Problem 46 - A Complete Resource Book in Chemistry for JEE Main

Question

The samples of \(\mathrm{NaCl}\) are produced when Na combines separately with two isotopes of chlorine \(\mathrm{Cl}^{35}\) and \(\mathrm{Cl}^{37}\). Which law is illustrated? (a) Law of constant volume (b) Law of multiple proportions (c) Law of reciprocal proportions (d) None of these

Step-by-Step Solution

Answer

(d) None of these

Step 1: Understanding the Problem

We are asked to identify which chemical law is illustrated by the formation of NaCl when sodium (Na) combines with two different isotopes of chlorine: Cl^{35} and Cl^{37}.

Step 2: Identify Relevant Chemical Laws

The options provided suggest different chemical laws: the law of constant volume, law of multiple proportions, law of reciprocal proportions, and an option for none of these. Let's briefly recall these laws: - The law of constant volume isn't directly related to chemical combinations. - The law of multiple proportions states that if two elements combine to form more than one compound, the mass ratios of the second element to a fixed mass of the first element are small whole numbers. - The law of reciprocal proportions states that the mass ratios of elements combine to form compounds are connected.

Step 3: Analyze the Isotope Combination

Sodium combines with two isotopes of chlorine to form NaCl. This creates two different compounds based on isotope variation, not different true compounds like those described under the law of multiple proportions.

Step 4: Evaluate the Law of Multiple Proportions

Remember, the law of multiple proportions applies to different compounds formed by the same elements. In this case, however, since Na is combining with Cl, not creating distinct multiple compounds, the law does not truly apply as traditionally formulated.

Step 5: Conclusion based on Analysis

Given the context of isotopic variation rather than forming distinct compounds with differing element ratios, none of the provided laws apply in the traditional sense. Therefore, none of the laws (options a, b, and c) fully describe the isotopic interaction occurring in this problem scenario.

Key Concepts

Law of Multiple Proportions

The Law of Multiple Proportions is an essential concept in chemistry that helps us understand how elements combine to form different compounds, but often gets mixed up with isotopic combinations. It states that when two elements combine to form more than one compound, the ratios of the mass of one element, which combines with a fixed mass of the other element, are in small whole numbers.

For example, consider carbon and oxygen forming carbon monoxide (CO) and carbon dioxide (CO₂). In carbon monoxide, for every 12 grams of carbon, there are 16 grams of oxygen. In carbon dioxide, for every 12 grams of carbon, there are 32 grams of oxygen. The ratio of oxygen masses (16:32) simplifies to a small whole number ratio of 1:2, perfectly illustrating the law.

• This law is crucial for distinguishing between different compounds made of the same elements.
• It’s based on quantitative mass ratios, not qualitative features like isotopic differences.

Thus, this law applies well to scenarios involving different compounds, but not to cases where the variation comes from isotopes, as isotopes do not create new compounds; they only differ by neutron count in the nucleus.

Isotopes

Isotopes are variants of a particular chemical element that have the same number of protons but different numbers of neutrons in their atomic nuclei, resulting in distinct mass numbers (atomic mass). Understanding isotopes is crucial, especially in nuclear chemistry and applications like medical imaging and radiometric dating.

For example, chlorine has two main isotopes:

• Cl-35: with 17 protons and 18 neutrons
• Cl-37: with 17 protons and 20 neutrons

Despite these differences, they have the same chemical properties because their electron configurations, which dictate chemical behavior, remain the same. Isotopes are thus crucial in scientific calculations and applications:

• They help in defining atomic weights as shown on the periodic table, which is a weighted average of these isotopes.
• They play an important role in understanding nuclear reactions and stability.

When two isotopes, like Cl-35 and Cl-37, form compounds such as NaCl, they do not illustrate laws dealing with element combination ratios, but rather reflect the isotope's role in the compound's physical properties.

Chemical Combination

Chemical combination is a term used to describe the way in which different elements combine together to form compounds. This process is ruled by several fundamental principles and laws.

When elements combine, they do so in specific ratios, usually represented by their valence or bonding preferences which arise from their electron configurations. These combinations follow distinct laws like:

• The Law of Definite Proportions: which states that a chemical compound will always contain the same proportion of elements by mass.
• The Law of Conservation of Mass: which dictates that mass is neither created nor destroyed in a chemical reaction.

Understanding chemical combination:

• Involves knowing how elements bond through ionic, covalent, or metallic interactions.
• Requires recognizing the role of electron transfer or sharing.

In the case of sodium (Na) combining with isotopes of chlorine (Cl), chemical combination principles ensure that no matter which isotopic form of chlorine is involved, the basic chemical properties of NaCl remain unaltered. Thus, while isotopic combinations do not fit into the laws of chemical proportions in specific ways, they definitely abide by the fundamental laws of chemical combination.