The purposes of these experiments are to utilize chemical trial to separate some biochemical molecules. As these molecules are really of import with our lives, it is necessary to prove them and understand their behaviour


Biology chemical molecules play an of import function in our lives, storage of energy such as amylum ( poly glucose ) , protecting constructions such as protein, insularity stuff such as lipid, the fast energy supplying molecules such as glucose, etc. Starch is a supermolecule which is easy tested. Starch is supermolecules made up of glucose units connect together with glycosidic bonds [ Google Web Definition, 2009 ] . Harmonizing to the information from practical chembook [ 2009 ] , iodine solution signifier I3- anion and can adhere to a amylum to do a spiral construction. The colour appears bluish because all other visible radiation is absorbed

The basic manner to separate these supermolecules is use some other chemical solution to respond or blend with them and watch any colour alterations. Testing cut downing sugar is another experiment that can be used to watch colour alterations, but it needs to be heated.

Reducing sugar is the sugar molecule that behaves like cut downing agent, it contains the aldehyde group ( COOH ) [ Google web definition, 2009 ] . Glucose is heated with Benedict ‘s reagent to organize a brick ruddy precipitate [ Chemistry comes alive, 2009 ] . In fact, the Benedict ‘s reagent is made from Cu sulfate and Na carbonate and it provides the Cu2+ anion and the Cu2+ was reduced to Cu+ , which in bend has its aldehyde group oxidesied to acid ( COOH ) .

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Protein is another sort of supermolecules, and it needs more stairss to prove it. Protein is made of aminic acids linked together, the signal portion of protein and the bond for this trial focal point on is the peptide bonds. The website [ Guangdong Biology Teaching, 2009 ] provinces that when the trial solution includes peptide bond, the trial reagent, Buiret Reagent, Cu ions can respond with the polypeptide and bring forth the complex compound with a violet colour observed.

Lipid is a long concatenation of saccharide which has a hydrophilic ionic ‘head ‘ and hydrophobic organic ‘tail ‘ . The experiment here looks at this significance of lipid by utilizing H2O and ethyl alcohol, to command its solubility and breakdown in both.


Equipments and Materials: several trial tubings, pipettes, a spile, I, Fehling reagent, Biuret Reagent A and B, ethyl alcohol, distilled H2O

Solution A: amylum solution Solution B: Glouse solution

Solution C: egg albumins ( protein ) Solution D: lipoid ( fat )


1 cm? of solution A was added into a trial tubing. 3-4drops of I was added into the trial tubing. The colour alteration in the tubing was noted.

Reducing sugar

2 cm? of solution B was added into a trial tubing. Before the trial tubing was heat in a H2O to bath about 60’C for 2 proceedingss, 5 cm? of Fehling reagent was dropped into

the tubing. The colour alteration in the tubing was noted.


2 cm? of solution C is added into a trial tubing. Before 1 cm? of Biuret Reagent B was trickled into the trial tubing by utilizing a pipette, 2 cm? of Buiret Reagent A was besides than added into the trial tubing. The colour alterations in the tubing were observed.


2 cm? of solution D was added into a trial tubing. Then, 2 cm? of ethyl alcohol was added tubing, after the tubing was shaken smartly ( utilize a knock ) , 2 cm? of cold H2O was added into the tubing. The alteration in the tubing was noted.


Table 1 shows the consequences of these experiments, with all the colour alterations, they show that all the experiments are achieved.

Observation of the experiments










Fehling reagent

Fehling A

Biuret B

Ethyl alcohol

Cold H2O


Clear trial solution to dark blue

Yellow or ruddy precipitate appear


Blue suspension on the underside

Cloudy white suspension signifiers

Table 1


The observations from the trials show clearly that alterations occurred in all the biological science molecules after utilizing some reagent. However, many mistakes were possible during the experiments. For case, when the protein trial was being done, the reagents may hold been dropped in the incorrect order, the colour of the solution did non alteration and show light blue. After 2 more experiments, the right one was process was established.

At the same clip, some more new thoughts from other pupils were gathered. Classmate Crystal ( 2009 ) suggested that while making the cut downing sugar trial, a alteration in the order of the Fehling reagent could be tried, but the consequences came from them were the same!

It was besides found that before the tubing with lipoid was shaken, there were two white beds and a clean bed between them. After the trial was shaken, the fantastic cloudy suspension appears. It may be that before the shaking, the oil was in the center and the hydrophilic caput react with the H2O and the hydrophobic react with the ethyl alcohol. After the tubing was agitating, they mixed.

Meanwhile, there were several differences between the consequences we obtained and the 1s from the theory. Such as the colour of the alterations of the trial tubing which with amylum. The colour seen was much darker than the description of the colour which was got from the theory. Possibly the iodine solution was added excessively much because it was non measured truth.


In brief, it is easy to prove the biological science molecules and distinguish each one by watching the colour alterations. In add-on, there are many things to be careful to during the experiments such as the order of the reagents, the clip that some tubings should be shaken or even het –failure is possible! Remembering the stairss to make them in order so success is possible.


Virtual chembook ( hypertext transfer protocol: //www.elmhurst.edu/~chm/vchembook/548starchiodine.html ) ( 16 November 2009 )

Chemistry comes alive! ( hypertext transfer protocol: //jchemed.chem.wisc.edu/jcesoft/CCA/CCA5/MAIN/1O RGANIC/ORG18/TRAM18/B/MENU.HTM ) ( 16 November 2009 )

Guangdong Biology Teaching ( hypertext transfer protocol: //www.gdswjx.net/Item/2004.aaspx ) ( 16 November 2009 )

Google web definition ( hypertext transfer protocol: //www.google.com/search? hl=en & A ; newwindow=1 & A ; defl= en & A ; q=define: amylum & A ; ei=inYKS8W0NouNkAX-oNzeCQ & A ; sa=X & A ; oi=glossary_ definition & A ; ct=title & A ; ved=0CAcQkA E ) ( 23 November 2009 )

Google web definition ( hypertext transfer protocol: //www.google.com/search? hl=en & A ; newwindow=1 & A ; q= specify % 3Areducing+sugar ) ( 23 November 2009 )


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