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Science Forum Index » Chemistry Forum » lactose and Fehling essay...
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| rossella... |
 Posted: Sat Jun 21, 2008 10:47 am |
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Hi and sorry again,
inorganic chemistry is now "past" (I passed my exam) while I'll have
to repeat in July the organic chemistry part.
One of the questions I found in the exam was about what happens to
lactose during the Fehling essay.
I just remember that lactose is made of galactose + glucose and that
the free OH group belongs to glucose.
The only thing that came to my mind was gluconic acid.
When the professor gave us the results he quickly said that lactose,
through the oxidation becomes .... acid... and I missed the name. I'd
like to avoid bugging my teacher again. Is that gluconic acid or
something like galacto-gluconic acid or... what else?
thanks in advance
Rossella |
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| Ron Jones... |
| Posted: Sat Jun 21, 2008 7:05 pm |
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rossella wrote:
Quote: Hi and sorry again,
inorganic chemistry is now "past" (I passed my exam) while I'll have
to repeat in July the organic chemistry part.
One of the questions I found in the exam was about what happens to
lactose during the Fehling essay.
I just remember that lactose is made of galactose + glucose and that
the free OH group belongs to glucose.
The only thing that came to my mind was gluconic acid.
When the professor gave us the results he quickly said that lactose,
through the oxidation becomes .... acid... and I missed the name. I'd
like to avoid bugging my teacher again. Is that gluconic acid or
something like galacto-gluconic acid or... what else?
thanks in advance
Rossella
Lactose is a reducing sugar - hence the use of Fehling's solution (unlike
sucrose, which doesn't work).
Therefore the oxidation product is one of lactose origin (not glucose or
galactose) - lactose is *not* easy to hydrolyse without lactase (hence
lactose intorrerant prople). If Fehling's hydrolyed lactose, then it would
easily do sucrose, which it does not.
Therefore I would suspect that the oxidation product was lactobionic acid.
--
Ron Jones
Process Safety & Development Specialist
Don't repeat history, unreported chemical lab/plant near misses at
http://www.crhf.org.uk Only two things are certain: The universe and
human stupidity; and I'm not certain about the universe. ~ Albert
Einstein |
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| Bob... |
| Posted: Sun Jun 22, 2008 10:18 am |
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On Sun, 22 Jun 2008 01:05:01 +0100, "Ron Jones" <ron at (no spam) ronjones.org.uk>
wrote:
Quote: rossella wrote:
One of the questions I found in the exam was about what happens to
lactose during the Fehling essay.
I just remember that lactose is made of galactose + glucose and that
the free OH group belongs to glucose.
Careful, it is the aldehyde that is oxidized. There are lots of OH
around.
Quote: The only thing that came to my mind was gluconic acid.
When the professor gave us the results he quickly said that lactose,
through the oxidation becomes .... acid... and I missed the name. I'd
like to avoid bugging my teacher again. Is that gluconic acid or
something like galacto-gluconic acid
yes, exactly. The name of that, as explained by Ron below, is
lactobionic acid.
Quote: or... what else?
thanks in advance
Rossella
Lactose is a reducing sugar - hence the use of Fehling's solution (unlike
sucrose, which doesn't work).
Therefore the oxidation product is one of lactose origin (not glucose or
galactose) - lactose is *not* easy to hydrolyse without lactase (hence
lactose intorrerant
Is that a new British word we are supposed to learn?
Or an attempt at a polite term for what happens to lactose-intolerant
people?
:-)
bob
Quote: prople). If Fehling's hydrolyed lactose, then it would
easily do sucrose, which it does not.
Therefore I would suspect that the oxidation product was lactobionic acid. |
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| Ron Jones... |
| Posted: Sun Jun 22, 2008 12:57 pm |
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Bob wrote:
Quote: On Sun, 22 Jun 2008 01:05:01 +0100, "Ron Jones" <ron at (no spam) ronjones.org.uk
wrote:
Therefore the oxidation product is one of lactose origin (not
glucose or galactose) - lactose is *not* easy to hydrolyse without
lactase (hence lactose intorrerant
Is that a new British word we are supposed to learn?
Or an attempt at a polite term for what happens to lactose-intolerant
people?
:-)
Spelinghe was never my stong poynt...
But I do know about lactose-intolerant - as I can't take much lactose
myself, without some unwanted symptom.
--
Ron Jones
Process Safety & Development Specialist
Don't repeat history, unreported chemical lab/plant near misses at
http://www.crhf.org.uk Only two things are certain: The universe and
human stupidity; and I'm not certain about the universe. ~ Albert
Einstein |
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| rossella... |
| Posted: Tue Jun 24, 2008 4:13 am |
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Guest
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On Sun, 22 Jun 2008 08:18:32 -0700, Bob <bbx107.XYZ at (no spam) excite.XYZ.com>
wrote:
Quote: On Sun, 22 Jun 2008 01:05:01 +0100, "Ron Jones" <ron at (no spam) ronjones.org.uk
wrote:
rossella wrote:
One of the questions I found in the exam was about what happens to
lactose during the Fehling essay.
I just remember that lactose is made of galactose + glucose and that
the free OH group belongs to glucose.
Careful, it is the aldehyde that is oxidized. There are lots of OH
around.
The only thing that came to my mind was gluconic acid.
When the professor gave us the results he quickly said that lactose,
through the oxidation becomes .... acid... and I missed the name. I'd
like to avoid bugging my teacher again. Is that gluconic acid or
something like galacto-gluconic acid
yes, exactly. The name of that, as explained by Ron below, is
lactobionic acid.
***I therefore suspect that my answer (gluconic acid) was wrong 
Rossella |
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