Calcium carbonate, hydrochloric acid, and their interaction
How CaCO₃ reacts with HCl
Let’s talk a little about the interaction between hydrochloric acid and calcium carbonate, and the nature of these compounds themselves.
CaCO₃ is a widespread compound found in chalk, lime, marble, and more. This substance is a crucial pillar of human life – it is used in construction, to manufacture paper and plastic, and in many other spheres. It is also popular in the food industry as a natural white colorant.
Calcium carbonate is a solid white substance that won’t dissolve in it completely: the water will turn a muddy color and a white precipitate will appear. But if the reaction with water takes place in the presence of carbon dioxide, it yields calcium hydrogen carbonate, a soluble acidic salt:
CaCO₃ + CO₂ + H₂O → Ca(HCO₃)₂
Let’s see how calcium carbonate is obtained
Most calcium carbonate is obtained from natural sources. A pure source, commonly marble, is usually used to obtain the calcium carbonate used in food coloring.
In the laboratory, pure calcium carbonate can be obtained via calcium oxide slaking followed by carbon dioxide gas bubbling. Water is mixed with calcium oxide to yield calcium hydroxide. Carbon dioxide is then passed through the previously-prepared solution. Calcium carbonate precipitates:
CaO + H₂O = Ca(OH)₂
Ca(OH)₂ + CO₂ = CaCO₃↓ + H₂O
Calcium oxide, also known as quicklime or burnt lime, is commonly used in construction. In industry, the calcium oxide needed for the above process is produced via calcination. Calcination is the general name for the chemical alteration of substances via firing or heating to high temperatures. If limestone or marble is heated to a temperature of 900-1000°C, the resulting chemical processes yield carbon dioxide and the desired calcium oxide CaO:
СаСO₃ = СаО+СО₂↑
But if the temperature is even higher (1500°C) and a carbon source is present, the reaction will produce calcium carbide and carbon monoxide:
СаСO₃ + 4C = СаC₂ + 3СО↑
Hydrochloric acid is a strong monobasic acid and is obtained via the dissolution of hydrogen chloride HCl in water. It is a colorless liquid, although industrial acid can have a yellow tint, often due to a mixture of iron. The properties of this solution depend directly on the concentration of hydrogen chloride. The salts of hydrochloric acid are called chlorides.
This substance is very caustic and requires careful handling: even a small drop on the skin will cause a severe chemical burn. When working with strong acids, you should always have neutralizers at hand – weak alkaline solutions, sodium bicarbonate (baking soda), etc. You should remember that opening a container with concentrated acid releases HCl fumes capable of harming the eyes and respiratory system. When conducting chemical experiments, it is recommended to use a respirator and protective eyewear.
Obtaining hydrochloric acid
Hydrogen chloride gas dissolves in water. Hydrogen chloride itself is obtained by burning hydrogen in chlorine to yield a synthetic acid. Hydrochloric acid can also be obtained from the secondary gases released in a number of chemical processes, such as when hydrocarbons are chlorinated. Acid obtained via this method is of technical or industrial grade.
Hydrochloric acid is used in medicine, industry, and chemical reactions.
The colorless acid with the harsh smell of hydrogen chloride reacts well with metals; the metal atoms reduce the hydrogen cations in an oxidation-reduction reaction.
Chemical reactions with metals are mainly accompanied by the release of hydrogen, the intensity of which depends on the activity of the metal. For example, the alkaline metal lithium reacts violently, while aluminum reacts only weakly due to its durable oxide film.
Hydrochloric acid and zinc:
2HCl + Zn = ZnCl₂ + H₂↑
Hydrochloric acid and iron:
2HCl + Fe = FeCl₂ + H₂↑
Hydrochloric acid and magnesium:
2HCl + Mg = MgCl₂ + H₂↑
The reaction of the acid with metal oxides forms salt and water:
CuO + 2HCl = CuCl₂ + H₂O
Reaction of hydrochloric acid and calcium carbonate
You will need:
a test tube;
solid calcium carbonate (marble);
Warning! Don’t try to perform this experiment without professional supervision!
Perform this experiment in a well-ventilated room. Observe caution when working with hydrochloric acid.
Add several pieces of marble to the vessel and drip hydrochloric acid on it using the pipette. There will be an instantaneous reaction involving the formation of bubbles (the release of carbon dioxide). This is an exchange reaction that produces a weak and unstable compound, carbonic acid, which breaks down into carbon dioxide and water. The equation of the dissolution reaction of calcium carbonate in hydrochloric acid reads as follows:
CaCO₃ + 2HCl(diluted) → CaCl₂ + CO₂↑ + H₂O