Today I Heard My First . . . . .
ChatterBank1 min ago
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I can't think of any substance offhand that's used used as a pH indicator and has the colour changes specified by hollytree.
The colour change of a red cabbage solution is not really similar to litmus. The colour changes are more or less as stated by Muppit.
There is a substance called delphinidin 3-glucoside which is present in hydrangea flowers combined with colourless quinic acid derivatives. This anthocyanin does meet the requirements of hollytree but it's difficult to isolate and totally impractical to use as a pH indicator in laboratory situations. In any case, the colour change is really from pink to blue rather than red to blue. It's also necessary for aluminium to be present in the soil for this change to occur in hydrangea bushes.
The colour change of a red cabbage solution is not really similar to litmus. The colour changes are more or less as stated by Muppit.
There is a substance called delphinidin 3-glucoside which is present in hydrangea flowers combined with colourless quinic acid derivatives. This anthocyanin does meet the requirements of hollytree but it's difficult to isolate and totally impractical to use as a pH indicator in laboratory situations. In any case, the colour change is really from pink to blue rather than red to blue. It's also necessary for aluminium to be present in the soil for this change to occur in hydrangea bushes.
This wouldn't be a quiz question by any chance hollytree, because I'm sorry to say they've got it wrong.
Congo Red is used as an indicator in the range pH 3.0 to pH 5.0. As you know, a neutral solution has a pH of 7, acids have a pH between 0 and 7and bases (alkalies) a pH from 7 to 14.
At pH 7.0, a solution of Congo Red is red. If you add acid to such a solution, it will remain red until it reaches pH 5.0. At pH 4.0 it's purplish red and from pH 3.0 to pH 0, it's blue. Here's a link for you to see it visually:
http://antoine.frostburg.edu/chem/senese/101/a cidbase/indicators.shtml
Now although a solution of Congo Red is red from pH 8.0 upwards this change will have already happened while the solution has an acid pH ie at pH 5.0. So it's incorrect to say that it's red in alkaline solutions and blue in acid.
Officially, Congo Red has the scale 3.0 (blue) to 5.0 (acid)
Incidentally, for those that want to check it out on Wikipedia, the Congo Red article has been copied and pasted verbatim from a biological suppliers page:
http://www.nilesbio.com/subcat277.html.
A solution of Congo Red is already red at pH 5.0 and not pH 5.2 as stated
Congo Red is used as an indicator in the range pH 3.0 to pH 5.0. As you know, a neutral solution has a pH of 7, acids have a pH between 0 and 7and bases (alkalies) a pH from 7 to 14.
At pH 7.0, a solution of Congo Red is red. If you add acid to such a solution, it will remain red until it reaches pH 5.0. At pH 4.0 it's purplish red and from pH 3.0 to pH 0, it's blue. Here's a link for you to see it visually:
http://antoine.frostburg.edu/chem/senese/101/a cidbase/indicators.shtml
Now although a solution of Congo Red is red from pH 8.0 upwards this change will have already happened while the solution has an acid pH ie at pH 5.0. So it's incorrect to say that it's red in alkaline solutions and blue in acid.
Officially, Congo Red has the scale 3.0 (blue) to 5.0 (acid)
Incidentally, for those that want to check it out on Wikipedia, the Congo Red article has been copied and pasted verbatim from a biological suppliers page:
http://www.nilesbio.com/subcat277.html.
A solution of Congo Red is already red at pH 5.0 and not pH 5.2 as stated
Check out this link.
http://en.wikipedia.org/wiki/Ph_indicator
http://en.wikipedia.org/wiki/Ph_indicator
Ha. Thanks wideboy for directing us to another Wikipedia site containing cr@p.
First of all, the first link I provided in my answer above showed the transition colours between blue and red of Congo Red as the pH increases. The link shows more clearly what happens as the pH rises including the purplish colour around pH4.0. The Wikipedia article shows the two end point pH colours which is not quite as useful.
The article you provide a link to claims that the "low pH colour" is blue-violet: it's not, it's blue. The article also says the "Transition Range" is between 3.0 and 5.0 which is exactly what I said, yet if you look at the Wikipedia Congo Red article, it's given as 3.0 to 5.2. It's a bit confusing for the unfamiliar, yes?
Finally, and probably most damning for me as a biochemist, the article states that anthocyanins are "are red in acidic solutions and blue in basic". Well, the reality is that some are but a considerable number are not. I've just written down fifty-two off the top of my head that are not and there are hundreds more.
To make matters worse, the article author appears to want to link this statement with the hydrangea photograph. He/She couldn't be more mistaken because, as I said in my 13:21 post on 9/6/07, the anthocyanin present in hydrangeas is blue in acidic conditions and pinkish-red in basic (alkaline) conditions, just like hollytree wanted.
Wikipedia has a lot to answer for.
First of all, the first link I provided in my answer above showed the transition colours between blue and red of Congo Red as the pH increases. The link shows more clearly what happens as the pH rises including the purplish colour around pH4.0. The Wikipedia article shows the two end point pH colours which is not quite as useful.
The article you provide a link to claims that the "low pH colour" is blue-violet: it's not, it's blue. The article also says the "Transition Range" is between 3.0 and 5.0 which is exactly what I said, yet if you look at the Wikipedia Congo Red article, it's given as 3.0 to 5.2. It's a bit confusing for the unfamiliar, yes?
Finally, and probably most damning for me as a biochemist, the article states that anthocyanins are "are red in acidic solutions and blue in basic". Well, the reality is that some are but a considerable number are not. I've just written down fifty-two off the top of my head that are not and there are hundreds more.
To make matters worse, the article author appears to want to link this statement with the hydrangea photograph. He/She couldn't be more mistaken because, as I said in my 13:21 post on 9/6/07, the anthocyanin present in hydrangeas is blue in acidic conditions and pinkish-red in basic (alkaline) conditions, just like hollytree wanted.
Wikipedia has a lot to answer for.
Then we'll have to differ in our opinions xud.
Wikipedia masquerades as a reliable, authoritative online resource. The reality is that it will never be this as long as everyone from a schoolchild to a world expert is allowed to edit, review and rewrite the articles it contains as often as they deem necessary. No matter how complex an article or subject, everyone is allowed to discard and rewrite whole swathes of an article that might, just might have been written by a true "expert" in that field originally. The end result is a right hodge-podge of information, that more often than not, does not provide a true picture of the subject concerned and is often misleading.
The website owners admit themselves that this is a major problem. Take a look at the article on George Bush and you'll see that they've had to prevent people from editing the article. The reason is that the users of the site have put malicious comments, lies and other claptrap amongst what would otherwise be a reliable article.
Likewise, having spent years as a biochemist, I know that not all anthocyanins are red in an acidic solutions and blue in basic solutions. Yet some idiot has gone and written that they are, without properly researching the subject. This is misleading to say the least and such things allow true scientists to dismiss Wikipedia. That's the bottom line because scientists work with fact not speculation.
Would you consider buying a textbook on a scientific or engineering subject that had been written by an unqualified, inexperienced individual? I can guess your answer, yet Wikipedia is saturated with such stuff that has been written by those that consider themselves knowledgeable no matter how old or experienced they are. How can such a site be considered a "good" source of info?
Try it yourself. You must have a hobby or a particular field of expertise that you know a lot about. Read the Wikipedia articles
Wikipedia masquerades as a reliable, authoritative online resource. The reality is that it will never be this as long as everyone from a schoolchild to a world expert is allowed to edit, review and rewrite the articles it contains as often as they deem necessary. No matter how complex an article or subject, everyone is allowed to discard and rewrite whole swathes of an article that might, just might have been written by a true "expert" in that field originally. The end result is a right hodge-podge of information, that more often than not, does not provide a true picture of the subject concerned and is often misleading.
The website owners admit themselves that this is a major problem. Take a look at the article on George Bush and you'll see that they've had to prevent people from editing the article. The reason is that the users of the site have put malicious comments, lies and other claptrap amongst what would otherwise be a reliable article.
Likewise, having spent years as a biochemist, I know that not all anthocyanins are red in an acidic solutions and blue in basic solutions. Yet some idiot has gone and written that they are, without properly researching the subject. This is misleading to say the least and such things allow true scientists to dismiss Wikipedia. That's the bottom line because scientists work with fact not speculation.
Would you consider buying a textbook on a scientific or engineering subject that had been written by an unqualified, inexperienced individual? I can guess your answer, yet Wikipedia is saturated with such stuff that has been written by those that consider themselves knowledgeable no matter how old or experienced they are. How can such a site be considered a "good" source of info?
Try it yourself. You must have a hobby or a particular field of expertise that you know a lot about. Read the Wikipedia articles
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