Problem 17 - A Complete Resource Book in Chemistry for JEE Main

Question

Among the following pairs of compounds, the one that illustrates the law of multiple proportions is (a) \(\mathrm{Cu}\) and \(\mathrm{CuSO}_{4}\) (b) \(\mathrm{CuO}\) and \(\mathrm{Cu}_{2} \mathrm{O}\) (c) \(\mathrm{H}_{2} \mathrm{~S}\) and \(\mathrm{SO}_{2}\) (d) \(\mathrm{NH}_{3}\) and \(\mathrm{NCl}_{3}\)

Step-by-Step Solution

Answer

The pair that illustrates the law of multiple proportions is (b) CuO and Cu₂O.

Step 1: Understanding Law of Multiple Proportions

The law of multiple proportions states that if two elements form more than one compound, the different masses of one element that combine with a fixed mass of the other are in ratios of small whole numbers.

Step 2: Analyzing Compound Pairs

We need to look at each pair of compounds to see if they consist of the same two elements combining in different ratios, which is key to the law of multiple proportions.

Step 3: Examine Pair (a)

Pair (a) consists of Cu and CuSO₄. These are not two compounds with the same elements; thus, they do not illustrate the law of multiple proportions.

Step 4: Examine Pair (b)

In pair (b), CuO and Cu₂O are both compounds made from copper (Cu) and oxygen (O). CuO has a ratio of 1 copper to 1 oxygen atom, while Cu₂O has a ratio of 2 coppers to 1 oxygen atom. The ratio of copper combining with oxygen in these compounds is 1:2.

Step 5: Examine Pair (c)

Pair (c) consists of H₂S and SO₂. These compounds have different elements (hydrogen and oxygen) combining with sulfur, thus not illustrating the law of multiple proportions.

Step 6: Examine Pair (d)

Pair (d) includes NH₃ and NCl₃. These compounds involve nitrogen combining with different other elements (hydrogen and chlorine), not the same element at different ratios.

Step 7: Conclusion

From the analysis, pair (b) with CuO and Cu₂O demonstrates the law of multiple proportions, as they involve the same two elements (copper and oxygen) combining in different ratios.

Key Concepts

Chemical Compounds

Chemical compounds are substances made up of two or more elements that are chemically bonded together. The elements are combined in fixed ratios, creating entirely new substances with unique properties different from the individual elements. For example, water (\(\text{H}_2\text{O}\)) is a compound made from the elements hydrogen and oxygen. The fixed ratio in water is two hydrogen atoms for every one oxygen atom.
Chemical compounds can be classified based on the types of elements they contain or the type of bond holding them together. They can be covalent, where electrons are shared between atoms, ionic where electrons are transferred between atoms, or metallic, where electrons are delocalized across metal ions.

• Covalent compounds: Typically involve non-metal elements combining.
• Ionic compounds: Generally form between metals and non-metals.
• Metallic compounds: Consist of metal elements bonded together.

Understanding chemical compounds is crucial for recognizing how substances interact and form the basis for more complex chemical principles.

Element Ratios

Element ratios refer to the proportion of different elements within a compound. For any given compound, these ratios are consistent and define the chemical formula of the compound. This concept is vital in understanding the law of multiple proportions.
For example, in water (\(\text{H}_2\text{O}\)), the ratio of hydrogen to oxygen is 2:1. In the context of the exercise, understanding element ratios helps in identifying if two compounds follow the law of multiple proportions. Consider the compounds CuO and Cu\(_2\)O:

• CuO has a copper to oxygen ratio of 1:1.
• Cu\(_2\)O has a copper to oxygen ratio of 2:1.

Here, the different ratios of the same two elements following the addition of a fixed mass of one demonstrate the law of multiple proportions. Interpreting these ratios is key in analyzing chemical behavior and reactions.

Chemical Bonding

Chemical bonding is the force that holds atoms together within a compound and is a fundamental concept of chemistry. It determines the structure, properties, and behavior of a compound. There are several types of chemical bonds, each with unique characteristics.

• Covalent Bond: Atoms share pairs of electrons to achieve stability. Common in organic compounds and molecules like water and carbon dioxide.
• Ionic Bond: Involves the transfer of electrons from one atom to another, resulting in positively and negatively charged ions. Found in salts like sodium chloride.
• Metallic Bond: Features a sea of delocalized electrons flowing through a lattice of metal ions, giving metals their conductive properties.

These bonds play a crucial role when considering chemical properties and reactions. In different compounds, the same elements can form different types of bonds depending on their environment, influencing the chemical characteristics such as melting point, solubility, and electrical conductivity.

JEE Main Chemistry

JEE Main chemistry is an essential subject for students aspiring to enter engineering programs in India. The exam assesses understanding in various topics of chemistry, including principles like the law of multiple proportions, chemical bonding, and element ratios.

• JEE Main requires thorough comprehension of inorganic, organic, and physical chemistry concepts.
• Understanding and applying core concepts like the law of multiple proportions helps in solving analytical problems efficiently.
• Strengthening problem-solving skills through practice exercises in various chemistry topics is key to success in JEE Main exam.

Students preparing for JEE Main chemistry should focus on building a robust foundation in these core areas to approach questions with confidence and accuracy. Consistent exercise on topics like chemical bonding and element ratios not only improves problem-solving speed but also deepens understanding of the subject.