Fehling´s test
Reaction with Fehling´s solution is used in order to differ between reducing and non-reducing sugars. Fehling´s solution is made by combining two different aqueous solutions - Fehling A and Fehling B. Fehling A contains copper(II) sulfate and is blue. Fehling B contains pottasium-sodium tartarate and sodium hydroxide.
In case of positive reaction the copper (II) is reduced to copper (I) and copper (0) which causes the colour to change from blue to orange.
Negative reaction means that the copper (II) is not reduced and the blue colour stays.
Fructose and glucose are reducing sugars, the reaction is positive.
Honey and juice contain reducing sugars, the reaction is positive.
Starch and sucrose are non-reducing sugars and the reaction is negative.
Pharaoh's snake is a simple experiment. We put sand in a fireproof bowl and we make a little hole in the middle. We mix together sucrose and sodium bicarbonate and mash them in a mortar until we make very smooth powder. Then we put the mixture into the hole in the sand and we pour a bit of ethanol on the sand and set it on fire. The fire changes sucrose to caramel. Sodium bicarbonate is decomposed by the heat and carbon dioxide is released. Caramel together with carbon dioxide from sodium bicarbonate creates dark foam.
Selivan's test
Seliwanoff´s test is a chemical test which distinguishes between aldose (glucose) and ketose (fructose) sugars. The test is based on the fact that ketosis is dehydrating faster when heated than aldose. If the sugar contains a ketone group, it is a ketose. If the sugar contains an aldehyde group, it is an aldose. When Seliwanoff´s solution is added to a solution containing ketoses, a red color is formed rapidly indicating a positive test. When it is added to a solution containing aldoses, a slower forming light pink is observed instead.
Fructose and sucrose are two common sugars which give a positive test. Juice have a positive result, too.
Iodine reacts with polysaccharides and changes its colour from brown to blue or purple. The change of colour is caused when iodine is catched in the structure of polysaccharides. Starch is polysaccharide and juice contains polysascharides. Starch and juice give positive reaction, while the other sugars give negative reaction.