Saliva vs. starch

Warn­ing! Only un­der adult su­per­vi­sion

Equip­ment

• starch;
• cold wa­ter;
• warm wa­ter;
• hot wa­ter;
• glass­es (200 mL / ½ pint);
• 2 tea­spoons of sali­va;
• io­dine so­lu­tion (an­ti­sep­tic);
• pipette;
• ta­ble­spoon.

Step-by-step in­struc­tions

Mix small amounts of starch and cold wa­ter, then add hot wa­ter to get a vol­ume of about 200 mL / ½ pint. Pour 2 ta­ble­spoons of the pre­pared so­lu­tion into two glass­es and di­lute with warm wa­ter to 200 mL / ½ pint. Add 2 tea­spoons of sali­va to one of the glass­es, stir, and leave for 1 hour. Then drip some io­dine so­lu­tion (an­ti­sep­tic) into each glass and ob­serve that the so­lu­tion in the glass with­out sali­va turns blue.

Sci­en­tif­ic de­scrip­tion

Sali­va is a clear liq­uid that is slight­ly more vis­cous than wa­ter. It is se­cret­ed by the sali­vary glands in the mouth. Sali­va moist­ens food and starts the process of its di­ges­tion due to the en­zymes con­tained in it, such as amy­lase. Amy­lase is an en­zyme that breaks down long starch chains into small­er ones. This process can be demon­strat­ed sim­ply and clear­ly by adding some sali­va to a starch so­lu­tion in wa­ter. Af­ter a while (about 1 hour), the amy­lase con­tained in the sali­va will de­stroy all of the starch, and adding an io­dine so­lu­tion will not turn the so­lu­tion blue: the blue com­plex com­pound of starch with io­dine will not form.

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