Problem 120 - A Complete Resource Book in Chemistry for JEE Main

Question

Amongst the following, the lowest degree of paramagnetism per mole of the compound at \(298 \mathrm{~K}\) will be shown by (a) \(\mathrm{MnSO}_{4} .4 \mathrm{H}_{2} \mathrm{O}\) (b) \(\mathrm{CuSO}_{4}^{4} \cdot 5 \mathrm{H}_{2}^{2} \mathrm{O}\) (c) \(\mathrm{FeSO}_{4} \cdot 6 \mathrm{H}_{2} \mathrm{O}\) (d) \(\mathrm{NiSO}_{4}-6 \mathrm{H}_{2} \mathrm{O}\)

Step-by-Step Solution

Answer

CuSO4·5H2O shows the lowest degree of paramagnetism.

Step 1: Determining Paramagnetism

Paramagnetism is related to the number of unpaired electrons in a compound. More unpaired electrons in an element lead to higher paramagnetism.

Step 2: Analyze MnSO4·4H2O

Manganese (Mn) in MnSO4·4H2O has an oxidation state of +2, corresponding to a d⁵ configuration (since Mn has an initial electron configuration of [Ar] 3d⁵ 4s²). This results in 5 unpaired electrons.

Step 3: Analyze CuSO4·5H2O

Copper (Cu) in CuSO4·5H2O is in the oxidation state of +2, giving it a d⁹ electron configuration. This leaves 1 unpaired electron.

Step 4: Analyze FeSO4·6H2O

Iron (Fe) in FeSO4·6H2O is in the +2 oxidation state, with a d⁶ configuration. As a result, it has 4 unpaired electrons.

Step 5: Analyze NiSO4·6H2O

Nickel (Ni) in NiSO4·6H2O is in the +2 oxidation state, giving it a d⁸ configuration. It has 2 unpaired electrons.

Step 6: Compare Paramagnetism

Comparing the number of unpaired electrons: MnSO4·4H2O has 5 unpaired electrons, CuSO4·5H2O has 1, FeSO4·6H2O has 4, and NiSO4·6H2O has 2. Hence, CuSO4·5H2O with just 1 unpaired electron shows the lowest paramagnetism.

Key Concepts

Unpaired Electrons

Unpaired electrons are electrons that are alone in an orbital and not paired with another electron having the opposite spin. Paramagnetism arises due to the presence of these unpaired electrons within a substance. The magnetic moment created by these unpaired electrons causes the substance to be attracted to an external magnetic field.

• If there are more unpaired electrons, the greater the magnetic attraction and hence, the higher the paramagnetism of the substance.
• Conversely, if a compound has fewer unpaired electrons, it will exhibit less paramagnetism.

In the given substances, CuSO₄·5H₂O is noted to have only 1 unpaired electron, resulting in the lowest paramagnetic behavior compared to MnSO₄·4H₂O, FeSO₄·6H₂O, and NiSO₄·6H₂O.

Oxidation State

The oxidation state is a number assigned to an element in a compound representing the number of electrons lost or gained by an atom of that element in the compound. It helps in understanding the electron configuration, which in turn tells us about the unpaired electrons.

• An element with a higher oxidation state generally loses more electrons and thus will have a different electron configuration.
• In compounds like CuSO₄·5H₂O, Cu is in the +2 oxidation state, meaning it has lost two electrons from its usual neutral state.

The oxidation state is pivotal because it directly informs how the electron distribution will be arranged around an atom, affecting properties such as paramagnetism.

Electron Configuration

Electron configuration is the arrangement of electrons around an atom's nucleus in various orbitals. Understanding electron configurations can help predict the chemical properties and behavior of an element.

• An element's electron configuration indicates how many electrons are unpaired in the outer orbitals, which is directly linked to the element's paramagnetic properties.
• For example, a copper ion in CuSO₄·5H₂O with a +2 oxidation state assumes a d⁹ configuration, resulting in 1 unpaired electron.

In the case of transition metals, electron configurations are especially important because these elements often have partially filled d orbitals, significant for chemical reactivity and magnetic properties.

Transition Metals

Transition metals are elements found in the d-block of the periodic table, known for their ability to form various oxidation states and complex compounds. This versatility is due to their unique electron configurations.

• Transition metals can have incomplete d sublevels even after forming ions, which leads to interesting properties like colored compounds and magnetic behavior.
• The compounds discussed (e.g., CuSO₄·5H₂O, MnSO₄·4H₂O) all contain transition metals like Cu, Mn, Fe, and Ni. These elements can change their number of unpaired electrons by altering their oxidation states.

Understanding the behavior of transition metals, such as their electron configurations and oxidation states, is crucial for predicting their interactions in chemistry, including potential paramagnetic effects.