Question

Apoisonous gas is obtained on oxidation of ${\mathrm{CHCl}}_3$. $$2{\mathrm{CHCl}}_3+{\mathrm{O}}_2\stackrel{\text{ Light }}{⟶}\text{ Gas }+2\mathrm{HCl}$$ The gasis (A) CO (B) ${\mathrm{CO}}_2$ (C) ${\mathrm{Cl}}_2$ (D) ${\mathrm{COCl}}_2$

Short answer

The correct choice for the unknown poisonous gas obtained on oxidation of CHCl₃ is (D) ${\mathrm{COCl}}_2$ (Carbonyl chloride), as it obeys the conservation of mass and uses all the elements present in the reactants.

Step-by-step solution

Determine the balanced reaction

Let's first write down the given reaction: 2 CHCl₃ + O₂ → Gas + 2 HCl Our first task is to find out which gas is produced in the balanced reaction, considering the chemical formulas of the reactants and products.

Identify the elements in the reactants

In the given reaction, the reactants are: 1. Dichloromethane (CHCl₃) 2. Oxygen (O₂) Let's identify the elements present in the reactants: - Carbon (C) - Hydrogen (H) - Chlorine (Cl) - Oxygen (O)

Examine the choices

Now, let's examine each choice for the unknown gas and see which obeys the law of conservation of mass: (A) CO - Carbon monoxide contains Carbon and Oxygen. (B) CO₂ - Carbon dioxide contains Carbon and Oxygen. (C) Cl₂ - Chlorine gas contains Chlorine. (D) COCl₂ - Carbonyl chloride contains Carbon, Oxygen, and Chlorine.

Conservation of mass

For the reaction to be balanced, every element present in the reactants must also appear in the products. We have HCl as one of the products, which has hydrogen and chlorine elements. Now, let's examine if any of the choices satisfy the conservation of mass. (A) CO - Carbon monoxide has no chlorine; therefore, it doesn't satisfy the conservation of mass. (B) CO₂ - Similarly, Carbon dioxide has no chlorine; therefore, it doesn't satisfy the conservation of mass. (C) Cl₂ - Although Chlorine gas contains Chlorine, there is no carbon in it. Therefore, it doesn't satisfy the conservation of mass. (D) COCl₂ - Carbonyl chloride contains Carbon, Oxygen, and Chlorine. These are the elements present in the reactants CHCl₃ and O₂.

Select the correct option

Since Carbonyl chloride (COCl₂) obeys the conservation of mass and uses all the elements present in the reactants, the correct choice for the unknown poisonous gas is: (D) ${\mathrm{COCl}}_2$

Key concepts

Phosgene formation

Phosgene, also known as carbonyl chloride (COCl₂), is a highly toxic gas with a malicious history as a chemical weapon. This compound can be formed through the oxidation of chloroform (CHCl₃) when exposed to light in the presence of oxygen. The overall reaction can be simplified to this equation: 2 CHCl₃ + O₂ → COCl₂ + 2 HCl. In this reaction, the chloroform acts as a precursor, and the introduction of light provides the necessary energy for the reaction to proceed. It's important to anticipate the formation of this poisonous gas during chemical processes involving chloroform, especially in industrial settings where light exposure and oxygen presence are common. Understanding this reaction is vital for safety and prevention measures.

Chemical equation balancing

Balancing chemical equations is a fundamental aspect of chemistry that ensures the equation adheres to the law of conservation of mass—a cornerstone principle stating that matter cannot be created or destroyed in an isolated system. In the reaction where phosgene is formed, the chemical equation must be balanced to reflect the conservation of mass. This means the number of atoms of each element in the reactants (CHCl₃ and O₂) must equal the number of atoms in the products (COCl₂ and HCl). To balance a chemical equation, follow these steps:

• Count the number of each type of atom on both sides of the equation.
• Adjust the coefficients (the numbers before molecules) to ensure equal numbers of atoms for each element on both sides.
• Begin with elements that appear in only one reactant and one product if possible.

Maintaining consistency in the number of atoms is crucial for documenting the reaction accurately.

Conservation of mass in reactions

The law of conservation of mass demonstrates that in a chemical reaction, the total mass of the reactants must be equal to the total mass of the products. This principle assures that all atoms from the reactants are accounted for in the products, either in their original state or rearranged into different compounds. In the case of phosgene production, the reactants include chloroform (CHCl₃) and oxygen (O₂). The products formed must contain all the elements—carbon, hydrogen, chlorine, and oxygen—in equal amounts: - Carbon and oxygen combine to form carbonyl chloride (COCl₂), ensuring these atoms are conserved. - Hydrogen and chlorine form hydrochloric acid (HCl), conserving these atoms as well. To verify conservation of mass:

• Calculate the total number of atoms for each element in both reactants and products.
• Ensure these numbers are equal for both sides of the reaction.

Applying this principle prevents mistakes and confirms the reaction's feasibility.