Question

What happens when calcium carbide is treated with water? (a) Ethane is formed. (b) Methane and ethane are formed. (c) Ethyne is formed. (d) Ethene and ethyne are formed.

Short answer

When calcium carbide is treated with water, ethyne (acetylene) is formed, so the correct answer is (c) Ethyne is formed.

Step-by-step solution

Understanding the Reaction

Calcium carbide (CaC2) reacts with water to produce acetylene (ethyne) gas, C2H2, and calcium hydroxide (Ca(OH)2). The chemical equation for this reaction is: CaC2(s) + 2H2O(l) -> C2H2(g) + Ca(OH)2(aq).

Choosing the Correct Option

Review the choices provided in the exercise, and select the one that corresponds to the production of ethyne gas (acetylene) as indicated by the balanced chemical equation.

Confirm the Product Formed

By comparing the products identified in the chemical equation and the given options, confirm that ethyne (acetylene) is indeed the correct product formed from the treatment of calcium carbide with water.

Key concepts

Acetylene Production

When it comes to generating acetylene, a crucial compound in various industrial processes, one of the classic methods is the interaction of calcium carbide with water. This exothermic reaction, which releases a significant amount of heat, is described by the chemical equation:
\[ \text{CaC}_2(s) + 2\text{H}_2\text{O}(l) \rightarrow \text{C}_2\text{H}_2(g) + \text{Ca(OH)}_2(aq) \].
Acetylene gas, also known as ethyne, is widely used in welding and cutting metals as it burns in oxygen with a very hot flame. In this reaction, calcium carbide (solid) and water (liquid) are the reactants, and they yield acetylene gas and calcium hydroxide (aqueous) as products. Understanding the exact nature of this reaction helps in various applications, ranging from the synthesis of organic compounds to industrial metalworking.

Chemical Reactions in Chemistry

Chemical reactions are foundational to understanding chemistry. They involve the transformation of substances into different compounds or elements via the breaking and formation of chemical bonds. In the calcium carbide and water reaction, two critical concepts are highlighted: chemical change and stoichiometry.
Chemical change refers to the reaction process where calcium carbide and water transform into distinct substances. This includes the production of acetylene, a hydrocarbon, and calcium hydroxide, an ionic compound. Stoichiometry, on the other hand, deals with the quantitative aspect of the reaction, as seen in the balanced equation provided earlier. It ensures that the number of atoms for each element is conserved in the reaction and indicates the ratio in which chemicals react or are produced. For students and professionals alike, understanding these concepts is pivotal for predicting reaction outcomes and for practical applications such as calculating yields and scaling reactions for industrial use.

Calcium Hydroxide Formation

Calcium hydroxide, commonly known as slaked lime, is another important product of the calcium carbide and water reaction. Its formation is indicated in the chemical equation:
\[ \text{CaC}_2(s) + 2\text{H}_2\text{O}(l) \rightarrow \text{C}_2\text{H}_2(g) + \text{Ca(OH)}_2(aq) \].
Calcium hydroxide is an inorganic compound with numerous uses, including water purification, soil stabilization, and as an ingredient in the preparation of traditional corn tortillas. The formation of calcium hydroxide is a consequence of the hydrolysis reaction where the calcium ion from calcium carbide reacts with two water molecules to yield two hydroxide ions which then combine with a calcium ion to form the calcium hydroxide. The process can be observed as a cloudy precipitate forming in water if the reaction is being conducted outside of a controlled environment like an industry or a laboratory.