Problem 40 - A Complete Resource Book in Chemistry for JEE Main

Question

Among the following compounds, the one with the least percentage of chlorine is (a) chloroform (b) vinyl chloride (c) gammexane (d) pyrene

Step-by-Step Solution

Answer

Pyrene has the least percentage of chlorine, with 0% present.

Step 1: Understanding the Compounds

The given compounds are chloroform, vinyl chloride, gammexane, and pyrene. Chloroform has the formula CHCl extsubscript{3}, vinyl chloride has the formula C extsubscript{2}H extsubscript{3}Cl, gammexane (also known as Lindane) has the formula C extsubscript{6}H extsubscript{6}Cl extsubscript{6}, and pyrene is a polycyclic aromatic hydrocarbon with the formula C extsubscript{16}H extsubscript{10} without any chlorine atoms.

Step 2: Calculating Molar Masses

Calculate the molar mass of each compound to determine the percentage of chlorine. **Chloroform (CHCl extsubscript{3})**: - Carbon (C): 12 g/mol - Hydrogen (H): 1 g/mol - Chlorine (Cl): 35.5 g/mol Total = 12 + 1 + 3(35.5) = 119.5 g/mol **Vinyl Chloride (C extsubscript{2}H extsubscript{3}Cl)**: - Carbon (C): 2×12 g/mol = 24 g/mol - Hydrogen (H): 3×1 g/mol = 3 g/mol - Chlorine (Cl): 35.5 g/mol Total = 24 + 3 + 35.5 = 62.5 g/mol **Gammexane (C extsubscript{6}H extsubscript{6}Cl extsubscript{6})**: - Carbon (C): 6×12 g/mol = 72 g/mol - Hydrogen (H): 6×1 g/mol = 6 g/mol - Chlorine (Cl): 6×35.5 g/mol = 213 g/mol Total = 72 + 6 + 213 = 291 g/mol **Pyrene (C extsubscript{16}H extsubscript{10})**: - Carbon (C): 16×12 g/mol = 192 g/mol - Hydrogen (H): 10×1 g/mol = 10 g/mol Total = 192 + 10 = 202 g/mol (No chlorine included)

Step 3: Calculating Chlorine Percentage

Now calculate the percentage of chlorine in each compound.**Chloroform (CHCl extsubscript{3})**: Cl % = \ \( \frac{3 \times 35.5}{119.5} \times 100 \) = 89.08%**Vinyl Chloride (C extsubscript{2}H extsubscript{3}Cl)**: Cl % = \ \( \frac{35.5}{62.5} \times 100 \) = 56.8%**Gammexane (C extsubscript{6}H extsubscript{6}Cl extsubscript{6})**: Cl % = \ \( \frac{213}{291} \times 100 \) = 73.2%**Pyrene (C extsubscript{16}H extsubscript{10})**: Cl % = 0% (No chlorine present)

Step 4: Identifying the Compound with Least Chlorine

From the calculations, pyrene has 0% chlorine, which is less than the percentages found in the other compounds with chlorine.

Key Concepts

Molar Mass Determination

Molar mass is an essential concept in chemistry that helps us determine the mass of one mole of a chemical compound. It is calculated by adding up the atomic masses of all the atoms present in a single molecule of the compound. For our exercise, knowing how to calculate molar mass is crucial because it allows us to figure out the percentage of chlorine in each compound. Here's how molar mass determination works:

• Identify the elements in the compound and their respective atomic masses from the periodic table. For example, Carbon (C) is about 12 g/mol, Hydrogen (H) is approximately 1 g/mol, and Chlorine (Cl) weighs around 35.5 g/mol.
• Count the number of atoms of each element present in the molecular formula of the compound.
• Multiply the atomic mass of each element by the number of times the element appears in the compound, and then sum these values to get the total molar mass of the compound.

By computing the molar mass, we can further dive into more complex analyses such as determining the proportion of a specific atom, like chlorine in the example, within the total molar mass.

Chemical Compounds Analysis

Chemical compounds analysis is the process of breaking down a compound to understand its structure and composition. This step involves identifying all the elements present within the compound and their corresponding percentages. In our example, our primary focus was determining the chlorine content within various compounds to figure out which had the least percentage of chlorine.

• First, recognize the chemical formula of the compound and use it to identify the type and number of atoms involved.
• Second, calculate the mass contribution of each element to the compound's total molar mass.
• Finally, determine each element's percentage composition by comparing its contribution to the total molar mass.

The accurate analysis aids in predicting the chemical behavior of compounds and can lead to practical applications such as chemical safety, environmental impact, and the synthesis of new materials.

Aromatic Hydrocarbons

Aromatic hydrocarbons are a fascinating group of molecules characterized by their distinct circular arrangement of carbon atoms, known as benzene rings. These molecules are crucial in both nature and industry, with applications ranging from substances in fragrances to components in fuels.

• Aromatic compounds typically contain alternating double bonds within a ring, giving them unique stability and certain chemical properties compared to non-aromatic compounds.
• Pyrene, mentioned in the exercise, is a type of aromatic hydrocarbon. It consists of four fused benzene rings and lacks chlorine atoms.
• The unique properties of aromatic hydrocarbons often make them a subject of study due to their stability and prevalent use in synthesizing other chemicals.

Understanding aromatic hydrocarbons, like pyrene, gives us insight into their role in chemical industries and environmental science, particularly concerning the synthesis of dyes, plastics, and aromatic compounds used in various applications.