbook of Chemistry and Physics 84th Ed. Chemical Rubber Publishing Company, Boca Raton, FL

P.S. This page is a disaster.

[edit] Pronunciation

What is the pronuncation for phenolphthalein? --139.103.73.75 23:23, 8 November 2007 (UTC)

[edit] pH

What is the pH of phenolphthalein? 72.67.175.145 (talk) 07:14, 13 December 2007 (UTC)

[edit] Contradictory

This article has contradictions. The orange in acid is contradictory to the text, or if not needs further explanation. —Preceding unsigned comment added by 80.176.155.189 (talk) 22:31, 2 January 2008 (UTC)

[edit] Orange color in concentrated strong acid

I tried the following reactions: Phenolphthalein + concentrated sulfuric acid -> orange Phenolphthalein + concentrated hydrochloric acid -> pale yellow According to my chemistry teacher, the orange is due to phenolphthalein reacting with the sulfate (instead of the protons) and the pale yellow is the natural color of phenolphthalein. Andrey (talk) 01:58, 24 January 2008 (UTC)

Doubt it. It's just that conc. HCl is not as strong an acid as conc. H2SO4, and so cannot deprotonate phenolphthalein to its red form.
What does your teacher suggest the sulfate is doing to cause the orange colour?
Ben (talk) 20:07, 24 January 2008 (UTC)

Maybe it's possible to redox iodine crystals in the presence of hydrogen to get concentrated hydroiodic acid. Then just mix HI powder, phenolphthalein, and a bit of water and see what happens, since Ka HI > Ka HCl. Andreyvul (talk) 18:53, 26 January 2008 (UTC)

[edit] Error concerning colour in acidic and alkaline solutions

I believe that the colour phenolphthalein turns in an acidic solution is COLOURLESS not orange and in a neutral solution a pink tinge and in alkaline pink. Is this correct? Several other websites back this up as does my chemistry teacher and a practical OCR chemistry paper. Please could someone infrom me if this is correct as i did not want to change the infomation on the page straight away. Many Thanks. —Preceding unsigned comment added by AdamJKB (talk • contribs) 11:48, 9 May 2008 (UTC)