What carbonate breaks down into carbon dioxide

 

1. Carbon dioxide
 
If you closely observe a bottle of mineral water “with gas”, you can see bubbles rising up. The effect is particularly enhanced if you shake the bottle, heat the water or simply fill a glass with it. When you drink it, you can feel a "fizzy effect", the mineral water tastes slightly sour. Similar phenomena can also be observed with Coca Cola.



Carbonated mineral water ("with gas").


With a suitable pH indicator it can be proven that mineral water “reacts with gas” in a slightly acidic manner and that it must contain an acid. The pH value is between 6 and 7. The acid contained is called carbonic acid. Can you also separate the carbon dioxide from the water?
  • With prolonged heating or shaking heating, all of the gas is expelled. If you lead the gas into lime water, it becomes cloudy. This indicates that the gas is carbon dioxide.
  • All the usual separation methods in the school laboratory fail in order to represent the carbonic acid in its pure form. You only get water and carbon dioxide: When the gas is expelled from the water, the carbonic acid always breaks down into these two substances.
  • Only scientists have managed, with great effort, to produce carbonic acid in its pure form at very low temperatures with the complete exclusion of water and metal salts.



Device with bottle and carbon dioxide cartridge
to make your own sparkling water.


You can make your own “sparkling water” with the devices or siphon bottles available in household goods. In this process, water is pressurized together with carbon dioxide from a cartridge. As soon as a saturation is reached, nothing works anymore. This can be explained as follows: When the carbon dioxide reacts with water, carbonic acid H is formed2CO3. In doing so, an equilibrium is established. This is illustrated by the equilibrium arrow:
 
CO2 + H2O H2CO3 
 
The balance is heavily on the left. The carbonic acid is therefore only a very weak acid. For a chemist, the acidic character of carbonic acid can be recognized by the fact that it can release protons. The carbon dioxide can even give off two:

(1.) Release of the first proton: H2CO3 + H2O H3O+ + HCO3

(2.) Release of the second proton: HCO3 + H2O H3O+ + CO32− 
 
The release of the protons takes place in two steps with carbon dioxide. In the first step, a hydronium ion H is obtained3O+ and a hydrogen carbonate ion HCO3, in the second step another hydronium ion H3O+ and a carbonate ion CO32−. Two different salts can be obtained from carbonic acid: The hydrogen carbonates with the anion HCO3 The first step in the equation reveals the carbonates with the anion CO32− from the second step.

Due to the lime cycle, the groundwater also always contains a small amount of carbonic acid. Carbonic acid and carbonates form a natural buffer system in the waters.


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2. Hydrogen carbonates

When reacting with an acid, sodium chloride, carbon dioxide and water are formed with foaming:

NaHCO3 + HCl NaCl + CO2 + H2O

With the exception of sodium hydrogen carbonate, the hydrogen carbonates are more soluble in water than the carbonates. They play a decisive role in water hardness.
 
 
 
3. carbonates

The best known carbonate in the household is sodium carbonate, which is also known under the name soda is known. It is still used to make soap today. Around 1878 "Henkel's bleaching soda" came onto the market. It was used to soak the laundry and soften the water. Today, other detergents are used that are more gentle on the laundry.





Soda occurs naturally as a mineral, and it is found in soda lakes and medicinal springs. In the mineral kingdom, the carbonates form a large group: The carbonate minerals include, for example, calcite, aragonite, dolomite, cerussite or smithsonite. The calcium and magnesium carbonates are rock-forming in many mountains, this is the case in the Jura or the Dolomites:
  
 

Dolomite and calcite are rock-forming in the Dolomites.


The alkali carbonates are relatively soluble in water, while the others are only sparingly soluble. The aqueous solutions have a strong alkaline reaction: the carbonate ion CO32- reacts as a base with a water molecule to form a hydrogen carbonate ion and a hydroxide ion:
    
CO32− + H2O HCO3 + OH   

With strong acids, the carbonates and hydrogen carbonates decompose with the formation of carbon dioxide and the corresponding salts. For example, sodium carbonate reacts with hydrochloric acid to form sodium chloride, water and carbon dioxide:
 
N / A2CO3 + 2 HCl 2 NaCl + H2O + CO2

The alkali carbonates such as sodium carbonate or potassium carbonate melt in the heat, others such as calcium carbonate disintegrate into an oxide and carbon dioxide when heated to a high degree of oxygen. Such a process takes place, for example, when burning lime.
 
 
additional Information

carbon dioxide
Mineral portrait calcite
The lime cycle
Calcium carbonate, a versatile substance
The history of the use of lime


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