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Lime mortar is a mixture of slaked lime and water; for plastering a newly built room sand is added. While this pulp hardens on the wall a chemical reaction of slaked lime and carbon dioxide of the air takes place. The product is a hard substance which is calcium carbonate.
Photo 3: Plastering can be combined with painting of ceilings and walls. The artist "frescos", which means he paints his portray on the fresh (it.: affreso painting in the fresh) lime mortar. The setting starts at the interface mortar/air, covering the painting with a thin transparent layer of solid calcium carbonate. Such a fresco painting of a young couple from Pompeji dates back to the 1. century before Christ.
Material
Tray, goggle, gloves, sample of slaked lime from the prvious experiment, stopper of an infusion bottle, match for stirring, 3 labeled dropper bottles with water, vinegar and limewater.
Material
1.Transfer the slaked lime from the previous experiment into the stopper Add water to make a pulp of lime mortar (Photo 1).
2.Keep it at the air for some days.
3. Add drops of vinegar (Photo 2). Hold a drop of limewater above the stopper.
Observations
a) A hard, brittle substance is formed.
b) After adding a drop of hydrochloric acid to the setted mortar gas bubbles can be seen.
c) This gas makes a drop of lime water (placed above it) milky.
Explanation
Calcium hydroxide of the mortar reacts with the carbon dioxide of the air forming lime stone Ca(OH)2 + CO2 --setting--> CaCO3 + H2O
The reaction of acid with the hardened product proves that the gas was newly built carbon dioxide. Erklärungen: Beim Erhärten von Kalkmörtel läuft eine chemische Reaktion ab, die man Abbinden nennt.
Addition: Changes at the interface between a drop of lime water and air are a model for the setting of lime.Ein Modell für das Abbinden ist die Veränderung eines Tropfens Kalkwasser an der Luft.
Photo 4: Setting of lime is the last step of the limestone cycle in industry: Calcium carbonate (after burning and slaking) is reclaimed here.