y do lemons float and limes sink?
You start with chalk which is calcium carbonate. You burn this - that is it is heated to a high temperature. The CaCO3 decomposes CaCO3 → CaO + CO2 The products are calcium oxide - which is known as quick lime- and carbon dioxide. If you add the CaO to water you get: CaO + H2O → Ca(OH)2 This reaction is exothermic and a lot of heat is liberated. The calcium hydroxide that is formed is known as slaked lime. The slaked lime can finally react with CO2 from the atmosphere. : Ca(OH)2 + CO2 → CaCO3 + H2O. This final reaction is the test for CO2 in the laboratory when you pass the CO2 gas into lime water and it turns from clear to milky. The final reaction is also the reaction that occurs when lime is used as a building material, and white wash paint finish on walls. At no time is the lime melted. It is heated for the first reaction, but this does not melt anything.
Turning CaO into a melt is a real chore. The melting point is 2572 °C which is hot enough to melt iron (m.p. 1538 °C) easily. Calcium oxide is a refractory material which means it stands up to heat very well. You can see that adding water to a material at such a high temperature would result in a tremendous explosion from the steam that is produced instantaneously. Chalk is derived from limestone. It is a mineral called calcite and is composed of CaCO3. Calcite is a softer mineral than some forms of limestone and can be used to write on harder surfaces. This form of chalk is used mostly for building materials. However, there are other materials that are called chalk such as gypsum (CaSO4*2H2O). Directions are given below to make your own sidewalk chalk if you should wish to do so.
