How Does Calcium Carbide React and What Are Its Practical Uses?
Calcium carbide is also called calcium acetylide, which is a chemical compound having the chemical formula of CaC2. Mainly, it is used industrially for the production of calcium cyanamide and acetylene.
This is a pure material of colorless, and, however, the pieces of technical-grade calcium carbide compound are either brown or grey and consist of about 80–85% of CaC2 (the remaining is CaO - calcium oxide), Ca3P2 (calcium phosphide), Ca3N2 (calcium nitride), CaS (calcium sulfide), SiC (silicon carbide), and more). In trace moisture presence, the calcium carbide’s technical-grade emits an unpleasant odor, which is reminiscent of garlic.
Note: The calcium carbide applications include acetylene gas manufacturing and for the generation of acetylene in carbide lamps; chemicals manufacturing for fertilizer; and also in steelmaking.
CaC2 Structure
Let's look at the calcium carbide structure.
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Production of Calcium Carbide
Calcium carbide is industrially produced in an electric arc furnace with a mixture of coke and lime, approximately at 2,200 °C (3,990 °F). This is an endothermic reaction that requires a high temperature to drive off the carbon monoxide at 110 kilocalories (460 kJ) per mole. Since its invention in 1892, this method has not changed.
CaO + 3C → CaC2 + CO
The high temperature that is required for this reaction is practically not achievable by traditional combustion. So, this reaction is performed in an electric arc furnace using graphite electrodes.By weight, the produced carbide product will contain around 80% of the calcium carbide. Also, carbide is further crushed to produce small lumps that can range up to a maximum of 50 mm, and the impurities are concentrated in the finer fractions.
The CaC2 content, that product is assayed by measuring the produced acetylene amount on hydrolysis. As an example, the German and British standards for the coarser fractions content are 295 L/kg and 300 L/kg, respectively (at a pressure of 101 kPa and 20 °C (68 °F) temperature). The impurities of carbide include phosphide, which produces phosphine when hydrolyzed.
In chemistry, this reaction was not an important part of the industrial revolution and was made possible in the United States as a result of excessive amounts of inexpensive hydroelectric power that was produced at Niagara Falls before the 20th century turn off.
Production of Calcium Cyanamide
Calcium carbide compound reacts with nitrogen at higher temperatures to produce calcium cyanamide. It is represented by using the below equation.
CaC2 + N2 → CaCN2 + C
Commonly the term called nitrolime, which is a calcium cyanamide, can be used as fertilizer. It is also hydrolyzed to cyanamide, H2NCN.
Steel Making
Let us look at the steel making uses of calcium cyanamide as listed below:
Calcium carbide can be used in the iron desulfurization (which are cast iron, pig iron, and steel).
We can use it as a powerful deoxidizer at the facilities of ladle treatment.
It can be used as a fuel in steelmaking to extend the scrap ratio to liquid iron, depending on the economics.
Carbide Lamps
Calcium carbide can be used in the carbide lamps. Dripping of water on the carbide produces acetylene gas, which in turn burns and produces light. While these lamps gave steadier and brighter light to that of candles, they were so dangerous in coal mines, a flammable methane gas that made them a serious hazard.
These flammable gases presence in coal mines led to miner safety lamps like the Davy lamp, where a wire gauze reduces the methane ignition risk. Still, carbide lamps were used extensively in copper, tin, and slate mines where methane is not considered a serious hazard. Most lamps of the miners have now been replaced by electric lamps.
But, still, the carbide lamps are used for mining in a few less wealthy countries. The silver mines near Potosí, Bolivia is an example. They are also used currently by a few cavers exploring caves and other underground areas, although they are increasingly replaced in this use by the LED lights.
Uses of Calcium Carbide (CaC2)
Calcium Carbide is used in producing polyvinyl chloride as acetylene, which is the derivative of calcium carbide and is used as a raw material for PVC production.
Calcium Carbide is also used in the production of acetylene and calcium hydroxide.
It can be used in the removal of sulphur from iron. The removal of sulphur from any material is referred to as desulphurization.
We can use it to produce calcium cyanamide.
This compound can also be used as a ripening agent such as ethylene.
It can be used in lamps like carbide lamps. Earlier, it was used as automobile headlights.
It is also used as a deoxidizer, which means it helps in oxygen removal during steel manufacturing.
It is also used in bamboo cannons and big-bang cannons.
FAQs on Calcium Carbide: Structure, Production, and Applications
1. What is calcium carbide and what are its key physical properties?
Calcium carbide, with the chemical formula CaC₂, is a chemical compound used primarily in the production of acetylene gas. In its pure form, it is a colourless solid, but technical-grade calcium carbide is a greyish-black lumpy solid with a garlic-like odour. Its key properties include a molar mass of 64.099 g/mol and a high melting point of 2160°C. It reacts exothermically with water.
2. What happens when calcium carbide reacts with water? Provide the chemical equation.
When calcium carbide (CaC₂) reacts with water (H₂O), it produces acetylene gas (C₂H₂) and calcium hydroxide (Ca(OH)₂). This is a vigorous exothermic reaction. The balanced chemical equation for this process is:
CaC₂(s) + 2H₂O(l) → C₂H₂(g) + Ca(OH)₂(aq)
This reaction is the primary method for the industrial and laboratory production of acetylene.
3. How is calcium carbide manufactured on an industrial scale?
Industrially, calcium carbide is produced by heating a mixture of lime (calcium oxide, CaO) and coke (a form of carbon) at very high temperatures, typically around 2200°C, in an electric arc furnace. The high temperature is necessary to drive the reaction. The overall chemical equation for the manufacturing process is:
CaO(s) + 3C(s) → CaC₂(s) + CO(g)
The molten calcium carbide is then cooled and solidified into lumps.
4. What are the main industrial applications of calcium carbide?
Calcium carbide has several important industrial uses, primarily stemming from its reaction to produce acetylene. Key applications include:
- Production of Acetylene: Acetylene is used for oxy-acetylene welding and cutting, and as a precursor for synthesising other organic chemicals.
- Steelmaking: It is used as a desulfurizing agent to remove sulfur from iron and steel.
- Production of Calcium Cyanamide: It reacts with nitrogen at high temperatures to form calcium cyanamide (CaCN₂), which is used as a fertilizer.
- Carbide Lamps: Historically used in mining and for vehicles, where dripping water onto the carbide produced acetylene for illumination.
5. How does a carbide lamp produce light using calcium carbide?
A carbide lamp works on a simple chemical reaction. The lamp has two chambers: an upper chamber containing water and a lower chamber containing lumps of calcium carbide. A valve controls the dripping of water from the upper chamber onto the carbide below. This initiates the reaction CaC₂ + 2H₂O → C₂H₂ + Ca(OH)₂, generating flammable acetylene gas. The gas is directed through a jet and, when ignited, burns with a bright, luminous flame, producing light.
6. Why is using calcium carbide for artificially ripening fruits banned in India?
The use of calcium carbide for ripening fruits is banned by the Food Safety and Standards Authority of India (FSSAI) due to significant health risks. The reasons for the ban are:
- Harmful Impurities: Technical-grade calcium carbide contains toxic impurities like arsenic and phosphorus hydride. When it reacts with moisture, it releases acetylene gas contaminated with these toxins.
- Health Hazards: Consuming fruits ripened this way can expose individuals to these toxins, potentially causing health issues ranging from headaches and dizziness to more severe neurological problems.
- Unsafe Ripening: The acetylene produced acts as a ripening agent, but it only changes the skin colour, leaving the fruit raw and tasteless inside. The approved and safe alternative for artificial ripening is using ethylene gas in a controlled manner.
7. What is the chemical structure of calcium carbide, and how does it explain its reactivity with water?
Calcium carbide is an ionic compound. Its structure consists of a calcium cation (Ca²⁺) and a carbide anion (C₂²⁻). The carbide anion has a triple bond between the two carbon atoms ([C≡C]²⁻). This C₂²⁻ anion is a very strong base. When calcium carbide comes into contact with water, this strongly basic anion readily pulls protons (H⁺) from the water molecules, forming the stable, neutral acetylene molecule (H-C≡C-H). This high affinity for protons is what makes the reaction with water so vigorous.
8. What are the essential safety precautions when handling calcium carbide?
Handling calcium carbide requires strict safety measures because of its reactivity with moisture. Key precautions include:
- Keep it Dry: It must be stored in a dry, well-ventilated area in a tightly sealed, moisture-proof container to prevent any contact with water or humidity.
- Avoid Inhalation and Contact: It is corrosive. Direct contact can cause skin and eye burns. Inhalation of its dust can irritate the respiratory tract. Always use appropriate personal protective equipment (PPE) like gloves and safety goggles.
- Fire Hazard: The acetylene gas produced is highly flammable and can form explosive mixtures with air. Therefore, keep it away from any sparks, flames, or sources of ignition.
