h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

what are reducing and non-reducing sugars, i know you do a Benedicts test to find them but what actually are they?

Without looking it up, sugars that can be oxidised by Benedict's test I would imagine.

If one thing is reduced then another is oxidised.

I suspect that means aldehyde based sugars such as glucose would be reducing sugars wheras ketone based sugars such as fructose would not be as an aldehyde is oxidisable easily whereas a ketone is not.

*runs off to look up how much tripe he just posted*

OK, now I've looked it up, how much tripe was that?

Lots sadly

>.Reducing Sugars (Benedict's test). All monosaccharides and most disaccharides (except sucrose) will reduce copper (II) sulphate, producing a precipitate of copper (I) oxide on heating, so they are called reducing sugars. Benedict’s reagent is an aqueous solution of copper (II) sulphate, sodium carbonate and sodium citrate. To approximately 2 cm³ of test solution add an equal quantity of Benedict’s reagent. Shake, and heat for a few minutes at 95°C in a water bath. A precipitate indicates reducing sugar. The colour and density of the precipitate gives an indication of the amount of reducing sugar present, so this test is semi-quantitative. The original pale blue colour means no reducing sugar, a green precipitate means relatively little sugar; a brown or red precipitate means progressively more sugar is present<<


There you go, they reduce copper II to copper I

I'm not overly convinced of the current usefulness of this test outside of a classroom these days though I have to say.

so there isn't much point in finding whether it is reducing or not

It's a test for more or less all monosaccharide sugars and some disaccharides (sucrose doesn't work though apparently) and can be useful for testing for the presence of them in foods it seems.

The only really good potential use for it that I could see was for detecting glucose in urine as a test for diabetes.

Add a bit of copper sulfate solution to a urine sample, heat a bit and if you get a red-brick precipitate you have a diabetic person's urine.

In the olden times before modern spectroscopes were invented then it would have been a useful test to identify aldehydes in a chemistry lab. Now though, one would run various spectra such as mass spectra and NMR to identity an unknown compound.

thanks very much, i understand now